An Overview of Silicon Nitride Ceramics

Introduction

Silicon nitride ceramics are made from both silicon and nitride in a ratio of 3:4, and the chemical formula is Si3N4. They are high-quality materials with remarkable hardness and impact resistance. These materials maintain high strength over a large temperature range. In addition, silicon nitride ceramics have a high melting point and are chemically inert.

Si3N4 ceramics are produced when powdered silicon is heated to about 1400 °C in the presence of atmospheric nitrogen. This forms the silicon nitride powder that is then sintered to a desired shape. Silicon nitride ceramics are one of the most thermodynamically stable ceramic materials. They are often used as components of machines requiring high speed and high temperature.

Interest in the potential of silicon nitride ceramics for engineering skyrocketed in the 1980s. This was when scientists discovered that silicon nitride ceramics could fare better as components of engines than most other ceramics. Silicon nitride has applications in various industries. It can be used in the automobile industry, medical field, and electronic industry.

Types of Silicon Nitride Ceramics

According to their fabrication method and properties, there are four types of silicon nitride ceramics.

Reaction-Bonded Silicon Nitride Ceramics (RBSN)

Reaction-Bonded Silicon Nitride Ceramics are fabricated by adding nitrate to compact silicon at a temperature of about 1450 °C. Compact silicon usually has substantial porosity. However, silicon nitride grows in the pores to make the compact denser.

This type of silicon nitride ceramic usually has about 30 % porosity. This is much more than the porosity of other types. RBSN is usually inexpensive to produce and is often used as a refractory material.

Hot Pressed Silicon Nitride Ceramics (HPSN)

Hot Pressed Silicon Nitride Ceramic was created to give engineers access to the beneficial properties of silicon nitride, some of which were not available with RBSN. It was fully developed by the 1970s.

HPSN is produced by adding magnesia to silicon nitride and pressing the powder. This process usually occurs at a temperature of about 1800 °C and a pressure of about 40 MPa. Hot Pressed Silicon Nitride Ceramic usually comes out denser than RBSN. It is commonly used as a cutting tool.

Sintered Reaction-Bonded Silicon Nitride Ceramics (SRBSN)

Sintered Reaction-Bonded Silicon Nitride Ceramic is manufactured in such a way that it has less porosity than RBSN. Its porosity is typically about 5 %. SRBSN is produced by sintering the material after the reaction-bonding stage. As a result, the material shrinks considerably. It is less expensive to produce than HPSN and SSN. Sintered Reaction-Bonded Silicon Nitride Ceramics are commonly used as cutting tools and wear components.

Gas Pressure Sintered Silicon Nitride (GPSN)

Gas pressure sintered silicon nitride (GPSN) is obtained at 1~10MPA pressure and around 2000℃. The high nitrogen pressure inhibits the pyrolysis of silicon nitride and promotes the growth of Si3N4 grains, so that high-toughness ceramics with a density of >99% can be obtained. GPSN has high toughness, high strength and excellent wear resistance; it has good processing performance and can be directly processed into the target shape, greatly reducing production costs and processing costs.

Sintered Silicon Nitride Ceramics (SSN)

To produce a Sintered Silicon Nitride Ceramic, silicon powder is sintered in the presence of nitrogen at a temperature of about 1750 °C and without pressure. Yttrium oxide, magnesium oxide, and aluminum oxide can be added during the sintering process to densify the material. Sintered Silicon Nitride Ceramics usually have the best mechanical properties of all types of silicon nitride ceramics. They are also the most used across various industries.

Properties of Silicon Nitride Ceramics

Silicon nitride ceramics have numerous desirable properties that make them a hit in various industries. They have a high fracture toughness. They do not break easily. In addition, these materials have low density and high flexural strength.

Silicon nitride ceramics can be used for high-temperature applications because they have low thermal expansion and are resistant to thermal shock. These two properties make them immune to some structural changes that could come from high temperatures. Furthermore, they are good electrical insulators. Some things you do not have to worry about while using silicon nitride ceramics are corrosion, oxidation, and wear. This is because they are usually corrosion-resistant, oxidation resistant, wear-resistant, and chemically inert.

Application of Silicon Nitride Ceramics

Medical Field

Silicon nitride ceramics are usually thermodynamically stable. This makes them ideal for the medical field because it means they do not change when sterilized in an autoclave repeatedly. Medical instruments are usually sterilized in an autoclave to prevent infection. In addition, they have a higher Weibull modulus than most ceramics. This means they have the mechanical strength to withstand any impact they may encounter as they are used for medical procedures.

Jewelry

Silicon nitride has a natural gray color, unlike other ceramics that are white. This means that silicon nitride ceramics do not have to be painted while making jewelry. Their grey color usually looks aesthetically appealing. Also, they have low density and high wear resistance. The low density makes them easy to adorn while the high resistance to wear ensures that they last long.

Cutting Tools

Silicon nitride ceramics are excellent cutting tools. They are durable cutting tools due to their high wear resistance and high Weibull modulus. Also, they are more thermally and mechanically stable than other ceramics used as cutting tools.

Further Reading: Silicon Nitride Ceramic Cutting Tools used in Machining Superhard Materials

Ball Bearing

Silicon nitride ceramics are popularly used as ball bearings. They have become even more popular than steel ball bearings due to their high thermal shock resistance. Silicon nitride ceramics can function efficiently at extremely high speeds thanks to their wear resistance.

Conclusion

Silicon nitride ceramics are versatile materials. There are different types of silicon nitride ceramics and each type has properties that make it important in various industries. A good understanding of the types of silicon nitride ceramics makes it easier to choose the most appropriate one for an application. For more information about high quality silicon nitride ceramic materials, please visit https://www.preciseceramic.com/.