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Properties of Silicon Nitride

Silicon nitride is a material that does not occur naturally. Man uses the compound for certain machine parts instead of metal, as the material shares some of the characteristics of metal. Because different manufacturing processes have varying effects on the finished product, silicon nitride comes in three main forms. These are sintered silicon nitride, reaction-bonded silicon nitride and hot-pressed silicon nitride. The applications that silicon nitride are suitable for include engine parts, such as turbochargers, and hybrid metal-silicon ball bearings.

Physical Traits
- Si3N4 contains three silicon atoms and four nitrogen atoms in one molecule. The molecular weight is 140.28 atomic units. It is a stable molecule that does not easily react with other materials. The melting point of the powder is 3,452 degrees Fahrenheit (1,900 degrees Celsius). It is insoluble in water and has no smell. Its specific gravity is 3.44 against a standard of 1.0 for the specific gravity of water. Reaction-bonded silicon nitride is less dense than the sintered or hot-pressed versions, but the compound is a low-density material anyway. The hot-pressed version has a density of 205.4 lbs. per cubic foot, for example.
Material Characteristics
- The different types of silicon nitride have various characteristics, although generally the material is gray or black and can come in powder form, or manufacturers can shape the compound into the required shape. Si3N4 is a tough material and resists high temperatures. It resists fractures well and does not wear down quickly, due to its slow oxidization breakdown and capability to withstand mechanical fatigue over time.
Differences
- The higher density of the sintered and hot-pressed versions make this type of Si3N4 more suitable than the reaction-bonded material for processes that are tough on the machine part. These denser types contain some other chemicals that are necessary to help the silicon and nitride ingredients form a compound of the required strength.
Dangers
- Silicon nitride is not explosive and is not flammable, which suits its purpose in machines that can reach high temperatures. If a person inhales the dust, it can cause irritation of the nose and throat, and the dust can also irritate the eyes. Swallowing the dust does not cause any known effect but it may be dangerous. Skin can also become irritated by the dust. The compound does not cause cancer and does not cause any chronic diseases through exposure.

Rocks & Minerals