CA1332065C - Sintered alpha silicon carbide body having equiaxed microstructure - Google Patents
Sintered alpha silicon carbide body having equiaxed microstructureInfo
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- CA1332065C CA1332065C CA 326261 CA326261A CA1332065C CA 1332065 C CA1332065 C CA 1332065C CA 326261 CA326261 CA 326261 CA 326261 A CA326261 A CA 326261A CA 1332065 C CA1332065 C CA 1332065C
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/515—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics
- C04B35/56—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbides or oxycarbides
- C04B35/565—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbides or oxycarbides based on silicon carbide
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Abstract
SINTERED ALPHA SILICON CARBIDE
CERAMIC BODY HAVING EQUIAXED MICROSTRUCTURE
Abstract of the Disclosure Pressureless sintered silicon carbide ceramic bodies, having an equiaxed microstructure and an alpha crystalline habit can be produced by firing shaped bodies, containing finely divided silicon carbide, boron source such as boron carbide, carbon source such as phenolic resin and a temporary binder, at a sintering temperature of from about 1900°C to about 2250°C, depending on the sintering atmosphere, under conditions such that a coating of carbon source is maintained on the finely divided silicon carbide, and sufficient boron is maintained within the shaped body during firing. Boron can be maintained within the shaped body by various techniques, such as the use of a "seasoned boat" or graphite container for the body being sintered, which has been saturated with boron by exposure to boron at or about the temperature of sintering.
There is also disclosed a process for producing a sintered silicon carbide ceramic body, with or without the equiaxed crystal microstructure, from silicon carbide powders of alpha or beta crystal structure, or amorphous noncrystalline silicon carbide, or mixtures thereof.
CERAMIC BODY HAVING EQUIAXED MICROSTRUCTURE
Abstract of the Disclosure Pressureless sintered silicon carbide ceramic bodies, having an equiaxed microstructure and an alpha crystalline habit can be produced by firing shaped bodies, containing finely divided silicon carbide, boron source such as boron carbide, carbon source such as phenolic resin and a temporary binder, at a sintering temperature of from about 1900°C to about 2250°C, depending on the sintering atmosphere, under conditions such that a coating of carbon source is maintained on the finely divided silicon carbide, and sufficient boron is maintained within the shaped body during firing. Boron can be maintained within the shaped body by various techniques, such as the use of a "seasoned boat" or graphite container for the body being sintered, which has been saturated with boron by exposure to boron at or about the temperature of sintering.
There is also disclosed a process for producing a sintered silicon carbide ceramic body, with or without the equiaxed crystal microstructure, from silicon carbide powders of alpha or beta crystal structure, or amorphous noncrystalline silicon carbide, or mixtures thereof.
Description
` 1 3 3 2 0 6 5 (KRS/ne) 00150-623 SINT~R$D ALPHA 8ILICON CARBID~
CBRAMIC BODY HAVING ~QUIAXgD MICR08TRUCTVR~
~ackground of the Inventlon :
The chemlcal and physlcal propertles of slllcon carblde make lt an excellent materlal for hlgh temperature structural appllcatlons. These propertle~ lnclude good oxldatlon reslstance and corroslon behavlour, qood heat transfer coefflclents, low expanslon coefflclent, hlgh thermal shock reslstance and hlgh strength at elevated temperature. It 18 ln partlcular deslrable to produce slllcon carblde bodles havlng hlgh denslty and sultable for englneerlng materlal uses, such as ~for example hlgh temperature gas turblne appllcatlons. Slllcon carblde 18 a preferred materlal for such use, because lt can ~; wlthstand stresses at hlgher temperatures than conventlonal 15~ materlals,~and can therefore lead to greater efflclency ln the transformatlon of energy.
Methods of produclng hlgh denslty slllcon carblde bodle~
have heretofore lncluded reactlon bondlng (also known a~
react~lon sinterlng), chemlcal vapour deposltlon and hot ; pr~ss~lnq. Reactlon slnterlng lnvolves the use of slllcon lmpre~nants to upgrade the denslty of the slllcon carblde and 18 useful ~for~many appllcatlons, bUt is undeslrable where excess ~ slllcon exudlng from the slllcon carblde body would be '"~,"?~ detrimental. f Slllcon carblde deposltlon 18 lmpractlcal for Z5 ~ produclng co plex shapes, and hot presslng (the productlon of hlgh denslty slllcon carblde bodles by slmultaneous appllcatlon - of heat and pressUre) 18 lmpractical for some shapes, slnce the pressure requlred durlng the hot presslng operatlon deforms the slllcon carblde body and re~ulres that only relatlvely slmple 30~ shapes can be produced by thls method. r ~
~,;
~ r ~ ` l 33 2065 ; ~ According to Canadian Patent application Serial No. 251,922, ~
corresponding to U.S. ~atent 4,124,667, there was provlded a sln- ¦
tered ceramic body having a high proportlon of sllicon carbide and a high (greater than 75% theoretical) density, and a process and raw batch for the productlon of such ceramio bodies, which did not require the use of finely divided "beta" (cubic crystal structure3 silicon carbide.
Production o~ pressureless sintered silicon carbide, and hot pressed silicon carbide has been the subject of substantial d: lnventive effort in recent years. In addition to J.A. Coppola et al, U.S. Patents 4,080,415, 4,123,286; 4,124,667; Y. Murata et al, U.S. Patents 4,135,937 and 4,135,938; and R.W. Ohnsorg, U.S.
Patent 4,144,207, all of which are assigned to The Carborundum Company, reference is made to G.Q. Weaver et al, U.S. Patent No.
~ :
3,836,673, patented September 17, 1974 and G.Q. Weaver, U.S.
Patent No. 3,998,646, patented December 21, 1976, both assigned to Norton Company; as well as Svante Prochazka, U.S. Patent Nos.
3,852,099, patented December 3, 1974; 3,853,566, patented December 10, 1974; 3,954,483, patented May 4, 1976; 3,960,577, patented June 1, 1976; 3,968,194, patented July 6 1976;
3,993,602, patented November 23, 1976; 4,004,934, patented January 25, 1977; 4,023,975, patented May 17, 1977; and 4,041,117, patented August 9, 1977; and Johnson et al, U.S.
Patent No. 4,031,178, patented June 21, 1977, all asæigned to General Electric Company.
In none of the~above-identified patents of General Electric Company and Norton Company ls there disclosed pressureless sin-tered alpha silicon carbide ceramic bodies having equiaxed micro~tructures. The disclosure of a process which comes the closest to this obJective iæ probably contained in U.S. Pat. No.
4,041,117 wherein there is disclosed a process '~
~ 2 1 3 3 2 0 6 5 (KRS/ne) 00150-623 comprlslng provldln~ a substantially homogeneous partlculate dlsperslon or mlxture, wherein the partlcles are sub-mlcron ln size, or beta slllcon carblde powder, alpha slllcon carblde seedlng powder, boron addltlve and a carbonaceous addltlve whlch is free carbon or a carbonaceou~ organlc materlal whlch 18 heat-decompo~able to produce a free carbon, shaplng the mlxture lnto a green body, and slnterlng the green body at temperatures ranglng from about 1950C to 2300C ln an atmo phere ln whlch the green body and resultlng slntered body 18 substantially lnert, to produce a slntered body havlng a den~lty ranglng from 80% to about 95% of the theoretlcal denslty for slllcon carblde and a ~; substantlally unlform relatlvely flne-gralned mlcrostructure whereln at least 70% by welght of the slllcon carblde present 18 composed of a}pha slllcon carblde ln the form of platelets or -~ 15 elongated gralns whlch may range ln the long dimenslon from about 5 to 150 mlcrons, and preferably from about 5 to 25 mlcrona.
; For some appllcatlons of slntered slllcon carblde bodles, however, there are advantages to employlng a slntered slllcon ~; carblde body havlng an equlaxed mlcrostructure, as opposed to a struatUre~ln the form o~f platelets or elongated gralns. Other factors~ being egual, there are dlfferences ln mechanlcal ; propertles, prlmarlly strength, whlch depend upon the largest flaw present ln a partlcular slntered ceramlc body. The large 2~5~ gralns~ln the form of platelets or elongated gralns act as large flawa~, and accordlngly there 19 an lnverse correlatlon between the~atrength of a slntered ceramlc body and the largest graln .
;~; slze observable ln the mlcrostructure. In other words, a flne~
~- gralned egulaxed mlcrostructure ln lnherently ~tronger i~
CBRAMIC BODY HAVING ~QUIAXgD MICR08TRUCTVR~
~ackground of the Inventlon :
The chemlcal and physlcal propertles of slllcon carblde make lt an excellent materlal for hlgh temperature structural appllcatlons. These propertle~ lnclude good oxldatlon reslstance and corroslon behavlour, qood heat transfer coefflclents, low expanslon coefflclent, hlgh thermal shock reslstance and hlgh strength at elevated temperature. It 18 ln partlcular deslrable to produce slllcon carblde bodles havlng hlgh denslty and sultable for englneerlng materlal uses, such as ~for example hlgh temperature gas turblne appllcatlons. Slllcon carblde 18 a preferred materlal for such use, because lt can ~; wlthstand stresses at hlgher temperatures than conventlonal 15~ materlals,~and can therefore lead to greater efflclency ln the transformatlon of energy.
Methods of produclng hlgh denslty slllcon carblde bodle~
have heretofore lncluded reactlon bondlng (also known a~
react~lon sinterlng), chemlcal vapour deposltlon and hot ; pr~ss~lnq. Reactlon slnterlng lnvolves the use of slllcon lmpre~nants to upgrade the denslty of the slllcon carblde and 18 useful ~for~many appllcatlons, bUt is undeslrable where excess ~ slllcon exudlng from the slllcon carblde body would be '"~,"?~ detrimental. f Slllcon carblde deposltlon 18 lmpractlcal for Z5 ~ produclng co plex shapes, and hot presslng (the productlon of hlgh denslty slllcon carblde bodles by slmultaneous appllcatlon - of heat and pressUre) 18 lmpractical for some shapes, slnce the pressure requlred durlng the hot presslng operatlon deforms the slllcon carblde body and re~ulres that only relatlvely slmple 30~ shapes can be produced by thls method. r ~
~,;
~ r ~ ` l 33 2065 ; ~ According to Canadian Patent application Serial No. 251,922, ~
corresponding to U.S. ~atent 4,124,667, there was provlded a sln- ¦
tered ceramic body having a high proportlon of sllicon carbide and a high (greater than 75% theoretical) density, and a process and raw batch for the productlon of such ceramio bodies, which did not require the use of finely divided "beta" (cubic crystal structure3 silicon carbide.
Production o~ pressureless sintered silicon carbide, and hot pressed silicon carbide has been the subject of substantial d: lnventive effort in recent years. In addition to J.A. Coppola et al, U.S. Patents 4,080,415, 4,123,286; 4,124,667; Y. Murata et al, U.S. Patents 4,135,937 and 4,135,938; and R.W. Ohnsorg, U.S.
Patent 4,144,207, all of which are assigned to The Carborundum Company, reference is made to G.Q. Weaver et al, U.S. Patent No.
~ :
3,836,673, patented September 17, 1974 and G.Q. Weaver, U.S.
Patent No. 3,998,646, patented December 21, 1976, both assigned to Norton Company; as well as Svante Prochazka, U.S. Patent Nos.
3,852,099, patented December 3, 1974; 3,853,566, patented December 10, 1974; 3,954,483, patented May 4, 1976; 3,960,577, patented June 1, 1976; 3,968,194, patented July 6 1976;
3,993,602, patented November 23, 1976; 4,004,934, patented January 25, 1977; 4,023,975, patented May 17, 1977; and 4,041,117, patented August 9, 1977; and Johnson et al, U.S.
Patent No. 4,031,178, patented June 21, 1977, all asæigned to General Electric Company.
In none of the~above-identified patents of General Electric Company and Norton Company ls there disclosed pressureless sin-tered alpha silicon carbide ceramic bodies having equiaxed micro~tructures. The disclosure of a process which comes the closest to this obJective iæ probably contained in U.S. Pat. No.
4,041,117 wherein there is disclosed a process '~
~ 2 1 3 3 2 0 6 5 (KRS/ne) 00150-623 comprlslng provldln~ a substantially homogeneous partlculate dlsperslon or mlxture, wherein the partlcles are sub-mlcron ln size, or beta slllcon carblde powder, alpha slllcon carblde seedlng powder, boron addltlve and a carbonaceous addltlve whlch is free carbon or a carbonaceou~ organlc materlal whlch 18 heat-decompo~able to produce a free carbon, shaplng the mlxture lnto a green body, and slnterlng the green body at temperatures ranglng from about 1950C to 2300C ln an atmo phere ln whlch the green body and resultlng slntered body 18 substantially lnert, to produce a slntered body havlng a den~lty ranglng from 80% to about 95% of the theoretlcal denslty for slllcon carblde and a ~; substantlally unlform relatlvely flne-gralned mlcrostructure whereln at least 70% by welght of the slllcon carblde present 18 composed of a}pha slllcon carblde ln the form of platelets or -~ 15 elongated gralns whlch may range ln the long dimenslon from about 5 to 150 mlcrons, and preferably from about 5 to 25 mlcrona.
