(1) Clay bonded silicon carbide brick
Clay bonded silicon carbide brick is a refractory product made of silicon carbide as the main raw material and clay as the binder.
It is characterized by high thermal conductivity, small thermal expansion coefficient, thermal shock resistance and good wear resistance, and is one of the earliest developed silicon carbide brick.
Clay bonded silicon carbide brick is made of black silicon carbide as raw material, its chemical composition: SiC 98.0%, free C 0.5%, Fe 0.2%, free SiO2 0.6%, with good bonding performance of soft clay, pulp waste liquid as binder.
In the past, the proportion of combined clay is larger, generally 10% ~ 15%. Now, 3% of clay and 5% of pulp waste liquid are used.
The thermal conductivity of the silicon carbide bricks with less clay is 3 ~ 4 times higher than that of the silicon carbide bricks with more clay. The softening temperature and slag resistance under load are also higher.
The manufacturing process of 3% clay bonded silicon carbide brick is to prepare coarse, medium and fine SiC according to the particle grading which can obtain the maximum bulk density.
After dry mixing for 3min, 4% pulp waste liquid (density 1.26-1.289 /cm3) was added for mixing.
The mud moisture is about 1.5%. After 12h of trapped material, the mud passes through the 4mm screen and is molded with a brick press.
The bulk density of the brick is 2.5 ~ 2.79/cm3.
After drying for 2 ~ 4 days under natural drying conditions, it was fired in tunnel kiln at 1400℃.
The products are used as ceramic kiln furniture (shed board, support, sagger, etc.), muffle cover for muffle furnace, aluminum refining furnace lining brick, zinc distillation furnace distillation pot, cement rotary kiln cooler, etc.
(2) Silicon nitride bonded silicon carbide brick
Silicon nitride bonded silicon carbide brick is a refractory product made of SiC and Si powder.
It is characterized by Si3N4 as the binding phase.
Si3N4 is an important new type of refractory, which exists in needle or fibrous crystals between SiC grains.
Using the reaction sintering principle, the SiC billet containing silicon powder is sintered by nitriding reaction, and the firing process is completed in a closed furnace with nitrogen and easy to control.
The temperature, pressure and atmosphere in the furnace should be strictly controlled.
Main process parameters: pressure of nitriding gas 0.02 ~ 0.04mpa, O2 content of furnace atmosphere less than 0.01%, final nitriding temperature 1350 ~ 1450℃, the total nitriding time varies with the shape and size of products.
Silicon nitriding bonded silicon carbide brick has good alkali resistance, resistance to melt crystal wettability, oxidation resistance, wear resistance, high thermal conductivity, thermal shock resistance and very low electrical conductivity.
Silicon nitriding combined with silicon carbide brick is mainly used as the lining of the lower body of blast furnace, which is more than one time longer than the traditional refractory material. In addition, it can be used as the lining of aluminum reduction electrolytic cell, ceramic kiln furniture, which has the advantages of energy saving, increasing life and no pollution to the environment. It can also be used as the water cooling tube sleeve brick of blast furnace tuyre.
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