CA1078106A

CA1078106A - Refractory material suitable in particular for the production and handling of aluminium

Info

Publication number: CA1078106A
Application number: CA253,624A
Authority: CA
Inventors: Michel L. Drouzy; Michel M. Richard; Francois P. Huet; Henri M. Lacau
Original assignee: Ucpi Pour L'utilisation Des Ceramiques Et Des Platres Dans L 'industrie Ste; Centre Technique des Industries de la Fonderie
Current assignee: Ucpi Pour L'utilisation Des Ceramiques Et Des Platres Dans L 'industrie Ste; Centre Technique des Industries de la Fonderie
Priority date: 1975-05-29
Filing date: 1976-05-28
Publication date: 1980-05-27
Also published as: FR2312468B1; NO143152B; NO761815L; NL167667C; BE842294A; SE7605934L; AU1412076A; JPS5230810A; GB1525032A; NL167667B; NO143152C; SE415754B; FR2312468A1; NL7605644A; DE2624137A1; IT1069781B; AU497682B2; CH614687A5

Abstract

ABSTRACT OF THE INVENTION

A process for inhibiting the effect of molten aluminium on an object with which it is intended to come into contact, comprising making the object of a material selected. from the group consisting of a solid material having a deflection temperature under load aboYe 1000°C, a content by weight of aluminium, expressed as Al2O3, of from 10% to 60%, a content by weight of silicon, expressed as SiO2 , of from 5% to 85% and a content by weight of fluorine, forming part of the structure of the material, of from 0.1 to 10%, a solid material having a deflection temperature under load above 1000°C, a content by weight of sodium, expressed as Na2O, of less than 5%, a content by weight of aluminium, zirconium, beryllium, chromium and carbon , expressed respectively as Al2O3, ZrO2,BeO, Cr2O3 and SiC of less than 60% and a content by weight of fluorine of from 0.1% to 10%, and a solid material having a deflection temperature under load above 1000°C, a content by weight of sodium, expressed as Na2O, of less than 5%, a content by weight of phosphorus, expressed as H3PO4, of less than 5% and a content by weight of fluorine of from 0.1% to 10%.

Description

~7~6 .
~`his invention relates to refrclctory materials and, more especially, to ~e~ractory mcl~erials intended to withstand contact with moltell met~llic masses o aluminium ~nd its alloys, ~oth for use in the cons~ruction of smelting fu~naces and for the manufacture of fittings for ~urnaces of this kind, such as ducts, chutes, transfer ladles or casting ladles, which remain ln con~act with molten alumini~n, often ~or prolonged periods.
Refractory compositions o the type uscd in the smelting of metals contain silica, generally in the ~onm of various silicates. The proportion of silica varies according to the r type of composition. It c~mounts to approximately 60% by - weight in so-caLled argillaceous or silico-aluminous products - (35% of alumina) and to 35% i.n aluminous products (60% of alumina) based on sillimanite, bauxite) mullite or others.
The "alumina" itself contains of the order of 1~'7/o o~ silica.
The magnesia or chrorne-magnesia products often contain close t~ 10% o silica.
This silica tends to react with the r~ducing metals, - 20 such as alumini~n, in accordance with the ~ollowlng scheme:
-4 Al ~ 3 SiO~ 2 3 3 Si ~ 000= -150.020 cal This reduction o~ the silica or silic~tes by the reducing me~al liberates a ~onsiderable amount of energy. Th~xetically, i~ could be contlnued until one of the two starting produrts

