Silicon Nitride

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Silicon Nitride, Si3N4 Ceramic Properties

       Silicon nitride is a man made compound synthesized through several different chemical reaction methods. Parts are pressed and sintered by well developed methods to produce a ceramic with a unique set of outstanding properties. The material is dark gray to black in color and can be polished to a very smooth reflective surface, giving parts with a striking appearance. High performance silicon nitride materials were developed for automotive engine wear parts, such as valves and cam followers and proven effective. The cost of the ceramic parts never dropped enough to make the ceramics feasible in engines and turbochargers. The very high quality bodies developed for these demanding high reliability applications are available today and can be used in many severe mechanical, thermal and wear applications.

Silicon nitride has better high temperature capabilities than most metals combining retention of high strength and creep resistance with oxidation resistance. In addition, its low thermal expansion coefficient gives good thermal shock resistance compared with most ceramic materials. Pure silicon nitride is difficult to produce as a fully dense material.  This covalently bonded material does not readily sinter and cannot be heated over 1850oC as it dissociates into silicon and nitrogen.  Dense silicon nitride can only be made using methods that give bonding through indirect methods, such as small chemical additions to aid densification. These chemicals are known as sintering aids, which commonly induce a degree of liquid phase sintering.

Key Silicon Nitride Properties

  • High strength over a wide temperature range
  • High fracture toughness
  • High hardness
  • Outstanding wear resistance, both impingement and frictional modes
  • Good thermal shock resistance
  • Good chemical resistance
  • low density
  • high temperature strength
  • superior thermal shock resistance
  • excellent wear resistance
  • good fracture toughness
  • mechanical fatigue and creep resistance
  • good oxidation resistance

Typical Silicon Nitride Uses

  • Rotating bearing balls and rollers
  • Cutting tools
  • Engine moving parts — valves, turbocharger rotors
  • Engine wear parts — cam followers, tappet shims
  • Turbine blades, vanes, buckets
  • Metal tube forming rolls and dies
  • Precision shafts and axles in high wear environments
  • Weld positioners

General Silicon Nitride Information

The material is an electrical insulator and is not wet by nonferrous alloys. Silicon nitride is a rather expensive material, but it’s performance to cost benefit ratio is excellent in the applications where it can outperform the normally utilized materials with long life and very reliable low maintenance operation.

Applications include:

There is a range of general industrial applications where the material properties can be exploited.  Reaction bonded silicon nitride (RBSN) is often used in these cases as the operating conditions are less demanding than in the preceding applications.

Non automotive wear components are a growing market for silicon nitride. For example, fixtures to position and transfer metal parts during processes such as induction heating and resistance welding exploit the electrical insulation, wear resistance, low thermal conductivity and thermal shock resistance of the material.

Spouts, nozzles, thermocouple sheaths and melting crucibles for handling molten aluminium, zinc, tin and lead alloys.  The increasing requirement for controlled metal purity makes the use of metallic components less desirable.

Arc welding nozzles are also a steady market for RBSN given the strength, electrical resistance and thermal shock resistance of the material

Specialized kiln furniture with low thermal mass and high thermal shock resistance for use in firing components such as dental porcelain where repeated thermal cycling is required.

Metallurgy, aviation, chemical, energy and machinery industries in making parts like ball/roller bearing, sleeve, valves and other wear resistants

Making of cutting tools, moulds, cylinder wall coatings, turbine rotor and blades

Making of composites such as ceramics, graphite, rubber, metals, adhesives, etc


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