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 of
titanium or its oxides/hydrides, with elemental
boron over 1000 °C,
carbothermal reduction by
thermite reaction of
titanium oxide and
boron 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) 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: • Solution phase reaction of NaBH4 and TiCl4, followed by annealing the amorphous precursor obtained at 900–1100 °C. • Mechanical alloying of a mixture of elemental Ti and B powders. •
Self-propagating high-temperature synthesis process involving addition of varying amounts of NaCl. • Milling assisted self-propagating high-temperature synthesis (MA-SHS). • Solvothermal reaction in benzene of metallic sodium with amorphous boron powder and TiCl4 at 400 °C: ::TiCl4 + 2 B + 4 Na → TiB2 + 4 NaCl 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 to
sintering. Admixture of about 10%
silicon nitride facilitates the sintering, though sintering without silicon nitride has been demonstrated as well. Thin films of TiB2 can be produced by several techniques. The
electroplating of TiB2 layers possess two main advantages compared with
physical vapor deposition or
chemical 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. ==Potential applications==