Editing Titanium diboride

{{chembox
| verifiedrevid = 402711744
| ImageFile = Magnesium-diboride-3D-balls.png
| ImageSize = 
| IUPACName = 
| OtherNames = 
|Section1={{Chembox Identifiers
| CASNo = 12045-63-5
| CASNo_Ref = {{cascite|correct|CAS}}
| ChemSpiderID = 21171261
| EINECS = 234-961-4
| PubChem = 11412340
| StdInChI=1S/B2.Ti/c1-2;
| StdInChIKey = TXVDUUNOLJOZCR-UHFFFAOYSA-N
| SMILES = [B].[Ti].[B]
}}
|Section2={{Chembox Properties
| Formula = TiB<sub>2</sub>
| MolarMass = 69.489 g/mol
| Appearance = non lustrous metallic grey
| Density = 4.52 g/cm<sup>3</sup>
| MeltingPtC = 3230
| BoilingPt = 
| Solubility = 
}}
|Section3={{Chembox Structure
| CrystalStruct = Hexagonal, [[Pearson symbol|hP1]] 
| SpaceGroup = P6/mmm
| Coordination = 
| LattConst_a = 302.36 [[picometer|pm]]
| LattConst_c = 322.04 pm
| MolShape = }}
|Section7={{Chembox Hazards
| MainHazards = 
| FlashPt = 
| AutoignitionPt = 
}}
}}
'''Titanium diboride''' (TiB<sub>2</sub>) is an extremely hard ceramic which has excellent heat conductivity, oxidation stability and [[wear resistance]]. TiB<sub>2</sub> is also a reasonable electrical conductor,<ref name="tib1">J. Schmidt et al. "Preparation of titanium diboride TiB2 by spark plasma sintering at slow heating rate" Sci. Technol. Adv. Mater. 8 (2007) 376 [https://dx.doi.org/10.1016/j.stam.2007.06.009 free download]</ref> so it can be used as a cathode material in [[aluminium smelting]] and can be shaped by [[electrical discharge machining]].

==Physical properties==
TiB<sub>2</sub> shares some properties with [[boron carbide]] and [[titanium carbide]], but many of its properties are superior to those of B<sub>4</sub>C & TiC:<ref name="basu">{{Cite journal|last1=Basu|first1=B.|last2=Raju|first2=G. B.|last3=Suri|first3=A. K.|date=2006-12-01|title=Processing and properties of monolithic TiB<sub>2</sub> based materials|journal=International Materials Reviews|volume=51|issue=6|pages=352–374|doi=10.1179/174328006X102529|bibcode=2006IMRv...51..352B |s2cid=137562554|issn=0950-6608}}</ref>

===Exceptional hardness at extreme temperature===
*2nd hardest material at 3000°C ([[diamond]])
*3rd hardest material at 2800°C ([[Cubic boron nitride|cBN]])
*4th hardest material at 2100°C ([[Boron carbide|B<sub>4</sub>C]])
*5th hardest material at 1000°C ([[Boron suboxide|B<sub>6</sub>O]])

===Advantages over other borides===
*Highest boride [[elastic modulus]]
*Highest boride [[fracture toughness]]
*Highest boride [[compressive strength]]
*3rd highest boride [[melting point]] (3230 °C) ([[Hafnium diboride|HfB<sub>2</sub>]])

===Other advantages===
*High [[thermal conductivity]] (60-120 W/(m K)),
*High [[electrical conductivity]] (~10<sup>5</sup> S/cm)

===Drawbacks===
* Difficult to [[Molding_(process)|mold]] due to high melting temperature
* Difficult to sinter due to the high [[covalent bonding]]
* Limited to pressing to small Monolithic pieces using of [[spark plasma sintering]]

==Chemical properties==
With respect to chemical stability, TiB<sub>2</sub> is more stable in contact with pure iron than [[tungsten carbide]] or [[silicon nitride]].<ref name="basu"/>

TiB<sub>2</sub> is resistant to oxidation in air at temperatures up to 1100&nbsp;°C,<ref name="basu"/> and to [[hydrochloric acid|hydrochloric]] and [[hydrofluoric acid|hydrofluoric]] acids, but reacts with [[alkali]]s, [[nitric acid]] and [[sulfuric acid]].

==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.

==Potential applications==
Current use of TiB<sub>2</sub> appears to be limited to specialized applications in such areas as impact resistant [[armor]], [[cutting tool]]s, [[crucible]]s, neutron absorbers and wear resistant coatings.<ref>{{cite web |url=https://www.preciseceramic.com/blog/top-10-ceramic-materials-with-the-highest-thermal-conductivity.html |title=Top 10 Ceramic Materials with the Highest Thermal Conductivity |date=Sep 24, 2024 |last=Ross |first=Lisa |website=Advanced Ceramic Materials |access-date=Nov 8, 2024}}</ref>

TiB<sub>2</sub> is extensively used for evaporation boats for vapour coating of [[aluminium]].<ref>{{cite journal |last1=McKinon |first1=Ruth |last2=Grasso |first2=Salvatore |year=2017 |title=Flash spark plasma sintering of cold-Pressed TiB2-hBN |journal=Journal of the European Ceramic Society |volume=37 |issue=8 |pages=2787-2794 |doi=10.1016/j.jeurceramsoc.2017.01.029}}</ref> It is an attractive material for the aluminium industry as an [[Grain refinement|inoculant]] to refine the [[crystallite|grain size]] when [[Casting (metalworking)|casting]] [[aluminium alloy]]s, because of its wettability by and low solubility in molten aluminium and good electrical conductivity.

[[Thin film]]s of TiB<sub>2</sub> can be used to provide wear and [[corrosion]] resistance to a cheap and/or tough substrate.<ref>{{cite journal |last1=Wu |first1=Zhengtao |last2=Ye |first2=Rongli |year=2022 |title=Reprint of: Improving oxidation and wear resistance of TiB2 films by nano-multilayering with Cr |journal=Surface and Coatings Technology |volume=442 |page=128602 |doi=10.1016/j.surfcoat.2022.128602}}</ref>

==References==
{{Reflist|2}}

==Compare==
*[[Magnesium diboride]]

==See also==
{{div col|colwidth=22em}}
*[[Boride]]
*[[Diboride]]
*[[Titanium carbide]]
*[[Cermet]]
*[[Sintering]]
*[[Hot pressing]]
{{div col end}}

{{Titanium compounds}}
{{Borides}}

[[Category:Borides]]
[[Category:Titanium(IV) compounds]]
[[Category:Superhard materials]]