Silicon carbide bricks are made of silicon carbide as the main raw material. SiC is covalently bonded and does not have the so-called sinterability. Instead, it relies on chemical reactions to generate new phases to achieve sintering, that is, reaction sintering. According to different bonding methods, silicon carbide bricks are divided into clay bonded silicon carbide bricks, bonded silicon carbide bricks, silicon oxynitride bonded silicon carbide bricks, silicon nitride bonded silicon carbide bricks, Sialon bonded silicon carbide bricks and recrystallized silicon carbide bricks.
1. Clay bonded silicon carbide brick
Made of black silicon carbide as raw material, soft clay with good bonding properties, and pulp waste liquid as bonding agent. Generally, it is combined with 10% to 15% of clay and 3% to 5% of pulp waste liquid. The maximum bulk density is used to calculate the composition of large, medium and fine particles of silicon carbide. When mixing, first add silicon carbide particles and fine powder, then add clay fine powder, dry mix for 3 minutes, then add 4% of pulp waste liquid (density is 1.26~1.28g/cm3) for mixing, and the mud will be mixed after 12 hours. Pass through a 4mm aperture screen and use a brick press to shape the bricks with a volume density of 2.5 to 2.7g/cm3. The bricks are naturally dried for 2 to 4 days and fired at 1400°C.
2. Silicon nitride bonded silicon carbide brick
Made of silicon carbide and silicon powder as raw materials and nitrided and fired. The silicon carbide raw material contains more than 97% SiC, and the silicon carbide particle ratio of the mud material is: coarse: medium: fine = 5:1:4. Silica powder contains more than 98%, more than 80% is less than 10 μm, and the largest particle cannot exceed 20 μm. After the silicon carbide particles and silicon powder are batched, mixed, shaped, and dried, the bricks are placed in a nitriding furnace for firing. During the firing process, nitrogen is introduced, and the temperature, pressure, and atmosphere in the furnace must be strictly controlled. The process parameters are: nitriding gas pressure is 0.02~0.04MPa, the O2 content in the furnace atmosphere is less than 0.01%, the final nitriding temperature is 1350~1450°C, and the total nitriding time varies with the shape and size of the product.
3. β-SiC bonded silicon carbide brick
Silicon carbide, silicon powder and carbon powder are mixed in a certain proportion, mixed, shaped, and fired in a reducing atmosphere at 1400°C. Most are fired using buried carbon. During the firing process, a β-SiC bonded silicon carbide brick is produced with α-SiC as the skeleton and fine-grained β-SiC as the matrix. β-SiC is generated by the reaction between silicon powder and carbon powder during the firing process. This product usually contains small amounts of residual silicon and carbon.
4. Silicon oxynitride bonded silicon carbide brick
The silicon powder in the ingredients is less than the proportion of Si3N4 bonded bricks. After molding, it is fired in an N2-rich atmosphere (a certain O2 partial pressure is required) at a temperature of 1350 to 1400°C. The finished product is a silicon oxynitride bonded silicon carbide brick with α-SiC as the skeleton and Si2ON2 as the matrix. There are often small amounts of Si and Si3 N4 in the matrix.
5. Sialon bonded silicon carbide brick
Made by mixing Si3N4 and Al203 powder into silicon carbide according to a certain particle size ratio, adding binder to knead, and then firing in a reducing atmosphere after molding. Refractory products with α-SiC as the skeleton and Sialon as the matrix are produced. Since the Sialon matrix exists between the particles, the strength of the product is improved and the thermal shock resistance is enhanced.
6. Recrystallized silicon carbide products are composed of 100% α-SiC and have no second phase.
The raw material contains more than 99.5% SiC. It adopts particle gradation with maximum packing density, high-pressure molding, and is fired in an electric furnace that is isolated from the air. The temperature is above 2100°C. The electric furnace is required to be burned to 2500°C. SiC evaporates and condenses, resulting in Shrink-free self-binding structure.
Silicon carbide bricks have high thermal conductivity and good wear resistance, thermal shock resistance and corrosion resistance. It can be used for aluminum electrolytic cell linings, molten aluminum conduits and kiln furniture for ceramic kilns, lower parts of large and medium-sized blast furnaces, waists and belly, aluminum refining furnace linings, zinc distillation tank linings, etc.