-2-~ .' ~ ' -~

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~ 6 has been completely conswned. I~ practice, the reaction velocity is slow enough for lightweight reducin~ metals and their alloys to be melted in furnaces made o materials r containing silica. ~lowever, various phenomena are encountered, S as a result o wllich ~he furnaces or t~leir fi~tings soon have to be taken out of service. rl`he re~ractory ma~erial grad~lally becomes impregnated. ~s a result, i~ changes into a black, extremely hard mass ~hich is ~n aggre~ate of corund~ and alumini~ll. This mass conducts both heat and electricity which can have serious consequences for an electric furnace and ~ives rise to significant losses of energy. Swelling and cracking occurs t above all when tlle alwnina content of the refrac~ory composition is low. Particles of refractory material become detached from the furnace and reappear in the aluminium àrticles in the fol~ of hard inclusions.
- "Mushrooms'7 o oxides are formed both on the hearth and - - above all on the walls of the furnace in contact with the ; bath. These mushrooms grow until they o~struct a large part of the furnace. They are extremely hard and, in practice, cannot be detached from the walls~
~ritish Patent Specification No. 1,135,147 and the ar~cle by W. Helling and E. Kistermann entitled "Salzimprag-nierverfahren fur Zustellung von Aluminium-Schmelz und Warmhalteofen" published in the Journal 'IAluminium" 33 (1957) No.8, pages 514 to 520, recall these serious dif~iculties o the aluminium industry and suggest overcoming them by coating the inner walls of the furnace wi~h a mixture of 8~/o o - -- sodium chloride and 20~/~ of cryolite. The melting point o~
this mixture is 795C. Because it is very fluid, it p~netrates readily into the surface pores of the chamotte-based refractory t - . -3 - .',, . , . 1 1: ................. . . . .
-- . - - . - - . . - - : -: . ~

material. Generally, it has a visible thickness of 1 to 2 mm, although the depth of penetration into the refrac~ory material - reaches 6 m~. The high sodiuln con~ent: of this so called glazing flux and its resulting relatlvely low mel~ing poin~
make it substantially non-re~rac~ory and rela~ively weak.
In time the impregllation has to be rep~al:ed, wllich the au~hors have recogllis~d. A tec~lnical le~El~t for co~nmercial cons~nption issued by Soclete Servimetal ~ncien department, fonderie soudure Otalu, 87 Rue Pierre Joigneaux, 92 Bois- ~
Colombes, France, entitled "Les ProccJ~s ~e glacage des r garnissages refractaires des fours de fusion et de coulee utilises dans les fonderies d'aluminium" [Methods of Glazing the ~efractory Linings of Smelting furnaces and Casting Furnaces used in Al~niniurn Foundries3, is more explicit. After having ~` 15 recalled the'detrimental effect of molten aluminium on the furnace, it proposes two glazing techniques using a mixture of 8~/o of NaCl and 20% of AlF3 - 3 NaF. The deep impregnation ; techniquet corresponding to that described ln the above-mentioned Gennan Article, has given way to a so-called I'sur~ace impregnation" method which is more advantageous because it is simpler and ~uicker, using less glazing flux ' and requiring lower working temperatures. Ater the furnace has been dried and fired, this improved method comprises regulating the surface temperature of the re~ractory lining ~5 to between 750 and 780C, spraying the hearth with a quan~y o flux amounting to between'7 and 10 ~ per cm using a compressed-air projection apparatus, charging al~ninium, - preerably ordinary alumini~n, approximately 1 hour after the beginning of melting, the charge being calculated in 30 - such ~way that it represents only one third of the normal ' _4_ .
~ '' ' " ;

capacity of ~te furnace3 distributing from 2 ~o3 kg of flux -- per square metre of hearth over the ~ath when the charge is half melted, distributing another ~lux over the dross at the end o~ melting, the temperature oE the bath being o~
the order of 730 to 750C, this o~ller 1ux making ~he dross dry and pow~ery and hence easy ~o remove by drossing after 4 to 5 minutes' reaction, ~egassing and puddlirlg in the us~lal way, completely emptying the furnace and carefully ~ soraping the hearth, applying another glaze in the same way as described above, except that the second charge of metal is calculated to amount to half the normal capacity of the furnace, followed by a third glaze applied in the same way as described above except for a ew modifications~ and renewing the glaze five days later. Since the furnace is thus prepared lS once and for all, it is sufficient to apply an interim glaze r once a month. The comple~ty and labour costs, the general immobilisation and materials involved in these initial and subsequent glazings have prevented the development of these techniques, especially since the addition of relatively volatile flux continuously contaminates the alurninlurn treated.
In fact al~ninium founders continue to work in thP same way æ
bPore and include in their manufacturing costs the investment required for the frequent replacement of the urnaces 9 their f ! rapid reduction in capacity, their immobilisation or cleaning purposes after each batch and the costs attributable to losses of alwninium, still with the fear that a "hard spot" in the molten al~ninium will not damage an expensive tooL downstream - of the furnace. These techniques have failed because they have been unable to escape from the following dilemma~ If a low melting point flux ,s used or impregna~ion, impregnation ~5_ .

