Refractory products formed by grains bound by carbon residues an

Details Refractory products formed by grains bound by carbon residues an Refractory products formed by grains bound by carbon residues an

1984-07-10

1985-10-01

Dixon, Jr., William R.

Compositions: ceramic

Ceramic compositions

Carbide or oxycarbide containing

501 88, 501 89, 501 90, 501 99, 501100, C04B 3552, C04B 3556

Patent

active

045446415

DESCRIPTION:

BRIEF SUMMARY
The present invention concerns refractory products which can be used either in aluminium electrolysis cells, in particular in the form of blocks or slabs forming the edge of such cells, or in the linings of blast furnace or electrothermy furnaces.
In the case of aluminium electrolysis cells, the introduction of high current strengths gave rise to accelerated wear of the edges of the cells when made with the existing products. The need has arisen, for refractory products which are even more resistant under those new operating conditions, while however remaining acceptable from the economic point of view.
The qualities required in respect of such refractory products, in the above-mentioned particular case of the edges of aluminium electrolysis cells, correspond to criteria such as: through the edges of the cells; maintenance of a crust of soldified aluminium along the edges of the cell, thereby to limit contact with the aluminium in the molten condition and the molten cryolite; the resistance to erosion of the edges of cells; cryolite).
If the last two criteria can be the subject of laboratory tests which give initial information which is comparative in nature, only tests under practical operating conditions can make it possible to arrive at a more precise opinion, concerning the performance of the material in actual service, which involves oxidation-erosion mechanisms with thermal stresses and occasional attack by the molten cryolite.
In the case of blast furnace linings, the qualities required are as follows: efficient action.
The requirements are similar in regard to electrometallurgical furnaces (production of steels and ferrous alloys in particular).
For the purposes of producing refractory products which are intended for those two types of use, agglomeration and firing or burning processes are most frequently used, with the starting material being in particular grains of silicon carbide in the case of the edging blocks for aluminium electrolysis furnaces, and in particular grains of alumina or aluminates in the case of blocks for forming the lining for blast furnaces and electrothermy furnaces.
Processes for the production of refractory blocks in which the essential component is silicon carbide seek to produce either silicon carbide throughout the material or silicon carbide in association with silicon nitride or oxynitride, and those processes use as their starting material, a mixture which essentially comprises silicon carbide in grain form, silicon in powder form and carbonaceous substances, the amount of silicon and the amount of carbonaceous material which is liberated by the coking operation being in a ratio which is intended to promote the formation of silicon carbide, which may or may not be associated with silicon nitride and oxynitride.
Thus, in the process described in German laid-open application (DE-OS) No. 22 32 719 which relates to refractory blocks used in blast furnaces, the composition is normally adjusted in such a way that the amount of silicon powder which is added to the starting material and the amount of coke formed from pitch or tar, which is possibly supplemented by a make-up amount of fine coke powder, stoichiometrically correspond to each other, and the improvement in strength of the refractory blocks which are fired in furnaces for firing carbonaceous materials at final temperatures which reach 1100.degree. to 1300.degree. C. is due to the fact that the framework or skeleton of the fired binder is composed of silicon carbide which is produced at the higher temperatures of the firing procedure, by the reaction of silicon with the coke formed by coking.
French patent application FR-A-No. 2286 806 states that the process described in German application DE-OS No. 22 32 719 can be improved, with the binding material produced being of a structure which has insufficient adhesion to the joining surfaces of the grains of SiC and which still contains metal silicon and/or carbon. The process described in French application FR-A No. 2286 806 promotes the formation of SiC in substantial

REFERENCES:
patent: 2013625 (1935-11-01), Buck
patent: 3291623 (1966-12-01), Saunders et al.
patent: 3442989 (1969-05-01), Hildekrandt
patent: 4294788 (1981-10-01), Laskow et al.
patent: 4393143 (1983-07-01), Yoshinaka et al.
Elettrocarbonium Works publication at AIME Congress, Feb. 1982, Letizia et al.
Billehaug et al., Aluminium (FRG), vol. 56, Oct. 1980, pp. 642-648 and 713-718.

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