Sintered Silicon Carbide

Silicon carbide is one of the most desirable ceramic materials, offering outstanding properties such as hardness, strength, heat resistance and corrosion/oxidation resistance.

Reaction sintering is the best solution for producing large, complex shape silicon carbide ceramics at scale. Unfortunately, however, its efficiency comes with some drawbacks such as uneven density distribution and cracking sintered products.

Hardness

Silicon carbide (SiC) is one of the hardest ceramic materials, offering exceptional strength at high temperatures and making it suitable for an array of applications such as hard-faced seal components, semiconductor production equipment parts and nuclear fusion reactor structural components. Furthermore, SiC boasts excellent chemical and wear resistance.

Reaction and pressureless sintering are two primary methods for producing SiC. Reaction sintering offers lower processing temperatures but suffers from poor flexural strength and resistance to chemicals such as strong acids and alkalis; in comparison, pressureless sintering offers better flexibility, high density sintering densification rates and good shape capability, but at higher processing costs due to metal additives like aluminium, boron and carbon additions.

Sintered silicon carbide stands out among its peers due to its extraordinary hardness. With a Vickers hardness rating of 2563 HV – far surpassing armor requirements of 1500 HV – sintered silicon carbide is also an exceptionally tough material and exhibits median type cracking making it suitable for multi-hit applications.

Sintering plays an essential part in producing quality sintered silicon carbide products. Reaction bonded grades offer coarse grain with lower hardness and use temperature; direct sintered grades offer finer particles for improved crack resistance and use temperature, making them better choices than Reaction Bonded grades when it comes to seal faces and high performance seal faces.

Corrosion Resistance

Sintered silicon carbide has proven itself resistant to corrosion in acidic environments due to its superior oxidation resistance, creating an oxygen barrier around its material to protect it from attack by acidic chemicals while providing further chemical degradation from other aggressive environments.

Silicon carbide’s corrosion resistance depends heavily on factors like impurities, sintering aids, grain boundary phases, porosity and immediate reaction history of its material. Such characteristics can alter its dominant reaction sequence under in-service conditions and thus affect its subsequent corrosion behavior.

Pressureless sintered silicon carbide typically outshone reactive bonded silicon carbide when it comes to high temperature resistance and mechanical hardness, but different applications require different properties of materials; hence your selection between sintered and reaction bonded depends on your particular requirements.

Machining sintered silicon carbide (SSiC) can be difficult and expensive due to its extreme hardness. GAB Neumann uses pressureless sintered silicon carbide monolithic parts manufactured via an intensive manufacturing process which includes powder preparation, mixing with binder, shape forming, cold isostatic pressing and finally sintering at high temperatures before finally being machined to precise tolerances using diamond-coated tools after sintering.

High Temperature Resistance

Silicon Carbide retains its hardness and strength even at very high temperatures, making it a highly-resistant ceramic to wear, corrosion and thermal shock. Furthermore, its oxidation resistance is among the highest among non-oxide ceramic materials and it weighs half as much as steel.

Reaction bonded and direct sintered manufacturing processes for silicon carbide production are two widely utilized techniques for its creation. Each forming method plays an integral part in shaping its final microstructure and properties of ceramic material produced.

Reaction bonded silicon carbide can be produced by infiltrating compacts composed of mixtures of a-SiC powder and carbon with liquid silicon, then reacting this new SiC with existing particles to form dense densified bodies of SiC that have complete density.

a-SiC microstructure with its associated a-SiC -b-SiC crystalline structure provides excellent wear and thermal shock resistance, but electrical resistivity is lower due to the presence of both a-SiC grains and b-SiC grains in this form of silicon carbide.

Reaction sintering is an efficient and economical method of creating extremely tough silicon carbide ceramics with superior toughness, making this method suitable for large size or complex-shape preparation. Low sintering temperatures ensure fast sintering times with near net size parts formed within minutes; its only drawbacks include high material requirements, energy consumption costs and expensive equipment costs.

Thermal Conductivity

Silicon Carbide is one of the hardest and most durable ceramic materials on the market. It retains its hardness and strength even at extremely high temperatures, which contributes to its outstanding wear resistance. Furthermore, this ceramic boasts thermal shock resistance as well as corrosion and oxidation resistance; being half as heavy as steel yet withstanding extreme pressure and temperature changes.

Thermal conductivity in SSiC depends heavily upon its sintering process of choice; pressureless or reaction bonding sintering produce different microstructures which affect its thermal conductivity properties.

Reaction-bonded SiC is created by infiltrating porous carbon or graphite preforms with liquid silicon, which reacts with the carbon to produce solidified SiC ceramic that can then be pressed into shapes. Reaction bonded ceramics tend to be softer and less dense than their SSiC counterparts but offer good wear resistance at higher temperatures while still having high levels of oxidation and corrosion resistance.

Rare earth oxides may be introduced as additives to enhance b-SiC sintering, however their large ionic radius prevents them from penetrating its crystal lattice and becomes trapped between grains – therefore selecting additives which can penetrate it is critical – aluminium, boron and carbon (ABC) is one such promising additive that can be added grain bound for lower processing temperatures sintering applications.