Semi-silica brick is an aluminosilicate refractory product containing 15-30% Al2O3. It is usually made of fire clay containing quartz, pyrophyllite (Al2O3 · 4SiO2 · H2O), refractory clay or tailings of kaolin.

According to the manufacturing method, semi-silica brick can be divided into fired brick and unfired brick. Unfired bricks are made with water glass as the binding agent. The manufacturing process of fired bricks is similar to that of fire clay brick.

Whether to add clinkers is up to the properties of raw materials and refractory bricks. Siliceous clay has small firing shrinkage and the clinker is not required. In order to improve the thermal shock resistance of semi-silica bricks, 10%-20% clinker is added.

If the raw materials contain a few fusible materials and coarse quartz grains, semi-silica bricks have low density and poor strength but good thermal shock resistance and high softening temperature under load. On the contrary, the refractory bricks have bad refractory performance and poor thermal shock resistance. Besides, according to the working conditions, fine or coarse quartz or silica clinker is added.

Under 1250℃, semi-silica brick has small volume shrinkage. At high temperature, with the increase of the liquid phase, the brick has large volume shrinkage. So, its firing temperature is higher than that of the fire clay brick, generally within 1350℃-1410℃ to obtain high density refractory bricks.

When pyrophyllite is used as the raw material of semi-silica brick, the manufacturing method is up to the chemical composition of pyrophyllite. The main chemical composition of pyrophyllite has small weight loss after dehydrated and can maintain its lattice structure. It can be directly used to manufacture bricks. In order to avoid firing expansion, it can also be calcined into clinker and added when batching.

Semi-silica brick has good volume stability at high temperature and can help to improve the integrity of the masonry and reduce the slag erosion to the masonry. When contacting hot slag, it can from a layer of glaze-like substances on the surface which can block pores, prevent the penetration of slags into the brick.

Semi-silica brick is mainly used in the ladle lining and the refractory layer of the lower steel casting system. In addition, it is also used in the roof of heating furnaces, regenerator checker bricks, the lining of Cupola furnaces, the hearth and flues of furnaces.

As we all know, alpha-beta fused cast alumina block is widely used in industrial furnaces. It is composed of alpha alumina and beta alumina crystals in a most ideal proportion which is approximately 50% and 50% respectively, where intertwined crystals of both materials result in a very dense structure.

Alpha-beta fused cast alumina block is made of high quality fused alumina as the raw material.

1) White fused alumina
White fused alumina is made of industrial alumina powder as the raw material. It is melted in an arc electric furnace and crystalized by cooling. White fused alumina is white and abbreviated as WFA.

2) Dense fused alumina
Dense fused alumina is made of industrial alumina powder as the raw material with the addition of additives. It is melted in an arc electric furnace and crystalized by cooling. It is gray or hoary and abbreviated as OFA.

3) Sub-white fused alumina
Sub-white fused alumina is also called high alumina corundum. It is made of bauxite as the main raw material with addition of additives. It is melted in an arc electric furnace and crystalized by cooling. It is brown grey or gray and abbreviated as SFA.

4) Gray fused alumina
Gray fused alumina is made of bauxite as the main raw material with addition of additives. It is melted in an arc electric furnace and crystalized by cooling. It is chocolate brown and abbreviated as BFA.

Below 1350 degree, alpha-beta fused cast alumina block has excellent corrosion resistance to glass liquid. It is widely used in the working tank of glass furnaces.

Bonded again fused cast alumina block is a type of bonded again sintered refractory brick made of fused corundum clinker as the granular material and fused corundum or sintered corundum powder as the matrix.

When using fused brown corundum or white corundum as raw materials, the frits should be smashed and then processed by removing the ferro-silicon alloy and other impurities. White corundum should be processed by removing the flaky sodium aluminate crystals and other low-melting substances. The impurities are easy to be identified since they have low density and float in the surface of corundum frits.

There are a few harmful ingredients in the corundum which will cause poor sintering or cracking, so corundum should be pre-calcined before use. The residual ferro-silicon alloy is oxidized and decomposed into Fe2O3 and SiO2 at 500-1000℃ and Ti in the minerals can be oxidized into TiO2 (rutile), which can cause large volume expansion. After pre-calcining, the stress caused by those decomposition reactions and oxidation reactions can be eliminated during the pre-calcining process and cracks caused by the volume expansion of those impurities can be avoided during the sintering process.

Fused corundum block has large volume, so it should be smashed with drop hammers and other ways and then pulverized. The pulverized fused corundum is stored by size after screened. Fused corundum is hard and difficult to grind. Therefore it is wet ground by ball mills or vibration ball mills. The grain size can be less than 40μm or even 10μm. The iron in the granular material can be removed with electromagnets and the iron in the fine powder can be washed with acids.

The batching of granular materials should be according to the principles of tightly packing, multilevel ratio, less intermediate particles and more fine powder. This can improve the density and sintering of the products. The additives include aluminum phosphate, phosphoric acid, aluminum chromium phosphate, cellulose and pulp waste solution. Among them, he most promising is active phosphate. Recently, ammonium phosphate is on the trial and achieves good results. The mud should be mixed evenly with a moisture content of 3-4%. After high pressure molding, high dense bricks are obtained.

The fused cast alumina block has high purity. It is difficult to sintere and should be sintered at 1800℃. The type of the kilns used depends on the production scale. For small batch production, high-temperature batch kiln is better. For batch stable production, the small high-temperature tunnel kiln is used.

Zhengzhou Sunrise Refractory is a refractory supplier from China. We provide various refractory materials such as fused cast AZS, fused cast alumina block, silica brick, zircon brick, etc..