Jan 6 2004
Background
Hot pressing of Silicon Nitride produces a material of virtually zero porosity. This hard, grey ceramic is, however, still very lightweight. Silicon Nitride shows good resistance to wear and abrasion.
It shows very little oxidation at elevated temperatures, and high hardness and strength above 1000 °C. One of its main assets is its resistance to thermal shock, due to the low thermal expansion coefficient.
This material can be diamond ground to precise tolerances. Silicon Nitride is used in gas turbine situations, as diesel engine components and as an electrical insulator.
Key Properties
The key properties of Silicon Nitride ( Si3N4 ) are tabulated below.
Table 1. Key properties
| Chemical Resistance |
| Acids – concentrated |
Fair |
| Acids – dilute |
Good |
| Alkalis |
Good-Poor |
| Halogens |
Good |
| Metals |
Fair |
| Electrical Properties |
| Dielectric constant |
10 |
| Volume resistivity ( Ohm.cm ) |
1012-1015 @ 25 °C |
| Mechanical Properties |
| Compressive strength ( MPa ) |
2000-3500 |
| Hardness - Vickers ( kgf.mm-2 ) |
1700-2200 |
| Shear strength ( MPa ) |
480-960 |
| Tensile modulus ( GPa ) |
280-310 |
| Tensile strength ( MPa ) |
400-580 |
| Physical Properties |
| Apparent porosity ( % ) |
0 |
| Density ( g.cm-3 ) |
3.11 |
| Thermal Properties |
| Coefficient of thermal expansion ( x10-6 K-1 ) |
3.3 @ 20-1000 °C |
| Specific heat ( J.K-1.kg-1 ) |
680-800 @ 25 °C |
| Sublimation point ( °C ) |
1900 |
| Thermal conductivity ( W.m-1.K-1 ) |
15-43 @ 20 °C |
| Upper continuous use temperature ( °C ) |
1100-1650 |
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