Boron carbide: Difference between revisions

{{short description|Extremely hard ceramic compound}}

{{About|B₄C|other boron carbides|Boron carbides}}

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|Section1={{Chembox Identifiers

| UNII_Ref = {{fdacite|correct|FDA}}

| UNII = T5V24LJ508

|Section2={{Chembox Properties

| Density = 2.50 g/cm³, solid.<ref name=crc>{{cite book |ref=Haynes| editor= Haynes, William M. | date = 2016| title = [[CRC Handbook of Chemistry and Physics]] | edition = 97th | publisher = [[CRC Press]] | isbn = 9781498754293|page=4.52}}</ref>

| MeltingPtC = 2350

| MeltingPt_ref = <ref name=crc/>

| BoilingPt = >3500 °C

| BoilingPt_ref = <ref name=crc/>

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|Section3={{Chembox Structure

| CrystalStruct = [[Rhombohedral lattice system|Rhombohedral]]

|Section7={{Chembox Hazards

| ExternalSDS = [http://www.logitech.uk.com/MSDS/Files%5C0CON-024%20to%20028.pdf External MSDS]

|Section8={{Chembox Related

| OtherCompounds = [[Boron nitride]]

'''Boron carbide''' (chemical formula approximately B₄C) is an extremely hard [[boron]]–[[carbon]] [[ceramic]], a [[covalent compound|covalent]] material used in [[Tank armour|tank armor]], [[bulletproof vest]]s, engine [[sabotage]] powders,<ref>

{{cite book

| last= Gray

| first= Theodore

| title= The Elements: A Visual Exploration of Every Known Atom in the Universe

| publisher= Black Dog & Leventhal Publishers

| date= 2012-04-03

| isbn= 9781579128951

| url= https://books.google.com/books?id=IOY-8hxTJVAC&q=boron+carbide+sabotage+powder&pg=PT24

| access-date= 6 May 2014

}}

</ref>

as well as numerous industrial applications. With a [[Vickers hardness test|Vickers hardness]] of >30 GPa, it is one of the hardest known materials, behind cubic [[boron nitride]] and [[diamond]].<ref>

{{cite news

| title= Rutgers working on body armor

| url= http://www.app.com/article/20120811/NJNEWS/308110051/Rutgers-working-on-body-armor

| quote= ... boron carbide is the third-hardest material on earth.

| newspaper= [[Asbury Park Press]]

| location = Asbury Park, N.J.

| date= August 11, 2012

| access-date= 2012-08-12

}}

</ref>

== History==

Boron carbide was discovered in the 19th century as a [[by-product]] of reactions involving metal borides, but its [[chemical formula]] was unknown. It was not until the 1930s that the chemical composition was estimated as B₄C.<ref>Ridgway, Ramond R [http://v3.espacenet.com/publicationDetails/biblio?CC=CA&NR=339873&KC=&FT=E "Boron Carbide"], European Patent CA339873 (A), publication date: 1934-03-06</ref>

Controversy remained as to whether or not the material had this exact 4:1 [[stoichiometry]], as, in practice the material is always slightly carbon-deficient with regard to this formula, and [[X-ray crystallography]] shows that its structure is highly complex, with a mixture of C-B-C chains and B₁₂ [[icosahedron|icosahedra]].

These features argued against a very simple exact B₄C empirical formula.<ref name=stoi>

{{cite journal

| title= Structure and bonding in boron carbide: The invincibility of imperfections

| first1= Musiri M.

| last1= Balakrishnarajan

| first2= Pattath D.

| last2= Pancharatna

| first3= Roald

| last3= Hoffmann

| journal= New J. Chem.

| year= 2007

| issue= 4

| volume= 31

| page= 473

| doi= 10.1039/b618493f

| url= http://www.rsc.org/Publishing/Journals/nj/Hotarticles/B618493F_Hoffmann.asp

}}

</ref>

Because of the B₁₂ structural unit, the chemical formula of "ideal" boron carbide is often written not as B₄C, but as B₁₂C₃, and the carbon deficiency of boron carbide described in terms of a combination of the B₁₂C₃ and B₁₂CBC units.

