Common Preparation Methods of Silicon Nitride Powder

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What is silicon nitride (SiN)?

Silicon nitride has the chemical formula Si3N4. It is a ceramic material of high strength, inherent lubricity and wear resistance. It is an atomic-crystal and resists oxidation in high temperatures. It is also resistant to the effects of both heat and cold. It will not break if it’s heated to over 1000degC and then quickly cooled, followed by a rapid heating. The excellent characteristics of silicon-nitride ceramic are the reason why it is used in many mechanical components, such as bearings and turbine blades. It can also be used to produce mechanical seal rings, permanent moldings, and more. When silicon nitride is used for the heating surfaces on engine components, it can not only improve the quality of an engine, but also fuel efficiency and thermal efficiency. China, Japan, the United States and other countries are developing such engines.

How to prepare silicon nitride

It is widely used in China. The method is simple and inexpensive. Metal silicon powder is heated with nitrogen or ammonia in an atmosphere. The metal silicon and nitrogen source directly react and form silicon nitride.

This method is cost-effective and requires little equipment. However, the metal silica powder nitridation is an exothermic process. If heat is not released at the right time during the process of nitriding, metal silicon powder nearby will melt and cause problems. The result of the nitriding. The nitriding process is controlled by the temperature, speed and particle size. The synthesised silicon nitride comes in a block-like shape. The silicon nitride must be prepared by other methods such as ball milling, which are not very efficient and introduce impurities into the process.

In the presence of high-temperature nitrogen, SiO2 is reduced with carbon powder. SiO2 is reduced to gas-phase SiO first, and the gas-phase SiO reacts to nitrogen in atmosphere to produce silicon nitride.

Thermal decomposition uses SiCl4 to react at low temperature with ammonia gas in order to obtain solid imino silica (Si(NH2)), or amino silicon(Si(NH2)4). These two silicides may be decomposed under high temperature conditions to yield nitride Silicon. This method can be used to prepare large quantities of high purity silicon nitride in a very short time. This method can produce silicon nitride that is high in purity and has uniform particle sizes. This method is currently the most popular method for commercial production high-purity, high-quality silicon powder.

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