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Chromium(III) boride
Names
	IUPAC name boranylidynechromium
	Other names Chromium monoboride
Identifiers
CAS Number	12006-79-0;
3D model (JSmol)	Interactive image;
ChemSpider	74710;
ECHA InfoCard	100.031.339
EC Number	234-487-8;
PubChem CID	82788;
	InChI InChI=1S/Cr.B Key: NUEWEVRJMWXXFB-UHFFFAOYSA-N;
	SMILES B#[Cr];
Properties
Chemical formula	CrB
Molar mass	62.81 g/mol
Appearance	silver, ceramic material
Density	6.17 g/cm3
Melting point	1,950 to 2,050 °C (3,540 to 3,720 °F; 2,220 to 2,320 K)
Solubility in water	insoluble
Structure
Crystal structure	orthorhombic (space group Cmcm)
Hazards
NFPA 704 (fire diamond)	0 0 0
	NIOSH (US health exposure limits):
PEL (Permissible)	TWA 1 mg/m3
REL (Recommended)	TWA 0.5 mg/m3
IDLH (Immediate danger)	250 mg/m3
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Chromium(III) boride, also known as chromium monoboride (CrB), is an inorganic compound with the chemical formula CrB.^[2] It is one of the six stable binary borides of chromium, which also include Cr₂B, Cr₅B₃, Cr₃B₄, CrB₂, and CrB₄.^[3] Like many other transition metal borides, it is extremely hard (21-23 GPa),^[4]^[5] has high strength (690 MPa bending strength),^[5] conducts heat and electricity as well as many metallic alloys,^[4]^[6]^[7] and has a high melting point (~2100 °C).^[8]^[3] Unlike pure chromium, CrB is known to be a paramagnetic, with a magnetic susceptibility that is only weakly dependent on temperature.^[9]^[10] Due to these properties, among others, CrB has been considered as a candidate material for wear resistant coatings and high-temperature diffusion barriers.^{[citation needed]}

It can be synthesized as powders by many methods including direct reaction of the constituent elemental powders,^[11] self-propagating high-temperature synthesis (SHS),^[5] borothermic reduction,^[12]^[13] and molten salt growth.^[14] Slow-cooling of molten aluminum solutions from high-temperatures has been used to grow large single crystals, with a maximum size of 0.6 mm x 0.6 mm x 8.3 mm.^[4]

CrB has an orthorhombic crystal structure (space group Cmcm) that was first discovered in 1951,^[15] and subsequently confirmed by later work using single crystals.^[16] The crystal structure can be visualized as slabs face-sharing BCr₆ trigonal prisms, in the ac-plane, that are stacked parallel to the <010> crystallographic direction. Similar to Cr₃B₄ and Cr₂B₃, the B atoms in the structure form covalent bonds with each other and are characterized by unidirectional B-B- chains parallel to the <001> crystallographic direction. The transition metal monoborides VB, NbB, TaB, and NiB have the same crystal structure. ^{[citation needed]}