; For some appllcatlons of slntered slllcon carblde bodles, however, there are advantages to employlng a slntered slllcon ~; carblde body havlng an equlaxed mlcrostructure, as opposed to a struatUre~ln the form o~f platelets or elongated gralns. Other factors~ being egual, there are dlfferences ln mechanlcal ; propertles, prlmarlly strength, whlch depend upon the largest flaw present ln a partlcular slntered ceramlc body. The large 2~5~ gralns~ln the form of platelets or elongated gralns act as large flawa~, and accordlngly there 19 an lnverse correlatlon between the~atrength of a slntered ceramlc body and the largest graln .
;~; slze observable ln the mlcrostructure. In other words, a flne~
~- gralned egulaxed mlcrostructure ln lnherently ~tronger i~
3 j ~j 1,''~;,' '', 1 332065 1 ~
;and possessed of other more desirable mechanical properties .than a material which is otherwise the same, but has larger grains. :
Summary of the Invention 1 Accordingly, the present invention provides a sintered ceramic body consisting essentially of from about 91 to about 99.85% by weight silicon carbide, wherein at least 95O by : weight of the silicon carbide is of the alpha phase; up to .
about 5.0% by weight carbonized organic material; from about 0.15 to about 3.0~ by weight boron; and up to about 1.0~ by : .
weight additional carbon; and havillg a predominantly equiaxed ~ :
, microstructure. Such a sintered ceramic body can be produced .
by mixing together a mixture comprising from about 91 to .~`
.about 99.85 parts by weight silicon carbide powder comprising :
at least 95% by weight alpha, non-cubic crystalline sllicon : :~
~, ,carbide and having a surface area of from about 1 to about 100 ,m2/g: from about 0.~7 to about 20 parts by weight of a carbon-izable organic material having a carbon content of at least ~:
3~% by weight; from about 0.15 to about 5 parts by weight of 20: la~boron source con~aining from abo~t 0.15 to about 3.0 parts by we~ight boron; up to about 15 parts by weight of temporary ; ~-binder; and from`about 25 to about.100% by weight off the sili~
con carbide powder, carbonizable organic material, boron source and temporary binder of a soIvent in which the carbonizable Z5~ 'organic~material is soluble; said mixing being done in such a way as to disperse the carbonizable organic material about ~:
the silicon carbide powder and coat the silicon carbide powder ~ -therewith; drying the mixture in such a way as to evaporate the solvent from the mixture; shaping the dried mixture in such a way as to produce a shaped body having a density of ~ :
:
;and possessed of other more desirable mechanical properties .than a material which is otherwise the same, but has larger grains. :
Summary of the Invention 1 Accordingly, the present invention provides a sintered ceramic body consisting essentially of from about 91 to about 99.85% by weight silicon carbide, wherein at least 95O by : weight of the silicon carbide is of the alpha phase; up to .
about 5.0% by weight carbonized organic material; from about 0.15 to about 3.0~ by weight boron; and up to about 1.0~ by : .
weight additional carbon; and havillg a predominantly equiaxed ~ :
, microstructure. Such a sintered ceramic body can be produced .
by mixing together a mixture comprising from about 91 to .~`
.about 99.85 parts by weight silicon carbide powder comprising :
at least 95% by weight alpha, non-cubic crystalline sllicon : :~
~, ,carbide and having a surface area of from about 1 to about 100 ,m2/g: from about 0.~7 to about 20 parts by weight of a carbon-izable organic material having a carbon content of at least ~:
3~% by weight; from about 0.15 to about 5 parts by weight of 20: la~boron source con~aining from abo~t 0.15 to about 3.0 parts by we~ight boron; up to about 15 parts by weight of temporary ; ~-binder; and from`about 25 to about.100% by weight off the sili~
con carbide powder, carbonizable organic material, boron source and temporary binder of a soIvent in which the carbonizable Z5~ 'organic~material is soluble; said mixing being done in such a way as to disperse the carbonizable organic material about ~:
the silicon carbide powder and coat the silicon carbide powder ~ -therewith; drying the mixture in such a way as to evaporate the solvent from the mixture; shaping the dried mixture in such a way as to produce a shaped body having a density of ~ :
:
at least about 1.60 y/cc; and firillg the shaped body under such conditions of time, temperature and atmosphere as to obtain a density of at least about 2.40 g~cc and an equiaxed microstructure, tlle temperature being between about l900~C
~and 2250C. It is preferred that the firing take place under conditions such that the level of boron retained in the body .being sintered is maintained, for example by enclosing the body being sintered within a sealed container which is impervious to boron at the temperature of sintering, and which has a volume approcimating the size of the body being sinterecl;
or by containing the body being sintered within a graphite ~
;container, which container has been saturated with boron by ~ :
.exposure to boron at or about the temperature of sintering.
There is also provided, according to this invention, a process for producing a sintered silicon carbide ceramic body, ~
with or without equiaxed crystal microstructure, from silicon . .
carbide powders of alpha or beta crystal microstructure, or :
amorphous silicon carbide, or mixtures thereof, comprising the ;.
steps of mixing together a mixture comprising the components:
,from about 91 to about 99.85 parts by weight silicon carbide powder having a surface area of from about 1 to about 100 m2~g; ~ ~;
,from about 0.67 to about 20 parts by weight of a carbonizable organic material having a carbon content of at least 33% by ~;
weight; from about 0.5 to about 5 parts by weight of a boror~
~source containiny from about 0.15 to about 3.0 parts by .. -:.
weight boron; up to about 15 parts hy weight of temporary h ~:
binder; and from about 25 to about 100% by weight of the ..
silicon carbide powder, carbonizable organic material, boron -source and temporary binder of a solvent in which the carboni~
zable organic material is soluble; said mixing being done in .
'.~'''" '".,:'."
;such a way as to disperse the carbonizable organic material labout the silicon carbide powder and coat the silicon carbide Ipowder therewith; drying the mixture in such a way as to l!evaporate the solvent from the mixture; shaping the dried mixture in such a way as to produce a shaped body having a ;~
density of at least about 1.60 g/cc; and firing the shaped ibody at a temperature of from about 1900C to about 2500C.
BrieE Description of the Drawings Fig. 1 of the drawing is a flow chart showing a typlcal sequence of process steps to produce the sintered ceramic body ;of the present invention.
~;~ Figs. 2-7 are photomicrographs. Figs. 2 and 3 show, at different magnifications, the equiaxed microstructure of the present invention produced by sintering at 2120C. Figs. 4-7 illustrate the microstructure which is obtained by sintering ;~ at higher temperatures.
Detailed Description ; The theoretical density of silicon carbide is 3.21 g/cc.
'IThe preferred minimum density of about 2.40 g/cc for sintered 20~ 'ceramic bodies according to the present invention corresponds, . ~ ~
therefore, to about 75% of theoretical density. The more -`~
~highly pre~ferred densities of 2.90 and 3.05 g/cc correspond to 90 and 95% of theoretical density, respectively.
I The primary constituent of the sintered ceramic body ~ 'according to the present invention is ~ilicon carbide, wherein ;
~.: ~ ;- ,.:
at least 95~ by weight of the silicon carbide is of the alpha (non-cubic crystalline) phase. While the process of the ,:
present invention is essentially immune to changes in the crystalline phase of the silicon carbide powder used as a start~ng material, i.e., the process of the present invention does not produce any substantial amount of phase transforma-tion, it has been observed that even if the silicon carbide powder used in the starting material for the present invention consists essentially of silicon car~ide of the alpha phase, ~some small degree of phase transformation may occur, so that some small proportion of the alpha phase material (probably ;
less than 1%, and certainly believed to be less than 5~) may transform to the beta phase. Thus, while in the broad aspects of the present invention the sintered ceramic body contains silicon carbide wherein at least 95~ by weight of the silicon carbide is of the alpha phase, it is preferred that at least about 99~ by weight of the silicon carbide be of the al~ha phase, or that the silicon carbide consists essentially of ;~
silicon carbide of the alpha phase. ;~
According to the processes of the prior art, it does not appear to have be~n possible to obtain a sintered silicon car-bide body wherein at least 95% by weight of the silicon car-bide is of the alpha phase, and wherein the sintered ceramic '~ody has a predominantly equiaxed microstructure. Although ;' 20 the product of the present inventian is therefore thus defined jbroadly~ it is preferred that the microstructure contain at ;~
least about 90% equiaxed grains, and more highly preferred `~;
that the microstructure consist essentially of equiaxed grains.
, The term "equiaxed grains" as used herein refers to a 25 crystal microstructure in which the grains have an aspect ;~-ratio of less than 3:1, i.e., the ratio of the maximum dimen-'sion of the grains of the crystal microstructure to the mini-`mum dimension of the grains of the crystal microstructure is less than 3:1. This microstructure is commonly known as "equiaxed" to distinguish it from crystal structures which are . ., .. . .. , . , . - . . . -~acicular, i.e., contain needle-shaped or tabular crystals, or ;a feathery microstructure such as illustrated in Fig. 2 of U.S. Patent l~o. 4,041,117. The product of the present inven-'tion is characterized by the combination of equiaxed grains land alpha phase in the silicon carbide of the sintered ceramic body, a combination not taught by the prior art, although the prior art does teach the production of sinter~d ceramic bodies having a beta phase and an equiaxed microstructure (using beta ,phase silicon carbide powder as the starting material).
I The preferred composition of tlle sintered ceramic body in accordance with the present invention consists essentially of from about 91 to about 99.85% by weight silicon carbide, up to about 5.0~ carbonized organic material, from about O.lS to about 3.0~ boron, and up to about 1.0% additional carbon. The "carbonized organic material" is free carbon or uncombined Icarbon produced in situ by the carbonization of the orsanic ¦material used as a raw material in the process of the present invention. The organic material is carbonized because the lorganic material is unstable at the temperature to which the Ibody being sintered is subjected, and the non-carbon compo- -~
Inents of this organic material are driven from the carbon --~
I Iskeleton of the organic material (i.e., volatilized away3.
Although the temperature attained during the process of the ;~
present invention is not sufficient to volatilize the carbon, ~-1 25 some carbon may be oxidized to carbon monoxide or carbon diox-:: I
de. Thus, depending upon the proportion of organic material 1-'used in the process of the present invention, the firing tem-perature, and other factors, there may be no carbon in the form of carbonized organic material present in the sintered body at ~ 1 , all. Usually, however, a minor proportion of carbon as ~ ' !
-8- ~
.... ~, . , , . ,, , , . . ,. .:
1 332~6~
carbonized organic material will remain. It is, however, very difficult to determine the amount of carbon present, since the oxidation test to determine the amount of carbon present ~
oxidize and remove a minor proportion of the silicon carbide matrix. The amount of carbon which is present as carbonized organic material will also depend upon the amount of such organic material which was added to the raw batch and the carbon content (char yield) of the organic material. While the preferred carbonizable organic materials for use in the process of the present invention are phenolic resin and coal - ;
tar pitch, which have carbon contents of from about 40 to . -:
about 42% and on the order of 60%, respectively, the carbon content of the organic material can be in excess of 90~, as ~for example in polyphenylene or polymethylphenylene.
Withill the b~oad composition recited above, it is pre-,~erred that the sintered ceramic body contain from about 0.5 to about 4% carbonized organic material, from about 0.18 to about 0.36~ boron and from about 0.05 to about 0.10~ additlon~
ial carbon, with the balance of the composition being silicon carbide. In particular, it is preLerred that the sintered ceramic body contain about 2% of carbonized organic material, about 0.36~ boron, and about 0.1~ additional carbon ~! All per~
centages herein are by weight, unless otherwise specified. -~
~The amount of "additional carbon" depends on the amount of 2S 'carbon associated with the boron present in the raw batch mix--ture from which the sintered ceramic body was made.
`In carrying out the process of the present invention, if the sintered body is to have a high alpha silicon carbide con- ~;
tent, it is preferred to begin with a silicon carbide powder which comprises at least 95% by weight alpha, non-cubic _9_ , .,. _ . , , , , , , , . :.
(KRS/ne) 00150-623 --` 1 332065 crystalline slllcon carbide. It is more hlghly preferred, however, that the sillcon carblde of the raw batch comprlses at least 99% by welght alpha ~lllcon carblde, or that the slllcon carblde of the raw batch consl~ts essentl~lly of alpha slllcon carblde.
