CA1043821A - Slag-resistant refractory - Google Patents

Abstract

ABSTRACT

A refractory composition consists of filler mat-erial, binder and water. It is improved by the addition of 0.5 - 10% by weight of colloidal silica, based upon the solids content of the composition.

Description

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It has previously been proposed to improve the properties of refractory linings in furnaces, crucibles and other vessels which are sub-jected to attack from aggressive slags, by impregnating the finished linings or moulded bodies ~bricks) from which the linings are built, with a water solution of colloidal silica so that after drying the pores and cracks of the linings or moulded bodies will at least be substantially filled with colloidal silica particles.
Continued experiments have shown now that better resistance can be -obtained, particularly against aggressive slags, if the colloidal silica is a mixed into the compositions or compounds from which the linings or moulded bodies (bricks) intended for these are manufactured.
The colloidal silica is suitably used in the form of a sol, pre-ferably as a colloidal silica dispersion in water, the silica being in the form of discrete particles having a particle size of up to 30 microns, suitably between 5 and 30 microns. Silica of this type is marketed under ~d~k ,.. .
the trade namo Ludox*. It has been found suitable to use this in a water solution or dispersion in an amount of around 40 ~ by weight SiO2.
The compositions or compounds which can be improved in this way according to the invention are compositions for rammed linings, and for cast and moulded articles, and also compositions for the manufacture of refractory moulded bodies (bricks) as well as mortar using for the joints between such bricks. The improved composition is also useful for ladles and saggers, for example saggers for the manufacture of sponge iron.
The present invention provides a slag resistant refractory lining material consisting essentially of refractory grains of a material selected from the group consisting of alumina, bauxite, kaolin and quarzite, and further containing refractory grains of silicon carbide in a quantity of up to 40 percent of the total weight of refractory grains, further containing from 2 to 15 per cent by weight of the total solids content of a binder selected from the group consisting of bond clay, spent sulphite liquor and ~, ,.

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carboxymethyl cellulose, and further containing an additional amount of a water suspension colloidal silica in a quantity corresponding to 0.5-10 %
SiO2 by weight of the solids content of the lining material.
Common for these compositions is that they consist of two primary components, namely a granular filler of refractory : . . .
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The refractory filler materials, generally designated grog, may be basic, such as magnesite and dolomite, neutral, such as A1203, bauxite, kaolin and silicon carbide, or acid such as quartzite. Mixtures of such grog material are also possible for example mixtures of magnesite and bauxite or various mixtures of up to about 40 % SiC in other grog materials.
In highly refractory basic brick, magnesite may be included in quan-tities of 90 - 99 %. In the highly refractory A1203-based brick, the content of A1203 is often 85 - 95 %, in the kaolin material the kaolin content is `
often 85 - 90 %, in the quartzite material the content of quartzite is 85 - 90 % or even higher, and in the pure silicon carbide moulded bodies the SiC con-tent is 85 - 95 %.
The binder normally used may also be of different types and is divided into three main groups for the various fields of application well known to the expert in refractory ceramics, namely:
1. Binder of the bond clay type forming a glass phase

2. Cement-type binder such as aluminates and chromates (chromic acid)

3. Temporary binders such as spent sulphite liquor and synthetic organic binders such as carboxymethyl cellulose (CMC). -Of course, the content of binder varies, as is well known in the art, according to the type of binder used and its application, but is usually between 2 - 15 % by weight.
Compositions of the type described above can be considerably im-proved according to the invention from the point of view of strength, and particularly with regard to the resistance to molten slag, by mixing into them -colloidal silica in a quantity corresponding to 0.5 - 10, preferably around 2 per cent by weight S102 calculated on the solids content of the finished com-position.
Compositions which are improved according to the invention by the ~;
addition of colloidal silica a~e used in the conventional manner for the manufacture of linings of furnaces or other vessels which at high t~mperatures ~ ~

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are subject to the attack of slag. When the lining consists of moulded bodies ~bricks), colloidal silica should also be mixed into the refractory mortar used. ~
In order to further improve the effect of the in~ention it may in ;
certain cases, for example when dealing with particularly aggressive slags, be advantageous after the lining is complete to impregnate the surfaces of the lining which are subject to slag attack with a water suspension of the colloi- ;~
dal silica and then dry them to fill out any remaining porosity or cracks with ;
particles of colloidal silica.
The following are some examples of compositions suitable for manu-facturing refractory moulded bodies (bricks). The type of binder has not been specified in the examples as this is well known to anyone skilled in the art for the brick compositions exemplified.

Basic brick composition Magnesite 96 parts Binder 5 parts 40 % solution of colloidal silica 5 parts Basic brick composition Magnesite 65 parts Bauxite 30 parts 40 % solution of colloidal silica 5 parts Binder 5 parts Acid brick composition Quartzite 98 parts Lime 2 parts 40 % solution of colloidal silica 5 parts '-''.~- '

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Silicon carbide brick composition SiC 95 parts Binder 5 parts : .
40 ~ solution of colloidal silica 5 parts . .
Magnesite brick composition Magnesite 99 parts Binder 1 part 40 % solution of colloidal silica 5 parts Water is included in all the examples if necessary to make the com- `
position mouldable or workable.
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Claims (2)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A slag resistant refractory lining material consisting essentially of refractory grains of a material selected from the group consisting of alumina, bauxite, kaolin and quarzite, and further containing refractory grains of silicon carbide in a quantity of up to 40 percent of the total weight of refractory grains, further containing from 2 to 15 per cent by weight of the total solids content of a binder selected from the group consisting of bond clay, spent sulphite liquor and carboxymethyl cellulose, and further containing an additional amount of a water suspension colloidal silica in a quantity corresponding to 0.5-10 % SiO2 by weight of the solids content of the lining material.

2. A slag resistant refractory lining material as claimed in claim 1, in which the amount of colloidal silica is 2 per cent SiO2 by weight of the solids content of the lining material.