CA1098435A - Metal-ceramic composite and method for making same - Google Patents
Metal-ceramic composite and method for making sameInfo
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- CA1098435A CA1098435A CA289,707A CA289707A CA1098435A CA 1098435 A CA1098435 A CA 1098435A CA 289707 A CA289707 A CA 289707A CA 1098435 A CA1098435 A CA 1098435A
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Abstract
ABSTRACT OF THE DISCLOSURE
The composite of the present invention comprises a layer of ceramic having completely imbedded therein a metal grid, such composite having been made by coating a metal grid with a viscous ceramic slurry and thereafter firing to form the ceramic to a unitary structure. At the temperature to which the composite is fired to form the unitary structure the metal grid is in an expanded condition because of its high coefficient of thermal expansion, and upon cooling the metal grid is put into tension thereby putting the ceramic in com-pression.
The composite of the present invention comprises a layer of ceramic having completely imbedded therein a metal grid, such composite having been made by coating a metal grid with a viscous ceramic slurry and thereafter firing to form the ceramic to a unitary structure. At the temperature to which the composite is fired to form the unitary structure the metal grid is in an expanded condition because of its high coefficient of thermal expansion, and upon cooling the metal grid is put into tension thereby putting the ceramic in com-pression.
Description
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The subject matter of the present invention is a metal-ceramic composite and a method for its manufacture.
Composites made in accordance with the invention have particu-lar utility as thermal insulation and hence the invention will be described chiefly in connection with this end use of the invention.
There are numerous instances where there are needs for a good thermal insulating material but which needs are not being filled adequately because of lack of an economically practical material which has all the characteristics and phy-sical properties required. An example of-this is the plaus-ibility for a thermal insulating liner in the exhaust system of an internal combustion engine fitted with a catalytic con-verter. This is because the efficiency of a catalytic conver-lS ter in catalyzing unburned hydrocarbons and carbon monoxide to carbon dioxide and water, or the reduction of the oxides of nitrogen, is dependent on the catalytic bed temperature. Hence, at engine start-up when the catalytic bed is cold the efficiency is low, and the less the time required to heat the catalyst bed to a high temperature, the greater the efficiency of the system. To this end, it is desirable to thermally insulate the inner surfaces of the exhaust system leading from the engine to the catalytic converter with thermal insulating material so that a maximum of the heat in the exhaust gases from the engine reaches the catalyst bed to increase and maintain its temperature.
; Due to the carrying of the heat to the catalyst bed away from the engine, the total underhood temperature will be reduced significantly, benefiting various underhood components. Any thermal insulating material used must, of course, have sufficient heat resistance to withstand the high temperatures encountered.
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~Q984:315 This suggests the use of ceramic since most ceramics have relativeIy low thermal conductivity and high temperature re-sistance. One solution would appear to be to coat the inner surfaces of the exhaust pipe with ceramic. However, this is l 5 unsatisfactory because of the considerable difference in the coefficients of thermal expansion of metal and ceramic and because ceramic, in solid monolithic form, is relatively brittle or non-elastic. As a result, the ceramic cracks, breaks and spalls off of the exhaust pipe surfaces. If, on the other hand, the ceramic used is not of solid monolithic structure but instead is of fibrous structure, the cracking and spalling problem takes a different aspect since the physical strength of the fibrous ceramic is not sufficient to withstand the relatively high velocity and pulsating flow of the exhuast gases and will therefore deteriorate rapidly. In short, ceramics of fibrous or the like structure will eventually break down or get blown off the exhaust pipe surfaces by the exhaust gases.
Hence, there is great need for relatively low cost thermal insulating materials having not only good thermal insu-lating properties but also good structural mechanical strength, :
resistance to severe cracking or other deterioration by thermal cycling, and ample physical strength to withstand deterioration or attrition from exposure to flowing and pulsating hot gases.
The present invention fulfills these and many such needs.
In the prior art is has been proposed to make high impact resistant plate by hot pressing, between graphite or the - like dies, ceramics such as aluminum oxide, and with a high - temperature resistant metal screen imbedded therein, thereby to provide a high strength, and hence impact resistant, plate consisting of a composite of hot pressed and therefore very P-307 ~ 3S
dense sintered ceramic with the high temperature resistant metal screen imbedded therein. But the difficulties with this are manifold. First, the requirement for hot pressing places severe limitations on the shapes that can be made.
Secondly, the requirement for hot pressing incurs manufactur-ing costs which prices the resulting composite out of most markets such as that for a good high temperature resistant thermal insul*tor. Thirdly, whereas the high density of such a composite might have value where impact resistance is essen-tial, it has no value, and indeed can be disadvantageous, where other properties are of importance such as the properties required for an effective high temperature resistant thermal insulator.
The present invention provides a high temperature in-sulation of a metal-ceramic composite comprising a rigid metal wall, a monolithic layer of ceramic positioned adjacent the metal wall and having imbedded therein a metal grid including openings of substantially the same size and shape, said com-posite having been made by coating said metal grid so as to fill the grid openings with ceramic slurry to provide a layer of the ceramic having imbedded therein said metal grid, heating said layer of ceramic with said metal grid therein to a tem-perature at which the ceramic forms into a monolithic ceramic body, and thereafter cooling said ceramic body with said metal grid therein, said metal grid having a melting temperature higher than said temperature at which said ceramic forms into said monolithic ceramic body and said metal grid having a higher coefficient of thermal expansion than that of said ceramic, and said grid openings having a size of from about 1/64 inch to 3/8 inch and the aggregate area of the openings constituting from about 30% to 80% of the total area of the grid.
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1'he present invention also discloses a method for making a high temperature insulation composite of metal and ceramic, said method comprising coating a metal grid with ceramic slurry thereby to provide a layer of the ceramic having imbedded therein said metal grid, said metal grid hav-ing openings with a size of from about 1/64 inch to 3/8 inch and the aggregate area of the openings constituting from about 30~ to 80~ of the total area of the grid, heating said layer of ceramic with said metal grid therein to a temperature at which the ceramic forms into a monolithic body, thereafter cooling said ceramic with said metal grid therein, said metal grid having a melting temperature higher than the temperature at which said ceramic forms into said monolithic ceramic body and said metal grid having a higher coefficient of thermal expansion than said ceramic, and positioning a metallic layer and the ceramic layer in an ad~acent relationship to each other.
Briefly, in accordance with the present invention there is provided a material which has the aforesaid combination of properties and which is a composite made by coating a metal grid with a ceramic slurry thereby to form a layer of the ceramic with the metal grid imbedded therein, and then firing the ceramic, at or less than ordinary atmospheric pressure, to a temperature at which the ceramic orms a monolithic structure~
~ 25 Upon cooling, the metal grid is in tension and the ceramic is - in compression--this because the grid is in an expanded condi-tion during firing because of its high coefficient of thermal expansion. Particularly because of the metal grid the composite has excellent physical strength and because the ceramic is of solid monolithic structure the composite can easily withstand the high velocity and pulsating flow of hot gases with good longevity and durability. Further, even though the metal grid ' f~
-3a-` ~-307 1~ 3~
and the ceramic have different coefficients of thermal ex-pansion, the composite has excellent resistance to cracking or other deterioration from thermal cycling--this because under most operating -3b-conditions the grid is in tension and the ceramic is in com-pression and due to the relativeIy thin walls of the ceramic there is a low temperature gradient which reduces cracking or converseIy enhances thermal shock resistance. Still further, the composite as hereinafter described has very low thermal conductivity in a direction perpendicular to the plane of the metal grid, and hence the composite provides the excellent thermal insulating properties desired.
The mechanisms by which the composite functions as an insulator are very complex although well documented in heat transfer and ceramics technologies. Based on a review of heat transfer technology, three factors contributing to the out-standing insulation characteristics of the composite structure of this invention are (1) the reflectivity and emissivity characteristics of multiple surfaces, (2) stagnant gases --in spaces between composite layers, and (3) the low thermal con-ductivity of ceramic. Of these the first is the most important.
The metal-ceramic composites, which can be quite thin, have excellent, and in fact unusual, capabilities of serving as a high temperature radiation shielding. There are, of course, many applications for such shielding and include all high tem-perature systems in which heat is to be conserved through effec-tive radiative insulation or an environment is to be protected from the presence of a high temperature body. All furnaces and combustion apparatus, including automobile exhausts, come under this category. The relative inertness of the metal-ceramic composites to extremely corrosive environments and this ability to withstand temperatures in excess of 2000F lend the compo-sites of the invention an unusually good ability to serve as an insulator where its characteristics of radiative transfer 343~
and multiple shielding can be utilized~
Addit~onal ~eatures of the insulating composite material are as follaws, The composites have good structural self~supporting characteristics~ They can, for instance r be preformed in their preferred condition to the desired shape and easily attached in application ~ithout the need of additional support materials.
; The composites can be preformed and machined to de-sired shape with a minimum of tooling. To line a cylindrical ; container, a sheet of the composite can be spirally wrapped upon itself to the inside diameter of the cylinder prior to firing or ~aking at the required temperature.
Due to the simplicity of construction, and method of manufacture as is hereinafter described, the insulation com-posite can be economically produced. The nature of the compo-site permits use of lower-cost metals in lower-temperature zones for structural components.
The composite can be inserted in a mold and cast around with molten metal, providing a simple method for insulating cast parts~
The composites have ~ery good heat insulating charac-teristics with a minimum of space required as hereinafter described and illustrated by tests in automotive applications.
~; 25 The composites have good thermal shock resistance.