, - .

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~ ~ 7 ~

can readily be carried out, but unÇortunately the flux - evaporates rapidly. If a re~ractory iux is used for - 'impregnatlon, the urnace has to be heated to a high temperature in order both to make the 1ux L~Iid and to enable it to be effectively applied. Unfortunately, r the furnace is inc~pable or substantiaLly incapa~le o~
withstanding this temperature and is pennatlently damaged.
In the article by Michel Drouzy and ~lichel Richard entitled " oxydation des alliages ondus, reaction avec les reractaires" [Oxidation of Molten Alloys, ~eaction with Refractory ~laterialsJ, published in the Journal r;onderie 332, pages 121 to 128' in l~arch 1974, it was recalled that J,W. ~`ruehling and J~D. I~anawalt demonstrated that a fluorine-containing atmosphere protected a furnace of refractory material intended for the treatment of liquid magnesium (Atmosphere protectrice pour la fusion des alliages du magnesium [Protective Atmosphere ~or Melting ~lagnesium Alloys], Modern Casting 56, August 1969, pages 159 to 164), and it was $ound tllat this fluorine-containing atmosphere was also suitable for protecting a refractory material of ¦ - an aluminium bath.
! - The protection obtained is temporary ~a ~ew days at the ' most~ and is governed by the quar~ity of fluorine which the - ' refractory composition is able to adsorb in its pores once j' ~5 the fluorine-containing compound placed in the furnace has been consumed. In the case of a furnace or ladle which does not work in a confined atmosphere~ the pennanent renewal of the atmosphere virtually prevents correct protec~ion from being obtained. In addition, the removal of large quantities of fluorine-containing gases is too dangerous for adoption ;

