There exist three crystallographic structures of silicon nitride (Si₃N₄), designated as α, β and γ phases. The α-Si₃N4 is low-temperature phase (can be produced at temperatures 1350-1450℃), and it would transform into β phase when temperature is above 1500℃.The α and β phases are always symbiotic, the γ phase can only be synthesized under high pressures and temperatures.

1. The material is prepared by heating powdered silicon between 1300 °C and 1400 °C in a nitrogen environment. With an iron catalyst, the reaction rate will be accelerated and can be completed in a few hours.

                                                   3 Si + 2 N₂→Si₃N₄

2. SiCl₄ and ammonia were used to produce iminodium silicon at low temperature and then decomposed to ultrafine Si3N4 at high temperature.

                              SiCl₄(l)+6 NH₃(g)→Si(NH)₂(s)+4 NH₄Cl(s)  at 0℃

                               3 Si(NH)₂(s)→Si₃N₄(s)+N₂(g)+3 H₂(g)  at 1000℃

3. Carbon powder was added with SiO₂, which was first reduced in nitrogen atmosphere and then nitrided to form Si3N4. The carbothermal reduction was the earliest used method for silicon nitride production and is now considered as the most-cost-effective industrial route to high-purity silicon nitride powder.

                                           3 SiO₂+6 C+2 N₂→Si₃N₄+6 CO

4. Electronic-grade silicon nitride films are formed using chemical vapor deposition (CVD). The raw materials are usually silane and ammonia, which react to form silicon nitride films. The silicon nitride films prepared by LPCVD and PECVD techniques are porous amorphous.

                                 3 SiH₄(g)+4 NH₃(g)→Si₃N₄(s)+12 H₂(g)

                                    3 SiCl₄(g)+4 NH₃(g)→Si₃N₄(s)+12 HCl(g)

                              3 SiCl₂H₂(g)+4 NH₃(g)→Si₃N₄(s)+6 HCl(g)+6 H₂(g)

If a certain flux is added, the silicon nitride ceramics can be sintered at a lower temperature. Discharge Plasma Sintering (SPS) is a very effective sintering method. Because the sintering process takes only a few seconds, the sintering of ceramic parts can be realized by SPS in the range of 1500-1700 ℃.

The reason why silicon nitride ceramics are not widely used is because of the high cost, not the performance. For example, the performance of silicon nitride bearings has outperformed that of metal bearings, and their cost reduction and increase of market share show a regular inverse ratio.

1.Automobile engine parts

2.High-end bearings

3.High temperature resistant parts of immersion heater

4.Human medical replacement parts

5.Cutting tool

6.Electronic shielding material

7.IGBT

8.Phase Change Thermal Storage Porous Ceramics 

9.Mssile-borne radome

10.Ceramic manned capsule for deep-sea exploration

11.Thermal conduction substrate

12.Solar polysilicon crucible