== Crystal structure ==

[[File:Borfig11a.png|thumb|left|upright=0.66|Unit cell of B₄C. The green sphere and [[icosahedron|icosahedra]] consist of boron atoms, and black spheres are carbon atoms.<ref name=zhangyb28.5c4>{{cite journal|vauthors=Zhang FX, Xu FF, Mori T, Liu QL, Sato A, Tanaka T |year=2001|title=Crystal structure of new rare-earth boron-rich solids: REB28.5C4|journal=J. Alloys Compd.|volume=329|issue=1–2|pages=168–172|doi=10.1016/S0925-8388(01)01581-X}}</ref>]]

[[File:Borfig12a.png|thumb|left|upright=0.66|Fragment of the B₄C crystal structure.]]

Boron carbide has a complex crystal structure typical of [[Crystal structure of boron-rich metal borides|icosahedron-based borides]]. There, B₁₂ [[icosahedron|icosahedra]] form a [[rhombohedral lattice system|rhombohedral]] lattice unit (space group: ''R{{overline|3}}m'' (No. 166), lattice constants: ''a'' = 0.56&nbsp;nm and ''c'' = 1.212&nbsp;nm) surrounding a C-B-C chain that resides at the center of the [[unit cell]], and both carbon atoms bridge the neighboring three icosahedra. This structure is layered: the B₁₂ icosahedra and bridging [[carbons]] form a network plane that spreads parallel to the ''c''-plane and stacks along the ''c''-axis. The lattice has two basic structure units – the B₁₂ icosahedron and the B₆ [[octahedron]]. Because of the small size of the B₆ octahedra, they cannot interconnect. Instead, they bond to the B₁₂ icosahedra in the neighboring layer, and this decreases bonding strength in the ''c''-plane.<ref name=zhangyb28.5c4/>

Because of the B₁₂ structural unit, the chemical formula of "ideal" boron carbide is often written not as B₄C, but as B₁₂C₃, and the carbon deficiency of boron carbide described in terms of a combination of the B₁₂C₃ and B₁₂C₂ units.<ref name=stoi/><ref name=gr/> Some studies indicate the possibility of incorporation of one or more carbon atoms into the boron icosahedra, giving rise to formulas such as (B₁₁C)CBC = B₄C at the carbon-heavy end of the stoichiometry, but formulas such as B₁₂(CBB) = B₁₄C at the boron-rich end. "Boron carbide" is thus not a single compound, but a family of compounds of different compositions. A common intermediate, which approximates a commonly found ratio of elements, is B₁₂(CBC) = B_6.5C.<ref name="Domnich2011">{{cite journal | last1 = Domnich | first1 = Vladislav | last2 = Reynaud | first2 = Sara | last3 = Haber | first3 = Richard A. | last4 = Chhowalla | first4 = Manish | year = 2011 | title = Boron Carbide: Structure, Properties, and Stability under Stress | url = http://nanotubes.rutgers.edu/PDFs/Domnich.2011.JACerS.pdf | journal = J. Am. Ceram. Soc. | volume = 94 | issue = 11 | pages = 3605–3628 | doi = 10.1111/j.1551-2916.2011.04865.x | access-date = 23 July 2015 | archive-url = https://web.archive.org/web/20141227081802/http://nanotubes.rutgers.edu/PDFs/Domnich.2011.JACerS.pdf | archive-date = 27 December 2014 | url-status = dead }}</ref> Quantum mechanical calculations have demonstrated that configurational disorder between boron and carbon atoms on the different positions in the crystal determines several of the materials properties – in particular, the crystal symmetry of the B₄C composition<ref>{{cite journal | last1 = Ektarawong | first1 = A. | last2 = Simak | first2 = S. I. | last3 = Hultman | first3 = L. | last4 = Birch | first4 = J. | last5 = Alling | first5 = B. | year = 2014 | title = First-principles study of configurational disorder in B₄C using a superatom-special quasirandom structure method | journal = Phys. Rev. B | volume = 90 | issue = 2| page = 024204 | doi = 10.1103/PhysRevB.90.024204 |arxiv = 1508.07786 |bibcode = 2014PhRvB..90b4204E | s2cid = 39400050 }}</ref> and the non-metallic electrical character of the B₁₃C₂ composition.<ref>{{cite journal | last1 = Ektarawong | first1 = A. | last2 = Simak | first2 = S. I. | last3 = Hultman | first3 = L. | last4 = Birch | first4 = J. | last5 = Alling | first5 = B. | year = 2015 | title = Configurational order-disorder induced metal-nonmetal transition in B₁₃C₂ studied with first-principles superatom-special quasirandom structure method | journal = Phys. Rev. B | volume = 92 | issue = 1| page = 014202 | doi = 10.1103/PhysRevB.92.014202 |arxiv = 1508.07848 |bibcode = 2015PhRvB..92a4202E | s2cid = 11805838 }}</ref>