t - . ' , , ~.
.
, ' ' ~ ~ 7 ~ 6 on a wide scale in foundry ~ork.
It had not been considered to overcome these difficulties by incorporating fluorine-containing compounds in the actual mass of the re~r~c~ory composit~;on because it was kno~l that the fluorine-containing colnpounds are fluxes wllich at~versely affect the re~ractory qualitles of the ~,roducts to which they are addecl. Ilowever, the addition o fluorine derivatives to construc~ion ma~erials which are not intended to corne into r contact wi~h molten alumini~n has already been carried out to the detriment of their refractory qualities essentially under two types o~ specific conditions. On the one hand, it has been proposed to mix a little fluoride with refractory compositions bonded by a phospllate (cf. inter alia the Article by ~erbert D. Sheetsg Jack J. ~ulloff and Wisto~
H. Duckworth of the Batelle Memorial Institute entitled "Phosphate Bonding of ~efractory Compositions" published in Brick and Clay Record in July, 1958, or the Article published in ~erichte der ~eutschen Keramischen Gesellschaft, Vol.37 (1960), No~8, pages 362 to 367 by ~ etchel and G. Ploss entitled "Uber das ~bbinden von Keramischer Ruhstoffen mit monoal~niniumphosphate Losung ~Feuerfestbinder 32)".
Thus, an attempt was made to improve the setting o concrete ~ by the addition of fluoride. It was hoped that the formation of fluophosphates would promote this effect. In order to 2~ offse~ ~he adverse effect upon refractory properties, use was made according to the first ~rticle of expensive refractory cons~tuents such as tabular aLumina, zirconia, etc. whert?as according to the second Article there is a - - warning that3 in practice, it is-generally not possible tc 30 ~ obtain a high pyroscopic resistance if the presence of - , .~
, . ' ' ' i 1~7~106 fluorine can be tolerated with a view to forming a vitreous fluophosphate phase to accelerate setting.
On the other hand, attempts have been made to produce vitreous sodi~n-containin~ products referred to as refractory concretes in the book entitled "tllt~ebestallcliger Beton" by Nekrassow (~auverl~g G~l~ll Wies~aden~~erlin 1961), especially in the third and four~h cha~l~rs, by tlle use of soluble glass and sodium ~luosilicate. 'rhe high sodium contents of these gla~es adversely affect their reractory quallty. A chamotte fire resistant up to 15~0C withstands a temperature of only 900C when a soluble glass and ` fluosilicate, ~oth po~erful 1uxes, are added to it. In order to withstand a temperature of 1000C, a chromite has to be used (cf. the Table on page 239). None of these publications reers to the particular case of a furnace or molten aluminium.
US Patent Specification No. 3,261~699 describes bricks intended for ~urnaces ~or the electrolysis of aluminiwn.
.....
The inventive idea of this patent is to make the furnace of the same constituents as the electrolysis bath, n~mely cryclite and A1203. As a result, the bath is never polluted, - even if the furnace is as it were attacked during electrolysis.
To obtain this result, it is specifically pointed out in column 5j lines30 to 32 of the above-mentioned Patent Specification that, if additives are used9 they must be t used in relatively small quantities, i.e. in-quantities ~f less than 1%. This is so true that the Patentee recommends using synthetic alumina, namely alumina produced by the Bayer process, whilst the cryolite is also artificial cryolite. AccordinglyJ the product in question is a very _ ~ .

i.

.~ . , .

expensive product o~ synthetic origin.
On the other hand, it has been found in accordance with the present invention that it is possible to use a re~ractory ma- -terial which is relatively inexpensive because it is produced from natural materials and which is sufficiently resistant to molten aluminium even when it contains an appxeciable quantity o~ silica.
By virtue o~ the present inventlon, it is possible to produce an object, such as a furnace or ~urnace fitting, intended to be in contact with molten aluminium which is substantially una~-f~ected both chemically and physically by the bath o~ aluminium andwhich withstands the high temperatures whilst at the same time being of ralatively low cost because it does not involve the use of special or synthetic refrac-tory products, such as tabular alu- .:
mina zirconia or synthetic alumina.
The invention relates to a solid material having a de-flection temperature under load above 1000C, a content by weight of aluminium, expressed as A1203, of from 10% to 60% and, better still, from 30% to 50% and a content by weight of ~luorine of from 0.1% to 10% and bet*er still from 0.2 to 5%, the fluorine forming part of the structure of the material, wherein it has a content by weight of silicon, expressed as SiO2, of from 5% to 85% and, : .
better still, from 20% to 60%.
The invention is also directed toward a process for in-hibiting the effect of molten aluminium on an object with which it is intended to come into contact. The process comprises making ths object of a concrete which has a de~lection temperature under load above 1000Cg a content by weight of aluminium, expressed as A1203, of from 10 to 90%, a content by weight o~ calcium expressed as CaO of from 4 to 14% and a content by weight of fluorine form- .
ing part of the structure of the concrete of from 0.1 to 10%.
The very small proportion of ~luorine incorporated in the mass has proved to be sufficient to prevent the material from _ -- .

