Editing Titanium diboride (section)

==Production==

TiB<sub>2</sub> 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&nbsp;°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 TiO<sub>2</sub> + B<sub>4</sub>C + 3C → 2 TiB<sub>2</sub> + 4 CO

(2) TiO<sub>2</sub> + 3NaBH<sub>4</sub> → TiB<sub>2</sub> + 2Na<sub>(g,l)</sub> + NaBO<sub>2</sub> + 6H<sub>2(g)</sub><ref>{{cite journal|last1=Zoli|first1=Luca|last2=Galizia|first2=Pietro|last3=Silvestroni|first3=Laura|last4=Sciti|first4=Diletta|title=Synthesis of group IV and V metal diboride nanocrystals via borothermal reduction with sodium borohydride|journal=Journal of the American Ceramic Society|volume=101|issue=6|pages=2627–2637|date=23 January 2018|doi=10.1111/jace.15401|url=https://zenodo.org/record/1292491|doi-access=free}}</ref>

The first synthesis route (1), however, cannot produce nanosized powders. Nanocrystalline (5–100&nbsp;nm) TiB<sub>2</sub> was synthesized using the reaction (2) or the following techniques: 
* Solution phase reaction of NaBH<sub>4</sub> and TiCl<sub>4</sub>, followed by annealing the amorphous precursor obtained at 900–1100&nbsp;°C.<ref>S. E. Bates et al. "Synthesis of titanium boride (TiB)2 nanocrystallites by solution-phase processing" [https://dx.doi.org/10.1557/JMR.1995.2599 J. Mater. Res. 10 (1995) 2599]</ref>
*Mechanical alloying of a mixture of elemental Ti and B powders.<ref>A. Y. Hwang and J. K. Lee "Preparation of TiB2 powders by mechanical alloying " [https://dx.doi.org/10.1016/S0167-577X(01)00526-2 Mater. Lett. 54 (2002) 1]</ref>
*[[Self-propagating high-temperature synthesis]] process involving addition of varying amounts of NaCl.<ref>A. K. Khanra et al. "Effect of NaCl on the synthesis of TiB2 powder by a self-propagating high-temperature synthesis technique" [https://dx.doi.org/10.1016/j.matlet.2003.06.003 Mater. Lett. 58 (2004) 733]</ref>
*Milling assisted self-propagating high-temperature synthesis (MA-SHS).<ref>{{Cite journal|last=Amin Nozari|date=2012|title=Synthesis and characterization of nano-structured TiB2 processed by milling assisted SHS route|journal=Materials Characterization|volume=73|pages=96–103|doi=10.1016/j.matchar.2012.08.003|display-authors=etal}}</ref>
*Solvothermal reaction in benzene of metallic sodium with amorphous boron powder and TiCl<sub>4</sub> at 400&nbsp;°C:<ref>Y. Gu et al. "A mild solvothermal route to nanocrystalline titanium diboride" [https://dx.doi.org/10.1016/S0925-8388(02)01173-8 J. Alloy. Compd. 352 (2003) 325]</ref>
::TiCl<sub>4</sub> + 2 B + 4 Na → TiB<sub>2</sub> + 4 NaCl

Many TiB<sub>2</sub> applications are inhibited by economic factors, particularly the costs of densifying a high melting point material - the melting point is about 2970&nbsp;°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,<ref>{{Cite web |url=http://www.patentgenius.com/patent/6420294.html |title=Titanium diboride sintered body with silicon nitride as a sintering aid and a method for manufacture thereof |access-date=2008-07-02 |archive-date=2016-03-03 |archive-url=https://web.archive.org/web/20160303183326/http://www.patentgenius.com/patent/6420294.html |url-status=dead }}</ref> though sintering without silicon nitride has been demonstrated as well.<ref name="tib1"/>

Thin films of TiB<sub>2</sub>  can be produced by several techniques. The [[electroplating]] of TiB<sub>2</sub> 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&nbsp;μm/s) and the inconveniences of covering complex shaped products are dramatically reduced.