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{{Short description|Class of chemical compounds}}
In chemistry a '''boride''' is a chemical compound between [[boron]] and a less [[electronegativity|electronegative]] element, for example [[silicon boride]] (SiB<sub>3</sub> and SiB<sub>6</sub>). The borides are a very large group of compounds that are generally high melting and are not ionic in nature.{{Citation needed|date=November 2014}} Some borides exhibit very useful physical properties. The term boride is also loosely applied to compounds such as B<sub>12</sub>As<sub>2</sub> (N.B. Arsenic has an electronegativity higher than boron) that is often referred to as [[boron arsenide|icosahedral boride]].
A '''boride''' is a compound between [[boron]] and a less [[electronegativity|electronegative]] element, for example [[silicon boride]] (SiB<sub>3</sub> and SiB<sub>6</sub>). The borides are a very large group of compounds that are generally high melting and are covalent more than ionic in nature. Some borides exhibit very useful physical properties. The term boride is also loosely applied to compounds such as B<sub>12</sub>As<sub>2</sub> (N.B. Arsenic has an electronegativity higher than boron) that is often referred to as [[boron arsenide|icosahedral boride]].


==Ranges of compounds==
==Ranges of compounds==
The borides can be classified loosely as boron rich or metal rich, for example the compound [[Yttrium borides|YB<sub>66</sub>]] at one extreme through to Nd<sub>2</sub>Fe<sub>14</sub>B at the other. The generally accepted definition is that if the ratio of boron atoms to metal atoms is 4:1 or more the compound is boron rich, if it is less, then it is metal rich.
The borides can be classified loosely as boron rich or metal rich, for example the compound [[Yttrium borides|YB<sub>66</sub>]] at one extreme through to Nd<sub>2</sub>Fe<sub>14</sub>B at the other. The generally accepted definition is that if the ratio of boron atoms to metal atoms is 4:1 or more, the compound is boron rich; if it is less, then it is metal rich.


===Boron rich borides (B:M 4:1 or more)===
===Boron rich borides (B:M 4:1 or more)===
The main group metals, [[lanthanide]]s and [[actinide]]s form a wide variety of boron-rich borides, with metal:boron ratios up to [[Yttrium borides|YB<sub>66</sub>]].
The main group metals, [[lanthanide]]s and [[actinide]]s form a wide variety of boron-rich borides, with metal:boron ratios up to [[Yttrium borides|YB<sub>66</sub>]].
⚫
The properties of this group vary from one compound to the next, and include examples of compounds that are semi conductors, superconductors, [[diamagnetism|diamagnetic]], [[paramagnetism|paramagnetic]], [[ferromagnetism|ferromagnetic]] or [[antiferromagnetism|anti-ferromagnetic]].<ref>{{cite journal|author=Lundstrom T |journal=Pure & Applied Chem|year=1985|volume=57|issue=10|page=1383|title=Structure, defects and properties of some refractory borides|type = free download pdf|doi=10.1351/pac198557101383}}</ref> They are mostly stable and refractory.


⚫
The properties of this group vary from one compound to the next, and include examples of compounds that are semi conductors, superconductors, [[diamagnetism|diamagnetic]], [[paramagnetism|paramagnetic]], [[ferromagnetism|ferromagnetic]] or [[antiferromagnetism|anti-ferromagnetic]].<ref>{{cite journal|author=Lundstrom T |journal=Pure Appl. Chem.|year=1985|volume=57|issue=10|page=1383|title=Structure, defects and properties of some refractory borides|type = free download pdf|doi=10.1351/pac198557101383|doi-access=free}}</ref> They are mostly stable and refractory.
⚫
Some metallic dodecaborides contain boron icosahedra, others (for example [[yttrium]], [[zirconium]] and [[uranium]]) have the boron atoms arranged in [[cuboctahedron|cuboctahedra]].<ref>{{cite journal |last=Matkovich |first=V.I.|author2=J Economy |author3=R F Giese Jr |author4=R Barrett |year= 1965 |title= The structure of metallic dodecaborides|journal= Acta Cryst.|volume=19 |pages=1056–1058 |url=http://journals.iucr.org/q/issues/1965/12/00/a04941/a04941.pdf |format = PDF|accessdate=2008-08-28 |doi=10.1107/S0365110X65004954 |issue=6}}</ref>


