boron carbide

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.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

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 icosahedra.

These features argued against a very simple exact B₄C empirical formula.

{{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

| url-access= subscription

}}

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.

File:Borfig11a.png consist of boron atoms, and black spheres are carbon atoms.{{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}}]]

File:Borfig12a.png

Boron carbide has a complex crystal structure typical of icosahedron-based borides. There, B₁₂ icosahedra form a rhombohedral lattice unit (space group: R{{overline|3}}m (No. 166), lattice constants: a = 0.56 nm and c = 1.212 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.

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. 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.{{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 }} 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{{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 }} and the non-metallic electrical character of the B₁₃C₂ composition.{{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 }}

Boron carbide is known as a robust material having extremely high hardness (about 9.5 up to 9.75 on Mohs hardness scale), high cross section for absorption of neutrons (i.e. good shielding properties against neutrons), stability to ionizing radiation and most chemicals.Weimer, p. 330 Its Vickers hardness (38 GPa), elastic modulus (460 GPa){{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}} and fracture toughness (3.5 MPa·m^1/2) approach the corresponding values for diamond (1150 GPa and 5.3 MPa·m^1/2).{{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}}

{{As of|2015}}, boron carbide is the third hardest substance known, after diamond and cubic boron nitride, earning it the nickname "black diamond".{{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 }}{{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 }}

Boron carbide is a semiconductor, with electronic properties dominated by hopping-type transport. 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. The material is typically p-type.

Boron carbide was first synthesized by Henri Moissan in 1899,{{Greenwood&Earnshaw2nd|p=149}} 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:Weimer, p. 131

:2 B₂O₃ + 7 C → B₄C + 6 CO

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

File:Plastic with boron carbide.jpg, UK]]

File:Bodyarmor.jpgs]]

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

• Padlocks
• Personal and vehicle ballistic armor plating
• Grit blasting nozzles
• High-pressure water jet cutter nozzles
• Scratch and wear resistant coatings
• Cutting tools and dies
• Abrasives
• Metal matrix composites
• In brake linings of vehicles

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

• Neutron absorber in nuclear reactors (see below)
• High energy fuel for solid fuel ramjets

The property of boron carbide to absorb neutrons without forming long-lived radionuclides makes it an attractive neutron radiation shielding or absorbing material, such as in use for control rods in nuclear power reactors.[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 Nuclear applications of boron carbide include shielding and reaction regulation (control rod).Weimer, p. 330

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.{{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|url-access=subscription }} In addition, boron carbide filaments are not affected by radiation due to its ability to absorb neutrons.{{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}} It is less harmful than filaments made of other materials, such as cadmium.{{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}}

• 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]
• [http://webbook.nist.gov/cgi/cbook.cgi?ID=C12069328&Units=SI&Mask=2#Thermo-Condensed NIST Chemistry Database Entry for Boron Carbide]

{{Boron compounds}}

{{Carbides}}

Category:Carbides

Category:Boron compounds

Category:Superhard materials

Category:Neutron poisons