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l~r78~

being ehem~cally or physicochemically at~ackad by the aluminium, and insufficient for adversely affecting the refractory properties o~ the material to an unacceptable extent. The incorporation of fluorine, even in small proportions, radically modifies the phe-nomenon of the wetting of the refractory material by the molten aluminium The refractory material is neither wetted nor attacked by the aluminium The fact that it is possible to produce a matexial with properties such as these is surprising in view of U S. Patent Specification No. 3,261,699 not only because this publication spe-ci~ically states that silica or any other additives must no$ be used in significant quantities, but above all because it was not foreseeable that the addition o~ silica, a fairly reducible mate-rial, would nevertheless be tolerated for a material intended to be in contact with molten aluminium on the conditivn that fluorine was added to the material. In the case of the U.S. Patent Speci~
fication, the addition of ~luorine to the alumina is motivated by the composition of the electrolyte and not by the need to protect the rest o~ the material consisting of Bayer alumina which is a non-reducible material. By contrast, the role and function of the fluorine are entirely different in the material according to the invention. They prevent the SiO2 from being attacked by the molten aluminium.
The deflection temperature under load (To 53 charact r-ises the refractory quality and the mechanical strength of the re~ractory material. It is det rmined in accordance with the Standard ISO R 1893 (F) of October, 1970. The test ess~ntially comprises placing a cylindrical test specimen 50 mm in diameter and 50 mm tall made of the material tested in a furnace between th~ compression rods of a ~ -- 1 0 . ~ Q~

compress on devic~ capable of applying a constant lo~d o 2 kgf/cm to the test specimen, and recor~ing the temperature ~ached on defonnation to 0.5~/O of the initial height o~ the test specimen for a given hea~ing rate of the furnace o 10oC
S~ per minute to 500OC, and then 5OC pcr Ininute beyon~ 500C~ ;
The statemell~ tllat the fluorine ~onns part of the structu~e is meant to show that the fluorine is not present in the form o~ a gas adsorbed in the pores a~ a basic aggregate or in the Çorm of a coating applied to the surace 10 ` and in the pores of that aggregate. The fluorine is present L
in and distributed throughout the mass in a solid form, combined with the aggregate, or in the ~orm of a solid fluorine compound associated with tlle aggregate. In general, the fluorine is uniformly distributed throughout the mass.
lS Analysis of samples taken a~ points situa~ed at different r distances from the surace intended to come into contact with the molten aluminium reveals the presence of fluorine.
` The 1uorine is virtually only desorbed at temperatures above the service temperature.
~`he invention also relates to a solid maErial having a deflection temperaturè under load above 1000oC, a content by weight of sodium, expre~sed as Na20, of less than 5% and better still less than 2%, a content by weight of aluminium, zirconium, beryllium, chromium and carbon, expressed respectively as A1203, Zr02, BeO, Gr2O3 and SiC, of less r - than 60% and a content by weight of fluorine of from 0.1%
- to l~io and better still from Or 2% to 5%, The invention also relates to a solid material having L
a deflection ~emperature under load above 1000C, a content by weight of alkali metal, éspecially sodiwn expressed a~ Na20, .

.
, ~ . . . - . . . . . . . . , ~ . - .. .

~ 7 ~ 1 0 ~ -of less than 5% and better still less than 2~/o J a content by weight of phosphorus, expressed as 133P04, of less than 5~/0 and better still l~ss than 2% and a content by weight of fluorine of the same order as indicated a~ove.
S Other materials accorcling to ~he inven~ion have a con~ent by ~eigllt o~ phospllorus expresse(l as ~l3P04 o~ less than 5% and ~etter sti~l less ttlan 2n/o.
Prefera~ly, these materlals which gener~lly contaln - oxidised silicon, have an average content ~y weight o~ 1 aluminium, expressed as A1203, of for example more than P
l~to~ better still more than 30% or even better more than 40%, but Less than 60%, better still less than ~% and even better less than 50/0.
Apart from the fact that it is surprising that a material of the kind in question has both the required - refractory quality and also the property of not being wetted by the molten aluminium for such low ~luorine contents and such high silicon contents1 its production has given rise to unexpected dif~iculties, because it has been ~ound that the fluorine compounds and the alumina, which are known to retard ~he setting o~ conventional cements and concretes, play a different part with the ~ reractory aggregates with which they are associated to - - form a material according to the invention. The presence of ~luorine gives rise to a ~alse setting phenomenon. r Accordingly~ special procedures have to be adopted.
According to the first of these procedures9 the aggregate, the fluorine compound, a hydraulic binder and wa~er have to be stirred for a sufficient period after they -have been combined in order to avoid this false setting .