Boron carbide is known as a robust material having extremely high hardness (about 9.5 up to 9.75 on [[Mohs scale of mineral hardness|Mohs hardness scale]]), high cross section for absorption of [[neutrons]] (i.e. good shielding properties against neutrons), stability to [[ionizing radiation]] and most chemicals.<ref name=w330>Weimer, p. 330</ref> Its [[Vickers hardness]] (38 GPa), [[Elastic Modulus|elastic modulus]] (460 GPa)<ref>{{cite journal | last1 = Sairam | first1 = K. | last2 = Sonber | first2 = J.K. | last3 = Murthy | first3 = T.S.R.Ch. | last4 = Subramanian | first4 = C. | last5 = Hubli | first5 = R.C. | last6 = Suri | first6 = A.K. | year = 2012 | title = Development of B4C-HfB2 composites by reaction hot pressing | journal = Int.J. Ref. Met. Hard Mater | volume = 35 | pages = 32–40 | doi=10.1016/j.ijrmhm.2012.03.004}}</ref> and [[fracture toughness]] (3.5 MPa·m^1/2) approach the corresponding values for diamond (1150 GPa and 5.3 MPa·m^1/2).<ref>{{cite journal| title = Ultimate Metastable Solubility of Boron in Diamond: Synthesis of Superhard Diamondlike BC5| first1 = V. L.|last1 = Solozhenko|journal = Phys. Rev. Lett.| volume = 102| page = 015506|year = 2009| doi = 10.1103/PhysRevLett.102.015506| last2 = Kurakevych| first2 = Oleksandr O.| last3 = Le Godec| first3 = Yann| last4 = Mezouar| first4 = Mohamed| last5 = Mezouar| first5 = Mohamed| pmid=19257210| bibcode=2009PhRvL.102a5506S| issue = 1| url = http://bib-pubdb1.desy.de/record/87949/files/GetPDFServlet.pdf}}</ref>

{{As of|2015}}, boron carbide is the third hardest substance known, after [[diamond]] and [[cubic boron nitride]], earning it the nickname "black diamond".<ref>{{cite web |url= http://www.precision-ceramics.co.uk/boron-carbide.htm |title= Boron Carbide |publisher= Precision Ceramics |access-date= 2015-06-20 |url-status= dead |archive-url= https://web.archive.org/web/20150620124737/http://www.precision-ceramics.co.uk/boron-carbide.htm |archive-date= 2015-06-20 }}</ref><ref>{{cite journal |doi= 10.1142/S2010194512001894 |author1=A. Sokhansanj |author2=A.M. Hadian |title= Purification of Attrition Milled Nano-size Boron Carbide Powder |journal= International Journal of Modern Physics: Conference Series |volume= 5 |year= 2012 |pages= 94–101 |bibcode = 2012IJMPS...5...94S }}</ref>

===Semiconductor properties===

Boron carbide is a [[semiconductor]], with electronic properties dominated by hopping-type transport.<ref name="Domnich2011" /> The energy [[band gap]] depends on composition as well as the degree of order. The band gap is estimated at 2.09 eV, with multiple mid-bandgap states which complicate the [[photoluminescence]] spectrum.<ref name="Domnich2011" /> The material is typically p-type.

