Chromium(III) boride

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Chromium(III) boride
Names
IUPAC name
boranylidynechromium
Other names
Chromium monoboride
Identifiers
3D model (
JSmol
)
ChemSpider
ECHA InfoCard
 100.031.339 Edit this at Wikidata
EC Number
  • 234-487-8
  • InChI=1S/Cr.B
    Key: NUEWEVRJMWXXFB-UHFFFAOYSA-N
  • B#[Cr]
Properties
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)
insoluble
Structure
orthorhombic (space group Cmcm)
Hazards
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 0: Exposure under fire conditions would offer no hazard beyond that of ordinary combustible material. E.g. sodium chlorideFlammability 0: Will not burn. E.g. waterInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
0
0
0
NIOSH (US health exposure limits):
PEL (Permissible)
 TWA 1 mg/m3[1]
REL (Recommended)
 TWA 0.5 mg/m3[1]
IDLH
(Immediate danger)
 250 mg/m3[1]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

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]

Crystal Structure of CrB in the space group Cmcm

References

  1. ^ a b c NIOSH Pocket Guide to Chemical Hazards. "#0141". National Institute for Occupational Safety and Health (NIOSH).
  2. doi:10.1016/0022-5088(67)90188-9
    .
  3. ^
    ISSN 0197-0216
    .
  4. ^
    doi:10.1016/0022-0248(95)00890-X
    .
  5. ^
    ISSN 0532-8799
    .
  6. S2CID 137007220
    .
  7. S2CID 109795656
    .
  8. S2CID 137532121
    .
  9. doi:10.1016/0022-3697(76)90123-2
    .
  10. S2CID 103421636
    .
  11. ISSN 0031-8086
    .
  12. ISSN 2185-0925
    .
  13. ISSN 1882-1022
    .
  14. S2CID 136085434
    .
  15. ISSN 0365-110X
    .
  16. doi:10.1016/0022-4596(87)90285-4
    .
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