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- . .
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~971~3106 phenomenon. A stirring time o approximately 10 minutes is generally sufficient. It is also advisable to select a fluorine content for the final material which is as low as possible within the effective range. It is also advisable to add a setting retar~r.
The ~irst stage of this me~hod compris~s mixing an aggregate and a hydraulic binder.
Products o high alumina content, for ex~mple with ~n alumina conten~ of more than 45% or even more than 55/0 by weight, may be used as aggregate.
Thus, it is possible to use an aggregate oomprising cyanite, siLimanite, ~auxite, ~iaspore, corundum, andalousite, gibbsite, synthetic mullite.
It is also possible to use aggregates lncorporating special refractory products, such ~s products of magnesia, t chromite, chrome-magnesia, orsterite~ dolomite, carbon products based on graphite or coke, silicon carbide products, zirconia products, zirconium silicate, nitride-containing products. I~owever, it is possible by virtue of the invention not to use th~ expensive products mentioned above, and to obtain satisfactory results with more common aggregates.
Aggregates such as these are in particular th~se with ~ a content by weight of alumina of from approximately 35%
to 45%, which are often referred to as argilaceous products, ~5 and those with a content by weight of alumina of from 10/~
to 35%, which are known as silico-argilaceous products, the complementary contents of the alumina bein~ fonmed by silica aside from a few impurities.
The grain size distribution of the aggregate is conventional. For example, the following distribution may be adopted:

.

O to 0.2 ~m5 to 25 %
0.2 to 2 mm20 to 50V/o 2 to 5 ~n5 ,:o 35%
5 to 10 t~n20 to 60%
,: r Suitable ~inders are the conventio~ ydraulic binders, especially al~ninous and silico-aluminous binders. Their alumina content is with advanta~e equal to at least ~O% by weight. It is possible to use in particular "Lafarg~" alumina S ` ~ement which is a calci~n alwninate containing 40% o-al~nina9 - ` Seca~ 162 ~hich contains 40% of alumina) Secar~250 which contains 70% of al~nina and Sup,_rsec~r~hicll contains 80%
o f alumina.
In general, the binder makes up from 10 to 35% of the t ;10 weight of the aggregate.
~ The aggregate and the binder are mixed for at least ; 1 minute and generally for 1 to lO minutes~ , - The ~econd phase of the metihod descri~ed above comprises - adding to the mass of aggre~ate and binder from 0.1 to 10%, expressed as fluorine, of one or more fluorine compounds, - followed by further mixing for a few minutesD ~ !
Suitable fluorine compounds include alkali metal and ', alkaline earth metal fluorides and ~luosilicates.
It is of advantage to use a mixture of two fluorine Z0 compounds9 one of which is more volatile or more solubLe than the other in water. ~hus, a system containing ~or example from 0.8 to 1. 27/~ of sodium fluosilisate and from 0.2 to 0.8% o calcium fluoride gives satisfactory results~
~ The third stage o the process using a hydraulic binder comprises mixing the mixture of aggregate, binder and fluorine ~ 7~~ '~Y ~ -14~ `

