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| Identifiers | |
|---|---|
3D model (JSmol) | |
| ChemSpider | |
| ECHA InfoCard | 100.031.771 |
| EC Number |
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| |
| |
| Properties | |
| TiB2 | |
| Molar mass | 69.489 g/mol |
| Appearance | non lustrous metallic grey |
| Density | 4.52 g/cm3 |
| Melting point | 3,230 °C (5,850 °F; 3,500 K) |
| Structure | |
| Hexagonal,hP1 | |
| P6/mmm | |
a = 302.36pm,c = 322.04 pm | |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Titanium diboride (TiB2) is an extremely hard ceramic which has excellent heat conductivity, oxidation stability andwear resistance. TiB2 is also a reasonable electrical conductor,[1] so it can be used as a cathode material inaluminium smelting and can be shaped byelectrical discharge machining.
TiB2 shares some properties withboron carbide andtitanium carbide, but many of its properties are superior to those two.[2]
With respect to chemical stability, TiB2 is more stable in contact with pure iron thantungsten carbide orsilicon nitride.[2]
TiB2 is resistant to oxidation in air at temperatures up to 1100 °C,[2] and tohydrochloric andhydrofluoric acids, but reacts withalkalis,nitric acid andsulfuric acid.
TiB2 does not occur naturally in the earth. Titanium diboride powder can be prepared by a variety of high-temperature methods, such as the direct reactions oftitanium or its oxides/hydrides, with elementalboron over 1000 °C,carbothermal reduction bythermite reaction oftitanium oxide andboron oxide, or hydrogen reduction of boron halides in the presence of the metal or its halides. Among various synthesis routes, electrochemical synthesis and solid state reactions have been developed to prepare finer titanium diboride in large quantity. An example of solid state reaction is the borothermic reduction, which can be illustrated by the following reactions:
(1) 2 TiO2 + B4C + 3C → 2 TiB2 + 4 CO
(2) TiO2 + 3NaBH4 → TiB2 + 2Na(g,l) + NaBO2 + 6H2(g)[3]
The first synthesis route (1), however, cannot produce nanosized powders. Nanocrystalline (5–100 nm) TiB2 was synthesized using the reaction (2) or the following techniques:
Many TiB2 applications are inhibited by economic factors, particularly the costs of densifying a high melting point material - the melting point is about 2970 °C, and, thanks to a layer of titanium dioxide that forms on the surface of the particles of a powder, it is very resistant tosintering. Admixture of about 10%silicon nitride facilitates the sintering,[9] though sintering without silicon nitride has been demonstrated as well.[1]
Thin films of TiB2 can be produced by several techniques. Theelectroplating of TiB2 layers possess two main advantages compared withphysical vapor deposition orchemical vapor deposition: the growing rate of the layer is 200 times higher (up to 5 μm/s) and the inconveniences of covering complex shaped products are dramatically reduced.
Current use of TiB2 appears to be limited to specialized applications in such areas as impact resistantarmor,cutting tools,crucibles, neutron absorbers and wear resistant coatings.[10]
TiB2 is extensively used for evaporation boats for vapour coating ofaluminium.[11] It is an attractive material for the aluminium industry as aninoculant to refine thegrain size whencastingaluminium alloys, because of its wettability by and low solubility in molten aluminium and good electrical conductivity.
Thin films of TiB2 can be used to provide wear andcorrosion resistance to a cheap and/or tough substrate.[12]
