Properties and Applications
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Titanium nitride is a compound of titanium (Ti) and nitrogen (N). Something special of Titanium nitride is that the content of nitrogen may vary, what is expressed by the chemical formula TiNx (x can vary between 0,4 and 1). If TiN is produced in a big scale without special boundary conditions to ensure high purity, it is called technical TiN which usually contains a small amount of oxygen that can only be completely removed at high temperatures. At room temperature TiN is solid and has a density of 5,2 g/cm3, that is about double the density of glass but lower than most metals. The melting point is high, around 3000 °C, but at temperatures above 500 °C it starts to form titanium oxides in air. TiN is very hard, comparable to Corundum (a form of aluminium oxide), a material that is used in abrasives, e.g. sandpaper (Vickers hardness of TiN is 2400). The electrical conductivity compares to that of steel. All physical properties depend on the nitrogen content and, partly, on the microstructure (grain size) of the material. Titanium nitride is insoluble in water and stable against cold acids but can be attacked by hot bases.
Thin layers of titanium nitride with a thickness in the range of a few micrometers are used for wear protection of tools. Layers with a high nitrogen content, e.g. TiN1.0, give the coated parts a gold-like colour. Titanium nitride powders with a particle size from nano- to micrometers are used as additive in the production of wear-resistant sintered materials like hard metals, silicon nitride or cermets. Furthermore it is added to plastics, particularly to PET. TiN improves the thermal properties of the material and allows increasing the production output of PET bottles. According to the German Foods and Commodities Ordinance the addition of titanium nitride is limited to 20 mg TiN per kg PET . Pure TiN powers can be used to manufacture ceramic crucibles or evaporation boats in which metals are melted.
Nanotitanium nitride is self-igniting. The mixture of nanotitanium nitride with air (dust) is flammable without the action of an ignition source.
Occurrence and Production
Titanium nitride is a technical product. There are no economically recoverable deposits in nature. Powders can be produced by reduction of titanium oxide (TiO2) in an atmosphere containing nitrogen. Also titanium hydride, titanium sponge or waste may react with nitrogen to give TiN. Nanoscaled titanium nitride powders can be generated by means of a reaction of titanium tetrachloride (TiCl4) with nitrogen or ammonia in a hydrogen atmosphere.
Thin titanium nitride layers with a thickness of several micrometers are manufactured by means of physical vapour deposition (PVD) or chemical vapour deposition (CVD). In physical deposition methods a titanium target is heated in a nitrogen atmosphere in a crucible or locally by plasma or an electron beam. Titanium vaporises, reacts in the gas phase with Nitrogen to TiN and is deposited on the substrate. In chemical methods mainly titanium tetrachloride is used as titanium source. The growth rate may amount up to several microns per hour.
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