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compound with a quantity of water representing from -- approximately 2 to 20~/o of the weight of this mixture.
A setting retarder is preferably added to the mixin~
water. The setting retarder generally represents rom 0.2 to 2% of the mixture of a~gregate, binder and 1uorine compound Suitable retarders are, prefera~ly, ~he "sea1ing retarders" which render the surace of t~e grains impermeable to the solubillty reducers.
. Water soluble or surface active se~llng retarders o - this type include in particular glycolic acid, glycolic aldehyde, tartronic acid, glyceric aldehyde, glycerol, pyruvic acid, glyceric aldehyde, dihydroxy acetone, maleic ~ . acid, succinic acid, malic acid, tartaric aci~, erythroI~ , ,.~ 15 dihydroxy tartaric acid, a- and ~- ketoglutaric acids, rarabitol, gluconic acid, galactonic acid, sorbitol9 citric . acid, salicylic acid~ diphenols (resorcinol, hydroquinone), - : benzoquinone, gal1ic acid, dioxane, organic materials which : flocculate in the presence of Ca , for example digallic acid, casein, proteins such as albumin, gum, pepsin9 melamine resin, lignosulphates, Cl2 - Cl8 atty acids; oleic acid, .
naphthenic acids, benzoic acid, pentachlorophenol, dialkyl~ne . -glycols, mono-and poly-ethanolamines, glucides, glucose, saccharose, starch, cellulose and other sugars, etc.
- 25 It is surprising that the presence of fluorine, a conventional retarder used in the hardening of concrete, necessitates the addition of another retarder to prevent ~alse setting in the particular case of the invention, whereas above all the alumina itself is also known for its j:
retarding effect on the setting of conventional structural - .
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- ' , ' j.
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~071~
mortars an~ concretes.
After the mixing water has been added, mixing is con-tinued for at least 8 minutes and better still for 10 minutes. --Thereafter a material is obtained which it is suf~icient to mould and harden and then to heat slowly, ~or example first to approximat~ly 100 to 120C and then to approximately 700C, to form the refractory material accordi.ng to the invention.
In a second procedure, the blnder used is a chemlcal binder~ such as ethyl silicate, sodium silicate, phosphoric acid or a phosphate. The phenomenon of false setting no longer occurs.
The quantities of chemical binder used are o~ -the same order Or magnitude as those mentiolled in reference to the hydraulic binders.
In this second process, mixing and cooking are carried out in the same way as before. The aggregate has a content by weight of silicon expressed as SiO2, a content by weight of aluminium expres-sed as A1~03 and/or a content by weight of zirconlum expressed as Zr2 of from 1% to 99%~
Finally, a ceramlc binder, especially clay, may be used.
The refractory material may be l-sed in the form of a pourable material or in the form of linings or bricks for the construction of furnaces and other fittings for the molten alu-minium. -The invention is illustrated by the following Examples.

..
Two pellets wi$h a height of 5 mm and a diameter of 15 ~m of each of three alloys ~ ~

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graduated from slight to very pronounced, are placed on the refractory material to be tested, l`lle pieces o refractory material together with their pellets are then placed in an electric muf1e ~urnace or 48 llours at a temperature of 800~C. l'his temperature oE $~0C is the average telnperature used in alulniniu~li slneltillg or holding furnaces, an~ the resid~llce tilne selected is suEicient to provide or clde(luate sensitivi~y to tlle test, The value of the reaction is detennined by an index which is the sum of three re~ction indices o each of the alloys, being de~ined as followsO
0 : no visible reaction or marlc on the refractory material, , -1 : slight mark on the refractory material, but volume of the pellet maintained, the pellet ~eing readily detached ~y hand.
- 2 : pellet detached from the refractory material, its - vol~ne having decreased by less than 507/o or the; - "ring" if any not exceeding 22 Inm in its largest dimenslon or the ~eginning of "mushrooming" on the refractory material.

3 : pellet detached from the refractory material, its volume having decreased by more than 50/0 or the ring formed having a di~neter of 22 ~n in its largest dimension or significant "mushrooming'~
on the refractory material, The tests (2 pellets of three alloys) are carried out twice in each case, ` Since the resuLts are characterised by a certain disperslon (it is generally accepted that the reaction only r .

