A synthetic ceramic material

Titanium nitride, abbreviated as TiN, is an extremely hard, synthetic ceramic material with hardness close to that of diamond. TiN is chemically stable at room temperature, but can be slowly attacked by concentrated acid solutions with rising temperatures. It will oxidize at 800 °C in a normal atmosphere. It has the reflection characteristics of infrared ray (IR), and the reflection spectrum is similar to that of gold (Au), so it has a pale yellow color. Depending on the substrate material and surface finish, TiN will have a coefficient of friction ranging from 0.4 to 0.9 against another TiN surface (non-lubricated). The typical TiN formation has a crystal structure of NaCl-type with a roughly 1:1 stoichiometry, and TiNx compounds with x ranging from 0.6 to 1.2, are however, thermodynamically stable. A thin film of TiN was chilled to near absolute zero, converting it into the first known superinsulator, with resistance suddenly increasing by a factor of 100,000.

Applications

• A well-known use for TiN coating is for edge retention and corrosion resistance on machine tooling, such as drill bits and milling cutters, often improving their lifetime by a factor of three or more.
• Because of TiN's metallic gold color, it is used to coat costume jewelry and automotive trim for decorative purposes. TiN is also widely used as a top-layer coating, usually with nickel (Ni) or chromium (Cr) plated substrates, on consumer plumbing fixtures and door & window hardware.
• As a coating it is also used in aerospace and military applications and to protect the sliding surfaces of suspension forks of bicycles and motorcycles as well as the shock shafts of radio controlled cars.
• TiN is non-toxic, meets FDA guidelines and has seen use in medical devices such as scalpel blades and orthopedic bone saw blades where sharpness and edge retention are important. TiN coatings have also been used in implanted prostheses (especially hip replacement implants) and other medical implants.
• Thin films of TiN are also used in microelectronics, where they serve as a conductive connection between the active device and the metal contacts used to operate the circuit, while acting as a diffusion barrier to block the diffusionof the metal into the silicon.It has a electric conductivity of 30-70μΩ•cm which ensures a good conductive connective.
• TiN is classified as a "barrier metal", even though it is clearly a ceramic from the perspective of chemistry or mechanical behavior. Recent chip design in the 45 nm technology and beyond also makes use of TiN as a "metal" for improved transistor performance. In the field of battery, in combination with gate dielectrics(e.g. HfSiO) that have a higher permittivity compared to standard SiO2 the gate length can be scaled down with low leakage, higher drive current and the same or better threshold voltage
• Due to their high biostability, TiN layers may also be used as electrodes in bioelectronic applications like in intelligent implants or in-vivo biosensors that have to withstand the severe corrosion caused by body fluids. TiN electrodes have already been applied in the subretinal prosthesis project as well as in biomedical microelectromechanical systems.

Reference

H. J. M. Bowen, Environmental Chemistry of the Elements,Academic Press, London, 1979.
U.S. Environmental Protection Agency, Health Assessment Document for Chromium, Final Report No. EPA600/8-83-014F, USEPA, Research Triangle Park, NC, 1984.
E. Lahmann et al., Heavy Metals: Identification of Air Quality and Environmental Problems in the European Community, Report No. EUR 10678 EN/I and EUR 10678 EN/II), Vols 1 and 2, Commission of the Europeans Communities, Luxembourg, 1986.