Titanium nitride
From Wikipedia, the free encyclopedia
| Titanium nitride | |
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| IUPAC name |
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| Identifiers | |
| CAS number | [] |
| Properties | |
| Molecular formula | TiN |
| Molar mass | 61.874 g/mol |
| Appearance | Coating of golden color |
| Odor | Odorless |
| Density | 5.40 g/cm3 |
| Melting point |
2930 °C |
| Solubility in water | None |
| Structure | |
| Crystal structure | Cubic, cF8 |
| Space group | Fm3m, No. 225 |
| Coordination geometry |
Octahedral |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox references |
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Titanium nitride (TiN) (sometimes known as “Tinite” or “TiNite” or “TiNi”) is an extremely hard ceramic material, often used as a coating on titanium alloys, steel, carbide, and aluminium components to improve the substrate's surface properties.
Applied as a thin coating, TiN is used to harden and protect cutting and sliding surfaces, for decorative purposes, and as a non-toxic exterior for medical implants.
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[edit] Characteristics
Summary of characteristics[1][2]
- Vickers hardness 18-21 GPa
- Modulus of elasticity 251 GPa
- Thermal conductivity 19.2 W/(m·°C)
- Thermal expansion coefficient 9.35 µm/°C
- Electrical resistivity 20 µOhm·cm
- Superconducting transition temperature 5.6 K
- Magnetic susceptibility +38x10-6 emu/mol
TiN will oxidize at 800 °C at normal atmosphere. It is chemically stable at room temperature and is attacked by hot concentrated acids.[1]
TiN has excellent infrared (IR) reflectivity properties, reflecting in a spectrum similar to elemental gold (Au). Depending on the substrate material and surface finish, TiN will have a coefficient of friction ranging from 0.4 to 0.9 versus itself (non-lubricated). Typical formation has a crystal structure of NaCl-type with a roughly 1:1 stoichiometry; however TiNx compounds with x ranging from 0.6 to 1.2 are thermodynamically stable.[3]
[edit] Uses
The most common 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 hardware. 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[4] and medical implants, as well as aerospace and military applications.
Such coatings have also been used in implanted prostheses (especially hip replacement implants). Such films are usually applied by either reactive growth (for example, annealing a piece of titanium in nitrogen) or physical vapor deposition (PVD), with a depth of about 3 micrometers. Its high Young's modulus (600 gigapascals)[5] relative to titanium alloys (100 GPa) means that thick coatings tend to flake away, making them much less durable than thin ones.
As a coating it is also used to protect the sliding surfaces of suspension forks of bicycles and motorcycles as well as the shock shafts of radio controlled cars.
Though less visible, thin films of TiN are also used in the semiconductor industry. In copper-based chips, such films find use as a conductive barrier between a silicon device and the metal contacts used to operate it. While the film blocks diffusion of metal into the silicon, it is conductive enough (30–70 μΩ·cm) to allow a good electrical connection. In this context, 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 material for improved transistor performance. 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 same or better threshold voltage.[6]
Led by Argonne senior scientist Valerii Vinokur and Russian scientist Tatyana Baturina, an international team of scientists from Argonne, Germany, Russia and Belgium fashioned a thin film of titanium nitride which they then chilled to near absolute zero. This converts the material to a superinsulator, with resistance suddenly increased by a factor of 100,000[7]
[edit] Fabrication
The most common methods of TiN thin film creation are physical vapor deposition (PVD, usually sputter deposition, cathodic arc deposition or electron beam heating) and chemical vapor deposition (CVD). In both methods, pure titanium is sublimated and reacted with nitrogen in a high-energy, vacuum environment. PVD is preferred for steel parts because the deposition temperatures lie beyond the austenitizing temperature of steel. PVD applied TiN is also for a variety of relatively higher melting point materials such as stainless steels, titanium and titanium alloys.[8]
Bulk ceramic objects can be fabricated by packing powdered metallic titanium into the desired shape, compressing it to the proper density, then igniting it in an atmosphere of pure nitrogen. The heat released by the chemical reaction between the metal and gas is sufficient to sinter the nitride reaction product into a hard, finished item. See powder metallurgy. Titanium nitride coatings can also be deposited by thermal spraying whereas TiN powders are produced by nitridation of titanium with nitrogen or ammonia at 1200 °C.[1]
[edit] Other commercial variants
There are several commercially-used variants of TiN that have been developed in the past decade, such titanium carbon nitride (TiCN) and titanium aluminium nitride (TiAlN), which may be used individually or in alternating layers with TiN. These coatings offer similar or superior enhancements in corrosion resistance and hardness, and additional colors ranging from light gray to nearly black, to a dark iridescent bluish-purple depending on the exact process of application. These coatings are becoming common on sporting goods, particularly knives and handguns, where they are used for both cosmetic and functional reasons.[9]
[edit] As a constituent in steel making
Titanium nitride is also produced intentionally within some steels by judicious addition of titanium to the alloy. TiN forms at very high temperatures because of its very low enthalpy of formation, and even nucleates directly from the melt in secondary steelmaking. It forms discrete, micrometre-sized cubic particles at grain boundaries and triple points, and prevents grain growth by Ostwald ripening up to very high homologous temperatures. Titanium nitride has the lowest solubility product of any metal nitride or carbide in austenite, a useful attribute in microalloyed steel formulas.
[edit] References
- ^ a b c Hugh O. Pierson (1996). Handbook of refractory carbides and nitrides: properties, characteristics, processing, and applications. William Andrew. p. 193. ISBN 0815513925. http://books.google.co.jp/books?id=pbt-RWodmVAC&pg=PA193.
- ^ Stone, D. S.; K. B. Yoder; W. D. Sproul (July 1991). "Hardness and elastic modulus of TiN based on continuous indentation technique and new correlation". Journal of Vacuum Science and Technology A 9 (4): 2543-2547. doi:.
- ^ Toth, L.E. (1971). Transition Metal Carbides and Nitrides. New York: Academic Press.
- ^ "Products". IonFusion Surgical. http://www.ionfusion.com/products.htm. Retrieved on 2009-06-25.
- ^ "Titanium Nitride (TiN) Coating". MatWeb. http://www.matweb.com/search/datasheet.aspx?MatGUID=ffbf753c500949db95e502e043f9a404. Retrieved on 2009-06-25.
- ^ Dziura, Thaddeus G.; Benjamin Bunday; Casey Smith; Muhammad M. Hussain; Rusty Harris; Xiafang Zhang; Jimmy M. Price (2008). "Measurement of high-k and metal film thickness on FinFET sidewalls using scatterometry". Proceedings of SPIE (International Society for Optical Engineering) 6922 (2): 69220V. doi:.
- ^ "Newly discovered 'superinsulators' promise to transform materials research, electronics design". PhysOrg.com. 2008-04-07. http://www.physorg.com/news126797387.html.
- ^ "Specialties". Molecular Metallurgy, Inc. http://www.mmicoating.com/technology.html. Retrieved on 2009-06-25.
- ^ "Product Guide". Molecular Metallurgy, Inc. http://www.mmicoating.com/product.html. Retrieved on 2009-06-25.
[edit] External links
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