Types of silicon nitride materials are as below:
- Reaction bonded silicon nitride (RBSN)
- Sintered Silicon Nitrides (SSN)
- Gas Pressured Sintered Silicon Nitrides (GPS- SSN)
- High pressured Sintered Silicon Nitride (HPSN)
Reaction bonded silicon nitride is made by direct nitridation of a compacted silicon powder, and because of the difficulty of ensuring complete reaction; it is hard to achieve a high component density. Usual densities are in the range 2.3 – 2.5g/cm3 compared with up to 3.3g/cm3 for gas and high pressured sintered silicon nitride.
The higher density gives the SSN, GPS-SSN and HPSN materials better physical properties and means they are used in more demanding applications at very high wearing including electrical insulating properties, chemical resistance, high temperature and corrosion resistance especially for non-ferrous molten metal handling parts.
The nitridation produces only a small volume change, which means that RBSN components do not need to be machined after fabrication and very complex near to net shapes can be produced in a single process stage, while SSN, GPS-SSN and HPSN will shrink for full densification without any porosity having very solid and strong structure for demanding applications in various high tech industrial applications.
Key Properties of Silicon Nitride
Applications exploit the following properties of silicon nitride:
- Low density
- High temperature capability and strength
- Superior thermal shock resistance
- Excellent wear and chemical resistance
- Good fracture toughness and electrical insulating properties
- Mechanical fatigue, excellent compressive strength and creep resistance
- Excellent non-wetting property with good oxidation resistance
Key Applications of Silicon Nitride
- Automotive: Bearings, Tappet Shims & Buckets, Cam Rollers, High pressured pumps parts, Turbocharge Rotors, Rocker arm tips, Welding location pins, Squeeze Rollers for radiator tube manufacturing etc. for its superior mechanical reliability and wear resistance and corrosion resistance
- Balls & Bearings: Fully dense various size balls from o.5mm up to 50mm OD, Fully dense ceramic Bearing, Roller Bearing, Tapper Roller bearings & Plain Bearings for 60% lighter weight, electrical- magnetic insulating, 70% higher speed, chemical resistance, high temperature etc. Also Hybrid bearing having ceramic Balls & rollers for high strength
- Non-ferrous Foundries: Thermocouples sheaths, Riser Tubes, Heater Tubes, Valve rods, Valve seats, aluminium powder atomizer tubes, Molten metal pumps parts, Rotor for de-gassing shaft, Launders due to high temperature capacity, excellent thermal shock, non-wetting properties
- CMM: Various types of styluses, styluses rods, Plain bearings, Ceramic balls etc.
- Oil & Gas Industries: Sleeves, Plungers, Needles, compression Rings, seals etc. are used for the harsh environment produces chemical, wear, corrosion and high temperature challenges that can be met through the use of dense silicon nitride
- Nuclear & Defence: Due to lightweight, hard wear and toughness, this advanced ceramic are used as a were resistance tiles, impact plates, discs, ring etc. and also used for personnel body armors, vehicle, vessel, helicopter and aircraft etc. applications
- Electrical & Electronics: A large variety of high performance parts are manufactured for the electrical electronic industry due ti insulating and non-magnetic properties. Parts include wafer processing components, microwave specialty ceramics etc.
Typical Technical Properties of Silicon Nitride
| Type of Silicon Nitride | Reaction Bonded-RBSN | Sitered-SSN | Gas Pressured GPS-SSN-HPSN |
|---|---|---|---|
| MECHANICAL | |||
| Density (g/cc) | 2.3 | 3.2 | 3.3 |
| Porosity % (sub-micron) | 18%/20% | 0.0% | 0.0% |
| Maximum Temperature (°C) | 1150°C | 1150°C | 1250°C |
| Flexural Strength (MPa) @ RT | 190 | 800 | 900 |
| Weibull Modulus | 10 | 15-30 | 18 |
| Elastic Modulus (GPa) | 175 | 310 | 315 |
| Poisson’s Ratio | 0.21 | 0.27 | 0.27 |
| Hardness HV (0.3) Kg/mm2 | 800 | 1800 | 1850 |
| Fracture Toughness (MPam1/2) | 2.5 | 5.5 | 5.8 |
| Abrasive Wear Resistance Parameter | 360 | 1110 | 1110 |
| THERMAL | |||
| Thermal Expansion Coeff. 10-6/C; (RT-1000 C) | 3.2 | 3.1 | 3.1 |
| Thermal Conductivity (W/mK) @ 25C | 14 | 26 | 28 |
| Thermal Shock Parameter (C) | 330 | 610 | 640 |
| ELECTRICAL | |||
| Electrical Resistivity (ohm-cm) | 10/14 | 10/14 | 10/14 |
| Di-electric Constant | 7.5 | 9 | 9 |
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