⚫
Some metallic dodecaborides contain boron [[Icosahedron|icosahedra]], others (for example [[yttrium]], [[zirconium]] and [[uranium]]) have the boron atoms arranged in [[cuboctahedron|cuboctahedra]].<ref>{{cite journal|author1=VI Matkovich |author2=J Economy |author3=R F Giese Jr |author4=R Barrett |year=1965 |title=The structure of metallic dodecaborides |journal= Acta Crystallographica|volume=19 |pages=1056–1058 |url=http://journals.iucr.org/q/issues/1965/12/00/a04941/a04941.pdf |accessdate=2008-08-28 |doi=10.1107/S0365110X65004954 |issue=6 |bibcode=1965AcCry..19.1056M |url-status=dead |archiveurl=https://web.archive.org/web/20141222104429/http://journals.iucr.org/q/issues/1965/12/00/a04941/a04941.pdf |archivedate=2014-12-22 }}</ref>
⚫
[[lanthanum hexaboride|LaB<sub>6</sub>]] is an inert [[refractory]] compound, used in [[hot cathode]]s because of its low [[work function]] which gives it a high rate of [[thermionic emission]] of electrons; YB<sub>66</sub> crystals, grown by an [[zone refining|indirect-heating floating zone]] method, are used as [[monochromator]]s for low-energy [[synchrotron]] X-rays.<ref>{{cite journal|last=Wong|first=Jo|author2=T Tanaka |author3=M Rowen |author4=F Schäfer |author5=B R Müller |author6=Z U Rek |journal=J Synchrotron Rad.|year=1999 |volume=6 |pages=1086–1095|doi=10.1107/S0909049599009000|title=YB66 – a new soft X-ray monochromator for synchrotron radiation. II. Characterization|issue=6}}</ref>

⚫
[[lanthanum hexaboride|LaB<sub>6</sub>]] is an inert [[refractory]] compound, used in [[hot cathode]]s because of its low [[work function]] which gives it a high rate of [[thermionic emission]] of electrons; YB<sub>66</sub> crystals, grown by an [[zone refining|indirect-heating floating zone]] method, are used as [[monochromator]]s for low-energy [[synchrotron]] X-rays.<ref>{{cite journal|last=Wong|first=Jo|author2=T Tanaka |author3=M Rowen |author4=F Schäfer |author5=B R Müller |author6=Z U Rek |journal= Journal of Synchrotron Radiation|year=1999 |volume=6 |pages=1086–1095|doi=10.1107/S0909049599009000|title=YB66 – a new soft X-ray monochromator for synchrotron radiation. II. Characterization|issue=6|doi-access=free|bibcode=1999JSynR...6.1086W }}</ref> VB<sub>2</sub> has shown some promise as potential material with higher energy capacity than lithium for batteries.<ref>{{Cite web |title=High Energy Density VB2/Air Batteries for Long Endurance UAVs {{!}} SBIR.gov |url=https://www.sbir.gov/node/414642 |access-date=2024-02-08 |website=www.sbir.gov}}</ref>


===Metal rich borides (B:M less than 4:1)===
===Metal rich borides (B:M less than 4:1)===
The transition metals tend to form metal rich borides. Metal-rich borides, as a group, are inert and have high melting temperature. Some are easily formed and this explains their use in making turbine blades, rocket nozzles, etc. Some examples include [[aluminium diboride|AlB<sub>2</sub>]] and [[titanium boride|TiB<sub>2</sub>]]. Recent investigations into this class of borides have revealed a wealth of interesting properties such as super conductivity at 39 K in [[magnesium diboride|MgB<sub>2</sub>]] and the ultra-incompressibility of [[osmium diboride|OsB<sub>2</sub>]] and [[rhenium diboride|ReB<sub>2</sub>]].
The transition metals tend to form metal rich borides. Metal-rich borides, as a group, are inert and have high melting temperature. Some are easily formed and this explains their use in making turbine blades, rocket nozzles, etc. Some examples include [[aluminium diboride|AlB<sub>2</sub>]] and [[titanium boride|TiB<sub>2</sub>]]. Recent investigations into this class of borides have revealed a wealth of interesting properties such as super conductivity at 39 K in [[magnesium diboride|MgB<sub>2</sub>]] and the ultra-incompressibility of [[osmium diboride|OsB<sub>2</sub>]] and [[rhenium diboride|ReB<sub>2</sub>]].<ref>{{Cite journal |last1=Chen |first1=Hui |last2=Zou |first2=Xiaoxin |date=2020 |title=Intermetallic borides: structures, synthesis and applications in electrocatalysis |url=http://xlink.rsc.org/?DOI=D0QI00146E |journal=Inorganic Chemistry Frontiers |language=en |volume=7 |issue=11 |pages=2248–2264 |doi=10.1039/D0QI00146E |s2cid=216259662 |issn=2052-1553|doi-access=free }}</ref>


===Boride structures===
===Boride structures===
The boron rich borides contain 3-dimensional frameworks of boron atoms that can include boron polyhedra.
The boron rich borides contain 3-dimensional frameworks of boron atoms that can include boron polyhedra.
The metal rich borides contain single boron atoms, B<sub>2</sub> units, boron chains or boron sheets/layers.
The metal rich borides contain single boron atoms, B<sub>2</sub> units, boron chains or boron sheets/layers.