The flrlng step of the process of the present lnventlon preferably takes from about 20 to about 60 minutes at temperatures of from about 1900 to about 2500C. Lower temperatures are in general lnoperable, and hlgher temperatures may cause subllmatlon of the slllcon carblde materlal. If a ~lntered ceramlc body having a predomlnantly e~ulaxed mlcrostructure 18 to be obtalned, the firing should be under such condltlons of tlme, temperature and atmosphere as to obtaln a denslty of at least about 2.40 g/cc and n egulaxed mlcrostructure, sald temperature belng between about 1900C and about 2250C. Wlthln thls range, the slntering temperature neces~ary to obtaln an equlaxed mlcrostructure, l.e., ln order to avold the formatlon of needles and platelet3 wlthln the crystal mlcrostructure, depends to a certaln extent on factors such as the lmpurlties present ln the slllcon carblde and the presence of absence of nltrogen ln the slnterlng atmosphere. If there are no exce~slve lmpurltles present, and the flrlng 18 to be done ln a vacuum or ln an atmosphere whlch excludes nltrogqn (such as an atmosphere of up to about 1 atmosphere of pressure of a ~as selected from the group con~lstlng of argon, carbon dloxlde, carbon monoxlde, hellum, hydrogen, neon and mlxtures thereof), the preferred temperature of flrlng on order to obtaln an egulaxed crystal mlcro~tructure 18 between about 1900C and about 2160C, more preferably from about 2100C to ~bout 2150C~
The pre~ence of impurltle~ ln the slllcon -- 10~
(KRS/ne) 00150-623 ~
t 3 3 2 0 6 5 ! ' ' carbide wlll lnfluence thls temperature range. In partlcular, when uslng "black" slllcon carblde contalnlng a hlgh alumlnlum content (on the order of 0.2% alumlnum by weight of sllicon ;;
carblde)~ temperature control is more lmportant, and even the .-temperature of 2160C may be too hlgh. The usual raw materlal for use ln the present lnventlon 18 "green" graln slllcon carblde, contalnlng about 0.02% or less alumlnlum. If the amount of the alumlnlum present ln the sillcon carblde 18 less ~;~than 0.02%, even hlgher temperatures can be tolerated wlthout . "
1088 of the predomlnantly equlaxed mlcrostructure. The presence of nltrogen ln the sinterlng atmosphere ralses the mlnlmum temperature necessary to achleve satlsfactory ~lnterlng, and also ralses the temperature at whlch the equlaxed mlcrostructure ~ ., .
18 lost, so that when slnterlng ln a nltrogen atmosphere, a ;~
15 ~ predomlnantly equlaxed mlcro6tructure can be obtalned even lf ~ -~
the temperature 18 between about 1975C and about 2300C. Wlthln ~ :-this range, ln a nltrogen atmosphere, a flrlng temperature of ; between about 2100C and about 2250C 18 preferred. In any event, the preferred flrlng tIme varles from about 20 to about~
20~ 60 mlnutes.
Ao used hereln, "predomlnantly" means greater than 50%. ~;;
In carrylng out the present lnventlon, lt 18 preferred to ;~-~
take steps to malntaln the level of boron retalned in the body -~
~;belng slntered. In thls connectlon, placlng the artlcle to be 25~ slntered ln a fresh graphlte "boat" whlch has never been used ln slnterlng before tends to have a detrlmental effect upon the denolty obtalned. Thi8 18 because the fresh graphlte boat acts as a ~boron slnk" whlch wlthdraws boron from the artlcle belng - ;
slntered, thus preventlng the boron from fully achlevlng lts role ln promotlng slnterlng and denslflcatlon of the artlcle ~ belng slntered. ~ ;
1 332~6~
- Various tecl~ni~ues can be used in order to maintain the . , , boron within the shaped body during the sintering operation.
U.S. Patent No. 4,080,415 describes, for example, the intro-duction of a gas such as boron trichloride into the sintering ~atmosphere and painting the furnace components with a solution , :
or slurry containing a boron compound. Another technique for malntaining the level of boron retained in the body being sin-tered: is to incorporate greater amounts of boron in the article ,;to be sintered. Another technique of maintaining the level of boron retained in the body being sintered is to enclose the -~
body being sintered wi~hin a sealed container which is imper-.viou~s to~boron at the temperature ~f sintering (such as a jglass~container)~ and which has a volume approximating the size~of the~body~;being;sintered~ ~ preferred techniaue of 5~ -,malntaining; the level oL boron retained in the body being intered~ ls~ to~ contal~n the body~ being sin~tered within a e~ boat~ i.e~ a graphlte container which has been ~ ~ ;
a ~ te~ withj~boron-by~exposure to boron at or about the ;`~
ù`rè~of~si*~ ing. Such expo~sure occurs naturally the~si ~ring operation, ~and it ha8 been~observed that ; ~ - ;
èr~esuits ~ :e`~, ~ igher ~densitles) can be obtained by the uselof~graphite boat~s~whlch have been used for sinte~ing usly~ sulil~lentl. often to becone saturated~
Tl`e~sl~licQn~c~arbide~powd~r for use ln the present inven~
` ~ has~ alsurfaoe~area o~f from about 1 to about lOO~m2/g.
h` lliC n~carbide~po ers are usually leis than 20 microns u~ partlcle~s;ize~ ore~particularly less than 10 miCrons in~
artlcle Size: an~ in particular sub-micron size particles are ~
~ 30 ,generally preferred. It is difficult, however, to obtain ~ ~r"''-' :~'; :~' . ', .',`,''' ' ,' ' . ' (KRS/ne) 00150-623 . ~ . I
accurate partlcle slze dlstrlbution~ for slllcon carblde powders havlng slze much less than 1 mlcron ln particle slze, and the surface area of the slllcon carblde partlcle 18 the more relevant conslderation ln determinlng sultable materlal.
Accordlngly, the preferred slllcon carblde powder for use ln the present lnventlon are speclfled as havlng from about 1 to about lOO mt/g surface area. Withln thls range, lt 18 more preferred that the surface area of the slllcon carbide partlcles range between about 5 and 50 ml/gt and wlthln thls range, surfQce areas ~ , between about 7 and about 15 m'/g have been found to be easlly obtalnable and qulte useful for produclng slntered ceramlc bodles of the present lnventlon.
;The slllcon carblde startlng materlal can be obtalned from any of a varlety of sourcés. Vapour phase reacted materlal 18 produced in fine partlcle slze, and can be used lf deslred.
Larger materlal can be ball mllIed untll sufflclent amounts of fine slllcon carblde are obtained, and the proper slze of slllaon carblde can be selected from the ball mllled product by conventlonal eans, such as water sedimentatlon.
Th-~crystallln-~hablt of the slllcon carblde 18 essentlal}y non-orltlcal except ln th- case where a hlgh alpha slllcon carbldé content ls deslred ln the slntered body. Alpha non~
cublc ~slllcon carblde ls;~more readlly avallable then beta slllaon carblde, and therefore the preferred startlng materlal 25~ oontalns slllcon carblde~whlch conslsts essentlally of alpha, non-oublc orystallln- slllcon carblde. It 18 qulte acceptable, how v r, to u8e slllcon carblde whlch has been made by a procesa whleh produces mlxtures of alpha and beta slllcon carblde, and an~operable startlng mat-rlal 18 slllcon carblde whlch 18 predomlnantly alpha, non-cublc crystalllne slllcon (KRS/ne) 00150-623 " 1 332065 carblde. It has Ql80 been shown to be operable to use raw batches whereln the slllcon carblde comprise~ at least 5% alpha, non-cublc crystalllne silicon carblcle, and amorphous slllcon carblde can al90 be used. It 18 even posslble to use hlgh purlty beta slllcon carblde ~tartlng materlal, but such materlal i8 not preferred because of the hlgh expense of obtalnlng hlgh purlty beta sillcon carblde powders.
In any event, it 18 pre~erred that the ~lllcon carblde materlal ~hall have been treated wlth acid (such as hyclro-' 0 f luorlc and/or nltrlc aclds, partlcularly mixtures of hydro-fluorlc and nltrlc aclds) to remove extraneous materlals whlch may lnterfere with the slnterlng operatlon.
One of the more lmportant features of the raw batch of the present lnventlon ls the carbonlzable organlc material. It ha~
been found deslrable that thi3 materlal be organlc ln order that lt be easlly dlspersable about the slllcon carblde powder, ln order to coat the slllcon carblde powder and provlde an lntimate availablllty of carbonlzed organic material upon flrlng of the shsped body produced from the raw batch. The organlc materlal can be organlc solvent ~oluble, or soluble in water lf a water solvent 19 used. It has been found deslrable that the slntered ceramlc body contain up to about 5.0% usually from about 0.5 to about 5.0% , of carbonlzed organlc materlal, wlth the result that lf the carbonlzable, or~anlc solvent soluble, organlc ~; .
materlal has a carbon content (char yleld) of from about 25 to about 75% by welght, as 18 common, there should be pre~ent from about 0.67 to about 20 part~ by welght of carbonlzable organlc materlal in the raw batch. Withln the range of from about 25 to about 75% by welght carbon content, lt 18 more common that the organlc materlal have ."~
~ - 14 - ~ ~;
1 332~65 'from about 33 to about 50~G by weic311t, more particularly from about 40 to about 45% by weight, carbon content. If the car-bon content is between about 33 and about 50~ by weight, the - :
amount of carbonizable organic material should range between 'about l and 12% by weiyht to produce the preferred amount of carbon in the form of carbonized organic material of from ,about 0.5 to about 4.0% by weight in the finished sintered ~ .
ceramic body. The most preferred amount of carbonized organic material in the sintered ceramic body is believed to be about 2% by weight, so that the optimum raw batch should contain about 5% by weight of organic material havin~i a carbon content between a~out 40 and 45~i by weight. Particularly preferred ; ,carbonizable organic materials are phenolic resin and coal tar u~ pitch, which have carbon contents of from about 40 to about 15 ~ ,4~2~ and on tbe order o2 60%f respectively. As between the ~;
phenolic resin and coal~tar pitch, the phenolic resin is more ;
definitely preferred, and particularly a B-stage resole phen~
c~resin has bee~l found to be particularly useful in the ;
present~i~nvent1on.
20~ The;boron can~be;added to the raw batch as either ele~en~
tal`boron or as boron carbide. ~oron carbide is essentially a non-stoichlometric material, and various~boron carbide i~
mater~ials~;having a mo}ar ratio~of boron to carbide between 8~
and~2~ have been reported. It is in general preferred to use ;25~ ;boron~carbide as the boron source, and in particularly boron carbide~which i9 so-called "solid state reacted boron carbide"
with a molar ratio of boron to carbon between about 3.5:1 and ;4.l:l. Such boron carbide can be produced in accordance with the process of U.S. Patent No. 3,379,647, P. A. Smudski. The 30~ process of the above Smudski patent is found to produce boron : ~, 1 3 3 2 ~ b ~ !
'carbides having such a molar ratio, and such a molar ratio is preferred because with the higher boron to carbon ratio, the ~oron carbide eith~r takes carbon or gives boron to the 'surrounding chemical species, which is desirable in the present ~instance as it promotes the desired densification during the firing step of the process of the present invention. Boron carbide materials having greater ratios of boron to carbide '' '~
are even more chemically active than the material havin~ a ; 'ratio of about 4.l:l to about 3.5:l, but such materials are ~relatively less available and more expensive, and therefore !are not preferred for that reason.
;~ The amount of boron source to be added to the raw batch ;depends on the boron content of the boron source and the amount of boron to be present in the final sintered ceramic ; 15 body. The sintered ceram1c body should contain from about 0.15 to about 3.0~ boron, and in particular from about 0.18 to about 0.36% boron is present in the most successfully ` '-' densified bodies produced in accordance with the present inven~
tion. 0.36~ is the optimum boron content of the sintered ~ceramic body. The amount of boron source should thus be cho~
sen accordingly. Thus,~if the boron source is elemental boron, "`-t should be present in the raw batch from about 0.18 to about Q.36 parts by by weight to`yield a sintered ceramic body hav~
!ing from about 0.18 to about 0.36% by weight boron. For the ,preferred solid state reacted boron carbide with a molar ratio ; IO~f boron to carbon between about 3.5:l and about 4.l:l, the `boron carbide should be ~resent in an amount from about 0.23 ''- ''' to about 0.46 parts by weight to produce such an amount of boron in the finished sintered ceramic body.
~ In any event, the boron source can be crystalline or ~:
-16- '~
1 332~5 ~non-crystalline, and preferably is particulate and of a slze less ~than 30 microns. Within this limitation, it is preferred that ~the boron source be of a size ranging from about 0.1 to about 10 microns.
The temporary binder, if used, is preferably polyvinyl alco-hol having associated therewith from about 5 to about 15 parts by weight water, per part of polyvinyl alcohol, as a temperary binder vehicle. In particular, it is preferred to use 10 parts by weight polyvinyl alcohol plus about 90 parts by weight water as a temporary binder vehicle. In addition to polyvinyl alcohol, however, other temporary binders can be used, such as coal tar pitch, long chain fatty material (for example CARBOWAX~ wax, I ;
available from Union Carbide Corporation), metallic stearates ; such as aluminum stearates and zinc stearates, sugars, starches, alginates, and polymethyl phenylene. Many of these materials ¦
are, of course, capable as functioning as the carbonizable orga-nic material which is added in sufficient quantity to yield the appropriate amount of carbonized organic materila in the finlshed sintered ceramic body. A single material can thus serve two functions in the raw batch.