The use of the composite insulation in an automotive exhaust system which incurs thermal shock has proven the thermal toughness o$ the matexial~ B~ use of the c~mposites there are no serious thermal expansion problems since multiple layers are ; 30 free to expand and contract independently.
p-307 These and other features and advantages of the compo-site as well as a preferred method for its manufacture, will now be described in detail~ the description being with refer-ence to the aCcompanying drawings in which;
FIGURE 1 is a side view with parts broken away and in partial section of an exhaust pipe embodying the present invention;
FIGURE 2 is a section taken on line 2~2 of FIGURE l;
FIGURE 3 is a fragmentary view with parts broken away 1~ of the lininq of the exhaust pipe shown in FIGURE l;
FIGURE 4 is a view similar to that of FIGURE 1 but showing another embodiment of the invention;
FIGURE 5 is a view taken on the line 5-5 of FIGURE 4;
and FIGURE 6 is a view similar to that of FIGURE 3 but showing the lining of the pipe shown in FIGURE 4.
Referring now to ~IGURE 1, there is shown a portion ; of an exhaust pipe 2 which functions to conduct exhaust gases from the exhaust manifold of an internal combustion engine, not shown, to a catalytic converter, likewise not shown. The exhaust pipe 2 iS formed of ordinary steel or alloy steel stock as conventionally used for exhaust pipes, and it has a tubular liner 4 which functions as a thermal insulator and which is constructed in accordance with the present invention as will now be described.
As can best be seen in ~IGURES 2 and 3, the liner 4 is a composite of a metal grid 6 which is imbedded in a layer of ceramic 8~ The metal grid is usually in tension and the ceramic is in compreæsion. Since ceramic is strong in com~
pression but weak in tension and metal is not only strong in ~Q9~ 5 compression but also strong in tension, the metal complements the ceramic in enhancing its mechanical properties while the ceramic serves to protect the metal from corrosion, abrasion, etc. As the temperature of the composite is raised, the greater expansion of the metal grid, relative to that of the ceramic at service temperatures, does not place a tensile force on the ceramic but instead only relieves some of the compressive force.
The end result is a composite which not only has the requisite heat resistance and resistance to cracking of the ceramic from heat cycling, but also much increased toughness and mechanical strength as compared to a structure consisting entirely of ceramic. In the embodiment shown in FIGURES 1-3, the metal grid is in the form of a metal screen, i.e. interwoven metal wires;
however, as will be discussed hereinafter, the metal grid can take other forms. Also, whereas in the embodiment shown in FIGURES` 1-3 the composite contains only a single layer of the metal grid, it is within the purview of the invention to use multiple layers of the composite material, such being advan-tageous where i~ is desired to have an insulating system of greater thermal insulation characteristics. A more complete understanding of the composite metal-aeramic structure will be gained from the description hereinafter to be given of a pre-ferred method for manufacturing same. But before proceeding to the manufacturing method it is appropriate to discuss the requirements for each component of the composite.
T~IE METAL GRID
In selecting the material for the metal grid to be used in the composite structure, several essential factors must be taken into consideration. The metal grid must have a melting temperature above the temperature required to fire . .
l~S4~35 the ceramic to a unitary structure and should have a higher coefficient of thermal expansion than that of the ceramic.
In general, the greater the coefficient of the thermal expan-sion of the metal grid relative to that of the ceramic, the greater the compression of the ceramic, and hence resistance to fracture from tensile forces, at operating temperatures below that at which the composite was fired whereas, conversely, the less the difference in the coefficients of thermal expan-sion of the metal grid and the ceramic, the greater the resistance of the composite to ceramic fracture at operating temperatures above that at which the composite was fired.
Many ceramics can, o~ course, withstand temperatures greater than that to which they are fired during manufacture.
Also, it is much preferred that the metal of the grid be chemically inert with respect to the ceramic composition and, particularly where the ceramic of the composite has porosity, also with respect to the atmosphere in which the composite is to be used. Hence, when selecting the metal for the grid it is desirable to consider whether the atmosphere in which the ; 20 composite is to operate will be oxidizing or reducing, car-burizing, sulfurizing, etc. Of course, as to factors such as the latter, compromise may be necessary or desirable in many instances taking into account the further factor of cost and availability of the metal.
Numerous commercially available metals and alloys are well suited for the practice of the invention. For moderate to high temperature service, some of the nickel base alloys are attract~ve cho~ces, They offer ~ood strength with medium~to high coefficient of thermal expansion, good oxidation and corrosion resistance and good toughness. Preferred commercial ~Q~3435 P~307 nickel base alloys falling into this cate~or~ are as follows:
Incone ~6Q0 (1~. see footnote Inconel~ 6Ql ~11 Ni~Chrome (21 Hastello~ X (3 RA 333 (4~
Another class of metal allo~s~ the common stainless steels, are also well suited for many end uses ~or the com~osites.
The ~err~tic stai~nless steels are paxt~cularly attractive~ They are low ~n cost, have sat~sfactor~ coeff~ci~ents of thermal expan-sionl low as compared w~th other metals such as the austenitic stainless steels~ and the.ir oxidat~on resistance can range from good to outstanding~ The~ are a good selection where low cost com-~ posites are needed for relatl~vel~ h.~gh.temperature applications, ; 15 The common austenitic stainless steels are stronger than the ferritic sta~nless steels at high temperatures. They are usuall~ more expens~ve, offer superiox corrosion resistance, ',~ and are characterized by higher coeffic~ents of thermal expansion, so~ewhat in the same range as th.e nickel base allo~s~ Typical 20 c~mercial sta~nless steels for use as the grid in the practice of the ~nvention ares ~Ferrit~c Stainless Austen~tic Stainle~s :~ MF~1 C5~ see fo~tnote T~3Q4 (6~ see footnote :' T~409 C6~ T~316 (6, T~43Q C6~. T~321 ~6~
T-442 C6) T~347 (6) T-446 (6~ T~30q (.6~
: KANT ~ A (.71 T-31Q (6, KANTHAL~DS ~71. R~330 (4~.
MULTrMET~N~155 ~32 - ~oX s~me ~p~l~cations other ~etals ma~ be desirable, For spec~al h~gh te~perature applicat~ons~ ~r exam~le the re~ractor~ metals and t~eir allo~s can be used~ examples of suc~ metals be~ng zirconium, tungsten, molybdenum~ platinum, r~r~
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paladium and tantalum~
The metal or metal alloy can be formed into various configurations to form the grid, such as wire screen, expanded sheet or perforated sheet. By ~'screenM is meant an interwoven relationship ~etween wires of the metal, such a screen being shown in FIGURE 3. Expanded sheet metal, as conventionally referred to, is a thin sheet of metal which is provided with slits of various configurations and arrangements throughout the entire sheet which is simultaneously or thereafter stretched in a direction to open the slits, thereby to provide a unitary metal grid with holes therein. Such a structure is illustrated in FIGURE 6. By perforated metal sheet is meant any of a number of patterns punched through a sheet of metal to provide a grid the same or similar to that provided by expanded metal sheet.
Both from the standpoint of ease of manufacture and from the standpoint of attaining composites having optimum physical characteristics, it is preferred that, as regards the precise structure of the grid, the openings therein be of sub-stantially uniform shape and size, and with the size of the ~; openings being, in their largest dimension, no greater than about 3/~ inch and no less than about 1/64 inch. (Where, ~or example, the openings are square, the largest dimension is the diagonal, and it is pre~erred that this dimension be no greater ; 25 Addit~onal information regarding source and designation of the alloys: Cl~ The International Nickel Company, Huntington Alloys Products Division~ Huntington~ West Virginia; (2) Driver-Harris Company, Harrison, New 3ersey; (3) Haynes Stellite Company, Kokomo, Indiana; ~4~ Rolled Alloys Company~ Detroit, Michigan;
C51 Allegheny~Ludlu~ Company~ Pittsburgh~ Pennsylvania; (6) The T numbers o~ t~e alloys so designated are the AISI (American Iron and Steel ~nstitutel designations; (7~ Kantha~ Corporation, Bethel~ Connecticut.
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P~307 than 3~8 inch and no less than 1/64 inch.~ Further, it is preferred that the ratio of the aggregate area of openings to the aggregate of the area of the metal between the openings be such that about 30% to 80~ of the total area of the grid constitute openings, and the remainder of the area of the metal between the openings.
THE CERAMIC
As has been indicated, it is essential that the ceramic formulation be one which can be fired to its final unitary or monolithic structure at a temperature below the melting temper-ature of the grid. Where the metal used for the grid is such that at a temperature below the melting point it undergoes ` significant degradation in tensile strength or other physical ; properties, as by way of metallurgical structural change, it is desirable that the ceramic be such as can be fired to its unitary or monolithic structure at a lesser temperature than that at which the degradation in properties of the metal occurs. Further, it is essential to the practice of the invention that the ceramic slurry formulation used to coat the grid be such that the slurry clings to the grid, filling the openings therein, and remains thereon upon drying. This property can best be accomplished by including a binder material in the slurry formulation. The binder can and preferably should be any one or more of numerous inorganic materials, examples of which will be given hereinafter, which have bonding properties, i.e. provide good green bond strength, in the pre~fired state of the ceramic after drying and which provide a strong unitary or monolithic ceramic structure in the final fired state~ ~s re~ards the latter, the inorganic binder remains in and constitutes a part of the ceramic through the fir~ng operationt though generally undergoing reaction with , ~ .. .