Examples of the different types of borides are:
Examples of the different types of borides are:
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*3-dimensional boron frameworks that include boron polyhedra, example NaB<sub>15</sub> with boron icosahedra
*3-dimensional boron frameworks that include boron polyhedra, example NaB<sub>15</sub> with boron icosahedra


{| class="Selected Metal Borides and Properties"
{| class="wikitable"
|-
|-
! Formula !! [[Chemical Abstracts|CAS registry number]] !! density (g/cm<sup>3</sup>)<ref>{{CRC91}}</ref> !! melting point (°C)!! electrical resistivity (10<sup>−8</sup>Ω·m) !! Knoop hardness (0.1 kp load)
! Formula !! [[Chemical Abstracts|CAS registry number]] !! density (g/cm<sup>3</sup>)<ref>{{CRC91}}</ref> !! melting point (°C)!! electrical resistivity (10<sup>−8</sup>Ω·m) !! Knoop hardness (0.1 kp load)
Line 35: Line 36:
|ZrB<sub>2</sub> ||12045-64-6|| 6.17|| 3050|| 7–10||1830
|ZrB<sub>2</sub> ||12045-64-6|| 6.17|| 3050|| 7–10||1830
|-
|-
|[[Hafnium diboride|HfB<sub>2</sub>]] ||12007-23-7 ||11.2 ||3650|| 10–12 ||2160
|[[Hafnium diboride|HfB<sub>2</sub>]] ||12007-23-7 ||11.2 ||3250|| 10–12 ||2160
|-
|-
|VB<sub>2</sub> ||12007-37-3 ||5.10 ||2450|| 16–38|| 2110
|VB<sub>2</sub> ||12007-37-3 ||5.10 ||2450|| 16–38|| 2110
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|[[Uranium boride|UB<sub>2</sub>]] ||12007-36-2|| 12.7|| 2430||-||-
|[[Uranium boride|UB<sub>2</sub>]] ||12007-36-2|| 12.7|| 2430||-||-
|}
|}
[[File:Unit Cell of RuB2.png|thumb|Unit cell of RuB<sub>2</sub>]]


==See also==
==See also==
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*[[Iron tetraboride]]
*[[Iron tetraboride]]
*[[Yttrium borides]] - a representative class of metal borides
*[[Yttrium borides]] - a representative class of metal borides
*[[Magnesium diboride]] - a superconductor


==References==
==References==
{{reflist}}
{{Reflist}}


==Books==
==Books==
*{{Greenwood&Earnshaw}}
*{{Greenwood&Earnshaw}}
*{{Cotton&Wilkinson6th}}
*{{Cotton&Wilkinson6th}}

{{Borides}}
{{Monatomic anion compounds}}


{{Authority control}}
{{Authority control}}

[[Category:Borides]]
[[Category:Borides| ]]

Latest revision as of 18:54, 27 April 2024

A boride is a compound between boron and a less electronegative element, for example silicon boride (SiB3 and SiB6). The borides are a very large group of compounds that are generally high melting and are covalent more than ionic in nature. Some borides exhibit very useful physical properties. The term boride is also loosely applied to compounds such as B12As2 (N.B. Arsenic has an electronegativity higher than boron) that is often referred to as icosahedral boride.

Ranges of compounds

[edit]

The borides can be classified loosely as boron rich or metal rich, for example the compound YB66 at one extreme through to Nd2Fe14B at the other. The generally accepted definition is that if the ratio of boron atoms to metal atoms is 4:1 or more, the compound is boron rich; if it is less, then it is metal rich.

Boron rich borides (B:M 4:1 or more)

[edit]

The main group metals, lanthanides and actinides form a wide variety of boron-rich borides, with metal:boron ratios up to YB66.

The properties of this group vary from one compound to the next, and include examples of compounds that are semi conductors, superconductors, diamagnetic, paramagnetic, ferromagnetic or anti-ferromagnetic.[1] They are mostly stable and refractory.

