The industrial production and excellent performance of silicon nitride

In the ranks of endless emerge new materials, silicon nitride ceramics can be said the best, very compelling, and increasingly the attention of scientists in the world. The silicon nitride is a compound of nitrogen and silicon. In nature, nitrogen and silicon are extremely common elements. Nitrogen is the basic of life, silicon is the inorganic world's protagonist, these two elements are ubiquitous in the world we live in, however, so far people have not yet discovered the two elements compounds in nature. Silicon nitride is the compound synthesized through artificial conditions. If there is not a strict and elaborate process for silicon nitride powder, it could not get the silicon nitride ceramics with excellent mechanical properties.

Excellent performance of silicon nitride ceramics have a special value in the working environment of high-temperature, high-speed, highly corrosive media, which modern technology often encountered. The outstanding performances have: (1) high mechanical strength, hardness is close to corundum, with self-lubricating, wear-resistant. Bending strength at room temperature can be as high as 980MPa, compared with alloy steel, the strength did not decrease can be maintained until the 1200. (2) good thermal stability, small thermal expansion coefficient, with good thermal conductivity, good thermal shock resistance, from room temperature to 1000°C will not crack in a thermal shock. (3) stable chemical properties, almost can resist all inorganic acids, except (HF) and the caustic soda (NaOH) erode which the concentration of corrosion less than 30%, but also have the ability of resisting many organic substances erode, can not wet a variety of non-ferrous metal melt (especially aluminum liquid), can withstand the intense radiation irradiation. (4) low density, small specific gravity, only 2/5 of the steel, have good electrical insulating properties.

To obtain high performance silicon nitride ceramics, in general, must have high quality silicon nitride powder first. The ideal silicon nitride powder should be high purity, ultra-fine, equiaxed, spherical, loose particles. In fact, it has not been fundamentally resolved how to get the ideal powder. Commercially available industrial silicon powder always contains metal oxide, such as potassium, sodium, iron, calcium oxide; industrial nitrogen and hydrogen also always contain a small amount of water, oxygen, etc., all of these must through rigorous testing, and purify to the allow content.

The demand for silica fume’s particle size should less than 40¼m, about the metal powder impurities generally can use pickling to remove, about the superhard alloy impurities can remove by gravity method or magnetic method. The oxide film of silicon powder surface can remove by a reductive activation method before nitriding, i.e. lower than the sintering temperature, repeated exchange treated by below atmospheric hydrogen reduction and vacuum, after the oxidized film was removed, then subjected to nitriding synthesis operation .

The industrial production of silicon nitride ceramics is absolutely not subject to resource constraints, synthesis silicon nitride can be conducted by a variety of methods, the sources of raw materials are generally very easy. Two decades, the preparation process of the silicon nitride ceramics continuous improving, production scale was expanding, the cost was decreasing, market demand was also doubled increasing. Therefore, the silicon nitride ceramic has obvious potential competitive force in the field of new materials, and have great future development.

Source:http://www.mhcmp.com