Boron carbide was first synthesized by [[Henri Moissan]] in 1899,<ref name=gr>{{Greenwood&Earnshaw2nd|p=149}}</ref> by reduction of [[boron trioxide]] either with [[carbon]] or [[magnesium]] in presence of carbon in an electric [[arc furnace]]. In the case of carbon, the reaction occurs at temperatures above the melting point of B₄C and is accompanied by liberation of large amount of [[carbon monoxide]]:<ref name=w131>Weimer, p. 131</ref>

If magnesium is used, the reaction can be carried out in a graphite [[crucible]], and the magnesium byproducts are removed by treatment with acid.<ref>Patnaik, Pradyot (2002). ''Handbook of Inorganic Chemicals''. McGraw-Hill. {{ISBN|0-07-049439-8}}</ref>

[[File:Plastic with boron carbide.jpg|thumb|upright|Plastic embedded with boron carbide used as shielding in neutron experiments at the [[Atomic Energy Research Establishment]], UK]]

==Applications==

[[File:Bodyarmor.jpg|thumb|upright|Boron carbide is used for inner plates of [[ballistic vest]]s]]

Boron's exceptional hardness can be used for the following applications:

*Personal and vehicle ballistic [[armor plating]]

*[[Sandblasting|Grit blasting]] nozzles

*[[Water jet cutter|High-pressure water]] jet cutter nozzles

*Scratch and wear resistant coatings

*Cutting tools and dies

*[[Abrasives]]

*[[Metal matrix composite]]s

*In brake linings of vehicles

Boron carbide's other properties also make it suitable for:

*[[Neutron_poison#Burnable_poisons|Neutron absorber]] in [[nuclear reactors]] (see below)

*[[High energy fuel]] for solid fuel [[ramjets]]

===Nuclear applications ===

The ability of boron carbide to [[neutron capture|absorb neutrons]] without forming long-lived [[radionuclide]]s makes it attractive as an [[Neutron poison#Burnable poisons|absorbent for neutron radiation arising in nuclear power plants]]<ref>''[https://books.google.com/books?id=czTi4G6-Hq8C&dq=Carborundum+B4C+nuclear&pg=PA311 Fabrication and Evaluation of Urania-Alumina Fuel Elements and Boron Carbide Burnable Poison Elements]'', Wisnyi, L. G. and Taylor, K.M., in "ASTM Special Technical Publication No. 276: Materials in Nuclear Applications", Committee E-10 Staff, [[American Society for Testing Materials]], 1959</ref> and from anti-personnel [[neutron bomb]]s. Nuclear applications of boron carbide include shielding.<ref name=w330>Weimer, p. 330</ref>

===Boron carbide filaments===

Boron carbide filaments exhibit auspicious prospects as reinforcement elements in resin and metal composites, attributed to their exceptional strength, elastic modulus, and low density characteristics.<ref>{{cite journal |last1=Higgins |first1=J.B |last2=Gatti |first2=A. |title=Preparation and Properties of Boron Carbide Continuous Filaments |url=https://iopscience.iop.org/article/10.1149/1.2411733 |journal=Journal of the Electrochemical Society |date=1969 |volume=116 |issue=1 |article-number=1 |page=137 |doi=10.1149/1.2411733 |bibcode=1969JElS..116..137H |access-date=May 28, 2024}} </ref> In addition, boron carbide filaments are not affected by radiation due to its ability to absorb neutrons.<ref>{{cite web |url=https://www.preciseceramic.com/blog/boron-carbide-filament-properties-applications.html |title=Boron Carbide Filament: Properties & Applications |last=Rose |first=Lisa |website=Precise Ceramic |access-date=May 28, 2024}}</ref> It is less harmful than filaments made of other materials, such as cadmium.<ref>{{cite web |url=https://www.nanotrun.com/blog/what-is-boron-carbide_b0434.html |title=What is boron carbide? |date=July 29, 2022 |website=Trunnano |access-date=May 28, 2024}}</ref>

==See also==

* [[List of compounds with carbon number 1]]

{{reflist|30em}}

*{{cite book|url=https://books.google.com/books?id=PC4f40ETjeUC&pg=PA330|author = Weimer, Alan W. | title = Carbide, Nitride and Boride Materials Synthesis and Processing| isbn = 0-412-54060-6| year = 1997| publisher = Chapman & Hall (London, New York)}}

*[https://web.archive.org/web/20060209040519/http://www.npi.gov.au/database/substance-info/profiles/15.html National Pollutant Inventory – Boron and compounds]

{{Carbides}}