Silicon Nitride

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For over 60 years we have been a precision machining and polishing fabricator of parts from all technical ceramics, sapphire, glass and quartz. We machine these materials to very precise tolerances (many times measured in millionths of an inch) for dimension, flatness, wedge and roundness or cylindricity. Our customers typically have a critical application that requires extremely tight tolerances in ultra-hard materials. We also have the capability to grind and polish spherical radius parts in a variety of hard materials, both inside and outside diameters, to optical requirements.

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Key properties of this material include thermal shock resistance as well as fracture toughness.  These coupled with high temperature strength and wear resistance even under oxidizing conditions make silicon nitride an excellent candidate for IC engine and turbine applications. 

Silicon nitride is difficult to produce as a bulk material in the preferred hot press sintering method as the components dissociate over 1850C.  Lower temperature methods have been developed using sintering aids or by spark sintering.  Results in every case though do drive the cost of this material above most technical ceramics. 

The sintered material can be further fabricated to precise features and tolerance by diamond grinding.  Some of the very properties of silicon nitride that make it attractive for application make it likewise more difficult to grind than other technical ceramics.  Grinding is most productive when the material submits to micro impacts and is less resistant to wear in general.  Grinding silicon nitride therefore forces lower material removal rates than with alumina for example which results in higher fabrication cost.

Silicon nitride does provide excellent performance for specific applications like turbochargers, rocket engines, ball bearings, and cutting tools for cast iron.  Precision machined components are possible for many new applications as well based on the unique properties of this material.  Such cases warrant careful analysis of design to minimize features requiring extensive machining. Cost can limit wider application but the unique property benefits to performance of key components can optimize project performance and make or break success.

PropertyValue
General
Chemical Formula

Si3N4

Mechanical
Density
3.2 - 3.31 gm/cc
Hardness

1500-2000 Knoop

Tensile Strength
85 kpsi
Modulus of Elasticity

45 - 49 x 106 psi

Flexural Strength
65 - 132 kpsi
Compressive Strength
435 - 500 kpsi
Poisson's Ratio
0.27
Fracture Toughness
4 - 6 MPa m<sup>½</sup>
Electrical
Dielectric Strength
450 ac V/mil
Dielectric Constant
8.4 (@ 1 MHz)
Volume Resistivity

> 1013 ohm-cm

Thermal
Coefficient of Thermal Expansion

3.0 - 3.9 x 10-6/°C

Thermal Conductivity
15 - 30 W/mK
Specific Heat
0.13 cal/g °C
Shock Resistance
750 °C Diff.
Maximum Working Temperature
1250 °C

All properties are at room temperature unless otherwise noted.

Engineering data are representative, and are not intended as absolute nor warrantable. Manufacturer’s Data shown is blended from multiple sources and therefore illustrates the marketplace.

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