~Q~S~35 other of the ceramic ingredients or transformation during the firing operation such as to appear at least partially in another form in the fired ceramic structure than the form in which added to the slurry. For example, where the binder is a sili-cate or colloidal silica, as the examples hereinafter given willillustrate, there may be transformation, as by reaction with other ingredients of the ceramic formulation, of the silica to a silicate or of the silicate to another silicate, such as a glass, in the final fired ceramic structure. But alternatively, or in addition to using an inorganic binder, organic binders can be used in the ceramic slurry, in which case the organic binder vaporizes or burns out during the ~firing operation. Hence, where the only ~inder used is an organic binder, the ceramic ingredient or ingredients of the slurry formulation should be such that during the firing operation there results the required bonding to provide the unitary or monolithic ceramic structure.
Typical examples of organic binders are polyvinly alcohol, dextrine and the water-emulsifiable waxes well known in the ceramics art as temporary binders.
Numerous ceramic formulations well known in the art and extensively used in the precision and investment casting ; technology are suitable for the practice of the invention. For example, slurries, made up of any of various one or more ceram-ics, such as those set forth hereinafter, and suitable binding ; 25 agents, examples of which are also listed hereinafter, are used in the mold making of ceramic shells and investment molds for the casting ~f co~plex shapes and high temperature turbine parts.
T~pical ceramic materials useful for the practice of the invention, either alone or in combination are: zircon, quartz or ~used silica, mullite, spodumene, magnesia, forsterite, magnesia-alumina spinel, silicon carbide, alumina, zirconia (stabilized~ r chromium oxide (Cr203~ and stoichiometric cordi-erite or composition modifications of cordierite as are known in the art. It is desirable that the ceramic material be of small part~cle size, preferably 325 mesh or finer.
Though liquids other than water can be used for the slurry it is much preferred from the standpoint of cost and convenience and from all other standpoints, that water be used.
Hence, it is desirable that the binder be either water soluble 1~ or such that it forms a colloidal suspension with water.
Examples of inorganic binders excellent for the practice of the invention are as follows: colloidal alumina, colloidal silica, sodium silicate, potassium silicate, calcium aluminate and kaolin or other clay. An example of an organic-inorganic binder suitable for use in the practice of theinvention is ethyl silicate.
The initial bonding of ceramic particles with the above blnders usually requires only relatively low temperatures;
in many cases ambient or room temperature drying usually pro-vides ample pre-fired bond strength. However, the full bond is not developed until the structure has been exposed to the temperature at which the ceramic formulation forms a unitary or monolithic structure. Where the composite is to be used in an environment which provides a high service temperature, this itself can be used to effect the final bonding. The required temperature naturally varies depending on the precise formu-lation, as well known in the ceramic art~ ~n the case of the sodium sil~cate and alum~na ceramic system~ exemplified here-inafter, the final bonding apparently takes place by at least localized melting of the sodium silicate followed by rapid - , ~t~ 8~a3s diffusion into, and at least partial reaction with, the alumina to form a highly bonded structure~ Bonding can also be obtained with colloidal partIcle type binders, apparently also by solid diffusion and at least part~al reaction with other of the in~-gredients at the required temperature to provide the unitary ormonolithic structure, The gelling of the colloidal type binders is of value in providing good pre.fired dry bond strength.
It is not essential that the ceramic of the fired composite ~e of extremely high density and, indeed, for many applications such as for thermal insulation, porosity of as high as 10% or even higher can be desirable. By adding flour, powered wax, wood flour or other powdered organic material to the slurry in the desired proportions and particle sizes the amount of porosity can be controlled since in the firing operation the combustible mater~al burns out and leaves pores.
The following are specific examples of ceramic slurries suitable for the practice of the invention:
EX, 1 112 grams of distilled water was added to 563 grams of commercial grade sodium silicate Type RU ~SiO2 33.2%, Na20 13.85%, H20 52.95%) and electric-motor~propeller stirred to insure total mixing. To this solution was added 825 grams of commercial tabular alumina of a particle size of -325 mesh. The addition of the alumina was made while the electric-motor-propeller stirring the solution to insure that all particles were fully wetted and the viscosity remained relatively constant. The slurry was then ready for coating of the metal grid.
EX. 2 4~Q grams of powdered fused silica (Nalcas ~P-lW2 was added to 210 grams o~ colloidal silica (Nalcoag~1030~ and was ~- stirred thoroughly wit~ an electric-motor-propeller, Mixing was continued for 1~1/2 hours to insure that the slurry reached ~f Tr~r~
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P~307 equilibrium-~that is, all of the particles were fully wetted and the viscosity remained relatively constant. The slurry was then ready for coating of the metal grid.
EX. 3 62 grams of water was added and thoroughly mixed into .
188 grams of aqueous colloidal silica (30% solids). Complete stirring was continued to insure an intimate solution of the silica and water. ~o this solution 750 grams of zircon powder was added while stirring with a motor~driven propeller. This stirring was continued ~or two hours to insure complete wetting of all the zircon particles and a uniform viscosity. The ; slurry was then ready for coating the metal grid, FORMING THE COMPOSITE
The composite is made by applying the viscous ceramic slurry to the grid so that the slurry ~ully coats and fills all the openings in the grid, after which the coated grid is dried and then fired, The slurry is best applied to the grid by dipping the grid into the slurry. In many cases a multiple dipping operation is desirable. That is, after a first dip the slurry thereby applied to the grid is allo~ed to dry after which there is application of additional ceramic by another dip into the slurry. Since the dried ceramic slurry is generally pliable it is possible to re-shape or machine the composite prior to the firing operation to cylindrical or other shape after the ceramic is applied to the grid. Alternatively, the grid can first be shaped into a cylinder, or other shape as desired, and the ceramic slurry then applied to the shaped grid, As ha5 ~een indicated~ after the ceramic is applied to the metal gri~d and allowed to dry~ the ceramic with the grid imbedded therein is fired to a temperature sufficient to ,.~
~(~9~35 convert the ceramic to a unitary or monolithic structure. At the firing temperature~ the metal grid, because of its higher coefficient of thexmal expansion, is in an expanded condition and the ceramic i5 a rigid monolithic structure while at the high temperature at which the metal grid is in its expanded condition. Hence, once cooling starts and as cooling continues, and the metal grid contxacts from its expanded con~ition, the metal grid is thereby put into tension and the rigid ceramic is put into compression. Upon completion of cooling, manufac-ture is complete, The following is a specific example of the practiceof the method of the invention, the slurry used being that set forth in Example 1 above:
A 16 mesh screen metal grid of Incone *600 ~as de-15 greased by rinsing in methanol and low temperature dried. Tocoat the screen with the slurry, it was dipped into the slurry ; and slowly removed vertically, permittlng the slurry to adhere to the ~res Gf the screen and fill all the interstices of the screen. After withdrawal from the container of slurrv and air drying for 30 minutes (during the early stages of which drying operation the coated grid was slowly revolved in a vertical plane to prevent ceramic build-up at one end due to gravitv) the composite was oven baked at 25F increments for about 15 minutes at each temperature from 100F to 500F. The tempera-ture was raised at a relatively 510w rate, as described, tobetter assure against the formation of gas bubbles or separation of the ceramic. The composite was then fired in air at 1800F
for 3a minutes at ordinary atmosphexic pressure and then allowed to cool to room temperature, If desired, other methods, such as use of a vacuum furnace or micro~wave heating or induc-~ ~.le~ L
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P~30'7 tion heating, can be used for the drying and heating to preclude localized internal gas build~up and the ensuing loss of integ-rity of the ceramic matrix structure.
FIGURES 4 through 6 show another embodiment of the invention wherein there are incorporated multiple layers of the composite~ adjacent la~ers being slightly spaced to provide thin air gaps between the layers. Referring to FIGURES 4 and 5, 10 is a metal tube and 12 is a tubular multiple layer composite made in accordance with the invention and functioning as a thermal insulator to prevent heat loss from hot gases or other fluid flowing through the tube~ As can best be seen in FIGURE
5 r the composite comprises a grid 14 which is imbedded in ceramic 16 and which is spirally wound thereby to provide a tu~e having three substantially parallel or concentric layers 18, 20 and 22, As best shown in FIGURE 6, spaced, spirally wound heat resistant wires, such as shown at 24 and 26, between the layers, provide the spacing, and hence an air gap, between adjacent layers, the thickness of the air gap being determined by the diameter of the spirally would wires. The metal grid of the FIGURES 4-6 embodiment instead of being a screen of interwoven wires is an expanded metal ~rid. One conventional and inexpensive method for making such a grid is to provide a thin sheet of the metal with staggered parallel rows of slits and thereafter pulling the sheet in a direction transverse to the slits whereupon the diamond shape openings, as shown, are formed, The metal grid can be used in the precise form as j results ~rom the pulling operation or can thereafter be put through roller$ to roll it into a flat configuration such as that shown in FT~URE 6~ A metal grid of the same structure can be accomplished by punching a metal sheet to provide the i~9~34~S
openings; however, this is far more expensi~e because of the large amount of metal scrap which results, Expanded metal grids are well known in the art and it should be understood that the precise method of manufacture ;s not important to the present invention nor is the shape of the openings so long as the grid structure is such that ~t can be put into tension not just in one direction but in directions perpendicular to each other.