The process for producing the sintered ceramic body according to the present invention can begin with the mi~ing together from about 91 to about 99.85 parts by weight silicon carbide; from about 0.67 to about 20 parts by weight of the car-bonizable organic material; from about 0.15 to about 5% by weight of the boron source; and up to about 15 parts by weight of tem-porary binder. The solvent can be added to this mixture, or the carbonizable organic material dissolved in the solvent first. If ¦
the temporary binder is polyvinyl alcohol including a quantity of water as temporary binder vehicle, this first ¦~
-;:
~ 33~9~
m~xing step prefera~ly includes stirring the powdered materials ~(silicon carbide, organic material and boron source) togetller with the temporary binder and temporary binder vehicle, prior to adding an organic solvent in which the organic material is soluble. AEter th~ organic solvent is added, the components ;are preferably stirred in such a way as to disperse the carbon- ~ --.:
izable organic material about the silicon carbide powder and ~ ;~
coat the silicon carbide powder therewith, suitably for at ~least about S minu~es, and preFerably about 15 minutes.
After the components have been stirred so as to disperse ;;
the organic material about the silicon carbide powder and coat the silicon carbide powder therewith, the stirred mixture is ~; dried by any suitable technique, such as passing a quantity of ~;
drying gas near the stirred mixture, vacuum treating or by ,: , ~ , lS spray-drying the mixture. Following this drying step, the dried mixture is shaped in such a way as to produce a shaped body preferahly having a density of at least about 1.60 g/cc.
This shaping can be accomplished by any of a variety of tech- `;~
niques which are in themselves known, for example by extrusion, ,'!
20 ~ I injection molding, transfer molding, casting, cold pressing, isostatic pressing, or by compression. If compresslon is used, ,pireferred pressures are between about 4,000 and about 100,000 -~
psi, wlth between about 16,000 and about 20,000 psi being pre~
ferred. If a temporary binder of polyvinyl alcohol is used, -~
the next step of curing the temporary binder can be preferably "~
accomplished by heating the shaped body at a temperature about 90 to about 100C for about 1 to about 2 hours. The shaped body is then fired to accomplish the densification necessary to produce the sintered ceramic body of the invention. ~iring ; , -.: :., takes from about 20 to about 60 minutes at temperatures of ~ ~
'`' ', ' :.
~' ....
-18- ;;-~
1 332~5 :
from about l900 to ab~ut 2500C. Lower temperatures are in general inoperable, and higher temperatures may cause suklima-tion of the silicon carbide material. The firing step can be ~carried out in a conventional tube furnace wherein the shaped body is passed through the hot zone of the tube furnace to have a residence time at the desired tem~erature and for the desired time. Details of such tube furnaces are known in the prior art, and are disclosed for example in P. A. Smudski, U.S. Patent No. 3,6B9,220. The firing step accomplished a -"pressureless sintering", referred to herein for simplicity merely as "sintering". By "sintering" or "pressureiess sin-; tering" i is meant that no mechanical pressure is applied to the object being fired or sintered to enhance the reaction.
Instead, the object being sintered is surrounded, usually in 1 15 'an~inert container such as a graphite crucible, in up to about l atmosphere of pressure of an inert gas, a reducing gas, a vacuum, or nitrogcn. Reducing gases include hydrogen, carbon dioxide and carbon monoxide; inert gases include argon, helium, and neon. The gases in which the sintering operation can be ,aarried out thus include argon, ca~bon dioxide, carbon monox-iide, helium, hydrogen, neon and nitrogen. Although nitrogen ~çnters into reaction in a minor dec3ree with the silicon ¢ar-~ I
bide raw material, it does so in sufficiently minor degreethat the composition of the sintered ceramic body is not ,noticeably changed. The use of nitrogen, however, does raise -the necessary sintering temperature about 200C, so that if nitrogen is the surrounding atmosphere, a preferred sintering temperature is from about 2260C to about 2300C. In the other gases, particularly inert gases such as argon, helium or neon, a preferred sintering temperature is from about 20~0C
:, ' --19-- ~ .
, ...... , .. . i .. . ... .. ., .. . . . . , . . , . , ., , ., , . : ~
1 332065 ~ -to about 2100C. If it is desired to maintain an equiaxed crystal microstructure, these temperatures should be more closely controlled, as described above. The firing can also be carried out under vacuum, i.e., without any surrounding atmosphere. By "vacuum" is meant a practical vacuum, i.e., an absolute pressure of 1.0 mmHg or less.
The invention will now be illustrated with several exam-ples.
~; ` EXAMPLE 1 Sintered silicon carbide bodies were produced from mixes ~-containing indicated amounts of submicron alpha silicon car-bide having a surface area between about 10 and 12 m2/g, B-stage phenol aldehyde resole resin containlng indicated amount of carbon, and boron carbide powder (smaller than 10 mesh) containing indicated amounts of boron. The proportions are set forth in Table 1. For each experiment, 4.9 parts resin were mixed with 150 parts acetone for 5 minutes, the boran carbide powder added, and the suspension stirred for an ~ ~
additional 5 minutes. The silicon carbide powder was slowly ~ ;
added to the mixture and the combined mixture stirred 30 min~
utes to disperse the ingredients thoroughly. The mix was stirred while the acetone evaporated. After the batich was dry . ~.
the powder cake was easily broken up into a granula-r array of particles by passing it through a 60 mesh screen. The , ,:, ., ~',''~',~
,.,,.j,....
'"'"'~
.. ~
~, ,.
-20- ;
., ' ",~'.''' -~1 332065 (KRS/ne) 00150~6Z3 partlcle~ were then pressed lnto compacts which were subsequently baked at 150C for 2 hour~ to cure the phenollc resln. The cured den~ltles of the plece~ ln all cases were ln excess of 1.70 g~cc.
STwo photomlcrographs for each experlment of pollshed and etched sectlons of these bodles are lllustrated ln the drawing.
Flg. 2 18 a lower magnlflcatlon photomlcrograph, orlglnally lOOX, lllu~tratlng a unlform equlaxed crystal mlcrostructure.
Flg. 3 is a hlgher magnlflcatlon photomlcrograph, orlglnally lO500X, lllustratlng thls equlaxed crystal mlcrostructure ln greater detall.
Flg. 4 ls a lower magnlflcatlon photomlcrograph, orlglnally 100X, llluqtratlng the somewhat aclcular microstructure obtalned at a hlgher slnterlng temperature. Flg. 5 18 a hlgher 15magnlflcatlon photomlcrograph orlglnally 500X, of the same .
materlal lllustrated ln Flg. 4, lllustrating the slze and shape of the larger equlaxed gralns (about 33% larger than that of the materlal flred at 2120C) produced by exerclslng cIose control ovet the proce~s tlme and temperature. These Flgs. 4 and 5 20lllustrate a predomlnantly equlaxed mlcrostructure contalnlng some elongated gralns or platelets.
Flg. 6 18 a lower magnlflcatlon photomlcrograph, orlglnally 100X, lllustratlng the qrowth of large elongated gralns or plateIets wlthln the matrlx of the slllcon carblde structure.
`~ 25Flg. 7 18 a hlgher magnlflcatlon photomlcrograph, orl~lnally 500X, lllustratlng the slze and shape of the large alpha slllcon carblde gralns and the way that these gralns lmplnge upon one another ln thls predomlnately aclcular mlcrostructure.
.
. (KRS/ne) 00150-6Z3 --` 1 332~6~ ~
The amounts of alpha slllcon carblde, carbon and boron used to produce the three slntered bodies ln the~e experlments, together wlth the bulk densltles, mean grain slzes for the flrst two experlments, bulk densltles, slnterlng condltlons and flgure deslgnatlons are set forth ln the followlng Table. -~
TABLE 1 ~-~
EXPERIMENT 1 2 3 _ Part~ SiC 97.6 97.5 97.5 ~ ~
Parts Carbon 2.0 2.0 2.0 -:
Parts Boron 0.4 0.5 0.5 Mean Graln Slze (Mlcrons) 7.5 10.0 *
Slnterlng Temperature 2120C 2140C 2200C
ælnterlng Tlme 30 mln 45 mln 45 mln Slntered Bulk Denslty 3.15 ~/cc 3.17g/cc3.11 g/cc `~
% Theoretlc~l Denslty 98.1 98.8 96.9 ... -Figures 2 & 3 4 & 5 6 & 7 ~Not po~slble to determlne because of the extreme .:~;
degree of exaggerated graln growth.
The differences observed between Flgs. 2 and 3) Flgs. 4 and :.
5~ and Flgs. 6 and 7, are belleved to be due to the dlfferent ,-.
tlmes snd temperatures of slntering, and not due to the mlnor varlatlon ln mlx content for the materlals whlch were used to ;,.',.
form the green bodles. .:.
'~ EXAMPLE 2 ...
Sllicon carblde powder compact~ were produced from alpha phase slllcon carblde powder, phenollc resln sufficlent to yleld .~ :~
2~ by welght o~ carbon when carbonized, and boron carblde contalnlng 0.3%, 1.0% and 3.0% by welght of boron. Two speclmens of each composltlon were slntered ln a 6-lnch dl~meter :~
tube furnace malntalned at a temperature of 2150C. The ' ~-~ 1 332065 tKRS/ne) 00150-623 specimenQ were run through the furnace at a ~peed of 1/2-lnch per mlnute, produclng a hot zone residence tlme of approxlmately 25 mlnutes ln elther a "sea~oned" (boron-~aturated) graphite boat or ~n "unsessoned" graphite boat. The result~ are set froth ln Table 2.
Type of Cured Flred Flred Bxperiment Graphlte Percent Density Denslty Denslty %
No. Boat Boron ~cc q/cc Theoretlcal 4UnseQsoned 0.3 1.73 2.83 88.2 5Unseasoned 1.0 1.73 3.05 95.0 6Unseasoned 3.0 1.71 3.01 93.8 7Seasoned 0.3 1.73 3.16 98.4 8Sea~oned 1.0 1.72 3.14 97.8 9Sea~oned 3~0 1.71 3.11 96.9 Thls example lllustrates the effect of the use of an un~easoned bost on the flred denslty of the ~intered slllcon carbide artlcle.
Thls example 18 ~lmllar to Example 2 except that instead of a tube furnace, the slllcon carblde bodies were slntered ln a la~oratory furnace, the temperature of which was varled whlle the speclmens remAlned statlonary wlthln the furnace. One pellet from each composltlon was placed in a graphlte cruclble whlch waQ well boronated and open. The ~urnace components other th~n the crucible were also well boronated. The atmosphere lnslde the furnace was argon. The temperature was ralsed to 1500C over a perlod of 4.5 hours, and then ralsed at Q rate of 300C per hour until a temperature of 2120C was -~
(KRS/ne) 00150-623 attalned, whlch wa~ held for 45 mlnutes. The experlment was then repeated, except that instead of placing the speclmens ln an open boronated graphite crucible, they were placed ln an unboronated graphlte cruclble, ~eparated by qraphite plates and covered to protect the bodles from the boron ln the furnace walls, etc. The result6 are set forth ln Table 3.
Type of Cured Flred Flred Experlment Graphlte Percent Denslty Denslty Denslty %
_ o. Boat_ oron a/cc a/cc Theoretlcal Uncovered 0.3 1.729 3.175 98.9 Sea~oned ,, 11 Uncovered 1.0 1.712 3.161 98.5 Seasoned ' ~,"~
12 Uncovered 3.0 1.72~ 3.137 97.7 Seasoned 13 Covered 9.3 1.729 3.007 93.7 Unseasoned 14 Covered 1.0 1.736 2.992 93.2 -Unseasoned ;~
Covered 3.0 1.729 2.931 91.3 Unseasoned --,- ~.,~
Thls example lllustrate~ that the effect of an unseasoned boat lllustrated ln the prevlous example 18 not speclfic to a --partlcul&r type of furnace, although ln the present example the lower flred densltles obtalned wlth an unseasoned boat mlght be partlally attributed to the temperature dlfferential prodùced by the graphite plates separating and coverlng the samples being sintered.
~'-' '' :, ~; .
~and 2250C. It is preferred that the firing take place under conditions such that the level of boron retained in the body .being sintered is maintained, for example by enclosing the body being sintered within a sealed container which is impervious to boron at the temperature of sintering, and which has a volume approcimating the size of the body being sinterecl;
or by containing the body being sintered within a graphite ~
;container, which container has been saturated with boron by ~ :
.exposure to boron at or about the temperature of sintering.