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takes pl~ce ~fter an initiation p~riod o~ arbitrary duration), the maximum index obtained is awarded to each alloy.
The alloys have the following composition:
~lloy A: Zn 0%
Alloy B: 0.22%
Alloy C: Zn 2%
For the three ~lloys, the other elements added to the aluminium are as follows:
iron 0.33~0 - silicon 8.7% - copper 3.1% - magnesium 0.22%
Table I b~low shows the type o~ ~luorine compound used i~ the second column~ the ~ontent o~ the fluorine compound in the third column and the index obtained in the ~ourth column. .
The test marked with an asterisk is a comparison test carried out on a fluorine-free refractory material. The aggregate is a mix- ::~
ture of chamotte and the binder, which represents 30% of its weight, is a calcium aluminate containing 40% of A12O3. .

TABLE I . .

20 ¦Example No. Fluorine Compound _ Content ~O Keaction Index -I 1 Na F 1 0 .;.~
I l* _ _ g ~. .:- -2 (N~4)2 Si~6 1 0 ~:
. Na2 Sl F6 0.1 8 -~

4 Na2 Si F6. 0.3 6 ~ Na2 Si F6 1 0 .. ::~
6 Na2 Si F6 1.5 0 ..
7 Ca Si F6 1 0 8 Ca F2 2 0 .

_ _ ~ Na Si F6 ~ ~ ~ -- 18 - ~ -.

78~V6 EXA~E 11 30 kg o chamotte with a grain size of from 2 to 4 ~
22.5 kg of chamotte ~ith a grain size of less than 0.1 mm and 22.5kg of Secar are mixed ~or 2 minutes ~n a concrete mixer.
~2 and 1 kg of Na2S']l ar~ tl1 l followecl by mixi.ng ~or another 2 minll~es.
~ solution o a retarding agent is prepare~ by adding 1 k~ of retardant to 10 l'itres of water.
~1is solution is poured into the concrete mixer~
followed by mixing for 9 minutes.
The mass iS discharged from the concrete mixer and poured between a male mould and a female mould separated from one another by an interval of 40 mm. - ~
, ' 15 , m e mass is left to harden and set for 24 hours ,r ,~ without drying. To this end, it is covered with damp sacks.
,- Th~ female mould is withdrawn, followed by drying inair j for 48 hours.
, I'he ladle of the material according to the invention is gently heated for 24 hours at 115C in the absence of any contact with a flame.
The ladle is then gradually heated to a temperature of 700C by increasing the temperature at a rate of 30C per hour. It is kept at 700C for a period of 6 hours. ~, A test ladle of this type withstands' the repeated attack of molten aluminium for more than 4 monthsO
XAMPLE ?2 The procedure is as in Example 11 except for the modifications indicated in Table Il-~19-- ~
.

.

.

~78~
EYAMPLES 13 to 15 The procedure is as in Example 11 except ~or the modi-fications indicated in Table II. The material is applied to the mould by tamping in the Iorm o:E a rammed clay.

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Claims

The embodiments of the inventlon in which an exclusive property or privilege is claimed are defined as follows:

1. A process for inhibiting the effect of molten alu-minium on an object with which it is intended to come into contact, comprising making the object of a concrete which has a deflection temperature under load above 1000°C, a content by weight of alumi-nium, expressed as Al2O3, of from 10 to 90%, a content by weight of calcium expressed as CaO of from 4 to 14% and a content by weight of fluorine forming part of the structure of the concrete of from 0.1 to 10%.

2. A process as claimed in claim 1 in which the content of aluminium is of from 40 to 60%.

3. A process as claimed in claim 1 or 2 in which the content of fluorine is of from 0.2 to 5%.

4. A process as claimed in claim 1 or 2 in which the concrete has a content by weight of silicon expressed as SiO2 of from 5 to 85%.

5. A process as claimed in claim 1 or 2 in which the concrete has a content by weight of silicon expressed as SiO2 of from 20 to 60%.

6. A process as claimed in claim 1 or 2 in which F is present as F2Ca.

7. A process as claimed in claim 1 or 2 in which F is present as a mixture of F2Ca and a fluosilicate.