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Introduction to Silicon Carbide Bricks

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Industry News

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2024-03-20

Silicon carbide bricks are mainly made from silicon carbide as the main raw material. SiC is covalently bonded and does not exhibit the usual sintering properties. Instead, it relies on chemical reactions to generate new phases for sintering, known as reactive sintering. Silicon carbide bricks can be divided into clay bonded silicon carbide bricks, bonded silicon carbide bricks, oxynitride bonded silicon carbide bricks, nitride bonded silicon carbide bricks, Sialon bonded silicon carbide bricks, and recrystallized silicon carbide bricks according to different bonding methods.
1. A product made by combining clay with silicon carbide bricks, using black silicon carbide as raw material, soft clay with good bonding properties, and pulp waste liquid as a bonding agent. Generally, the composition of large, medium, and fine particles of silicon carbide is calculated based on the maximum bulk density by combining 10% to 15% clay and 3% to 5% pulp waste liquid. When mixing, first add silicon carbide particles and fine powder, then add clay fine powder, dry mix for 3 minutes, and then add 4% pulp waste liquid (density 1.26-1.28g/cm3) for mixing. After 12 hours of trapping, the mud is sieved through a 4mm aperture sieve and formed using a brick press. The volume density of the brick blank is 2.5-2.7g/cm3. Bricks are naturally dried for 2-4 days and fired at 1400 ℃.
2. The product is made by combining silicon nitride with silicon carbide bricks, using silicon carbide and silicon powder as raw materials, and then nitriding and firing.
The silicon carbide raw material contains more than 97% SiC, and the proportion of silicon carbide particles in its slurry is: coarse: medium: fine=5:1:4. Silicon powder contains more than 98% but less than 10% μ M accounts for over 80%, and the maximum particle size cannot exceed 20 μ M. After batching, mixing, shaping, and drying, silicon carbide particles and silicon powder are placed in a nitriding furnace to burn the bricks. During the firing process, nitrogen is introduced, and the temperature, pressure, and atmosphere inside the furnace must be strictly controlled. The process parameters are: nitriding gas pressure is 0.02-0.04 MPa, the oxygen content in the furnace atmosphere is less than 0.01%, the final nitriding temperature is 1350-1450 ℃, and the total nitriding time varies with the shape and size of the product.
3 β- SiC combined with silicon carbide bricks, silicon carbide, silicon powder and carbon powder are mixed in a certain proportion, formed, and fired in a reducing atmosphere at 1400 ℃. Most of them are fired using buried carbon. During the firing process, a mixture of α— SiC as the skeleton, with fine particles β SiC based matrix β A SiC bonded silicon carbide brick. β SiC is generated by the reaction between silicon powder and carbon powder during the firing process. This product typically contains small amounts of residual silicon and carbon.
4. Silicon oxynitride combined with silicon carbide bricks, with silicon powder less than the proportion of Si3N4 combined bricks in the ingredients, is fired in a rich N2 atmosphere (with a certain O2 partial pressure required) at a temperature of 1350-1400 ℃. The finished product is a type of α— Silicon oxynitride bonded silicon carbide bricks with SiC as the skeleton and Si2ON2 as the matrix. There are often small amounts of Si and Si3 N4 present in the matrix.
5. Sialon combined with silicon carbide bricks, Si3N4 and Al203 powder are added to a certain particle size ratio of silicon carbide, mixed with a binder, and fired in a reducing atmosphere after forming. To be able to control α— Refractory products with SiC as the skeleton and Sialon as the matrix. Due to the presence of Sialon matrix between particles, the strength of the productImproved thermal shock resistance.
6. Recrystallized silicon carbide products, made of 100% α— SiC composition, with no second phase present.
The raw materials contain over 99.5% SiC, and are formed by particle size distribution with maximum packing density, high-pressure molding, and fired in an electric furnace isolated from air. The temperature is above 2100 ℃, and the electric furnace is required to be able to burn to 2500 ℃. SiC undergoes evaporation and condensation, resulting in a self bonding structure without shrinkage.
Silicon carbide bricks have high thermal conductivity, good wear resistance, thermal shock resistance, and corrosion resistance. Can be used for lining aluminum electrolytic cells, molten aluminum conduits and ceramic kiln furniture, lower part of large and medium-sized blast furnace shaft, waist and belly, aluminum refining furnace lining, zinc distillation tank lining, etc.
How to judge the quality of silicon carbide bricks
Silicon carbide bricks are refractory materials made mainly from SiC. Containing 72% to 99% SiC. Divided into clay bonding, Si3N4 bonding, Sialon bonding β- SiC bonded, Si2ON2 bonded, and recrystallized silicon carbide bricks have high thermal conductivity, good wear resistance, thermal shock resistance, and corrosion resistance. Can be used for lining aluminum electrolytic cells, molten aluminum conduits and ceramic kiln furniture, lower part of large and medium-sized blast furnace shaft, waist and belly, aluminum refining furnace lining, zinc distillation tank lining, etc.
Due to lack of experience, many users of silicon carbide bricks cannot distinguish the quality of silicon carbide products when purchasing them. As a result, they often purchase unqualified silicon carbide products, which greatly affects the service life of the kiln, increases investment in refractory materials, and brings unnecessary losses to the enterprise. So how to distinguish the advantages and disadvantages of silicon carbide bricks?
Firstly, the size specifications of silicon carbide bricks should be precise. The specific gravity of silicon carbide bricks is generally between 2.45 and 2.6. If the specific gravity is too small or too large, it indicates that the material itself is not pure, and other refractory materials must be added, which greatly affects the silicon carbide content and the heat transfer performance of silicon carbide. When purchasing silicon carbide bricks, it is necessary to check whether there are any missing corners or cracks on the surface of the bricks. The missing corners and cracks should be acceptable within the range of the national standard. If they seriously exceed the national standard, the quality of the batch of products is unqualified. Hongfeng Refractory reminds you to supervise the packaging truck on site when purchasing silicon carbide bricks to avoid product defects and damage caused by rough construction.
(Source from My Steel Network)