Pressureless sintering process of silicon carbide ceramics

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Silicon carbide ceramics have the characteristics of high strength, high hardness, high rigidity, high thermal conductivity, low expansion, and stable chemical properties. It is not only an excellent high-temperature structural material, but also has been increasingly widely used in semiconductor equipment as photolithography machine moving parts, vacuum chucks, transfer arms, etc. It is also an irreplaceable high-temperature structural material in diffusion welding furnaces.

Silicon carbide is a structural-functional integrated material with great application value.

Comparison and application of preparation processes of different silicon carbide materials:

Project	Reaction bonded silicon carbide	Pressureless sintered silicon carbide
SiC content/(wt%)	≥85	90~98
Bulk density/(g/cm3)	3.05~3.10	3.05~3.15
Room temperature flexural strength/(MPa)	250~350	300~600
Apparent porosity/%	≤0.1	≤0.1
Firing temperature/℃	1500~1700	1900~2200
High temperature flexural strength (MPa)	≥250	300~600

Reaction sintered SiC ceramics:

Reaction sintered silicon carbide ceramics are made of α-SiC and C powders of different particle sizes pressed into green blanks, which are infiltrated with liquid silicon at a high temperature of 1500~1600℃. The carbon in the blank infiltrates into silicon to react and generate β-SiC, which combines with α-SiC. Free silicon fills the pores, thus obtaining a highly dense ceramic material.

Advantages of reaction sintered SiC ceramics:

Short sintering time and low sintering temperature

Reaction sintered blanks basically do not shrink and have small deformation

Large-sized products can be prepared

Multiple molding methods (extrusion, grouting, pressing, etc.)

Low preparation cost

The presence of 2~12% free SiC affects the use temperature

Pressureless sintered SiC ceramics:

Pressureless sintered SiC ceramics are made of high-purity and high-fine carbonization as raw materials, with a small amount of sintering aids such as boron and carbon. They are sintered in an inert gas at a high temperature of 1900~2200℃. The resulting products are almost completely dense and have excellent mechanical properties.

Advantages of pressureless sintered SiC ceramics:

The SiC ceramics prepared by pressureless sintering process are dense, high in strength, large in elastic modulus, good in rigidity, and have a very high thermal conductivity, second only to beryllium oxide and aluminum nitride ceramics, so they are suitable for various harsh environments.

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