To manufacture the embodiment shown in FIGURES 4 through 6, a rectangular shaped piece of the metal grid is coated with the ceramic slurry, as described with reference to the FIGURES 1-3 embodiment, and then, after drying, spaced parallel heat resistant metal wires are placed on the ceramic coated metal grid. This assembly is then spirally wound in a direction in which the metal wires extend thereby to result in the spirall~ wound configuration as shown in the drawings. The resultant tubular structure is then fired to a temperature to cause the ceramic to form a monolithic structure and is there-after cooled to complete the manufacture~
Means other than the wires 24 and 26 can be used to provide the spacing between adjacent layers. For example, prior to spirally winding the ceramic coated metal grid to a tu~ular shape the surface thereof can be provided with a plurality of relatively widely spaced relatively large grains of ceramic or other re~ractory material, the size of the grains determining the spacing between adjacent layers when such structure ~s spirally wound. As still another alternative, the metal gxid ~tself can be provided with spaced dimples to pro~
vide the desired spacing between adjacent layers~ A thin air gap between adjacent layers provides additional thermal insula~
tion; however, it should be understood for some applications it P~307 may be desirable to use multiple layers of the composite material but with no large spacing between the ceramic layers imbedding the metal grid, To manufacture such structure it is necessar~ only to eliminate the heat resistant metal wires or other means for providing the gap between the layers.
The composites of the invention are particularly suit-ed for tubular shapes such as shown in the drawings; however, it should be understood that whereas the two embodiments shown are of tubular shape, composites of the present invention can take other forms such, for example, as a flat planar form.
As regards internal combustion engines, another application for the composite of the invention is as a thermal insulator for the combustion chamber and the engine head adjacent to the exhaust gas ports to thereby regulate localized heat flow to the engine coolant~ This is desirable because if heat flow to the coolant is too rapid the coolant at such loca-tion can be yaporized thereby forming gas bubbles or pockets which tend to ~nhibit heat flow. By using the thermal insula-tion in the head or in the engine block adjacent the combustion chambers, there is increased temperature control and hence decreased harmful emission and increased fuel economy.
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', The ceramic-metal grid composite of the present invention has been described particularly with reference to its use as a thermal insulator because the composite demonstrates such remarkable thermal insulating properties.
An investigation of the insulating propexties of three layers of the composite material was conducted in the following method~
~ 4-1~2 inch diameter cylinder of stainless steel 7 inches long and ,Q72 inches thickness was lined with three ~q~3s concentric cylindrical sections of the composite insulation.
A slurry of tabular alumina and sodium silicate such as that made in Example 2 above was prepared~ Three cylinders of 16 mesh Incone screen were made by joining the seam of the indi~idual cylinder By tack welding. These concentric cylinders were degreased in methanol and after drying dipped in the slurry mixture providing a viscous coating. After air drying the slurry, the structures were oven dried at temperature steps of 25F starting at 100F. After reaching 500F the structures were then fired at 1750F in air at ordinary atmospheric pres-sure to complete the sintering process. The metal grid-ceramic composite cylinders were then concentrically mounted within the stainless steel cylinder, separating their surfaces by spaced circumferentially extending Inconel 600 wires to provide a 15 stagnant air space between adjacent cylinders. The thickness of each cylinder was about 1/16 inch and the size of the cylin-ders was such that the spacing between adjacent cylinders was about .06 inches~ Thermocouples (T4) were welded in place on the outer surface of the metallic cylinder~ Additional thermo-couples tTl~ were secured to the inner surface of the inner-most compasite cylinder; thermocouples (T2~ were set in place between the innermost and middle composite cylinders and thermocouples (T3 ~ between the middle and outermost composite cylinder. The entire unit was placed on fire brick supports and a burner nozzle placed in the top opening pointing downward, The burner was also supported by fire brick and covered by asbestos sheet in such a manner that all secondary air was brought to the buxner ~rom outside the apparatus, A mixture of propane and air was burned at several throttle settings and 30 when temperatures stabilized temperatures were recorded provid-S~35 ing comparative data showing the insulating effect of each successive layer~ Table I gives the results of the test.
TABLE I
INSIDE TEMP, TEMP. TEMP.
TEMP. F~ F, F.
~Tl)F~ (T2~ (T32 (T4) 15~0 1355 1050 728 A second test apparatus was prepared in accordance with the above apparatus except that zircon refractory was sub-stituted for the tabular alumina. Similar test procedures were conducted with the results given in Table II.
TABLE II
INS$DE TEMP. TEMP. TEMP.
TEMP~ F. F. F.
(Tl)F. (T2~ (T31 (T4) 1500 1320 1~00 670 These tests show a significant temperature drop across , approximately 5/16 inch of the composite insulation with small ~-~ 20 air spaces between adjacent layers.
,~ In another application, the insulation was wrapped concentrically upon itself to provide three la~ers totaling 3~16 inch thick and inserted into a cylindrical stainless steel container 3-3/4 inches in diameter and 10 inches long. An '5 25 automotive reducing catalyst was then placed within the insula-tion and the contàiner welded shut with entry and exit pipes to conduct eng~ne exhaust through the catalyst, This test shows a sign~ficant temperature drop across approximately 3~16 inch o~ insulation with minimal air spaces 3Q between layers. Thermocouples were placed in the center of the P~307 catalyst and on the surace of the stainless steel container, the metal thickness of which was 0.040 inches, The catalyst canister was attached to the standard exhaust manifold of an independent testing laboratory's Plymouth~ 18 CID-V8 engine for dynamometer testing. Steady state loads and throttle settings were conducted and when temperatur~sstabilized gas temperatures in the catalyst and skin temperatures were recorded.
These are listed in Table III and show the insulation's signi-ficant effect in reducing temperatures.
TABLE III
Exhaust Canister Gas Temp~ F Skin Temp F
Another test of an insulated catalyst canister and insulated exhaust manifold made similarly to that of the pre-vious stationary dynomometer test was conducted by an indepen-dent testing laboratory. This test was conducted on a 1975 Plymouth~318 CID-V8 Furyrautomobile with the catalyst installed and instrumented with thermocouples to determine the gas and surface temperatures. The automobile was placed on a chassis rolls dynamometer and run in accordance with the EPA Hot Start CVS emission test procedures, Exhaust gas temperatures and canister and insulated exhaust manifold skin temperatures were recorded~ These are presented in Table IV. It can be seen that the insulati~e capabilities of the composite material are outstandin~, ~ .
1rc~ k 43~
P~307 TABLE IV
Exhaust Gas Canister E~haust Manifold Temperature F Skin Temp F Skin Temp F
122~ 412 495 Table IV results are somewhat scattered compared to those of Table III due to the type of tests conducted. Table III data were obtained from a steady state dynamometer test, whereas Table rV data were taken during an EPA Hot Start CVS
test where the engine temperatures are in a transient condition -for the most part~
It should be understood that the composites of the present invention may find other uses, such, for example, as structural elements requiring high heat resistance. It should ! -~ be further mentioned that the composites of the present inven- `
- tion not only demonstrate excellent thermal insulating proper-ties but also excellent acoustical barrier properties. This is significant, for example, when the composites are used in -~ 20 automotive vehicle exhaust systems since they not only provide good thermal insulation but also acoustical barrier properties thereby reduclng the noise level normally associated with such exhaust systems Additionally, the composites of the present invention ~- 25 permit development of materials with special properties not ' possible by other techni~ues such as heat resistant catalyst supparts, Such use can be illustrated by reference to the embodi~ent de~cribe~ w~th reference to PIGURES 1~3 wherein the compos~te shown constitutes the lining in the exAaust pipe leading from the engine to aicatalytic converter of an automotive ; `
P~307 vehicle. By catalyzing the interior surfaces of the tubular lining, the lining serves not only as a thermal insulator and acoustical barrier, but also as a catalytic device for catal- ;
yzing the oxidation of unburned or partially burned hydro-carbons in the exhaust gases to carbon dioxide and water or, alternatively, for reducing the oxides of nitrogen in the exhaust gases. The catalytic materials which demonstrate the catalytic activity for performing such functions are well known in the art, for example, platinum, palladium, copper and the transition metals, or the oxides of these metals. To in-; corporate such a catalyst into the composite, the catalytic material can be applied in powder form~ for example, to the ~; surface of the ceramic prior to firing or, alternatively, can be incorporated into the ceramic itself.
Hence, it will be understood that whereas the inven-tion has been described with reference to certain embodiments thereof, various changes and modifications may be made all within the full and intended scope of the claims which follow.
' .
.
The subject matter of the present invention is a metal-ceramic composite and a method for its manufacture.
Composites made in accordance with the invention have particu-lar utility as thermal insulation and hence the invention will be described chiefly in connection with this end use of the invention.
There are numerous instances where there are needs for a good thermal insulating material but which needs are not being filled adequately because of lack of an economically practical material which has all the characteristics and phy-sical properties required. An example of-this is the plaus-ibility for a thermal insulating liner in the exhaust system of an internal combustion engine fitted with a catalytic con-verter. This is because the efficiency of a catalytic conver-lS ter in catalyzing unburned hydrocarbons and carbon monoxide to carbon dioxide and water, or the reduction of the oxides of nitrogen, is dependent on the catalytic bed temperature. Hence, at engine start-up when the catalytic bed is cold the efficiency is low, and the less the time required to heat the catalyst bed to a high temperature, the greater the efficiency of the system. To this end, it is desirable to thermally insulate the inner surfaces of the exhaust system leading from the engine to the catalytic converter with thermal insulating material so that a maximum of the heat in the exhaust gases from the engine reaches the catalyst bed to increase and maintain its temperature.
; Due to the carrying of the heat to the catalyst bed away from the engine, the total underhood temperature will be reduced significantly, benefiting various underhood components. Any thermal insulating material used must, of course, have sufficient heat resistance to withstand the high temperatures encountered.