There is also provided, according to this invention, a process for producing a sintered silicon carbide ceramic body, ~
with or without equiaxed crystal microstructure, from silicon . .
carbide powders of alpha or beta crystal microstructure, or :
amorphous silicon carbide, or mixtures thereof, comprising the ;.
steps of mixing together a mixture comprising the components:
,from about 91 to about 99.85 parts by weight silicon carbide powder having a surface area of from about 1 to about 100 m2~g; ~ ~;
,from about 0.67 to about 20 parts by weight of a carbonizable organic material having a carbon content of at least 33% by ~;
weight; from about 0.5 to about 5 parts by weight of a boror~
~source containiny from about 0.15 to about 3.0 parts by .. -:.
weight boron; up to about 15 parts hy weight of temporary h ~:
binder; and from about 25 to about 100% by weight of the ..
silicon carbide powder, carbonizable organic material, boron -source and temporary binder of a solvent in which the carboni~
zable organic material is soluble; said mixing being done in .
'.~'''" '".,:'."
;such a way as to disperse the carbonizable organic material labout the silicon carbide powder and coat the silicon carbide Ipowder therewith; drying the mixture in such a way as to l!evaporate the solvent from the mixture; shaping the dried mixture in such a way as to produce a shaped body having a ;~
density of at least about 1.60 g/cc; and firing the shaped ibody at a temperature of from about 1900C to about 2500C.
BrieE Description of the Drawings Fig. 1 of the drawing is a flow chart showing a typlcal sequence of process steps to produce the sintered ceramic body ;of the present invention.
~;~ Figs. 2-7 are photomicrographs. Figs. 2 and 3 show, at different magnifications, the equiaxed microstructure of the present invention produced by sintering at 2120C. Figs. 4-7 illustrate the microstructure which is obtained by sintering ;~ at higher temperatures.
Detailed Description ; The theoretical density of silicon carbide is 3.21 g/cc.
'IThe preferred minimum density of about 2.40 g/cc for sintered 20~ 'ceramic bodies according to the present invention corresponds, . ~ ~
therefore, to about 75% of theoretical density. The more -`~
~highly pre~ferred densities of 2.90 and 3.05 g/cc correspond to 90 and 95% of theoretical density, respectively.
I The primary constituent of the sintered ceramic body ~ 'according to the present invention is ~ilicon carbide, wherein ;
~.: ~ ;- ,.:
at least 95~ by weight of the silicon carbide is of the alpha (non-cubic crystalline) phase. While the process of the ,:
present invention is essentially immune to changes in the crystalline phase of the silicon carbide powder used as a start~ng material, i.e., the process of the present invention does not produce any substantial amount of phase transforma-tion, it has been observed that even if the silicon carbide powder used in the starting material for the present invention consists essentially of silicon car~ide of the alpha phase, ~some small degree of phase transformation may occur, so that some small proportion of the alpha phase material (probably ;
less than 1%, and certainly believed to be less than 5~) may transform to the beta phase. Thus, while in the broad aspects of the present invention the sintered ceramic body contains silicon carbide wherein at least 95~ by weight of the silicon carbide is of the alpha phase, it is preferred that at least about 99~ by weight of the silicon carbide be of the al~ha phase, or that the silicon carbide consists essentially of ;~
silicon carbide of the alpha phase. ;~
According to the processes of the prior art, it does not appear to have be~n possible to obtain a sintered silicon car-bide body wherein at least 95% by weight of the silicon car-bide is of the alpha phase, and wherein the sintered ceramic '~ody has a predominantly equiaxed microstructure. Although ;' 20 the product of the present inventian is therefore thus defined jbroadly~ it is preferred that the microstructure contain at ;~
least about 90% equiaxed grains, and more highly preferred `~;
that the microstructure consist essentially of equiaxed grains.
, The term "equiaxed grains" as used herein refers to a 25 crystal microstructure in which the grains have an aspect ;~-ratio of less than 3:1, i.e., the ratio of the maximum dimen-'sion of the grains of the crystal microstructure to the mini-`mum dimension of the grains of the crystal microstructure is less than 3:1. This microstructure is commonly known as "equiaxed" to distinguish it from crystal structures which are . ., .. . .. , . , . - . . . -~acicular, i.e., contain needle-shaped or tabular crystals, or ;a feathery microstructure such as illustrated in Fig. 2 of U.S. Patent l~o. 4,041,117. The product of the present inven-'tion is characterized by the combination of equiaxed grains land alpha phase in the silicon carbide of the sintered ceramic body, a combination not taught by the prior art, although the prior art does teach the production of sinter~d ceramic bodies having a beta phase and an equiaxed microstructure (using beta ,phase silicon carbide powder as the starting material).
I The preferred composition of tlle sintered ceramic body in accordance with the present invention consists essentially of from about 91 to about 99.85% by weight silicon carbide, up to about 5.0~ carbonized organic material, from about O.lS to about 3.0~ boron, and up to about 1.0% additional carbon. The "carbonized organic material" is free carbon or uncombined Icarbon produced in situ by the carbonization of the orsanic ¦material used as a raw material in the process of the present invention. The organic material is carbonized because the lorganic material is unstable at the temperature to which the Ibody being sintered is subjected, and the non-carbon compo- -~
Inents of this organic material are driven from the carbon --~
I Iskeleton of the organic material (i.e., volatilized away3.
Although the temperature attained during the process of the ;~
present invention is not sufficient to volatilize the carbon, ~-1 25 some carbon may be oxidized to carbon monoxide or carbon diox-:: I
de. Thus, depending upon the proportion of organic material 1-'used in the process of the present invention, the firing tem-perature, and other factors, there may be no carbon in the form of carbonized organic material present in the sintered body at ~ 1 , all. Usually, however, a minor proportion of carbon as ~ ' !
-8- ~
.... ~, . , , . ,, , , . . ,. .:
1 332~6~
carbonized organic material will remain. It is, however, very difficult to determine the amount of carbon present, since the oxidation test to determine the amount of carbon present ~
oxidize and remove a minor proportion of the silicon carbide matrix. The amount of carbon which is present as carbonized organic material will also depend upon the amount of such organic material which was added to the raw batch and the carbon content (char yield) of the organic material. While the preferred carbonizable organic materials for use in the process of the present invention are phenolic resin and coal - ;
tar pitch, which have carbon contents of from about 40 to . -:
about 42% and on the order of 60%, respectively, the carbon content of the organic material can be in excess of 90~, as ~for example in polyphenylene or polymethylphenylene.
Withill the b~oad composition recited above, it is pre-,~erred that the sintered ceramic body contain from about 0.5 to about 4% carbonized organic material, from about 0.18 to about 0.36~ boron and from about 0.05 to about 0.10~ additlon~
ial carbon, with the balance of the composition being silicon carbide. In particular, it is preLerred that the sintered ceramic body contain about 2% of carbonized organic material, about 0.36~ boron, and about 0.1~ additional carbon ~! All per~
centages herein are by weight, unless otherwise specified. -~
~The amount of "additional carbon" depends on the amount of 2S 'carbon associated with the boron present in the raw batch mix--ture from which the sintered ceramic body was made.
`In carrying out the process of the present invention, if the sintered body is to have a high alpha silicon carbide con- ~;
tent, it is preferred to begin with a silicon carbide powder which comprises at least 95% by weight alpha, non-cubic _9_ , .,. _ . , , , , , , , . :.
(KRS/ne) 00150-623 --` 1 332065 crystalline slllcon carbide. It is more hlghly preferred, however, that the sillcon carblde of the raw batch comprlses at least 99% by welght alpha ~lllcon carblde, or that the slllcon carblde of the raw batch consl~ts essentl~lly of alpha slllcon carblde.
The flrlng step of the process of the present lnventlon preferably takes from about 20 to about 60 minutes at temperatures of from about 1900 to about 2500C. Lower temperatures are in general lnoperable, and hlgher temperatures may cause subllmatlon of the slllcon carblde materlal. If a ~lntered ceramlc body having a predomlnantly e~ulaxed mlcrostructure 18 to be obtalned, the firing should be under such condltlons of tlme, temperature and atmosphere as to obtaln a denslty of at least about 2.40 g/cc and n egulaxed mlcrostructure, sald temperature belng between about 1900C and about 2250C. Wlthln thls range, the slntering temperature neces~ary to obtaln an equlaxed mlcrostructure, l.e., ln order to avold the formatlon of needles and platelet3 wlthln the crystal mlcrostructure, depends to a certaln extent on factors such as the lmpurlties present ln the slllcon carblde and the presence of absence of nltrogen ln the slnterlng atmosphere. If there are no exce~slve lmpurltles present, and the flrlng 18 to be done ln a vacuum or ln an atmosphere whlch excludes nltrogqn (such as an atmosphere of up to about 1 atmosphere of pressure of a ~as selected from the group con~lstlng of argon, carbon dloxlde, carbon monoxlde, hellum, hydrogen, neon and mlxtures thereof), the preferred temperature of flrlng on order to obtaln an egulaxed crystal mlcro~tructure 18 between about 1900C and about 2160C, more preferably from about 2100C to ~bout 2150C~
The pre~ence of impurltle~ ln the slllcon -- 10~
(KRS/ne) 00150-623 ~
t 3 3 2 0 6 5 ! ' ' carbide wlll lnfluence thls temperature range. In partlcular, when uslng "black" slllcon carblde contalnlng a hlgh alumlnlum content (on the order of 0.2% alumlnum by weight of sllicon ;;
carblde)~ temperature control is more lmportant, and even the .-temperature of 2160C may be too hlgh. The usual raw materlal for use ln the present lnventlon 18 "green" graln slllcon carblde, contalnlng about 0.02% or less alumlnlum. If the amount of the alumlnlum present ln the sillcon carblde 18 less ~;~than 0.02%, even hlgher temperatures can be tolerated wlthout . "
1088 of the predomlnantly equlaxed mlcrostructure. The presence of nltrogen ln the sinterlng atmosphere ralses the mlnlmum temperature necessary to achleve satlsfactory ~lnterlng, and also ralses the temperature at whlch the equlaxed mlcrostructure ~ ., .
18 lost, so that when slnterlng ln a nltrogen atmosphere, a ;~
15 ~ predomlnantly equlaxed mlcro6tructure can be obtalned even lf ~ -~
the temperature 18 between about 1975C and about 2300C. Wlthln ~ :-this range, ln a nltrogen atmosphere, a flrlng temperature of ; between about 2100C and about 2250C 18 preferred. In any event, the preferred flrlng tIme varles from about 20 to about~
20~ 60 mlnutes.
Ao used hereln, "predomlnantly" means greater than 50%. ~;;
In carrylng out the present lnventlon, lt 18 preferred to ;~-~
take steps to malntaln the level of boron retalned in the body -~
~;belng slntered. In thls connectlon, placlng the artlcle to be 25~ slntered ln a fresh graphlte "boat" whlch has never been used ln slnterlng before tends to have a detrlmental effect upon the denolty obtalned. Thi8 18 because the fresh graphlte boat acts as a ~boron slnk" whlch wlthdraws boron from the artlcle belng - ;
slntered, thus preventlng the boron from fully achlevlng lts role ln promotlng slnterlng and denslflcatlon of the artlcle ~ belng slntered. ~ ;
1 332~6~
- Various tecl~ni~ues can be used in order to maintain the . , , boron within the shaped body during the sintering operation.
U.S. Patent No. 4,080,415 describes, for example, the intro-duction of a gas such as boron trichloride into the sintering ~atmosphere and painting the furnace components with a solution , :
or slurry containing a boron compound. Another technique for malntaining the level of boron retained in the body being sin-tered: is to incorporate greater amounts of boron in the article ,;to be sintered. Another technique of maintaining the level of boron retained in the body being sintered is to enclose the -~
body being sintered wi~hin a sealed container which is imper-.viou~s to~boron at the temperature ~f sintering (such as a jglass~container)~ and which has a volume approximating the size~of the~body~;being;sintered~ ~ preferred techniaue of 5~ -,malntaining; the level oL boron retained in the body being intered~ ls~ to~ contal~n the body~ being sin~tered within a e~ boat~ i.e~ a graphlte container which has been ~ ~ ;
a ~ te~ withj~boron-by~exposure to boron at or about the ;`~
ù`rè~of~si*~ ing. Such expo~sure occurs naturally the~si ~ring operation, ~and it ha8 been~observed that ; ~ - ;
èr~esuits ~ :e`~, ~ igher ~densitles) can be obtained by the uselof~graphite boat~s~whlch have been used for sinte~ing usly~ sulil~lentl. often to becone saturated~
Tl`e~sl~licQn~c~arbide~powd~r for use ln the present inven~
` ~ has~ alsurfaoe~area o~f from about 1 to about lOO~m2/g.
h` lliC n~carbide~po ers are usually leis than 20 microns u~ partlcle~s;ize~ ore~particularly less than 10 miCrons in~
artlcle Size: an~ in particular sub-micron size particles are ~
~ 30 ,generally preferred. It is difficult, however, to obtain ~ ~r"''-' :~'; :~' . ', .',`,''' ' ,' ' . ' (KRS/ne) 00150-623 . ~ . I
accurate partlcle slze dlstrlbution~ for slllcon carblde powders havlng slze much less than 1 mlcron ln particle slze, and the surface area of the slllcon carblde partlcle 18 the more relevant conslderation ln determinlng sultable materlal.
