Silica Raw Materials

Silica raw materials have crystalline silica, cemented quartzite and vein quartz, etc., collectively known as silica.

Silica for refractory materials, SiO content should be greater than 96%, and should be high purity, high density, suitable quartz crystal size, less impurities and uniform distribution.

Crystalline silica is made up of quartz particles in close contact with each other. Quartz has large grain size and high hardness, so it is difficult to transform when heated. Most of silica belongs to such minerals in our country, widely used in refractory industry; cemented quartzite is composed of quartz particles combined with siliceous cements.The quartz particles are fine and ultrafine, and there are many cements such as amorphous silica, which are easy to transform when heated. Colloidal quartz crystalline grain large , high purity,solid, slow transformation when heated.

The main component of silica is silicon dioxide. During the heating process, silicon dioxide has various variants, accompanied by a change in volume.The Crystalline variants include β-quartz, α-quartz, γ-tridymite, β-tridymite, α-tridymite, α-cristobalite, β-cristobalite and non-crystallizing variants ---- quartz glass.

At a temperature of 573℃, β-quartz quickly converts to α-quartz with a volume expansion of 0.82%; At 870°C, the α-quartz changes into α-tridymite with a volume expansion of 12.7%. When the temperature is 1470°C, α-tridymite changes to α-cristobalite with a volume change of 4.7%. Therefore, it is necessary to pay attention to the crystal transformation of silica in the application of amorphous refractories.

When preparing the material, the waste silicon brick should be added as refractory aggregate and powder, or iron scale and other mineralizing agents, to generate a certain liquid phase, buffer the stress caused by crystallization change, and promote the conversion of quartz to stable tridymite and cristobalite. In addition,When heating, care should be taken to avoid sharp fluctuations in temperature.