Corundum Refractory

Corundum refractory refers to an article having an Al2O3 content of more than 90%, also known as alumina refractory. The hardness of the corundum is very high (Mohs hardness of 9), and the melting point is also high. These are closely related to the firmness of the Al-O bond in the structure, and therefore, the Al-Al2O3 is the main phase of the high-temperature refractory material and the high-temperature electrical insulation material.

The corundum has good stability against acid, alkaline slag, metal and glass melt. It can be used in an oxidizing atmosphere at a high temperature or in a reducing atmosphere, and a good effect can be obtained.

The basic raw material of the corundum product is fused corundum or sintered corundum. In order to improve some properties of the product, some manufacturers often add some mineral materials to the corundum material to form a composite material, such as a corundum brick, a chrome corundum brick, a titanium corundum brick, and the like to improve the performance of the product.

Combined Sintered Corundum Product

The sintered corundum is used as a granular material and is mixed with the fine powder of the corundum to form a mud material, and the product formed, dried and sintered is called a re-bonded sintered corundum product, and is also referred to as a corundum-clinker refractory material. The main points of the production process are as follows:

Composition of mud:

Pure corundum clinker with the same composition should be used in high purity sintered corundum products. In order to improve the thermal shock resistance and slag resistance of ordinary sintered corundum products, the second component less than 10% is generally allowed to be added, so that the Al2O3 content is still above 90%, which is within the low value range of corundum refractories. The second component is mullite, which is mainly mullite in the form of synthetic mullite clinker, or silica, clay, kaolin, cyanite-sillimanite concentrate powder and so on, so that mullite is synthesized in the matrix part of the firing process. Except that the synthetic mullite can be added in the form of particles. The other additives were added with fine powder less than 60 μ m.

H3PO4 was used as binder, and the dosage varied from 1% to 6% depending on the performance of the product. In order to improve the formability, proper amount of organic binder is often added. The addition of fine powder has obvious influence on the density and strength of the product. When the fine powder increases from 15% to 45%, the density and strength of the product are greatly improved. if about 5% of the fine powder is less than 1 μ m Al _ 2O _ 3 superfine powder, it is of great significance to improve the properties of the product.

Shaping

There are the following methods for molding:

Products with complex shape and large size are rammed or vibrated by air hammer.

The common products are molded by semi-dry high pressure.

Special products with special design of the mold, using isostatic pressing molding.

Sintering

The corundum clinker product must be sintered at a high temperature. The firing temperature is about 1650-1800 & deg; C, and sometimes reaches 1850 & deg; C. The firing temperature is appropriately increased, and the strength and the density of the article can be improved accordingly.

combined electric melting corundum product

Brown corundum contains a small amount of harmful ingredients.

Brown corundum contains a small amount of harmful components that will cause poor sintering or cracking, so it is calcined in advance before use. The unsorted ferrosilicon alloy oxidized to Fe2O3 and SiO2, titanium minerals to TiO2 at 500 ℃ produced large volume expansion. After pre-firing, the failure stress caused by these oxidation reactions was eliminated in the pre-firing process, and the cracking of the product caused by the reaction of these impurity minerals during the firing of the product was avoided.

Ingredients, mixing, molding

According to the principle of tight stacking, the multi-stage ratio should be adopted to reduce the intermediate particles and increase the amount of fine powder, which is beneficial to improve the density and sintering of the products. A certain amount of binders are mainly aluminum phosphate, phosphate, chromium aluminum phosphate, cellulose, pulp waste liquor and so on. The mixing of mud should be uniform, and the moisture content is about 3% ≤ 4%. High pressure molding is needed to obtain dense brick billet.

Sintering

The electric melting corundum brick is of high purity and difficult to be sintered. Common burning equipment includes high-temperature intermittent kiln or small high-temperature tunnel kiln.

The physical and chemical indexes of corundum products are shown in Table 11 / 48, Table 11 / 49, Table 11 / 50, Table 11-51.