, .
- . ~
:. , ~.
~Q984:315 This suggests the use of ceramic since most ceramics have relativeIy low thermal conductivity and high temperature re-sistance. One solution would appear to be to coat the inner surfaces of the exhaust pipe with ceramic. However, this is l 5 unsatisfactory because of the considerable difference in the coefficients of thermal expansion of metal and ceramic and because ceramic, in solid monolithic form, is relatively brittle or non-elastic. As a result, the ceramic cracks, breaks and spalls off of the exhaust pipe surfaces. If, on the other hand, the ceramic used is not of solid monolithic structure but instead is of fibrous structure, the cracking and spalling problem takes a different aspect since the physical strength of the fibrous ceramic is not sufficient to withstand the relatively high velocity and pulsating flow of the exhuast gases and will therefore deteriorate rapidly. In short, ceramics of fibrous or the like structure will eventually break down or get blown off the exhaust pipe surfaces by the exhaust gases.
Hence, there is great need for relatively low cost thermal insulating materials having not only good thermal insu-lating properties but also good structural mechanical strength, :
resistance to severe cracking or other deterioration by thermal cycling, and ample physical strength to withstand deterioration or attrition from exposure to flowing and pulsating hot gases.
The present invention fulfills these and many such needs.
In the prior art is has been proposed to make high impact resistant plate by hot pressing, between graphite or the - like dies, ceramics such as aluminum oxide, and with a high - temperature resistant metal screen imbedded therein, thereby to provide a high strength, and hence impact resistant, plate consisting of a composite of hot pressed and therefore very P-307 ~ 3S
dense sintered ceramic with the high temperature resistant metal screen imbedded therein. But the difficulties with this are manifold. First, the requirement for hot pressing places severe limitations on the shapes that can be made.
Secondly, the requirement for hot pressing incurs manufactur-ing costs which prices the resulting composite out of most markets such as that for a good high temperature resistant thermal insul*tor. Thirdly, whereas the high density of such a composite might have value where impact resistance is essen-tial, it has no value, and indeed can be disadvantageous, where other properties are of importance such as the properties required for an effective high temperature resistant thermal insulator.
The present invention provides a high temperature in-sulation of a metal-ceramic composite comprising a rigid metal wall, a monolithic layer of ceramic positioned adjacent the metal wall and having imbedded therein a metal grid including openings of substantially the same size and shape, said com-posite having been made by coating said metal grid so as to fill the grid openings with ceramic slurry to provide a layer of the ceramic having imbedded therein said metal grid, heating said layer of ceramic with said metal grid therein to a tem-perature at which the ceramic forms into a monolithic ceramic body, and thereafter cooling said ceramic body with said metal grid therein, said metal grid having a melting temperature higher than said temperature at which said ceramic forms into said monolithic ceramic body and said metal grid having a higher coefficient of thermal expansion than that of said ceramic, and said grid openings having a size of from about 1/64 inch to 3/8 inch and the aggregate area of the openings constituting from about 30% to 80% of the total area of the grid.
:. :
- \
` P-307 ~Q~3S
1'he present invention also discloses a method for making a high temperature insulation composite of metal and ceramic, said method comprising coating a metal grid with ceramic slurry thereby to provide a layer of the ceramic having imbedded therein said metal grid, said metal grid hav-ing openings with a size of from about 1/64 inch to 3/8 inch and the aggregate area of the openings constituting from about 30~ to 80~ of the total area of the grid, heating said layer of ceramic with said metal grid therein to a temperature at which the ceramic forms into a monolithic body, thereafter cooling said ceramic with said metal grid therein, said metal grid having a melting temperature higher than the temperature at which said ceramic forms into said monolithic ceramic body and said metal grid having a higher coefficient of thermal expansion than said ceramic, and positioning a metallic layer and the ceramic layer in an ad~acent relationship to each other.
Briefly, in accordance with the present invention there is provided a material which has the aforesaid combination of properties and which is a composite made by coating a metal grid with a ceramic slurry thereby to form a layer of the ceramic with the metal grid imbedded therein, and then firing the ceramic, at or less than ordinary atmospheric pressure, to a temperature at which the ceramic orms a monolithic structure~
~ 25 Upon cooling, the metal grid is in tension and the ceramic is - in compression--this because the grid is in an expanded condi-tion during firing because of its high coefficient of thermal expansion. Particularly because of the metal grid the composite has excellent physical strength and because the ceramic is of solid monolithic structure the composite can easily withstand the high velocity and pulsating flow of hot gases with good longevity and durability. Further, even though the metal grid ' f~
-3a-` ~-307 1~ 3~
and the ceramic have different coefficients of thermal ex-pansion, the composite has excellent resistance to cracking or other deterioration from thermal cycling--this because under most operating -3b-conditions the grid is in tension and the ceramic is in com-pression and due to the relativeIy thin walls of the ceramic there is a low temperature gradient which reduces cracking or converseIy enhances thermal shock resistance. Still further, the composite as hereinafter described has very low thermal conductivity in a direction perpendicular to the plane of the metal grid, and hence the composite provides the excellent thermal insulating properties desired.
The mechanisms by which the composite functions as an insulator are very complex although well documented in heat transfer and ceramics technologies. Based on a review of heat transfer technology, three factors contributing to the out-standing insulation characteristics of the composite structure of this invention are (1) the reflectivity and emissivity characteristics of multiple surfaces, (2) stagnant gases --in spaces between composite layers, and (3) the low thermal con-ductivity of ceramic. Of these the first is the most important.
The metal-ceramic composites, which can be quite thin, have excellent, and in fact unusual, capabilities of serving as a high temperature radiation shielding. There are, of course, many applications for such shielding and include all high tem-perature systems in which heat is to be conserved through effec-tive radiative insulation or an environment is to be protected from the presence of a high temperature body. All furnaces and combustion apparatus, including automobile exhausts, come under this category. The relative inertness of the metal-ceramic composites to extremely corrosive environments and this ability to withstand temperatures in excess of 2000F lend the compo-sites of the invention an unusually good ability to serve as an insulator where its characteristics of radiative transfer 343~
and multiple shielding can be utilized~
Addit~onal ~eatures of the insulating composite material are as follaws, The composites have good structural self~supporting characteristics~ They can, for instance r be preformed in their preferred condition to the desired shape and easily attached in application ~ithout the need of additional support materials.
; The composites can be preformed and machined to de-sired shape with a minimum of tooling. To line a cylindrical ; container, a sheet of the composite can be spirally wrapped upon itself to the inside diameter of the cylinder prior to firing or ~aking at the required temperature.
Due to the simplicity of construction, and method of manufacture as is hereinafter described, the insulation com-posite can be economically produced. The nature of the compo-site permits use of lower-cost metals in lower-temperature zones for structural components.
The composite can be inserted in a mold and cast around with molten metal, providing a simple method for insulating cast parts~
The composites have ~ery good heat insulating charac-teristics with a minimum of space required as hereinafter described and illustrated by tests in automotive applications.
~; 25 The composites have good thermal shock resistance.
The use of the composite insulation in an automotive exhaust system which incurs thermal shock has proven the thermal toughness o$ the matexial~ B~ use of the c~mposites there are no serious thermal expansion problems since multiple layers are ; 30 free to expand and contract independently.
p-307 These and other features and advantages of the compo-site as well as a preferred method for its manufacture, will now be described in detail~ the description being with refer-ence to the aCcompanying drawings in which;
FIGURE 1 is a side view with parts broken away and in partial section of an exhaust pipe embodying the present invention;
FIGURE 2 is a section taken on line 2~2 of FIGURE l;
FIGURE 3 is a fragmentary view with parts broken away 1~ of the lininq of the exhaust pipe shown in FIGURE l;
FIGURE 4 is a view similar to that of FIGURE 1 but showing another embodiment of the invention;
FIGURE 5 is a view taken on the line 5-5 of FIGURE 4;
and FIGURE 6 is a view similar to that of FIGURE 3 but showing the lining of the pipe shown in FIGURE 4.
Referring now to ~IGURE 1, there is shown a portion ; of an exhaust pipe 2 which functions to conduct exhaust gases from the exhaust manifold of an internal combustion engine, not shown, to a catalytic converter, likewise not shown. The exhaust pipe 2 iS formed of ordinary steel or alloy steel stock as conventionally used for exhaust pipes, and it has a tubular liner 4 which functions as a thermal insulator and which is constructed in accordance with the present invention as will now be described.
As can best be seen in ~IGURES 2 and 3, the liner 4 is a composite of a metal grid 6 which is imbedded in a layer of ceramic 8~ The metal grid is usually in tension and the ceramic is in compreæsion. Since ceramic is strong in com~
pression but weak in tension and metal is not only strong in ~Q9~ 5 compression but also strong in tension, the metal complements the ceramic in enhancing its mechanical properties while the ceramic serves to protect the metal from corrosion, abrasion, etc. As the temperature of the composite is raised, the greater expansion of the metal grid, relative to that of the ceramic at service temperatures, does not place a tensile force on the ceramic but instead only relieves some of the compressive force.
The end result is a composite which not only has the requisite heat resistance and resistance to cracking of the ceramic from heat cycling, but also much increased toughness and mechanical strength as compared to a structure consisting entirely of ceramic. In the embodiment shown in FIGURES 1-3, the metal grid is in the form of a metal screen, i.e. interwoven metal wires;
however, as will be discussed hereinafter, the metal grid can take other forms. Also, whereas in the embodiment shown in FIGURES` 1-3 the composite contains only a single layer of the metal grid, it is within the purview of the invention to use multiple layers of the composite material, such being advan-tageous where i~ is desired to have an insulating system of greater thermal insulation characteristics. A more complete understanding of the composite metal-aeramic structure will be gained from the description hereinafter to be given of a pre-ferred method for manufacturing same. But before proceeding to the manufacturing method it is appropriate to discuss the requirements for each component of the composite.
