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Titanium nitride (TiN) is an extremely hard material that is used as coating material for various tools and implants (TiN coating). It is also used in plastics such as PET flasks to improve the physical properties of these flasks and to improve the efficiency of PET manufacturing processes.
How can I come into contact with this material?
It is generally assumed that no titanium nitride nanoparticles are being released from the various applications since the nanomaterial is always used in a bound form within the product, e.g. in coatings or plastic products.
Is there any risk from this material to humans and the environment?
So far the potential negative effects of titanium nitride nanoparticles have been scarcely investigated. But the expert opinion today is that the use of titanium nitride in very thin layers (10 – 100 nm) on joint implants does not shown any harmful effect to human cells and thus is well-tolerated by the recipient of such prosthetic implants. However, whether titanium nitride nanoparticles could pose a danger to the environment has not been studied sufficiently to provide complete understanding here.
Conclusion
In everyday life, humans and the environment are exposed to very low levels of titanium nitride nanoparticles. Titanium nitride is considered to be non-toxic and therefore used as coating material for prosthetic implants
By the way…
- Titanium nitride is a synthetic product that does not occur naturally.
- No negative effects have been found upon dermal contact with titanium nitride particles.
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.
Further information
- Kieffer, R & Benesovsky, F (1963). Hartstoffe, Springer-Verlag, Wien.
- Schedler, W (1988). Hartmetall für den Praktiker, VDI-Verlag GmbH, Düsseldorf.
- Richter, V & Mueller, K (2007). In Schatt,Wieters, Kieback: Pulvermetallurgie,Technologien und Werkstoffe, Springer Verlag, 2. erweiterte Auflage. ISBN 978-3-540-23652-8.
- Bedarfsgegenständeverordnung (BedGgstV) (2011), gesetze-im-internet.de (last access date: Jul 2011).
Studies have shown different degrees of cytotoxic effects of titanium nitride particles.
Studies on Living Organisms - in vivo
Both a skin irritation test on rabbits and an acute systemic toxicity test on mice resulted in no effects caused by titanium nitride (TiN) . The titanium nitride solutions tested here are used for the coating of implants.
Studies Outside of Organisms - in vitro
As part of the BMBF funded project INOS, titanium nitride (TiN) nanoparticles were examined in the human cell lines A549 (lung), HaCaT (skin), and CaCo-2 (intestine). These in vitro tests showed a cytotoxic effect of the titanium nitride particles, which turned out to vary depending on the cell line with applied concentrations up to 50 µg/ml over 3 hours and 3 days. The strongest toxic effect was observed with human skin cells (HaCaT). The LOEL was at 10 µg/ml. In addition, a study into the effect of TiN nanoparticles on brain cells showed that in one cell type the treatment resulted in an increase of cell death (apoptosis, necrosis).
However, very thin layers (10-100 nm) of titanium nitride, as used to coat joint implants, led to an improved adhesion of human fat cells to these layers. This study concludes that the biocompatibility of titanium nitride coatings is good . This result is supported by other studies in which cells cultivated in contact with TiN coated materials showed no effect . It is generally assumed that no TiN components detach from these coatings.
Further Information
- INOS project Scientific Reports (see Publications of the Project INOS)
Currently there are no studies known that deal with the environmental exposure of titanium nitride (TiN) nanoparticles.
There are currently no studies on the uptake via the lung, skin or gastrointestinal tract.
Currently, there are no in vivo studies available regarding uptake and risk for environmental organisms. As part of the BMBF funded project INOS, titanium nitride (TiN) nanoparticles were examined in a gill cell line and an intestinal cell line from rainbow trout using concentrations up to 50 µg/ml over 3 hours and 3 days. In comparison to other cell lines tested, these in vitro tests showed low cytotoxic effects of the TiN particles. On intestinal cells, TiN was slightly toxic, while in the gill cells no toxicity was observed.
Further information
- INOS Scientific Reports (see Publications of the Project INOS)
The uptake behavior of titanium nitride nanoparticles was investigated in various cell lines. Consistently, an uptake of the particles into the cells could be confirmed. It is assumed that particles accumulate in certain cell organelles, the lysosomes .
Further information
- INOS Scientific Reports (see Publications of the Project INOS)
Currently there are no studies known that deal with the environmental behaviour of titanium nitride (TiN) nanoparticles.