Accordlngly, the preferred slllcon carblde powder for use ln the present lnventlon are speclfled as havlng from about 1 to about lOO mt/g surface area. Withln thls range, lt 18 more preferred that the surface area of the slllcon carbide partlcles range between about 5 and 50 ml/gt and wlthln thls range, surfQce areas ~ , between about 7 and about 15 m'/g have been found to be easlly obtalnable and qulte useful for produclng slntered ceramlc bodles of the present lnventlon.
;The slllcon carblde startlng materlal can be obtalned from any of a varlety of sourcés. Vapour phase reacted materlal 18 produced in fine partlcle slze, and can be used lf deslred.
Larger materlal can be ball mllIed untll sufflclent amounts of fine slllcon carblde are obtained, and the proper slze of slllaon carblde can be selected from the ball mllled product by conventlonal eans, such as water sedimentatlon.
Th-~crystallln-~hablt of the slllcon carblde 18 essentlal}y non-orltlcal except ln th- case where a hlgh alpha slllcon carbldé content ls deslred ln the slntered body. Alpha non~
cublc ~slllcon carblde ls;~more readlly avallable then beta slllaon carblde, and therefore the preferred startlng materlal 25~ oontalns slllcon carblde~whlch conslsts essentlally of alpha, non-oublc orystallln- slllcon carblde. It 18 qulte acceptable, how v r, to u8e slllcon carblde whlch has been made by a procesa whleh produces mlxtures of alpha and beta slllcon carblde, and an~operable startlng mat-rlal 18 slllcon carblde whlch 18 predomlnantly alpha, non-cublc crystalllne slllcon (KRS/ne) 00150-623 " 1 332065 carblde. It has Ql80 been shown to be operable to use raw batches whereln the slllcon carblde comprise~ at least 5% alpha, non-cublc crystalllne silicon carblcle, and amorphous slllcon carblde can al90 be used. It 18 even posslble to use hlgh purlty beta slllcon carblde ~tartlng materlal, but such materlal i8 not preferred because of the hlgh expense of obtalnlng hlgh purlty beta sillcon carblde powders.
In any event, it 18 pre~erred that the ~lllcon carblde materlal ~hall have been treated wlth acid (such as hyclro-' 0 f luorlc and/or nltrlc aclds, partlcularly mixtures of hydro-fluorlc and nltrlc aclds) to remove extraneous materlals whlch may lnterfere with the slnterlng operatlon.
One of the more lmportant features of the raw batch of the present lnventlon ls the carbonlzable organlc material. It ha~
been found deslrable that thi3 materlal be organlc ln order that lt be easlly dlspersable about the slllcon carblde powder, ln order to coat the slllcon carblde powder and provlde an lntimate availablllty of carbonlzed organic material upon flrlng of the shsped body produced from the raw batch. The organlc materlal can be organlc solvent ~oluble, or soluble in water lf a water solvent 19 used. It has been found deslrable that the slntered ceramlc body contain up to about 5.0% usually from about 0.5 to about 5.0% , of carbonlzed organlc materlal, wlth the result that lf the carbonlzable, or~anlc solvent soluble, organlc ~; .
materlal has a carbon content (char yleld) of from about 25 to about 75% by welght, as 18 common, there should be pre~ent from about 0.67 to about 20 part~ by welght of carbonlzable organlc materlal in the raw batch. Withln the range of from about 25 to about 75% by welght carbon content, lt 18 more common that the organlc materlal have ."~
~ - 14 - ~ ~;
1 332~65 'from about 33 to about 50~G by weic311t, more particularly from about 40 to about 45% by weight, carbon content. If the car-bon content is between about 33 and about 50~ by weight, the - :
amount of carbonizable organic material should range between 'about l and 12% by weiyht to produce the preferred amount of carbon in the form of carbonized organic material of from ,about 0.5 to about 4.0% by weight in the finished sintered ~ .
ceramic body. The most preferred amount of carbonized organic material in the sintered ceramic body is believed to be about 2% by weight, so that the optimum raw batch should contain about 5% by weight of organic material havin~i a carbon content between a~out 40 and 45~i by weight. Particularly preferred ; ,carbonizable organic materials are phenolic resin and coal tar u~ pitch, which have carbon contents of from about 40 to about 15 ~ ,4~2~ and on tbe order o2 60%f respectively. As between the ~;
phenolic resin and coal~tar pitch, the phenolic resin is more ;
definitely preferred, and particularly a B-stage resole phen~
c~resin has bee~l found to be particularly useful in the ;
present~i~nvent1on.
20~ The;boron can~be;added to the raw batch as either ele~en~
tal`boron or as boron carbide. ~oron carbide is essentially a non-stoichlometric material, and various~boron carbide i~
mater~ials~;having a mo}ar ratio~of boron to carbide between 8~
and~2~ have been reported. It is in general preferred to use ;25~ ;boron~carbide as the boron source, and in particularly boron carbide~which i9 so-called "solid state reacted boron carbide"
with a molar ratio of boron to carbon between about 3.5:1 and ;4.l:l. Such boron carbide can be produced in accordance with the process of U.S. Patent No. 3,379,647, P. A. Smudski. The 30~ process of the above Smudski patent is found to produce boron : ~, 1 3 3 2 ~ b ~ !
'carbides having such a molar ratio, and such a molar ratio is preferred because with the higher boron to carbon ratio, the ~oron carbide eith~r takes carbon or gives boron to the 'surrounding chemical species, which is desirable in the present ~instance as it promotes the desired densification during the firing step of the process of the present invention. Boron carbide materials having greater ratios of boron to carbide '' '~
are even more chemically active than the material havin~ a ; 'ratio of about 4.l:l to about 3.5:l, but such materials are ~relatively less available and more expensive, and therefore !are not preferred for that reason.
;~ The amount of boron source to be added to the raw batch ;depends on the boron content of the boron source and the amount of boron to be present in the final sintered ceramic ; 15 body. The sintered ceram1c body should contain from about 0.15 to about 3.0~ boron, and in particular from about 0.18 to about 0.36% boron is present in the most successfully ` '-' densified bodies produced in accordance with the present inven~
tion. 0.36~ is the optimum boron content of the sintered ~ceramic body. The amount of boron source should thus be cho~
sen accordingly. Thus,~if the boron source is elemental boron, "`-t should be present in the raw batch from about 0.18 to about Q.36 parts by by weight to`yield a sintered ceramic body hav~
!ing from about 0.18 to about 0.36% by weight boron. For the ,preferred solid state reacted boron carbide with a molar ratio ; IO~f boron to carbon between about 3.5:l and about 4.l:l, the `boron carbide should be ~resent in an amount from about 0.23 ''- ''' to about 0.46 parts by weight to produce such an amount of boron in the finished sintered ceramic body.
~ In any event, the boron source can be crystalline or ~:
-16- '~
1 332~5 ~non-crystalline, and preferably is particulate and of a slze less ~than 30 microns. Within this limitation, it is preferred that ~the boron source be of a size ranging from about 0.1 to about 10 microns.
The temporary binder, if used, is preferably polyvinyl alco-hol having associated therewith from about 5 to about 15 parts by weight water, per part of polyvinyl alcohol, as a temperary binder vehicle. In particular, it is preferred to use 10 parts by weight polyvinyl alcohol plus about 90 parts by weight water as a temporary binder vehicle. In addition to polyvinyl alcohol, however, other temporary binders can be used, such as coal tar pitch, long chain fatty material (for example CARBOWAX~ wax, I ;
available from Union Carbide Corporation), metallic stearates ; such as aluminum stearates and zinc stearates, sugars, starches, alginates, and polymethyl phenylene. Many of these materials ¦
are, of course, capable as functioning as the carbonizable orga-nic material which is added in sufficient quantity to yield the appropriate amount of carbonized organic materila in the finlshed sintered ceramic body. A single material can thus serve two functions in the raw batch.
The process for producing the sintered ceramic body according to the present invention can begin with the mi~ing together from about 91 to about 99.85 parts by weight silicon carbide; from about 0.67 to about 20 parts by weight of the car-bonizable organic material; from about 0.15 to about 5% by weight of the boron source; and up to about 15 parts by weight of tem-porary binder. The solvent can be added to this mixture, or the carbonizable organic material dissolved in the solvent first. If ¦
the temporary binder is polyvinyl alcohol including a quantity of water as temporary binder vehicle, this first ¦~
-;:
~ 33~9~
m~xing step prefera~ly includes stirring the powdered materials ~(silicon carbide, organic material and boron source) togetller with the temporary binder and temporary binder vehicle, prior to adding an organic solvent in which the organic material is soluble. AEter th~ organic solvent is added, the components ;are preferably stirred in such a way as to disperse the carbon- ~ --.:
izable organic material about the silicon carbide powder and ~ ;~
coat the silicon carbide powder therewith, suitably for at ~least about S minu~es, and preFerably about 15 minutes.
After the components have been stirred so as to disperse ;;
the organic material about the silicon carbide powder and coat the silicon carbide powder therewith, the stirred mixture is ~; dried by any suitable technique, such as passing a quantity of ~;
drying gas near the stirred mixture, vacuum treating or by ,: , ~ , lS spray-drying the mixture. Following this drying step, the dried mixture is shaped in such a way as to produce a shaped body preferahly having a density of at least about 1.60 g/cc.
This shaping can be accomplished by any of a variety of tech- `;~
niques which are in themselves known, for example by extrusion, ,'!
20 ~ I injection molding, transfer molding, casting, cold pressing, isostatic pressing, or by compression. If compresslon is used, ,pireferred pressures are between about 4,000 and about 100,000 -~
psi, wlth between about 16,000 and about 20,000 psi being pre~
ferred. If a temporary binder of polyvinyl alcohol is used, -~
the next step of curing the temporary binder can be preferably "~
accomplished by heating the shaped body at a temperature about 90 to about 100C for about 1 to about 2 hours. The shaped body is then fired to accomplish the densification necessary to produce the sintered ceramic body of the invention. ~iring ; , -.: :., takes from about 20 to about 60 minutes at temperatures of ~ ~
'`' ', ' :.
~' ....
-18- ;;-~
1 332~5 :
from about l900 to ab~ut 2500C. Lower temperatures are in general inoperable, and higher temperatures may cause suklima-tion of the silicon carbide material. The firing step can be ~carried out in a conventional tube furnace wherein the shaped body is passed through the hot zone of the tube furnace to have a residence time at the desired tem~erature and for the desired time. Details of such tube furnaces are known in the prior art, and are disclosed for example in P. A. Smudski, U.S. Patent No. 3,6B9,220. The firing step accomplished a -"pressureless sintering", referred to herein for simplicity merely as "sintering". By "sintering" or "pressureiess sin-; tering" i is meant that no mechanical pressure is applied to the object being fired or sintered to enhance the reaction.
Instead, the object being sintered is surrounded, usually in 1 15 'an~inert container such as a graphite crucible, in up to about l atmosphere of pressure of an inert gas, a reducing gas, a vacuum, or nitrogcn. Reducing gases include hydrogen, carbon dioxide and carbon monoxide; inert gases include argon, helium, and neon. The gases in which the sintering operation can be ,aarried out thus include argon, ca~bon dioxide, carbon monox-iide, helium, hydrogen, neon and nitrogen. Although nitrogen ~çnters into reaction in a minor dec3ree with the silicon ¢ar-~ I
bide raw material, it does so in sufficiently minor degreethat the composition of the sintered ceramic body is not ,noticeably changed. The use of nitrogen, however, does raise -the necessary sintering temperature about 200C, so that if nitrogen is the surrounding atmosphere, a preferred sintering temperature is from about 2260C to about 2300C. In the other gases, particularly inert gases such as argon, helium or neon, a preferred sintering temperature is from about 20~0C
:, ' --19-- ~ .
, ...... , .. . i .. . ... .. ., .. . . . . , . . , . , ., , ., , . : ~
1 332065 ~ -to about 2100C. If it is desired to maintain an equiaxed crystal microstructure, these temperatures should be more closely controlled, as described above. The firing can also be carried out under vacuum, i.e., without any surrounding atmosphere. By "vacuum" is meant a practical vacuum, i.e., an absolute pressure of 1.0 mmHg or less.
The invention will now be illustrated with several exam-ples.
