Some Issues about Silicon Carbide Bricks

Home » Some Issues about Silicon Carbide Bricks

Silicon carbide bricks are high-grade refractory bricks made primarily from silicon carbide. The production involves blending high-purity silicon carbide powder with highly reactive silicon carbide fines, followed by injection molding and high-temperature vacuum sintering to induce recrystallization, resulting in advanced refractory bricks.

Silicon Carbide Bricks

The primary component of silicon carbide bricks is SiC, with a content ranging from 72% to 99%. The application of silicon carbide bricks varies across industries and thermal equipment based on different binding methods. It includes clay binding, Sialon binding, aluminum oxide binding, self-binding, high alumina binding, and silicon nitride binding, among others. What are the uses of silicon carbide bricks?

Silicon carbide bricks, owing to their raw material being silicon carbide, also known as carborundum, are produced through the high-temperature smelting of raw materials such as quartz sand, coke, and wood chips in an electric furnace. Due to its stable chemical properties, high thermal conductivity, low thermal expansion coefficient, and excellent abrasion resistance, silicon carbide is commonly used in the manufacturing of advanced refractory materials.

Silicon Carbide Bricks

Applications of Silicon Carbide Bricks

Silicon carbide bricks leverage the corrosion resistance, high-temperature resistance, high strength, good thermal conductivity, and impact resistance of silicon carbide for the fabrication of refractory linings in various high-temperature thermal equipment.

Silicon carbide bricks are utilized in:

  • Furnace Linings: The primary application of silicon carbide bricks is as linings in high-temperature furnaces, such as arc furnaces, induction furnaces, and vacuum furnaces. Its high-temperature stability and corrosion resistance effectively protect the furnace, prolonging equipment lifespan.
  • Metallurgical Industry: Silicon carbide bricks find applications in various processes within the metallurgical industry, including casting, heating, and insulation. For example, during casting, the use of silicon carbide bricks ensures the quality and surface finish of cast products. In heating and insulation, it provides efficient insulation, reducing energy wastage.
  • Glass Industry: Silicon carbide bricks are widely used in the glass industry as linings and partitions in glass kilns. Their exceptional performance effectively prevents glass adhesion to kiln walls and provides sound insulation.
  • Chemical Industry: Silicon carbide bricks are employed in the chemical industry for lining high-temperature reactors and kilns. Their corrosion resistance effectively protects equipment from chemical substances.
  • Foundry Industry: Silicon carbide is crucial in the foundry industry for improving the quality of molten iron, reducing impurities. Substituting silicon carbide for silicon iron in deoxidation processes can save resources.

In summary, silicon carbide bricks, as high-temperature materials, find extensive applications in industrial production due to their characteristics of high temperature resistance and corrosion resistance.

Classification of Silicon Carbide Bricks

Clay-Bonded Silicon Carbide Bricks

Clay-bonded silicon carbide bricks are refractory products made from silicon carbide as the main raw material and clay as the binder. Silicon carbide bricks are characterized by high thermal conductivity, low thermal expansion coefficient, excellent resistance to thermal shock, and good wear resistance. They represent one of the early developments in the field of silicon carbide bricks.

These bricks, produced from black silicon carbide, have the following chemical composition: SiC 98.0%, free C 0.5%, Fe 0.2%, free SiO2 0.6%, soft clay, and paper pulp waste. The traditional use of clay as a bonding agent had a relatively high proportion, typically ranging from 10% to 15%. However, modern practices involve using 3% clay and 5% paper pulp waste. Silicon carbide bricks with less clay content exhibit a thermal conductivity 3 to 4 times higher than clay-bonded silicon carbide bricks. The manufacturing process involves preparing coarse, medium, and fine SiC based on particle size. After homogeneous dry mixing, clay is added, followed by the introduction of 4% paper pulp waste (density 1.26-1.289/cm3) after 3 minutes of dry mixing. The moisture content of the slurry material is approximately 1.5%. After being captured for 12 hours, the slurry material passes through a 4mm sieve and is formed by a brick press. The bulk density of the brick ranges from 2.5 to 2.79/cm3. It is then dried under natural conditions for 2 to 4 days and fired in a tunnel kiln at a temperature of 1400℃.

Silicon Carbide Bricks

Silicon Nitride-Bonded Silicon Carbide Bricks

Silicon nitride-bonded silicon carbide bricks are a type of refractory product produced through nitriding using SiC and Si powder as raw materials. A distinctive feature is the presence of Si3N4 as the bonding phase. Si3N4 takes the form of needle-like or fibrous crystals between SiC particles, representing an important new type of refractory material.

The nitriding reaction sintering principle involves the nitriding of SiC bodies containing silicon powder. The process is completed in a closed furnace where nitrogen gas, easy to control, is introduced. The temperature, pressure, and atmosphere inside the furnace are rigorously controlled.

Silicon nitride-bonded silicon carbide bricks exhibit excellent resistance to alkali corrosion, resistance to molten cryolite, oxidation resistance, wear resistance, high thermal conductivity, resistance to thermal shock, and extremely low electrical conductivity. Used primarily as the lining of lower furnace bodies, these bricks have a lifespan over twice that of traditional refractory materials. Additionally, they find application in aluminum reduction electrolytic cell linings and ceramic kiln furniture, offering advantages such as energy efficiency and increased lifespan.

Recrystallized Silicon Carbide Products

Recrystallized (or re-crystallized) silicon carbide products are refractory items where silicon carbide directly combines with itself. The distinctive feature of SiC bricks in this category is the absence of a second phase, consisting entirely of 100% α-SiC. The chemical composition of raw materials used to manufacture recrystallized silicon carbide includes SiC 99.5%, free C 0.2%, Fe 0.08%, and free SiO2 0.08%.

Recrystallized silicon carbide products are primarily used as kiln furniture, offering advantages such as energy efficiency, increased effective volume in kilns, shortened firing cycles, enhanced kiln production efficiency, and high economic benefits. SiC bricks are also employed as burner nozzles, ceramic radiation heating tubes and components, and protective tubes (especially suitable for atmospheric furnaces).

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