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Dr. Dmitri Kopeliovich
The most important carbide ceramic is Silicon Carbide (SiC).
Silicon Carbide materials are produced by in either porous or dense form and by using different technological methods:
Oxide binder (aluminosilicate) in amounts of 5-15% is added to relatively coarse Silicon Carbide powder.
Manufacturing technique of Silicate Bonded Silicon Carbide is cost effective; however the presence of oxides decreases high temperature strength and corrosion resistance of the material.
Recrystallized Silicon Carbide ceramics are produced from pure silicon carbide powders.
Since no binders are added, the manufacturing process requires high sintering temperature 4170-4530 ºF (2300-2500 ºC).
Absence of binders allows using the materials at temperatures up to 3000 ºF (1650 ºC).
Recrystallized Silicon Carbide materials have 10-15% of open porosity favoring their high thermal shock resistance.
Due to their porosity mechanical strength and corrosion resistance of the materials are lower than those of dense silicon carbide ceramics.
Nitride Bonded Silicon Carbide ceramics are produced from a mixture of silicon carbide and silicon powders, which is sintered first in Nitrogen atmosphere and then in oxidizing atmosphere.
The resulting material has small pores with open porosity up to 5%.
Nitride Bonded Silicon Carbide materials possess better corrosion resistance and higher mechanical strength than Recrystallized Silicon Carbides, but their maximum service temperature is lower – up to 2730 ºF (1500 ºC).
Nitride Bonded Silicon Carbides are hardly wetted by molten non-ferrous metals.
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Liquid Phase Sintered Silicon Carbideceramics are produced from a mixture of silicon carbide and oxides powders, which is sintered at a temperature above 3630 ºF (2000 ºC) and under high pressure up to 4400 psi (30 MPa).
Fine Grain structure and absence of pores provide high mechanical strength and fracture toughness of the material.
Reaction Bonded Silicon Infiltrated Silicon Carbide ceramics are produced from a mixture of silicon carbide and carbon powders, through which molten silicon is infiltrated. Silicon, reacting with carbon, forms bonding between the silicon carbide grains.
The material possesses high mechanical strength, corrosion, wear and thermal shock resistance at temperatures below 2515 ºF (1380 ºC).
Hot Pressed and hot isostatically pressed Silicon Carbide ceramics are produced under pressure up 2000 atm. and they possess high mechanical strength.
Sintered Silicon Carbide ceramics are produced by conventional sintering technique under natural pressure of inert gas atmosphere and at temperatures 3630-4000 ºF (2000-2200 ºC).
The material possesses high corrosion resistance and high hardness and mechanical strength up to 2900 ºF (1600 ºC).
The following characteristics are typical for the most of Silicon Carbide Ceramics:
Silicon Carbide ceramics are used for manufacturing melting crucibles, kiln furniture, heat exchangers, burner nozzles, sealing rings for pumps and other parts working at high temperature and in aggressive media, milling balls, wear plates, heating elements.
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