~; ` EXAMPLE 1 Sintered silicon carbide bodies were produced from mixes ~-containing indicated amounts of submicron alpha silicon car-bide having a surface area between about 10 and 12 m2/g, B-stage phenol aldehyde resole resin containlng indicated amount of carbon, and boron carbide powder (smaller than 10 mesh) containing indicated amounts of boron. The proportions are set forth in Table 1. For each experiment, 4.9 parts resin were mixed with 150 parts acetone for 5 minutes, the boran carbide powder added, and the suspension stirred for an ~ ~
additional 5 minutes. The silicon carbide powder was slowly ~ ;
added to the mixture and the combined mixture stirred 30 min~
utes to disperse the ingredients thoroughly. The mix was stirred while the acetone evaporated. After the batich was dry . ~.
the powder cake was easily broken up into a granula-r array of particles by passing it through a 60 mesh screen. The , ,:, ., ~',''~',~
,.,,.j,....
'"'"'~
.. ~
~, ,.
-20- ;
., ' ",~'.''' -~1 332065 (KRS/ne) 00150~6Z3 partlcle~ were then pressed lnto compacts which were subsequently baked at 150C for 2 hour~ to cure the phenollc resln. The cured den~ltles of the plece~ ln all cases were ln excess of 1.70 g~cc.
STwo photomlcrographs for each experlment of pollshed and etched sectlons of these bodles are lllustrated ln the drawing.
Flg. 2 18 a lower magnlflcatlon photomlcrograph, orlglnally lOOX, lllu~tratlng a unlform equlaxed crystal mlcrostructure.
Flg. 3 is a hlgher magnlflcatlon photomlcrograph, orlglnally lO500X, lllustratlng thls equlaxed crystal mlcrostructure ln greater detall.
Flg. 4 ls a lower magnlflcatlon photomlcrograph, orlglnally 100X, llluqtratlng the somewhat aclcular microstructure obtalned at a hlgher slnterlng temperature. Flg. 5 18 a hlgher 15magnlflcatlon photomlcrograph orlglnally 500X, of the same .
materlal lllustrated ln Flg. 4, lllustrating the slze and shape of the larger equlaxed gralns (about 33% larger than that of the materlal flred at 2120C) produced by exerclslng cIose control ovet the proce~s tlme and temperature. These Flgs. 4 and 5 20lllustrate a predomlnantly equlaxed mlcrostructure contalnlng some elongated gralns or platelets.
Flg. 6 18 a lower magnlflcatlon photomlcrograph, orlglnally 100X, lllustratlng the qrowth of large elongated gralns or plateIets wlthln the matrlx of the slllcon carblde structure.
`~ 25Flg. 7 18 a hlgher magnlflcatlon photomlcrograph, orl~lnally 500X, lllustratlng the slze and shape of the large alpha slllcon carblde gralns and the way that these gralns lmplnge upon one another ln thls predomlnately aclcular mlcrostructure.
.
. (KRS/ne) 00150-6Z3 --` 1 332~6~ ~
The amounts of alpha slllcon carblde, carbon and boron used to produce the three slntered bodies ln the~e experlments, together wlth the bulk densltles, mean grain slzes for the flrst two experlments, bulk densltles, slnterlng condltlons and flgure deslgnatlons are set forth ln the followlng Table. -~
TABLE 1 ~-~
EXPERIMENT 1 2 3 _ Part~ SiC 97.6 97.5 97.5 ~ ~
Parts Carbon 2.0 2.0 2.0 -:
Parts Boron 0.4 0.5 0.5 Mean Graln Slze (Mlcrons) 7.5 10.0 *
Slnterlng Temperature 2120C 2140C 2200C
ælnterlng Tlme 30 mln 45 mln 45 mln Slntered Bulk Denslty 3.15 ~/cc 3.17g/cc3.11 g/cc `~
% Theoretlc~l Denslty 98.1 98.8 96.9 ... -Figures 2 & 3 4 & 5 6 & 7 ~Not po~slble to determlne because of the extreme .:~;
degree of exaggerated graln growth.
The differences observed between Flgs. 2 and 3) Flgs. 4 and :.
5~ and Flgs. 6 and 7, are belleved to be due to the dlfferent ,-.
tlmes snd temperatures of slntering, and not due to the mlnor varlatlon ln mlx content for the materlals whlch were used to ;,.',.
form the green bodles. .:.
'~ EXAMPLE 2 ...
Sllicon carblde powder compact~ were produced from alpha phase slllcon carblde powder, phenollc resln sufficlent to yleld .~ :~
2~ by welght o~ carbon when carbonized, and boron carblde contalnlng 0.3%, 1.0% and 3.0% by welght of boron. Two speclmens of each composltlon were slntered ln a 6-lnch dl~meter :~
tube furnace malntalned at a temperature of 2150C. The ' ~-~ 1 332065 tKRS/ne) 00150-623 specimenQ were run through the furnace at a ~peed of 1/2-lnch per mlnute, produclng a hot zone residence tlme of approxlmately 25 mlnutes ln elther a "sea~oned" (boron-~aturated) graphite boat or ~n "unsessoned" graphite boat. The result~ are set froth ln Table 2.
Type of Cured Flred Flred Bxperiment Graphlte Percent Density Denslty Denslty %
No. Boat Boron ~cc q/cc Theoretlcal 4UnseQsoned 0.3 1.73 2.83 88.2 5Unseasoned 1.0 1.73 3.05 95.0 6Unseasoned 3.0 1.71 3.01 93.8 7Seasoned 0.3 1.73 3.16 98.4 8Sea~oned 1.0 1.72 3.14 97.8 9Sea~oned 3~0 1.71 3.11 96.9 Thls example lllustrates the effect of the use of an un~easoned bost on the flred denslty of the ~intered slllcon carbide artlcle.
Thls example 18 ~lmllar to Example 2 except that instead of a tube furnace, the slllcon carblde bodies were slntered ln a la~oratory furnace, the temperature of which was varled whlle the speclmens remAlned statlonary wlthln the furnace. One pellet from each composltlon was placed in a graphlte cruclble whlch waQ well boronated and open. The ~urnace components other th~n the crucible were also well boronated. The atmosphere lnslde the furnace was argon. The temperature was ralsed to 1500C over a perlod of 4.5 hours, and then ralsed at Q rate of 300C per hour until a temperature of 2120C was -~
(KRS/ne) 00150-623 attalned, whlch wa~ held for 45 mlnutes. The experlment was then repeated, except that instead of placing the speclmens ln an open boronated graphite crucible, they were placed ln an unboronated graphlte cruclble, ~eparated by qraphite plates and covered to protect the bodles from the boron ln the furnace walls, etc. The result6 are set forth ln Table 3.
Type of Cured Flred Flred Experlment Graphlte Percent Denslty Denslty Denslty %
_ o. Boat_ oron a/cc a/cc Theoretlcal Uncovered 0.3 1.729 3.175 98.9 Sea~oned ,, 11 Uncovered 1.0 1.712 3.161 98.5 Seasoned ' ~,"~
12 Uncovered 3.0 1.72~ 3.137 97.7 Seasoned 13 Covered 9.3 1.729 3.007 93.7 Unseasoned 14 Covered 1.0 1.736 2.992 93.2 -Unseasoned ;~
Covered 3.0 1.729 2.931 91.3 Unseasoned --,- ~.,~
Thls example lllustrate~ that the effect of an unseasoned boat lllustrated ln the prevlous example 18 not speclfic to a --partlcul&r type of furnace, although ln the present example the lower flred densltles obtalned wlth an unseasoned boat mlght be partlally attributed to the temperature dlfferential prodùced by the graphite plates separating and coverlng the samples being sintered.
~'-' '' :, ~; .
Claims (52)
1. A sintered ceramic body consisting essentially of:
(a) from about 91 to about 99.85% by weight silicon carbide, wherein at least 95% by weight of the silicon carbide is of the alpha phase;
(b) up to about 5.0% by weight carbonized organic material;
(c) from about 0.15 to about 3.0% by weight boron;
and (d) up to about 1.0% by weight additional carbon; and having a predominantly equiaxed microstructure.
(a) from about 91 to about 99.85% by weight silicon carbide, wherein at least 95% by weight of the silicon carbide is of the alpha phase;
(b) up to about 5.0% by weight carbonized organic material;
(c) from about 0.15 to about 3.0% by weight boron;
and (d) up to about 1.0% by weight additional carbon; and having a predominantly equiaxed microstructure.
2. A sintered ceramic body according to claim 1, having a density of at least about 2.40 g/cc.
3. A sintered ceramic body according to claim 2, wherein at least about 99% by weight of the silicon carbide 18 of the alpha phase.
4. A sintered ceramic body according to claim 2, wherein the silicon carbide consists essentially of silicon carbide of the alpha phase.
5. A sintered ceramic body according to claim 2, having a microstructure containing at least about 90% equiaxed grains.
6. A sintered ceramic body according to claim 2, having a microstructure consisting essentially of equiaxed grains.
7. A sintered ceramic body according to claim 1, having a density of at least about 2.90 g/cc.
8. A sintered ceramic body according to claim 7, wherein at least about 99% by weight of the silicon carbide is of the alpha phase.
9. A sintered ceramic body according to claim 7, wherein the silicon carbide consists essentially of silicon carbide of the alpha phase.
10. A sintered ceramic body according to claim 7, having a microstructure containing at least about 90% equiaxed grains.
11. A sintered ceramic body according to claim 7, having a microstructure consisting essentially of equiaxed grains.
12. A sintered ceramic body according to claim 1, having a density of at least about 3.05 g/cc.
13. A sintered ceramic body according to claim 12, wherein at least about 99% by weight of the silicon carbide is of the alpha phase.
14. A sintered ceramic body according to claim 12, wherein the silicon carbide consists essentially of silicon carbide of the alpha phase.
15. A sintered ceramic body according to claim 12, having a microstructure containing at least about 90% equiaxed grains.
16. A sintered ceramic body according to claim 12, having a microstructure consisting essentially of equiaxed grains.
17. A process for producing a sintered alpha silicon carbide ceramic body having equiaxed microstructure, comprising the steps of:
(a) mixing together a mixture comprising the components:
(i) from about 91 to about 99.85 parts by weight silicon carbide powder comprising at least 95% by weight alpha, non-cubic crystalline silicon carbide and having a surface area of from about 1 to about 100 m2/g;
(ii) from about 0.67 to about 20 parts by weight of a carbonizable organic material having a carbon content of at least 33% by weight;
(iii) from about 0.15 to about 5 parts by weight of a boron source containing from about 0.15 to about 3.0 parts by weight boron;
(iv) up to about 15 parts by weight of temporary binder; and (v) from about 25 to about 100% by weight of the silicon carbide powder, carbonizable organic material, boron source and temporary binder of a solvent in which the carbonizable organic material is soluble;
said mixing being done in such a way as to disperse the carbonizable organic material about the silicon carbide powder and coat the silicon carbide powder therewith;
(b) drying the mixture in such a way as to evaporate the solvent from the mixture;
(c) shaping the dried mixture in such a way as to produce a shaped body having a density of at least about 1.60 g/cc; and (d) firing the shaped body under such conditions of time, temperature and atmosphere as to obtain a density of at least about 2.40 g/cc and an equiaxed microstructure, said temperature being between about 1900°C and about 2250°C.
(a) mixing together a mixture comprising the components:
(i) from about 91 to about 99.85 parts by weight silicon carbide powder comprising at least 95% by weight alpha, non-cubic crystalline silicon carbide and having a surface area of from about 1 to about 100 m2/g;
(ii) from about 0.67 to about 20 parts by weight of a carbonizable organic material having a carbon content of at least 33% by weight;
(iii) from about 0.15 to about 5 parts by weight of a boron source containing from about 0.15 to about 3.0 parts by weight boron;
(iv) up to about 15 parts by weight of temporary binder; and (v) from about 25 to about 100% by weight of the silicon carbide powder, carbonizable organic material, boron source and temporary binder of a solvent in which the carbonizable organic material is soluble;
said mixing being done in such a way as to disperse the carbonizable organic material about the silicon carbide powder and coat the silicon carbide powder therewith;
(b) drying the mixture in such a way as to evaporate the solvent from the mixture;
(c) shaping the dried mixture in such a way as to produce a shaped body having a density of at least about 1.60 g/cc; and (d) firing the shaped body under such conditions of time, temperature and atmosphere as to obtain a density of at least about 2.40 g/cc and an equiaxed microstructure, said temperature being between about 1900°C and about 2250°C.
18. A process according to claim 17, wherein the silicon carbide of the raw batch comprises at least 99% by weight alpha, non-cubic crystalline silicon carbide.
19. A process according to claim 17, wherein the silicon carbide of the raw batch consists essentially of alpha, non-cubic crystalline silicon carbide.
20. A process according to claim 17, wherein the body is fired for a time varying from about 20 to about 60 minutes;
wherein said temperature is between about 1900°C and about 2160°C; and said conditions of atmosphere are firing in a vacuum or up to about 1 atmosphere of pressure of a gas selected from the group consisting of argon, carbon dioxide, carbon monoxide, helium, hydrogen, neon, and mixtures thereof.
wherein said temperature is between about 1900°C and about 2160°C; and said conditions of atmosphere are firing in a vacuum or up to about 1 atmosphere of pressure of a gas selected from the group consisting of argon, carbon dioxide, carbon monoxide, helium, hydrogen, neon, and mixtures thereof.
