Silicon Nitride

Silicon Nitride (Si3N4) has the most versatile combination of mechanical, thermal, and electrical properties of any technical ceramic material. It is a high performance technical ceramic that is extremely hard and has exceptional thermal shock and impact resistance. It surpasses most metals high temperature capabilities and has a superior combination of creep and oxidation resistance. Additionally, its low thermal conductivity and high wear resistance make it an excellent material that can withstand the toughest of conditions in the most demanding industrial applications. Silicon Nitride is an excellent choice when high-temperature and high-load abilities are needed.

Applications

  • Rotating ball bearings & rollers bearings
  • Cutting tools
  • Engine components: valves, rocker arm pads, seal faces
  • Induction heating coil supports
  • Turbine blades, vanes, buckets
  • Welding & brazing jigs
  • Heating Element components
  • Crucibles
  • Metal tube forming rolls and dies
  • TIG / Plasma welding nozzles
  • Weld positioners
  • Precision shafts and axles in high wear environments
  • Thermocouple sheaths & tubes
  • Semiconductor Process Equipment

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Material Properties

  • High strength over a large temperature range
  • High fracture toughness
  • Good flexural strength
  • Mechanical fatigue & creep resistant
  • Lightweight – Low density
  • High hardness and wear resistance, both impingement and frictional modes
  • Superior thermal shock resistance
  • Low thermal expansion
  • Electrical insulator
  • Good oxidation resistance
  • Good chemical corrosion resistance
  • Wear resistant
  • High stiffness

Mechanical Properties

Density
Unit
g/cm3
Value
3.21
Compressive Strength
Unit
MPa
Value
3000
Flexural Strength
Unit
MPa
Value
800
Weibull-Modulus m
Unit
-
Value
15
Fracture Toughness KIc
Unit
MPa m1/2
Value
6.5
Young‘s Modulus E
Unit
GPa
Value
320
Poisson Ratio
Unit
-
Value
0.28
Hardness Vickers (HV 1)
Unit
GPa
Value
16

Thermal Properties

Max Temp (Inert Gas)
Unit
°C
Value
1200
Max Temp (Air)
Unit
°C
Value
1100
Thermal Conductivity @ 20°C
Unit
W/mK
Value
28
Thermal Conductivity @ 1000
Unit
W/mK
Value
16
Thermal Expansion @ 20–100°C
Unit
10-6/K
Value
2
Thermal Expansion @ 20–1000°C
Unit
10-6/K
Value
3.5
Thermal Shock Parameter R1
Unit
K
Value
600
Thermal Shock Parameter R2
Unit
W/mm
Value
15

Electrical Properties

Resistivity at 20°C
Unit
Ωcm
Value
1012
Resistivity at 800°C
Unit
Ωcm
Value
107
Dielectric Constant
Unit
1 MHz
Value
6

Related Materials

Ceramic Material - CeramaCil-C (Silicon Carbide)

Silicon Carbide

Silicon Carbide (SiC) is one of the lightest, hardest, and strongest technical ceramic materials with exceptional thermal conductivity, acid resistance, and low thermal expansion.

Material Grades

There are several different methods used to produce Silicon Nitride. Each method produces materials with slightly differing properties.

PCSN1000 – Gas Over-Pressure Sintered

This is the most popular method for producing high-strength and complex geometry silicon nitride components. The GPSN method uses a silicon nitride powder that has been mixed with sintering aids to promote liquid phase sintering (typically yttria, magnesium oxide, and/or alumina) as-well-as binders to improve the mechanical strength of green ceramic body. The powder is pressed into the desired form and green-machining can take place. The compacts are then placed into a furnace that has a pressurized nitrogen atmosphere to aid with densification and prevent the evaporation/decomposition of the silicon, nitrogen, and additives.

Precision Ceramics stocks a range of standard silicon nitride ceramic rods, which are all precision turned to an excellent surface finish. These rods can be used as bearings, pistons, engine components, or in a variety of other assemblies. In addition, Precision Ceramics offers full machining/grinding services for custom silicon nitride component manufacturing.

PCSN2000 – Hot Pressed

HPSN is produced by uniaxially pressing silicon nitride powder with sintering additives while applying heat at the same time. This process requires a special type of press and die. It produces a silicon nitride with excellent mechanical properties. However, only simple shapes can be produced. Because it is impossible to green-machine a component that is hot-pressed, diamond grinding is the only way to create complex geometries. Because of the high costs and difficulties associated with diamond grinding and hot-pressing, its use is typically limited to the production of simple components in small quantities.

PCSN3000 – Hot Isostatic Pressed

This method consolidates the silicon nitride powder by using high pressures and high temperatures. A silicon nitride body with closed porosity is isostatically pressed (uniform pressure on all sides) via an inert gas at up to 2000 bar while the chamber is simultaneously heated. This process effectively squeezes any pores/defects from the material while it is sintering and brings the density closer to theoretical. HIPing improves the mechanical properties and reliability, however, it is an expensive process that is typically only used in very select circumstances.

PCSN4000 – Extruded Gas Over-Pressure Sintered

Silicon Nitride Machining

Silicon Nitride can be machined in green, biscuit, or fully dense states. It can be machined relatively easily into complex geometries while in the green or biscuit form. However, the sintering process that is required to fully densify the material causes the silicon nitride body to shrink approximately 20%. This shrinkage means that it is impossible to hold very tight tolerances when machining silicon nitride pre-sintering. In order to achieve very tight tolerances, fully sintered material must be machined/ground with diamond tools. This processes uses a very precise diamond coated tool/wheel to abrade away the material until the desired form is created. This can be a time-consuming and costly process due to the inherent toughness and hardness of the material.

Frequently Asked Questions

  • image/svg+xmlimage/svg+xml
    What is Silicon Nitride used for?
    • Rotating ball bearings & rollers bearings
    • Cutting tools
    • Engine components: valves, rocker arm pads, seal faces
    • Induction heating coil supports
    • Turbine blades, vanes, buckets
    • Welding & brazing jigs
    • Heating Element components
    • Crucibles
    • Metal tube forming rolls and dies
    • TIG / Plasma welding nozzles
    • Weld positioners
    • Precision shafts and axles in high wear environments
    • Thermocouple sheaths & tubes
    • Semiconductor Process Equipment
  • image/svg+xmlimage/svg+xml
    What are the advantages of Silicon Nitride?

    Compared with other technical ceramics, its low thermal expansion coefficient provides good thermal shock resistance. It is extremely hard, surpasses the high temperature capabilities of most metals and also has a superior oxidation resistance. As a consequence, silicon nitride can withstand the toughest conditions in the most demanding high temperature, high-load applications.

    Even NASA scientists recognized its unique properties when silicon nitride bearings were used in the main engines of the Space Shuttle. It was identified as one of the few monolithic ceramic materials capable of surviving the severe thermal shock and thermal gradients generated in hydrogen / oxygen rocket engines and proved completely reliable throughout the entire Space Shuttle program.

  • image/svg+xmlimage/svg+xml
    What is the formula for Silicon Nitride?

    The formula for silicon nitride is Si3N4.