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What is Silicon Nitride Ceramics?

Silicon Nitride (Si3N4 ceramic) is a non-oxide engineering ceramics material.

It is usually black or dark gray in color and can be polished to give a smooth, reflective appearance. Silicon nitride is porous and therefore has low density and resistance to oxidation.

When processed properly, silicon nitride has good hardness at very high- temperature applications, good creep resistance, high wear resistance, low coefficient of thermal expansion, oxidation resistance, and higher mechanical strength. Its general parameters are shown in the table below

Density >3.2g/cm3
Si3N4 content >92%
Flexural strength >750Mpa
Compressive strength >1500Mpa
Thermal conductivity(W/mk) >22
Porosity 0
Thermal expansion coeff.(RT-1000℃) 3.2
Max temperature in air 1400℃
Hardness(HRA) >92

Because silicon nitride can withstand severe high temperature and wear conditions, it is ideal for high-quality components used in extremely demanding applications. The largest application of silicon nitride is in the automotive industry, where various wear and combustion components in engines, such as pre-chambers and turbochargers, are made of silicon nitride. It is also common for rocket and missile ducts to use silicon nitride to improve strength, electrical properties and impact resistance.

In contrast, sialon is a ceramic alloy based on the elements silicon (Si), aluminum (Al), oxygen (O) and nitrogen (N), an advanced form of silicon nitride based ceramics. In the case of SiAlON, the corresponding atoms of Si are replaced by Al and the corresponding atoms of N are replaced by O to satisfy the valence requirement. The resulting “solution” (Sialon) has properties superior to the original pure solvent (silicon nitride).

Sialon ceramics have been widely used in non-ferrous molten metal processing, especially aluminum and its alloys, including metal feed tubes for aluminum die castings, injectors for non-ferrous metals, thermocouple protection tubes. Compared to hot-pressed silicon nitride, the high temperature resistance of Sialon materials produced by pressureless sintering is limited by the glassy phase formed at the grain boundaries during sintering. These materials are only suitable for long-term use at temperatures < 1200 °C. The two most common crystalline phases formed in Sialon ceramics are beta-Sialon and alpha-Sialon, and combinations of the two can be incorporated into a single monolithic ceramic and develop compositions suitable for specific applications. Typical parameters of SiAlON (Syalon 101) are as follows:

Density (g.cm-3) 3.25
Young’s Modulus (GPa) 288
Bend Strength (MPa) 945
Fracture Toughness K1c (MPa.m 0.5) 7.7
Hardness, (GPa) 15.0
Thermal Expansion Coefficient (x 10-6/°C) 3.04
Thermal Conductivity (W/m.K) 28
Maximum Operating Temperature (°C) 1200
Weibull Modulus 11

Types of Silicon Nitride

The synthetic formula for silicon nitride is the chemical reaction of metallic silicon and gaseous nitrogen. Different types of silicon nitrides including RBSN, HPSN, SRBSN and SSN are produced by their heat treatment methods, which determine their properties and applications. The four types of silicon nitride ceramics are introduced below.

Reaction-bonded silicon nitride (RBSN)

Reactive bonded silicon nitride (RBSN) is made by compacting silicon nitride (Si) at about 1450°C.

It allows parts to be made in near-net shape without the need for subsequent grinding operations.

The result of this reaction is that the final product contains pores and therefore its mechanical properties are inferior to other types of silicon nitride ceramics. But it is relatively cost-effective and can be used in applications such as kiln furniture.

Hot-pressed silicon nitride (HPSN)

Compared with RBSN, which has higher density and better mechanical properties, HPSN is more expensive and is less used now.

Sintered reaction-bonded silicon nitride (SRBSN)

SRBSN is an upgraded version of RBSN. Porosity is reduced and toughness and mechanical properties are improved.

Sintered silicon nitride (SSN)

(SSN) covers silicon nitride ceramic materials that are densified by pressureless sintering in a nitrogen atmosphere at approximately 1750°C. . To aid densification, various combinations of sintering additives such as yttria, magnesia, and alumina are used. It has the strongest mechanical properties of these materials and is most widely used in industrial applications such as molten metal handling, industrial wear, metal forming, oil and gas industries, and chemical and process industries. But its cost is relatively high.

Which is most effective: sialon or silicon ceramics?

Industry requires harder, stronger heat-resistant and wear-resistant materials that can operate in harsh environments at low cost. For this reason, alternative materials are in high demand. Silicon carbide and Sialon have a series of applications. Sialon’s various parameters including bending strength, fracture toughness, thermal expansion coefficient, thermal conductivity, etc. are slightly weaker than SSN, but stronger than RBSN. That is to say, the performance of Sialon ceramics is stronger than that of low-end silicon nitride, but weaker than that of high-end silicon nitride. Considering the cost factor, perhaps Theron Ceramics is a better choice.

Advanced technical silicon nitride and sialon ceramics company

Taishengtech was established in 2002, covering an area of 21,000 square meters, specializing in the production of advanced technical ceramics. Over the years, we have always adhered to the tenet of providing customers with high-quality products and perfect services.

Focus on silicon nitride, silicon carbide, aluminum titanate, alumina, calcium silicate materials, solve problems such as heat resistance, wear resistance, corrosion resistance, insulation, etc., serving the aluminum industry, mining power plants, chemicals, polysilicon and other industries.

In addition to this, taisheng also provides custom advanced technical ceramics.

If you are interested in Silicon Nitride, please feel free to contact us!