Some metallic dodecaborides contain boron icosahedra, others (for example yttrium, zirconium and uranium) have the boron atoms arranged in cuboctahedra.[2]

LaB6 is an inert refractory compound, used in hot cathodes because of its low work function which gives it a high rate of thermionic emission of electrons; YB66 crystals, grown by an indirect-heating floating zone method, are used as monochromators for low-energy synchrotron X-rays.[3] VB2 has shown some promise as potential material with higher energy capacity than lithium for batteries.[4]

Metal rich borides (B:M less than 4:1)

[edit]

The transition metals tend to form metal rich borides. Metal-rich borides, as a group, are inert and have high melting temperature. Some are easily formed and this explains their use in making turbine blades, rocket nozzles, etc. Some examples include AlB2 and TiB2. Recent investigations into this class of borides have revealed a wealth of interesting properties such as super conductivity at 39 K in MgB2 and the ultra-incompressibility of OsB2 and ReB2.[5]

Boride structures

[edit]

The boron rich borides contain 3-dimensional frameworks of boron atoms that can include boron polyhedra. The metal rich borides contain single boron atoms, B2 units, boron chains or boron sheets/layers.

Examples of the different types of borides are:

  • isolated boron atoms, example Mn4B
  • B2 units, example V3B
  • chains of boron atoms, example FeB
  • sheets or layers of boron atoms CrB2
  • 3-dimensional boron frameworks that include boron polyhedra, example NaB15 with boron icosahedra
Formula CAS registry number density (g/cm3)[6] melting point (°C) electrical resistivity (10−8Ω·m) Knoop hardness (0.1 kp load)
TiB2 12045-63-5 4.38 3225 9–15 2600
ZrB2 12045-64-6 6.17 3050 7–10 1830
HfB2 12007-23-7 11.2 3250 10–12 2160
VB2 12007-37-3 5.10 2450 16–38 2110
NbB 12045-19-1 7.5 2270 - -
NbB2 12007-29-3 6.97 3050 12–65 2130
TaB 12007-07-7 14.2 2040 - -
TaB2 12007-35-1 11.2 3100 14–68 2500
CrB2 12007-16-8 5.20 2170 21–56 1100
Mo2B5 12007-97-5 7.48 2370 18–45 2180
W2B5 12007-98-6 14.8 2370 21–56 2500
Fe2B 12006-85-8 7.3 1389 - 1800
FeB 12006-84-7 7 1658 30 1900
CoB 12006-77-8 7.25 1460 26 2350
Co2B 12045-01-1 8.1 1280 - -
NiB 12007-00-0 7.13 1034 23 -
Ni2B 12007-01-1 7.90 1125 - -
LaB6 12008-21-8 6.15 2715 15 2010
UB4 12007-84-0 9.32 2530 30 1850
UB2 12007-36-2 12.7 2430 - -
Unit cell of RuB2

See also

[edit]

References

[edit]
  1. ^ Lundstrom T (1985). "Structure, defects and properties of some refractory borides". Pure Appl. Chem. (free download pdf). 57 (10): 1383. doi:10.1351/pac198557101383.
  2. ^ VI Matkovich; J Economy; R F Giese Jr; R Barrett (1965). "The structure of metallic dodecaborides" (PDF). Acta Crystallographica. 19 (6): 1056–1058. Bibcode:1965AcCry..19.1056M. doi:10.1107/S0365110X65004954. Archived from the original (PDF) on 2014-12-22. Retrieved 2008-08-28.
  3. ^ Wong, Jo; T Tanaka; M Rowen; F Schäfer; B R Müller; Z U Rek (1999). "YB66 – a new soft X-ray monochromator for synchrotron radiation. II. Characterization". Journal of Synchrotron Radiation. 6 (6): 1086–1095. Bibcode:1999JSynR...6.1086W. doi:10.1107/S0909049599009000.
  4. ^ "High Energy Density VB2/Air Batteries for Long Endurance UAVs | SBIR.gov". www.sbir.gov. Retrieved 2024-02-08.
  5. ^ Chen, Hui; Zou, Xiaoxin (2020). "Intermetallic borides: structures, synthesis and applications in electrocatalysis". Inorganic Chemistry Frontiers. 7 (11): 2248–2264. doi:10.1039/D0QI00146E. ISSN 2052-1553. S2CID 216259662.
  6. ^ Haynes, William M. (2010). Handbook of Chemistry and Physics (91 ed.). Boca Raton, Florida, USA: CRC Press. ISBN 978-1-43982077-3.

Books

[edit]
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