KR810001023B1 - Method for producing of alumina refractory - Google Patents

Abstract

Unshaped, unfired refractory material for use in monolithic refractory construction comprises a mixture (I) of a volatilised silica slurry and a refractory batch. The silica slurry comprises (a) 60-90 wt. % water; (b) 10-40 wt. % volatilised silica; (c) 0.1-2.0 wt. % concentrate acid, preferably HCl; and (d) 0.05-1.5 wt. % dispersant. Mixture (I) comprises (1) 15-60 wt. % of an aggregate alumina containing refractory of relatively large particle size; (2) 6-45 wt. % calcined alumina of relatively small particle size; (3); 5-20 wt. % graphite; (4) 1-35 wt. % of a green strength binder; (5) 2-20 wt. % of the volatilised silica slurry; (6) 0-5wt. % water.

Description

Alumina Refractory

The present invention relates to an alumina refractory material having a volatilized silica binder, in particular a refractory material having a high alumina content.

This usually includes refractory materials containing about 50-99% Al ₂ O ₃ . Although the present invention describes a refractory material having a high alumina content, the present invention is not limited only to the alumina refractory material, but includes all refractory materials that can use volatilized silica as a binder. Volatilized silica includes all refractory materials that can be used. It is known that volatilized silica binders exhibit excellent properties when used in alumina refractory mixtures. The increased properties by containing the volatilized silica in an appropriate ratio include the fracture coefficient, the apparent porosity, the linear change, the capacity change, and the mineral balance.

Volatilized silica, also called fumed silica, is amorphous silica deposited from the vapor phase. Typical silica in this form is obtained by reducing the silicon forming a silicon alloy such as silicon silicon. Similar fumed silicas are also prepared by reducing quartz with carbon or other suitable reducing agent and then treating the reduced evaporation product with an oxygen generating gas and also condensing the silica in finely divided form. The analysis of the silica is at least 90%, usually 95% SiO ₂ , with _2-3 % FeO, MgO and Al ₂ O ₃ .

This type of refractory material is prepared by grinding, screening and mixing the desired alumina material so that the refractory material has the desired alumina composition together with the remaining material composed of other natural components of the alumina ore used. Accurate sizing by sieve depends on the purpose of the raw materials and refractory materials used, but its knowledge and skills are well known in the field of fire resistance. Mixing the volatilized silica into the batch in an amount of at least 1-10% based on the batch weight is a common method and the volatilized silica is added in dry form. Various known binders used in the manufacture of refractory materials are added to the batch and the batch is then adjusted with water to obtain the desired firmness. References to the use of silica volatilized in alumina refractory materials are cited in US Pat. Nos. 3,067,050 and 3,652,307. These refractory materials are used to make walls, to crush materials, or to fire. All particles of volatilized silica are typical particles that are substantially finer than 0.3 microns and have a size between 0.3 and 0.003 microns.

The volatilized silica is prepared in the form of acidified slurry prior to mixing with the refractory particles and other components. The volatilized silica is mixed with water acid and a dispersion medium to prepare a slurry. The following table shows the preferred compositions for the slurries and the range of acceptable compositions.

This slurry is different from a colloidal silica suspension about 10 times as large as silica particles. Colloidal suspensions are much more expensive because they are produced by starting with sodium silicate solution and using ion exchange processes. Volatilized silica is a cheap silica source of cheap silica. The use of acidic and aqueous slurries in place of the dry mixture of silica and refractory materials increases the silica in water by at least one or more parts, thus enhancing the bonding properties. The aqueous slurry also obtains a more uniform silica dispersion in the refractory particles than was obtained using dry mixtures. The slurry form also reduces the loss of fumes during mixing. The fact that the slurry is acidified shows much better properties than those obtained using the unacidified slurry. The acid has the effect of reacting with the volatilized silica to perform better as a binder to form adherent silicic acid. Hydrochloric acid is preferred but phosphoric acid is also used because it forms a bond with silica that is the same as or corresponds to the silicic acid bond formed by calculation. The concentrated hydrochloric acid mentioned in the table above is 20 ° Be '(32% hydrochloric acid) but is used in equivalent amounts of other concentrations.

The volatilized silica slurry also contains a dispersion medium that withstands the high solid load of the slurry. The same burden on the particular material in the acidified slurry causes the particles to repel each other and remain in flow. This prevents solids from agglomerating into viscous masses. The dispersion medium used is a water-soluble powder having the trade name ToranilB, which is an extract obtained from coniferous wood composed of 96% calcium salt of ligno sulfonic acid and 1.2% glucose. Other dispersants used include alkali salts of highly polymerized naphthalene sulfonates and polyacrylates. Other dispersants may be used as long as they are compatible with the system. Strong alkaline dispersion media, such as sodium silicate, cause precipitation in acidic intermediates and are incompatible.

The volatilized silica slurries of the present invention are mixed with refractory aggregates of relatively large particles, calcined or with relatively fine particles of alumina, graphite and wet strength binders. Other optional ingredients are described below.

The binder material is selected from alumina-containing materials or alumina, such as fused alumina, tubular alumina and calcined roadway. The aggregate material has a distribution of particle sizes in the range of 3 mesh to 100 mesh.

Some examples are shown below.

The calcined fine alumina particles have a size of 325 mesh or less and only 5% or less remain in the 325 mesh sieve. The calcined alumina particles combine with silica fume to form a strong mullite (aluminum silicate). Graphite in the mixture retards corrosion of the resulting refractory material. It is appropriate that graphite, which is present in nature, contains 75 to 80% of carbon. Lower graphite provides very harmful pollen. Graphite generally has a particle size represented by Magnus 40 mesh. The typical 40 mesh Mexican graphite has the following particle size distribution.

Wet strength binders are selected from conventional materials used for this purpose, such as western bentonite and various bonds and blclays. All of these materials are relatively finely sized particles, with only about 7% remaining in the 270 mesh sieve upon washing. Other binders are also used, such as the aforementioned metoranyl B ＂binder and earth bituminous binder. The earth bitumen binder used is sold under the trade name of “Koretzresin” and consists of a composition of natural earth bitumen with a complex structure, an additive of an organic binder, and an inert filler.

Selective components of the compounds of the present invention are chianeite and silicon carbide. The kyanite is heated and expanded by a process called materialization to compensate for normal shrinkage of clay refractory materials and to prevent cracking due to shrinkage. Silicon carbide has high thermal conductivity and excellent fire resistance and increases the outflow of heat to the cooling zone, thereby strengthening the ceramic bonds excluded from the fire resistant heating surface. Preferred particle size distributions are -30 and +50 mesh as shown in the following table.

Some examples of alumina refractory materials according to the present invention are shown below.

Example 1

Example 2

Example 3

Example 4

While describing particular formulations for the present invention, it should be understood that these are limited only by the claims set out below.

Claims (1)

As a mixture of volatilized silica slurry and refractory batches consisting of 60.0 to 90.0 wt% water, 10.0 to 40 wt% volatilized silica, 0.1 to 2.0 wt% concentrated acid and 0.05 to 1.5 wt% dispersion medium Containing 60% by weight mixed alumina and having a relatively large particle size refractory material, 6 to 45% by weight calcined alumina with a relatively small particle size, 5 to 20% by weight graphite, 1 to 35% by weight wet strength ( Green strength) An intangible and non-combustible refractory for use in a one-piece fire resistant building comprising a binder material, 2 to 20% by weight or less of the volatilized silica sludge and 5% by weight of water.