References

^ ^a ^b ^c NIOSH Pocket Guide to Chemical Hazards. "#0141". National Institute for Occupational Safety and Health (NIOSH).
^ Peshev, P.; Bliznakov, G.; Leyarovska, L. (1967). "On the preparation of some chromium, molybdenum and tungsten borides". Journal of the Less Common Metals. 13 (2): 241. doi:10.1016/0022-5088(67)90188-9.
^ ^a ^b Liao, P. K.; Spear, K. E. (June 1986). "The B−Cr (Boron-Chromium) system". Bulletin of Alloy Phase Diagrams. 7 (3): 232–237. doi:10.1007/BF02868996. ISSN 0197-0216.
^ ^a ^b ^c Okada, Shigeru; Kudou, Kunio; Iizumi, Kiyokata; Kudaka, Katsuya; Higashi, Iwami; Lundström, Torsten (September 1996). "Single-crystal growth and properties of CrB, Cr3B4, Cr2B3 and CrB2 from high-temperature aluminum solutions". Journal of Crystal Growth. 166 (1–4): 429–435. Bibcode:1996JCrGr.166..429O. doi:10.1016/0022-0248(95)00890-X.
^ ^a ^b ^c Hiroki, Yuji; Yoshinaka, Masaru; Hirota, Ken; Yamaguchi, Osamu (2003). "Hot Isostatic Pressing of CrB Prepared by Self-propagating High-temperature Synthesis". Journal of the Japan Society of Powder and Powder Metallurgy. 50 (5): 367–371. doi:10.2497/jjspm.50.367. ISSN 0532-8799.
^ L'vov, S. N.; Nemchenko, V. F.; Kislyi, P. S.; Verkhoglyadova, T. S.; Kosolapova, T. Ya. (1964). "The electrical properties of chromium borides, carbides, and nitrides". Soviet Powder Metallurgy and Metal Ceramics. 1 (4): 243–247. doi:10.1007/BF00774426. ISSN 0038-5735. S2CID 137007220.
^ Ohishi, Yuji; Sugizaki, Mitsuyuki; Sun, Yifan; Muta, Hiroaki; Kurosaki, Ken (2019-03-22). "Thermophysical and mechanical properties of CrB and FeB". Journal of Nuclear Science and Technology. 56 (9–10): 859–865. Bibcode:2019JNST...56..859O. doi:10.1080/00223131.2019.1593893. ISSN 0022-3131. S2CID 109795656.
^ Kislyi, P. S.; L'vov, S. N.; Nemchenko, V. F.; Samsonov, G. V. (1964). "Physical properties of the boride phases of chromium". Soviet Powder Metallurgy and Metal Ceramics. 1 (6): 441–443. doi:10.1007/BF00773921. ISSN 0038-5735. S2CID 137532121.
^ Guy, C.N. (1976). "The electronic properties of chromium borides". Journal of Physics and Chemistry of Solids. 37 (11): 1005–1009. Bibcode:1976JPCS...37.1005G. doi:10.1016/0022-3697(76)90123-2.
^ Kota, Sankalp; Wang, Wenzhen; Lu, Jun; Natu, Varun; Opagiste, Christine; Ying, Guobing; Hultman, Lars; May, Steven J.; Barsoum, Michel W. (October 2018). "Magnetic properties of Cr2AlB2, Cr3AlB4, and CrB powders". Journal of Alloys and Compounds. 767: 474–482. doi:10.1016/j.jallcom.2018.07.031. S2CID 103421636.
^ Lundquist, N.; Myers, H. P.; Westin, R. (July 1962). "The paramagnetic properties of the monoborides of V, Cr, Mn, Fe, Co and Ni". Philosophical Magazine. 7 (79): 1187–1195. Bibcode:1962PMag....7.1187L. doi:10.1080/14786436208209119. ISSN 0031-8086.
^ Okada, Shigeru; Iizumi, Kiyokata; Ogino, Tomoyuki; Kudaka, Katsuya; Kudou, Kunio (1996). "Preparation of CrB Single Crystals by the Reaction between Chromium Oxide and Amorphous Boron Powders". Nippon Kagaku Kaishi. 1996 (3): 260–263. doi:10.1246/nikkashi.1996.260. ISSN 2185-0925.
^ Iizumi, Kiyokata; Kudaka, Katsuya; Okada, Shigeru (1998). "Synthesis of Chromium Borides by Solid-State Reaction between Chromium Oxide (III) and Amorphous Boron Powders". Journal of the Ceramic Society of Japan. 106 (1237): 931–934. doi:10.2109/jcersj.106.931. ISSN 1882-1022.
^ Cao, Weixiao; Wei, Ya'nan; Meng, Xin; Ji, Yuexia; Ran, Songlin (2017-04-13). "A general method towards transition metal monoboride nanopowders". International Journal of Materials Research. 108 (4): 335–338. Bibcode:2017IJMR..108..335C. doi:10.3139/146.111484. ISSN 1862-5282. S2CID 136085434.
^ Frueh, A. J. (1951-01-01). "Confirmation of the structure of chromium boride, CrB". Acta Crystallographica. 4 (1): 66–67. Bibcode:1951AcCry...4...66F. doi:10.1107/S0365110X51000118. ISSN 0365-110X.
^ Okada, Shigeru; Atoda, Tetsuzo; Higashi, Iwami (May 1987). "Structural investigation of Cr2B3, Cr3B4, and CrB by single-crystal diffractometry". Journal of Solid State Chemistry. 68 (1): 61–67. Bibcode:1987JSSCh..68...61O. doi:10.1016/0022-4596(87)90285-4.