The main component of silica bricks is silica, and polycrystalline transformation will occur during the production process, so the expansion coefficient of silica bricks is large.
The characteristics of silica bricks are high load softening temperature, but low thermal shock stability and lower refractoriness than general high-alumina bricks. Silica bricks have a volume expansion rate of 1.5~2.2% at a use temperature of 1450℃. Even when silica bricks are produced, the molds must be appropriately scaled according to the expansion coefficient. Leave space for expansion to make the size of silica bricks more accurate.
When silica bricks are produced, the transformation between quartz, tridymite, and cristobalite in the raw materials will destroy the original crystal structure and rearrange the structure. Because the activation performance is large during the firing process, the transformation temperature is high but slow, which produces a large volume expansion effect.
The silicon bricks have little solution formed at the firing temperature and are difficult to fire. A series of physical and chemical changes that occur during the firing process of silicon bricks will cause the size of silicon bricks to increase.
The temperature of silicon bricks changes greatly during the firing process: residual water is discharged from the bricks at 150°C, decomposition begins at 450°C, and dehydration is completed at 450~500°C. There will be a 0.82% volume expansion in the range of 550~650°C, and the solid phase reaction begins between 600~700°C, and the strength of the bricks increases. At 1100°C, the transformation rate of quartz increases, but the specific gravity of the bricks begins to decrease. At this time, the volume of the bricks increases due to the transformation of quartz into a low-specific gravity variant. Cracks will occur in silicon bricks in the range of 1100~1200°C.
The volume of silicon bricks changes during the heating process, at different temperature steps. The changes of silica are divided into 600°C, 600~1100°C, 1100~1250°C and above 1250°C. At 500~600℃, expansion occurs. At 700~800℃, there is micro-contraction. At 1000~1100℃, the contraction is greater. At 1200℃, the quartz transformation accelerates and the body begins to expand violently. The expansion range is different according to the expansion coefficient of different raw material types.
The biggest disadvantage of silica bricks is low thermal shock stability and low refractoriness, but high refractoriness under load. It is suitable for use in kiln linings in acidic atmospheres. To purchase high-quality silica bricks and zero-expansion silica bricks, please contact Rongsheng for free samples and quotes.