Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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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
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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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material and a binder, as well as sufficient water to make the composition
workable for the manufacture of a lining or moulded body.
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.
EXAMPLE 1
Basic brick composition
Magnesite 96 parts
Binder 5 parts
40 % solution of colloidal silica 5 parts
EXAMPLE 2
Basic brick composition
Magnesite 65 parts
Bauxite 30 parts
40 % solution of colloidal silica 5 parts
Binder 5 parts
EXAMPLE 3
Acid brick composition
Quartzite 98 parts
Lime 2 parts
40 % solution of colloidal silica 5 parts
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EXAMPLE 4
Silicon carbide brick composition
SiC 95 parts
Binder 5 parts : .
40 ~ solution of colloidal silica 5 parts
EXAMPLE 5
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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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