T~IE METAL GRID
In selecting the material for the metal grid to be used in the composite structure, several essential factors must be taken into consideration. The metal grid must have a melting temperature above the temperature required to fire . .
l~S4~35 the ceramic to a unitary structure and should have a higher coefficient of thermal expansion than that of the ceramic.
In general, the greater the coefficient of the thermal expan-sion of the metal grid relative to that of the ceramic, the greater the compression of the ceramic, and hence resistance to fracture from tensile forces, at operating temperatures below that at which the composite was fired whereas, conversely, the less the difference in the coefficients of thermal expan-sion of the metal grid and the ceramic, the greater the resistance of the composite to ceramic fracture at operating temperatures above that at which the composite was fired.
Many ceramics can, o~ course, withstand temperatures greater than that to which they are fired during manufacture.
Also, it is much preferred that the metal of the grid be chemically inert with respect to the ceramic composition and, particularly where the ceramic of the composite has porosity, also with respect to the atmosphere in which the composite is to be used. Hence, when selecting the metal for the grid it is desirable to consider whether the atmosphere in which the ; 20 composite is to operate will be oxidizing or reducing, car-burizing, sulfurizing, etc. Of course, as to factors such as the latter, compromise may be necessary or desirable in many instances taking into account the further factor of cost and availability of the metal.
Numerous commercially available metals and alloys are well suited for the practice of the invention. For moderate to high temperature service, some of the nickel base alloys are attract~ve cho~ces, They offer ~ood strength with medium~to high coefficient of thermal expansion, good oxidation and corrosion resistance and good toughness. Preferred commercial ~Q~3435 P~307 nickel base alloys falling into this cate~or~ are as follows:
Incone ~6Q0 (1~. see footnote Inconel~ 6Ql ~11 Ni~Chrome (21 Hastello~ X (3 RA 333 (4~
Another class of metal allo~s~ the common stainless steels, are also well suited for many end uses ~or the com~osites.
The ~err~tic stai~nless steels are paxt~cularly attractive~ They are low ~n cost, have sat~sfactor~ coeff~ci~ents of thermal expan-sionl low as compared w~th other metals such as the austenitic stainless steels~ and the.ir oxidat~on resistance can range from good to outstanding~ The~ are a good selection where low cost com-~ posites are needed for relatl~vel~ h.~gh.temperature applications, ; 15 The common austenitic stainless steels are stronger than the ferritic sta~nless steels at high temperatures. They are usuall~ more expens~ve, offer superiox corrosion resistance, ',~ and are characterized by higher coeffic~ents of thermal expansion, so~ewhat in the same range as th.e nickel base allo~s~ Typical 20 c~mercial sta~nless steels for use as the grid in the practice of the ~nvention ares ~Ferrit~c Stainless Austen~tic Stainle~s :~ MF~1 C5~ see fo~tnote T~3Q4 (6~ see footnote :' T~409 C6~ T~316 (6, T~43Q C6~. T~321 ~6~
T-442 C6) T~347 (6) T-446 (6~ T~30q (.6~
: KANT ~ A (.71 T-31Q (6, KANTHAL~DS ~71. R~330 (4~.
MULTrMET~N~155 ~32 - ~oX s~me ~p~l~cations other ~etals ma~ be desirable, For spec~al h~gh te~perature applicat~ons~ ~r exam~le the re~ractor~ metals and t~eir allo~s can be used~ examples of suc~ metals be~ng zirconium, tungsten, molybdenum~ platinum, r~r~
_9_ 3~
paladium and tantalum~
The metal or metal alloy can be formed into various configurations to form the grid, such as wire screen, expanded sheet or perforated sheet. By ~'screenM is meant an interwoven relationship ~etween wires of the metal, such a screen being shown in FIGURE 3. Expanded sheet metal, as conventionally referred to, is a thin sheet of metal which is provided with slits of various configurations and arrangements throughout the entire sheet which is simultaneously or thereafter stretched in a direction to open the slits, thereby to provide a unitary metal grid with holes therein. Such a structure is illustrated in FIGURE 6. By perforated metal sheet is meant any of a number of patterns punched through a sheet of metal to provide a grid the same or similar to that provided by expanded metal sheet.
Both from the standpoint of ease of manufacture and from the standpoint of attaining composites having optimum physical characteristics, it is preferred that, as regards the precise structure of the grid, the openings therein be of sub-stantially uniform shape and size, and with the size of the ~; openings being, in their largest dimension, no greater than about 3/~ inch and no less than about 1/64 inch. (Where, ~or example, the openings are square, the largest dimension is the diagonal, and it is pre~erred that this dimension be no greater ; 25 Addit~onal information regarding source and designation of the alloys: Cl~ The International Nickel Company, Huntington Alloys Products Division~ Huntington~ West Virginia; (2) Driver-Harris Company, Harrison, New 3ersey; (3) Haynes Stellite Company, Kokomo, Indiana; ~4~ Rolled Alloys Company~ Detroit, Michigan;
C51 Allegheny~Ludlu~ Company~ Pittsburgh~ Pennsylvania; (6) The T numbers o~ t~e alloys so designated are the AISI (American Iron and Steel ~nstitutel designations; (7~ Kantha~ Corporation, Bethel~ Connecticut.
4~
P~307 than 3~8 inch and no less than 1/64 inch.~ Further, it is preferred that the ratio of the aggregate area of openings to the aggregate of the area of the metal between the openings be such that about 30% to 80~ of the total area of the grid constitute openings, and the remainder of the area of the metal between the openings.
THE CERAMIC
As has been indicated, it is essential that the ceramic formulation be one which can be fired to its final unitary or monolithic structure at a temperature below the melting temper-ature of the grid. Where the metal used for the grid is such that at a temperature below the melting point it undergoes ` significant degradation in tensile strength or other physical ; properties, as by way of metallurgical structural change, it is desirable that the ceramic be such as can be fired to its unitary or monolithic structure at a lesser temperature than that at which the degradation in properties of the metal occurs. Further, it is essential to the practice of the invention that the ceramic slurry formulation used to coat the grid be such that the slurry clings to the grid, filling the openings therein, and remains thereon upon drying. This property can best be accomplished by including a binder material in the slurry formulation. The binder can and preferably should be any one or more of numerous inorganic materials, examples of which will be given hereinafter, which have bonding properties, i.e. provide good green bond strength, in the pre~fired state of the ceramic after drying and which provide a strong unitary or monolithic ceramic structure in the final fired state~ ~s re~ards the latter, the inorganic binder remains in and constitutes a part of the ceramic through the fir~ng operationt though generally undergoing reaction with , ~ .. .
~Q~S~35 other of the ceramic ingredients or transformation during the firing operation such as to appear at least partially in another form in the fired ceramic structure than the form in which added to the slurry. For example, where the binder is a sili-cate or colloidal silica, as the examples hereinafter given willillustrate, there may be transformation, as by reaction with other ingredients of the ceramic formulation, of the silica to a silicate or of the silicate to another silicate, such as a glass, in the final fired ceramic structure. But alternatively, or in addition to using an inorganic binder, organic binders can be used in the ceramic slurry, in which case the organic binder vaporizes or burns out during the ~firing operation. Hence, where the only ~inder used is an organic binder, the ceramic ingredient or ingredients of the slurry formulation should be such that during the firing operation there results the required bonding to provide the unitary or monolithic ceramic structure.
Typical examples of organic binders are polyvinly alcohol, dextrine and the water-emulsifiable waxes well known in the ceramics art as temporary binders.
Numerous ceramic formulations well known in the art and extensively used in the precision and investment casting ; technology are suitable for the practice of the invention. For example, slurries, made up of any of various one or more ceram-ics, such as those set forth hereinafter, and suitable binding ; 25 agents, examples of which are also listed hereinafter, are used in the mold making of ceramic shells and investment molds for the casting ~f co~plex shapes and high temperature turbine parts.
T~pical ceramic materials useful for the practice of the invention, either alone or in combination are: zircon, quartz or ~used silica, mullite, spodumene, magnesia, forsterite, magnesia-alumina spinel, silicon carbide, alumina, zirconia (stabilized~ r chromium oxide (Cr203~ and stoichiometric cordi-erite or composition modifications of cordierite as are known in the art. It is desirable that the ceramic material be of small part~cle size, preferably 325 mesh or finer.
Though liquids other than water can be used for the slurry it is much preferred from the standpoint of cost and convenience and from all other standpoints, that water be used.
Hence, it is desirable that the binder be either water soluble 1~ or such that it forms a colloidal suspension with water.
Examples of inorganic binders excellent for the practice of the invention are as follows: colloidal alumina, colloidal silica, sodium silicate, potassium silicate, calcium aluminate and kaolin or other clay. An example of an organic-inorganic binder suitable for use in the practice of theinvention is ethyl silicate.