21. A process according to claim 20, wherein said temperature is from about 2100°C to about 2150°C.
22. A process according to claim 17, wherein the body is fired for a time varying from about 20 to about 60 minutes;
wherein the temperature is between about 1975°C and about 2300°C;
and the atmosphere is up to about 1 atmosphere of pressure of nitrogen.
wherein the temperature is between about 1975°C and about 2300°C;
and the atmosphere is up to about 1 atmosphere of pressure of nitrogen.
23. A process according to claim 22, wherein the temperature is between about 2100°C and about 2250°C.
24. A process according to claim 17, wherein the level of boron retained in the body being sintered is maintained by enclosing the body being sintered within a sealed container which is impervious to boron at the temperature of sintering, and which has a volume approximating the size of the body being sintered.
25. A process according to claim 17, wherein the level of boron retained in the body being sintered is maintained by containing the body being sintered within a graphite container, which container has been saturated with boron by exposure to boron at or about the temperature of sintering.
26. A process for producing a sintered silicon carbide ceramic body, comprising the steps of:
(a) mixing together a mixture comprising the components:
(i) from about 91 to about 99.85 parts by weight silicon carbide powder having a surface area of from about 1 to about 100 m2/g;
(ii) from about 0.67 to about 20 parts by weight of a carbonizable organic material having a carbon content of at least 33% by weight;
(iii) from about 0.15 to about 5 parts by weight of a boron source containing from about 0.15 to about 3.0 parts by weight boron;
(iv) up to about 15 parts by weight of temporary binders and (v) from about 25 to about 100% by weight of the silicon carbide powder, carbonizable organic material, boron source and temporary binder of a solvent in which the carbonizable organic material is soluble;
said mixing being done in such a way as to disperse the carbonizable organic material about the silicon carbide powder and coat the silicon carbide powder therewith;
(b) drying the mixture in such a way as to evaporate the solvent from the mixture;
(c) shaping the dried mixture in such a way as to produce a shaped body having a density of et least about 1.60 g/cc; and (d) firing the shaped body at a temperature of from about 1900°C to about 2500°C.
(a) mixing together a mixture comprising the components:
(i) from about 91 to about 99.85 parts by weight silicon carbide powder having a surface area of from about 1 to about 100 m2/g;
(ii) from about 0.67 to about 20 parts by weight of a carbonizable organic material having a carbon content of at least 33% by weight;
(iii) from about 0.15 to about 5 parts by weight of a boron source containing from about 0.15 to about 3.0 parts by weight boron;
(iv) up to about 15 parts by weight of temporary binders and (v) from about 25 to about 100% by weight of the silicon carbide powder, carbonizable organic material, boron source and temporary binder of a solvent in which the carbonizable organic material is soluble;
said mixing being done in such a way as to disperse the carbonizable organic material about the silicon carbide powder and coat the silicon carbide powder therewith;
(b) drying the mixture in such a way as to evaporate the solvent from the mixture;
(c) shaping the dried mixture in such a way as to produce a shaped body having a density of et least about 1.60 g/cc; and (d) firing the shaped body at a temperature of from about 1900°C to about 2500°C.
27. A process according to claim 26, wherein the mixing together of the components comprises:
(a) mixing together a raw batch comprising:
(i) from about 91 to about 99.85 parts by weight silicon carbide powder having a surface area of from about 1 to about 100 m2/g;
(ii) from about 0.67 to about 20 parts by weight of carbonizable organic material having a carbon content of at least 33% by weight;
(iii) from about 0.15 to about 5 parts by weight of a boron source containing from about 0.15 to about 3.0 parts by weight boron;
(iv) up to about 15 parts by weight of temporary binder;
(b) adding to the raw batch from about 25 to about 100% by weight of the raw batch of a solvent in which the carbonizable organic material is soluble; and (c) stirring the raw batch and organic solvent in such a way as to disperse the carbonizable organic material about the silicon carbide powder and coat the silicon carbide powder therewith.
(a) mixing together a raw batch comprising:
(i) from about 91 to about 99.85 parts by weight silicon carbide powder having a surface area of from about 1 to about 100 m2/g;
(ii) from about 0.67 to about 20 parts by weight of carbonizable organic material having a carbon content of at least 33% by weight;
(iii) from about 0.15 to about 5 parts by weight of a boron source containing from about 0.15 to about 3.0 parts by weight boron;
(iv) up to about 15 parts by weight of temporary binder;
(b) adding to the raw batch from about 25 to about 100% by weight of the raw batch of a solvent in which the carbonizable organic material is soluble; and (c) stirring the raw batch and organic solvent in such a way as to disperse the carbonizable organic material about the silicon carbide powder and coat the silicon carbide powder therewith.
28. A process according to claim 27, wherein the stirring continues for at least about 5 minutes.
29. A process according to claim 28, wherein the stirring continues about 15 minutes.
30. A process according to claim 26, wherein the mixing together of the components comprises:
(a) dissolving the carbonizable organic material in the solvent; and (b) mixing the solution so formed with the remaining components.
(a) dissolving the carbonizable organic material in the solvent; and (b) mixing the solution so formed with the remaining components.
31. A process according to claim 26, wherein the shaping is by extrusion.
32. A process according to claim 26, wherein the shaping is by compression at a pressure between about 40,000 and about 100,000 psi.
33. A process according to claim 32, wherein the shaping is by compression at a pressure between about 16,000 and about 20,000 psi.
34. A process according to claim 27, wherein the shaping is by injection moulding.
35. A process according to claim 27, wherein the shaping is by transfer moulding.
36. A process according to claim 27, wherein the shaping is by casting.
37. A process according to claim 27, wherein the shaping is by cold pressing.
38. A process according to claim 27, wherein the shaping is by isostatic pressing.
39. A process according to claim 26, wherein the temporary binder is used in an amount of from about 5 to about 15 parts.
40. A process according to claim 39, wherein the temporary binder is curable; and comprising a step of curing the temporary binder, after shaping the dried mixture, but prior to firing the shaped body.
41. A process according to claim 40, wherein the temporary binder is polyvinyl alcohol and the curing is accomplished by heating the shaped body at a temperature of about 90° to about 100°C for about 1 to about 2 hours.
42. A process according to claim 26, wherein the shaped body is fired for from about 20 to about 60 minutes; at a temperature of from about 1900°C to about 2500°C; and in a vacuum.
43. A process according to claim 26, wherein the shaped body is fired for from about 20 to about 60 minutes; at a temperature of from about 1900°C to about 2500°C; and in up to about 1 atmosphere of pressure of a gas selected from the group consisting of argon, carbon dioxide, carbon monoxide, helium, hydrogen, neon, nitrogen and mixtures thereof.
44. A process according to claim 43, wherein the gas is approximately 1 atmosphere of the member selected from the group consisting of argon, helium and neon; and the temperature is from about 2060°C to about 2100°C.
45. A process according to claim 43, wherein the gas is about 1 atmosphere of nitrogen, and the temperature is from about 2260°C to about 2300°C.
46. A process according to claim 26, wherein the level of boron retained in the body being sintered is maintained by enclosing the body being sintered within a sealed container which is impervious to boron at the temperature of sintering, and which has a volume approximating the size of the body being sintered.
47. A process according to claim 26, wherein the level of boron retched in the body being sintered is maintained by containing the body being sintered within a graphite container, which container has been saturated with boron by exposure to boron at or about the temperature of sintering.
48. A process according to claim 26, wherein the silicon carbide powder comprises predominantly alpha, non-cubic crystalline silicon carbide.
49. A process according to claim 26, wherein the silicon carbide powder comprises at least 95% by weight alpha, non-cubic crystalline silicon carbide.
50. A process according to claim 26, wherein the silicon carbide powder comprises at least 99% by weight alpha, non-cubic crystalline silicon carbide.
51. A process according to claim 26, wherein the silicon carbide powder consists essentially of alpha, non-cubic crystalline silicon carbide.
52. A process according to claim 26, wherein the silicon carbide powder is amorphous.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US90140678A | 1978-05-01 | 1978-05-01 | |
| US901,406 | 1986-08-28 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1332065C true CA1332065C (en) | 1994-09-20 |
Family
ID=25414107
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 326261 Expired - Lifetime CA1332065C (en) | 1978-05-01 | 1979-04-24 | Sintered alpha silicon carbide body having equiaxed microstructure |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPS54144411A (en) |
| CA (1) | CA1332065C (en) |
| DE (1) | DE2916817A1 (en) |
| FR (1) | FR2424889B2 (en) |
| GB (1) | GB2019891A (en) |
Families Citing this family (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3023425C2 (en) * | 1979-06-25 | 1989-02-02 | United Kingdom Atomic Energy Authority, London, Gb | High density sintered silicon carbide - mix of silicon carbide carbon and boron sintered in carbon contg. atmos. |
| DE3044161A1 (en) * | 1980-11-24 | 1982-06-03 | Annawerk Keramische Betriebe GmbH, 8633 Rödental | METHOD FOR PRODUCING A POLYCRYSTALLINE MOLDED BODY FROM SILICON CARBIDE |
| DE3044162A1 (en) * | 1980-11-24 | 1982-06-03 | Annawerk Keramische Betriebe GmbH, 8633 Rödental | POLYCRYSTALLINE SHAPED BODY MADE FROM SILICON CARBIDE AND METHOD FOR THE PRODUCTION THEREOF |
| JPS6036377A (en) * | 1984-06-26 | 1985-02-25 | 旭硝子株式会社 | Manufacture of high density silicon carbide sintered body |
| US4853299A (en) * | 1985-09-06 | 1989-08-01 | Kabushiki Kaisha Toshiba | Silicon carbide sintered body and method of manufacturing the same |
| DE19616788A1 (en) † | 1996-04-26 | 1997-11-06 | Bayerische Motoren Werke Ag | Vehicle door |
| ES2814948T3 (en) * | 2012-03-22 | 2021-03-29 | Saint Gobain Ceramics | Sintered-bonded ceramic articles |
| US9290311B2 (en) | 2012-03-22 | 2016-03-22 | Saint-Gobain Ceramics & Plastics, Inc. | Sealed containment tube |
| WO2013142829A1 (en) * | 2012-03-22 | 2013-09-26 | Saint-Gobain Ceramics & Plastics, Inc. | Extended length tube structures |
Family Cites Families (13)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3836673A (en) * | 1972-03-23 | 1974-09-17 | Norton Co | Sintered silicon carbide |
| US3852099A (en) * | 1972-11-27 | 1974-12-03 | Gen Electric | Dense silicon carbide ceramic and method of making same |
| US3853566A (en) * | 1972-12-21 | 1974-12-10 | Gen Electric | Hot pressed silicon carbide |
| US4004934A (en) * | 1973-10-24 | 1977-01-25 | General Electric Company | Sintered dense silicon carbide |
| US3968194A (en) * | 1974-01-08 | 1976-07-06 | General Electric Company | Dense polycrystalline silicon carbide |
| US3954483A (en) * | 1974-01-08 | 1976-05-04 | General Electric Company | Dense polycrystalline silicon carbide |
| US3998646A (en) * | 1974-11-11 | 1976-12-21 | Norton Company | Process for forming high density silicon carbide |
| US4312954A (en) * | 1975-06-05 | 1982-01-26 | Kennecott Corporation | Sintered silicon carbide ceramic body |
| US4041117A (en) * | 1975-06-30 | 1977-08-09 | General Electric Company | Silicon carbide sintered body |
| US4023975A (en) * | 1975-11-17 | 1977-05-17 | General Electric Company | Hot pressed silicon carbide containing beryllium carbide |
| US3993602A (en) * | 1975-11-17 | 1976-11-23 | General Electric Company | Polycrystalline silicon carbide with increased conductivity |
| US4031178A (en) * | 1976-04-09 | 1977-06-21 | General Electric Company | Strength improvement in machined SiC bodies |
| US4080415A (en) * | 1976-11-22 | 1978-03-21 | The Carborundum Company | Method of producing high density silicon carbide product |
-
1979
- 1979-04-24 CA CA 326261 patent/CA1332065C/en not_active Expired - Lifetime
- 1979-04-26 DE DE19792916817 patent/DE2916817A1/en not_active Ceased
- 1979-04-27 FR FR7910955A patent/FR2424889B2/en not_active Expired
- 1979-04-27 JP JP5160579A patent/JPS54144411A/en active Granted
- 1979-04-30 GB GB7914922A patent/GB2019891A/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| JPS54144411A (en) | 1979-11-10 |
| FR2424889A2 (en) | 1979-11-30 |
| FR2424889B2 (en) | 1985-07-05 |
| JPS649269B2 (en) | 1989-02-16 |
| DE2916817A1 (en) | 1979-11-08 |
| GB2019891A (en) | 1979-11-07 |
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