Silicon Nitride: What it is & Where it’s Used

Silicon nitride is a ceramic that exists in three distinct crystallographic phases: α, β, and γ. Both alpha and beta-phase silicon nitride are comprised of corner-sharing, tetrahedral SiN₄ with short, strong Si-N bonds. The result is an extremely rigid 3D framework of compactly layered silicon and nitrogen atoms.

The microstructure of silicon nitride ceramics is strongly dependent on the densification mechanism. Typically, α-Si3N4 is used as a starting powder as it transitions to the more chemically stable β-phase when fired. Although grain size and shape vary depending on the properties of the starting powder and the presence of additives, β-Si₃N₄ typically consists of elongated grains that interlock in a tightly compacted microstructure.

Properties of Silicon Nitride

• Low density (3.17 g/cm³)

• High fracture toughness (7 MPa m^1/2)

• Excellent flexural strength (850 MPa)

• Exceptional thermal shock resistance

• High maximum operating temperatures

Silicon nitride can readily be deployed in some of the world’s toughest working environments, owing to its unique intersection of chemical and thermodynamic properties. Hot pressed silicon nitride offers excellent high-temperature performance and is ideal for seal face components challenging conditions, including boiler water reactor pumps, pressurized water reactor pumps, corrosive borated water service, and within rotating bearings.

Pump components comprised of silicon nitride are also used in the oil and gas sector, and throughout the petrochemical industry at large. The chemical integrity of Si₃N₄ makes it suitable for surfaces within pumps (impellers, shafts, seals, etc.) that routinely come into contact with abrasive slurries and corrosive fluids.

Saint-Gobain Performance Ceramics & Refractories has decades of expertise in the producing precision technical ceramics for tough industries. We have a solid grasp of the complexities associated with generating silicon nitride ceramics and are well-equipped to produce high-purity, hot pressed and sintered Si₃N₄ with minimal need for post-production grinding and finishing. This preserves the inherent mechanical strengths of silicon nitride and ensures the longevity of components.