The initial bonding of ceramic particles with the above blnders usually requires only relatively low temperatures;
in many cases ambient or room temperature drying usually pro-vides ample pre-fired bond strength. However, the full bond is not developed until the structure has been exposed to the temperature at which the ceramic formulation forms a unitary or monolithic structure. Where the composite is to be used in an environment which provides a high service temperature, this itself can be used to effect the final bonding. The required temperature naturally varies depending on the precise formu-lation, as well known in the ceramic art~ ~n the case of the sodium sil~cate and alum~na ceramic system~ exemplified here-inafter, the final bonding apparently takes place by at least localized melting of the sodium silicate followed by rapid - , ~t~ 8~a3s diffusion into, and at least partial reaction with, the alumina to form a highly bonded structure~ Bonding can also be obtained with colloidal partIcle type binders, apparently also by solid diffusion and at least part~al reaction with other of the in~-gredients at the required temperature to provide the unitary ormonolithic structure, The gelling of the colloidal type binders is of value in providing good pre.fired dry bond strength.
It is not essential that the ceramic of the fired composite ~e of extremely high density and, indeed, for many applications such as for thermal insulation, porosity of as high as 10% or even higher can be desirable. By adding flour, powered wax, wood flour or other powdered organic material to the slurry in the desired proportions and particle sizes the amount of porosity can be controlled since in the firing operation the combustible mater~al burns out and leaves pores.
The following are specific examples of ceramic slurries suitable for the practice of the invention:
EX, 1 112 grams of distilled water was added to 563 grams of commercial grade sodium silicate Type RU ~SiO2 33.2%, Na20 13.85%, H20 52.95%) and electric-motor~propeller stirred to insure total mixing. To this solution was added 825 grams of commercial tabular alumina of a particle size of -325 mesh. The addition of the alumina was made while the electric-motor-propeller stirring the solution to insure that all particles were fully wetted and the viscosity remained relatively constant. The slurry was then ready for coating of the metal grid.
EX. 2 4~Q grams of powdered fused silica (Nalcas ~P-lW2 was added to 210 grams o~ colloidal silica (Nalcoag~1030~ and was ~- stirred thoroughly wit~ an electric-motor-propeller, Mixing was continued for 1~1/2 hours to insure that the slurry reached ~f Tr~r~
,~
P~307 equilibrium-~that is, all of the particles were fully wetted and the viscosity remained relatively constant. The slurry was then ready for coating of the metal grid.
EX. 3 62 grams of water was added and thoroughly mixed into .
188 grams of aqueous colloidal silica (30% solids). Complete stirring was continued to insure an intimate solution of the silica and water. ~o this solution 750 grams of zircon powder was added while stirring with a motor~driven propeller. This stirring was continued ~or two hours to insure complete wetting of all the zircon particles and a uniform viscosity. The ; slurry was then ready for coating the metal grid, FORMING THE COMPOSITE
The composite is made by applying the viscous ceramic slurry to the grid so that the slurry ~ully coats and fills all the openings in the grid, after which the coated grid is dried and then fired, The slurry is best applied to the grid by dipping the grid into the slurry. In many cases a multiple dipping operation is desirable. That is, after a first dip the slurry thereby applied to the grid is allo~ed to dry after which there is application of additional ceramic by another dip into the slurry. Since the dried ceramic slurry is generally pliable it is possible to re-shape or machine the composite prior to the firing operation to cylindrical or other shape after the ceramic is applied to the grid. Alternatively, the grid can first be shaped into a cylinder, or other shape as desired, and the ceramic slurry then applied to the shaped grid, As ha5 ~een indicated~ after the ceramic is applied to the metal gri~d and allowed to dry~ the ceramic with the grid imbedded therein is fired to a temperature sufficient to ,.~
~(~9~35 convert the ceramic to a unitary or monolithic structure. At the firing temperature~ the metal grid, because of its higher coefficient of thexmal expansion, is in an expanded condition and the ceramic i5 a rigid monolithic structure while at the high temperature at which the metal grid is in its expanded condition. Hence, once cooling starts and as cooling continues, and the metal grid contxacts from its expanded con~ition, the metal grid is thereby put into tension and the rigid ceramic is put into compression. Upon completion of cooling, manufac-ture is complete, The following is a specific example of the practiceof the method of the invention, the slurry used being that set forth in Example 1 above:
A 16 mesh screen metal grid of Incone *600 ~as de-15 greased by rinsing in methanol and low temperature dried. Tocoat the screen with the slurry, it was dipped into the slurry ; and slowly removed vertically, permittlng the slurry to adhere to the ~res Gf the screen and fill all the interstices of the screen. After withdrawal from the container of slurrv and air drying for 30 minutes (during the early stages of which drying operation the coated grid was slowly revolved in a vertical plane to prevent ceramic build-up at one end due to gravitv) the composite was oven baked at 25F increments for about 15 minutes at each temperature from 100F to 500F. The tempera-ture was raised at a relatively 510w rate, as described, tobetter assure against the formation of gas bubbles or separation of the ceramic. The composite was then fired in air at 1800F
for 3a minutes at ordinary atmosphexic pressure and then allowed to cool to room temperature, If desired, other methods, such as use of a vacuum furnace or micro~wave heating or induc-~ ~.le~ L
- ~`q~43S
P~30'7 tion heating, can be used for the drying and heating to preclude localized internal gas build~up and the ensuing loss of integ-rity of the ceramic matrix structure.
FIGURES 4 through 6 show another embodiment of the invention wherein there are incorporated multiple layers of the composite~ adjacent la~ers being slightly spaced to provide thin air gaps between the layers. Referring to FIGURES 4 and 5, 10 is a metal tube and 12 is a tubular multiple layer composite made in accordance with the invention and functioning as a thermal insulator to prevent heat loss from hot gases or other fluid flowing through the tube~ As can best be seen in FIGURE
5 r the composite comprises a grid 14 which is imbedded in ceramic 16 and which is spirally wound thereby to provide a tu~e having three substantially parallel or concentric layers 18, 20 and 22, As best shown in FIGURE 6, spaced, spirally wound heat resistant wires, such as shown at 24 and 26, between the layers, provide the spacing, and hence an air gap, between adjacent layers, the thickness of the air gap being determined by the diameter of the spirally would wires. The metal grid of the FIGURES 4-6 embodiment instead of being a screen of interwoven wires is an expanded metal ~rid. One conventional and inexpensive method for making such a grid is to provide a thin sheet of the metal with staggered parallel rows of slits and thereafter pulling the sheet in a direction transverse to the slits whereupon the diamond shape openings, as shown, are formed, The metal grid can be used in the precise form as j results ~rom the pulling operation or can thereafter be put through roller$ to roll it into a flat configuration such as that shown in FT~URE 6~ A metal grid of the same structure can be accomplished by punching a metal sheet to provide the i~9~34~S
openings; however, this is far more expensi~e because of the large amount of metal scrap which results, Expanded metal grids are well known in the art and it should be understood that the precise method of manufacture ;s not important to the present invention nor is the shape of the openings so long as the grid structure is such that ~t can be put into tension not just in one direction but in directions perpendicular to each other.
To manufacture the embodiment shown in FIGURES 4 through 6, a rectangular shaped piece of the metal grid is coated with the ceramic slurry, as described with reference to the FIGURES 1-3 embodiment, and then, after drying, spaced parallel heat resistant metal wires are placed on the ceramic coated metal grid. This assembly is then spirally wound in a direction in which the metal wires extend thereby to result in the spirall~ wound configuration as shown in the drawings. The resultant tubular structure is then fired to a temperature to cause the ceramic to form a monolithic structure and is there-after cooled to complete the manufacture~
Means other than the wires 24 and 26 can be used to provide the spacing between adjacent layers. For example, prior to spirally winding the ceramic coated metal grid to a tu~ular shape the surface thereof can be provided with a plurality of relatively widely spaced relatively large grains of ceramic or other re~ractory material, the size of the grains determining the spacing between adjacent layers when such structure ~s spirally wound. As still another alternative, the metal gxid ~tself can be provided with spaced dimples to pro~
vide the desired spacing between adjacent layers~ A thin air gap between adjacent layers provides additional thermal insula~
tion; however, it should be understood for some applications it P~307 may be desirable to use multiple layers of the composite material but with no large spacing between the ceramic layers imbedding the metal grid, To manufacture such structure it is necessar~ only to eliminate the heat resistant metal wires or other means for providing the gap between the layers.
The composites of the invention are particularly suit-ed for tubular shapes such as shown in the drawings; however, it should be understood that whereas the two embodiments shown are of tubular shape, composites of the present invention can take other forms such, for example, as a flat planar form.
As regards internal combustion engines, another application for the composite of the invention is as a thermal insulator for the combustion chamber and the engine head adjacent to the exhaust gas ports to thereby regulate localized heat flow to the engine coolant~ This is desirable because if heat flow to the coolant is too rapid the coolant at such loca-tion can be yaporized thereby forming gas bubbles or pockets which tend to ~nhibit heat flow. By using the thermal insula-tion in the head or in the engine block adjacent the combustion chambers, there is increased temperature control and hence decreased harmful emission and increased fuel economy.
',!
', The ceramic-metal grid composite of the present invention has been described particularly with reference to its use as a thermal insulator because the composite demonstrates such remarkable thermal insulating properties.
An investigation of the insulating propexties of three layers of the composite material was conducted in the following method~
~ 4-1~2 inch diameter cylinder of stainless steel 7 inches long and ,Q72 inches thickness was lined with three ~q~3s concentric cylindrical sections of the composite insulation.
