Silicon Nitride

About Silicon Nitride

As it is one of the most thermodynamically stable technical ceramic materials with high hardness as well, silicon nitride ceramic is ideal for bearing parts, especially for those required to work at high speed and high temperature. Si3N4 bearing balls have already been applied in automobiles, rocket high-speed engines, equipment working in a corrosive environment, and some performance model cars. Compared with steel, high-performance ceramic balls have better mechanical properties under high temperatures and could survive most of the corrosive chemicals.

Silicon nitride has also been used in high-temperature applications, such as rocket engines. It was considered one of the few monolithic ceramic materials that could survive the severe thermal shock and thermal gradients generated in hydrogen-oxygen rocket engines.

Types of Silicon Nitride Ceramics

Silicon nitride ceramics are available in several types, each produced using different manufacturing methods, resulting in variations in their properties and applications. The main types include:

1. Reaction-Bonded Silicon Nitride (RBSN):

   • Made by nitriding a silicon compact at around 1450°C.

   • Si₃N₄ grows in the porosity of the compact, resulting in minimal dimensional change.

   • Allows for near-net shape production, reducing the need for expensive grinding.

   • Contains porosity, leading to lower mechanical properties compared to other types.

   • Relatively inexpensive to produce.

   • Applications: kiln furniture.

2. Hot-Pressed Silicon Nitride (HPSN):

   • Applications as cutting tools.

   • Simple shapes due to the need for diamond grinding.

   • More expensive and largely superseded by SSN.

3. Sintered Reaction-Bonded Silicon Nitride (SRBSN):

   • An attempt to reduce the final porosity of RBSN, improving its mechanical properties.

   • More recent developments have shown improvements in toughness and impact resistance due to the growth of crack-deflecting silicon nitride grains.

4. Gas Pressure Sintered Silicon Nitride (GPSN):

   • Obtained at 1~10MPA pressure and around 2000℃.

   • The high nitrogen pressure inhibits the pyrolysis of silicon nitride and promotes the growth of Si3N4 grains so that high-toughness ceramics with a density of >99% can be obtained.

   • GPSN has high toughness, high strength, and excellent wear resistance; it has good processing performance and can be directly processed into the target shape, greatly reducing production costs and processing costs.

5. Sintered Silicon Nitride (SSN):

   • Densified by pressureless sintering in a nitrogen atmosphere at around 1750°C.

   • Uses sintering additives such as yttrium oxide, magnesium oxide, and aluminum oxide to aid densification.

   • Offers the best mechanical properties for silicon nitride.

   • Most widely used in industrial applications.

   • Applications: molten metal handling, industrial wear, metal forming, the oil and gas industries, and the chemical and process industries.

Properties of Silicon Nitride

• High Strength: Maintains its strength even at high temperatures.
• Hardness: Very hard material (8.5 on the Mohs scale).
• Toughness: Resistant to fracture and wear.
• Thermal Stability: Excellent resistance to thermal shock and maintains dimensional stability at high temperatures.
• Chemical Inertness: Relatively chemically inert, resisting attack by most acids and alkalis.
• Low Density: Lightweight material with a density of about 3.2 g/cm³.
• Electrical Insulation: Good electrical insulator.

Applications of Silicon Nitride

Silicon nitride's unique properties make it suitable for a wide range of demanding applications:

• Automotive Industry: Used for engine components like glow plugs, rocker arms, and turbocharger rotors.
• Aerospace: Components requiring high-temperature strength and thermal shock resistance.
• Industrial Wear Parts: Bearings, seals, and cutting tools.
• Molten Metal Handling: Thermocouple sheaths and crucibles.
• Electronics: Substrates and insulators.
• Medical: Surgical instruments and dental implants.

Silicon Nitride Powder

High-purity silicon nitride powder is produced using the imide-decomposition process, known for its purity, controlled morphology, and crystal phase. Different grades of powder are available with varying particle sizes and distributions to meet specific application requirements.

Crystal Structure

Silicon nitride exists in three main crystallographic structures: α, β, and γ phases. The α and β phases are the most common and can be produced under normal pressure conditions, while the γ phase is synthesized under high pressures and temperatures. The α- and β-Si₃N₄ have trigonal and hexagonal structures, respectively, built from corner-sharing SiN₄ tetrahedra.

Silicon Nitride Products

A variety of silicon nitride products are available, including powders, components, and custom-engineered parts. These products are tailored to meet the specific requirements of diverse applications across various industries.

Silicon Nitride Video