A slurry of tabular alumina and sodium silicate such as that made in Example 2 above was prepared~ Three cylinders of 16 mesh Incone screen were made by joining the seam of the indi~idual cylinder By tack welding. These concentric cylinders were degreased in methanol and after drying dipped in the slurry mixture providing a viscous coating. After air drying the slurry, the structures were oven dried at temperature steps of 25F starting at 100F. After reaching 500F the structures were then fired at 1750F in air at ordinary atmospheric pres-sure to complete the sintering process. The metal grid-ceramic composite cylinders were then concentrically mounted within the stainless steel cylinder, separating their surfaces by spaced circumferentially extending Inconel 600 wires to provide a 15 stagnant air space between adjacent cylinders. The thickness of each cylinder was about 1/16 inch and the size of the cylin-ders was such that the spacing between adjacent cylinders was about .06 inches~ Thermocouples (T4) were welded in place on the outer surface of the metallic cylinder~ Additional thermo-couples tTl~ were secured to the inner surface of the inner-most compasite cylinder; thermocouples (T2~ were set in place between the innermost and middle composite cylinders and thermocouples (T3 ~ between the middle and outermost composite cylinder. The entire unit was placed on fire brick supports and a burner nozzle placed in the top opening pointing downward, The burner was also supported by fire brick and covered by asbestos sheet in such a manner that all secondary air was brought to the buxner ~rom outside the apparatus, A mixture of propane and air was burned at several throttle settings and 30 when temperatures stabilized temperatures were recorded provid-S~35 ing comparative data showing the insulating effect of each successive layer~ Table I gives the results of the test.
TABLE I
INSIDE TEMP, TEMP. TEMP.
TEMP. F~ F, F.
~Tl)F~ (T2~ (T32 (T4) 15~0 1355 1050 728 A second test apparatus was prepared in accordance with the above apparatus except that zircon refractory was sub-stituted for the tabular alumina. Similar test procedures were conducted with the results given in Table II.
TABLE II
INS$DE TEMP. TEMP. TEMP.
TEMP~ F. F. F.
(Tl)F. (T2~ (T31 (T4) 1500 1320 1~00 670 These tests show a significant temperature drop across , approximately 5/16 inch of the composite insulation with small ~-~ 20 air spaces between adjacent layers.
,~ In another application, the insulation was wrapped concentrically upon itself to provide three la~ers totaling 3~16 inch thick and inserted into a cylindrical stainless steel container 3-3/4 inches in diameter and 10 inches long. An '5 25 automotive reducing catalyst was then placed within the insula-tion and the contàiner welded shut with entry and exit pipes to conduct eng~ne exhaust through the catalyst, This test shows a sign~ficant temperature drop across approximately 3~16 inch o~ insulation with minimal air spaces 3Q between layers. Thermocouples were placed in the center of the P~307 catalyst and on the surace of the stainless steel container, the metal thickness of which was 0.040 inches, The catalyst canister was attached to the standard exhaust manifold of an independent testing laboratory's Plymouth~ 18 CID-V8 engine for dynamometer testing. Steady state loads and throttle settings were conducted and when temperatur~sstabilized gas temperatures in the catalyst and skin temperatures were recorded.
These are listed in Table III and show the insulation's signi-ficant effect in reducing temperatures.
TABLE III
Exhaust Canister Gas Temp~ F Skin Temp F
Another test of an insulated catalyst canister and insulated exhaust manifold made similarly to that of the pre-vious stationary dynomometer test was conducted by an indepen-dent testing laboratory. This test was conducted on a 1975 Plymouth~318 CID-V8 Furyrautomobile with the catalyst installed and instrumented with thermocouples to determine the gas and surface temperatures. The automobile was placed on a chassis rolls dynamometer and run in accordance with the EPA Hot Start CVS emission test procedures, Exhaust gas temperatures and canister and insulated exhaust manifold skin temperatures were recorded~ These are presented in Table IV. It can be seen that the insulati~e capabilities of the composite material are outstandin~, ~ .
1rc~ k 43~
P~307 TABLE IV
Exhaust Gas Canister E~haust Manifold Temperature F Skin Temp F Skin Temp F
122~ 412 495 Table IV results are somewhat scattered compared to those of Table III due to the type of tests conducted. Table III data were obtained from a steady state dynamometer test, whereas Table rV data were taken during an EPA Hot Start CVS
test where the engine temperatures are in a transient condition -for the most part~
It should be understood that the composites of the present invention may find other uses, such, for example, as structural elements requiring high heat resistance. It should ! -~ be further mentioned that the composites of the present inven- `
- tion not only demonstrate excellent thermal insulating proper-ties but also excellent acoustical barrier properties. This is significant, for example, when the composites are used in -~ 20 automotive vehicle exhaust systems since they not only provide good thermal insulation but also acoustical barrier properties thereby reduclng the noise level normally associated with such exhaust systems Additionally, the composites of the present invention ~- 25 permit development of materials with special properties not ' possible by other techni~ues such as heat resistant catalyst supparts, Such use can be illustrated by reference to the embodi~ent de~cribe~ w~th reference to PIGURES 1~3 wherein the compos~te shown constitutes the lining in the exAaust pipe leading from the engine to aicatalytic converter of an automotive ; `
P~307 vehicle. By catalyzing the interior surfaces of the tubular lining, the lining serves not only as a thermal insulator and acoustical barrier, but also as a catalytic device for catal- ;
yzing the oxidation of unburned or partially burned hydro-carbons in the exhaust gases to carbon dioxide and water or, alternatively, for reducing the oxides of nitrogen in the exhaust gases. The catalytic materials which demonstrate the catalytic activity for performing such functions are well known in the art, for example, platinum, palladium, copper and the transition metals, or the oxides of these metals. To in-; corporate such a catalyst into the composite, the catalytic material can be applied in powder form~ for example, to the ~; surface of the ceramic prior to firing or, alternatively, can be incorporated into the ceramic itself.
Hence, it will be understood that whereas the inven-tion has been described with reference to certain embodiments thereof, various changes and modifications may be made all within the full and intended scope of the claims which follow.
' .
.
Claims (10)
1. A high temperature insulation of a metal-ceramic composite comprising a rigid metal wall, a monolithic layer of ceramic positioned adjacent the metal wall and having imbedded therein a metal grid including openings of substantially the same size and shape, said composite having been made by coating said metal grid so as to fill the grid openings with ceramic slurry to provide a layer of the ceramic having imbedded therein said metal grid, heating said layer of ceramic with said metal grid therein to a temperature at which the ceramic forms into a monolithic ceramic body, and thereafter cooling said ceramic body with said metal grid therein, said metal grid having a melting temperature higher than said temperature at which said ceramic forms into said monolithic ceramic body and said metal grid having a higher coefficient of thermal expansion than that of said ceramic, and said grid openings having a size of from about 1/64 inch to 3/8 inch and the aggregate area of the openings constituting from about 30% to 80% of the total area of the grid.
2. A metal-ceramic composite as set forth in Claim 1 wherein said composite contains at least two layers of said metal grid spaced from each other by said ceramic.
3. A metal-ceramic composite as set forth in Claim 1 wherein said metal grid is an expanded metal grid formed from sheet metal.
4. A metal-ceramic composite as set forth in Claim 1 wherein said metal grid is a metal screen.
5. A metal-ceramic composite as set forth in Claim 1 wherein there are a plurality of layers of said ceramic each with a metal grid imbedded therein and wherein adjacent layers of said ceramic are spaced from each other.
6. A metal-ceramic composite as set forth in Claim 1 wherein said composite is of tubular shape.
7. A metal-ceramic composite as set forth in Claim 6 wherein said composite is of cylindrical shape.
8. A metal-ceramic composite as set forth in Claim 7 wherein said composite is formed of a spirally wound layer of said ceramic with said grid imbedded therein to provide a plurality of generally concentric layers of said grid im-bedded in said ceramic.
9. A metal-ceramic composite as set forth in Claim 1 wherein said ceramic is alumina.
10. A method for making a high temperature insulation composite of metal and ceramic, said method comprising coating a metal grid with ceramic slurry thereby to provide a layer of the ceramic having imbedded therein said metal grid, said metal grid having openings with a size of from about 1/64 inch to 3/8 inch and the aggregate area of the openings constitut-ing from about 30% to 80% of the total area of the grid, heat-ing said layer of ceramic with said metal grid therein to a temperature at which the ceramic forms into a monolithic body, thereafter cooling said ceramic with said metal grid therein, said metal grid having a melting temperature higher than the temperature at which said ceramic forms into said monolithic ceramic body and said metal grid having a higher coefficient of thermal expansion than said ceramic, and positioning a metallic layer and the ceramic layer in an adjacent relationship to each other.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA289,707A CA1098435A (en) | 1977-10-27 | 1977-10-27 | Metal-ceramic composite and method for making same |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA289,707A CA1098435A (en) | 1977-10-27 | 1977-10-27 | Metal-ceramic composite and method for making same |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1098435A true CA1098435A (en) | 1981-03-31 |
Family
ID=4109880
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA289,707A Expired CA1098435A (en) | 1977-10-27 | 1977-10-27 | Metal-ceramic composite and method for making same |
Country Status (1)
| Country | Link |
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| CA (1) | CA1098435A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114315403A (en) * | 2021-12-22 | 2022-04-12 | 北京科技大学 | Wire-implanted reinforced brazing connection method for C/C and C/SiC composite material and metal |
-
1977
- 1977-10-27 CA CA289,707A patent/CA1098435A/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114315403A (en) * | 2021-12-22 | 2022-04-12 | 北京科技大学 | Wire-implanted reinforced brazing connection method for C/C and C/SiC composite material and metal |
| CN114315403B (en) * | 2021-12-22 | 2023-02-24 | 北京科技大学 | Wire-implanted reinforced brazing connection method for C/C and C/SiC composite materials and metal |
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