iron boride
{{about|the well defined borides of iron|the ferroalloy|Ferroboron}}
{{Chembox
| Name=Diiron boride
| ImageFile = Fe2B structure.png
| ImageSize =
| ImageAlt =
| IUPACName = Iron boride
| OtherNames = Diiron boride, Fe2B
|Section1={{Chembox Identifiers
| index_label = Fe2B
| CASNo = 12006-85-8
| CASNo_Ref = {{cascite|correct|CAS}}
| index1_label=FeB
| CASNo1 = 12006-84-7
| CASNo1_Ref = {{Cascite|changed|CAS}}
| ChemSpiderID = 4891846
| ChemSpiderID1 = 74711
| DTXSID = DTXSID401015517
| DTXSID1 = DTXSID9065154
| EINECS = 234-490-4
| EC_number1 = 234-489-9
| PubChem = 6336853
| PubChem1= 82789
| InChI=1S/B.Fe
| InChI1=1S/B.2Fe
| InChIKey1 = FSDZRQFSRALZQJ-UHFFFAOYSA-N
| InChIKey = ZDVYABSQRRRIOJ-UHFFFAOYSA-N
| SMILES =[B].[Fe].[Fe]
| SMILES1 =[B]#[Fe]
}}
|Section2={{Chembox Properties
| Formula = Fe2B
| Appearance = refractory solid
| MeltingPtC = 1389
| BoilingPt =
| Solubility = insoluble
}}
| Section3 = {{Chembox Structure
| CrystalStruct = Tetragonal, tI12
| SpaceGroup = I4/mc, No. 140
| LattConst_a = 0.511 nm
| LattConst_b = 0.511 nm
| LattConst_c = 0.4249 nm
| LattConst_alpha =
| LattConst_beta =
| LattConst_gamma =
| LattConst_ref =
| LattConst_Comment =
| UnitCellVolume =
| UnitCellFormulas = 4
}}
|Section8={{Chembox Hazards
| MainHazards =
| FlashPt =
| AutoignitionPt =
}}
}}
{{Chembox
| Name=Iron boride
| ImageFile = FeB structure 2.png
| ImageName = Iron boride structure
| ImageFile1 = Iron boride.webp
| ImageName1 = Iron boride powder
| ImageSize =
| ImageAlt =
| IUPACName = Iron boride
| OtherNames = Iron monoboride, FeB
|Section1={{Chembox Identifiers
| index_label=FeB
| index1_label=Fe2B
| CASNo = 12006-84-7
| CASNo1 = 12006-85-8
| CASNo_Ref = {{cascite|correct|CAS}}
| PubChem = 82789
| EINECS = 234-489-9
| EC_number1 = 234-490-4
| ChemSpiderID = 74711
| ChemSpiderID1 = 4891846
| InChI=1S/B.Fe
| InChI1=1S/B.2Fe
| InChIKey = ZDVYABSQRRRIOJ-UHFFFAOYSA-N
| InChIKey1 = FSDZRQFSRALZQJ-UHFFFAOYSA-N
| SMILES =[B].[Fe]
| SMILES1 =[B].[Fe].[Fe]
}}
|Section2={{Chembox Properties
| Formula = FeB
| MolarMass = 66.656{{cite book | editor= Haynes, William M. | year = 2011 | title = CRC Handbook of Chemistry and Physics | edition = 92nd | publisher = CRC Press | isbn = 978-1439855119|page=4.68| title-link = CRC Handbook of Chemistry and Physics }}
| Appearance = grey powder
| MeltingPtC = 1658
| BoilingPt =
| Solubility= insoluble
}}
| Section3 = {{Chembox Structure
| CrystalStruct = Orthorhombic, oP8
| SpaceGroup = Pnma, No. 62
| PointGroup =
| LattConst_a = 0.4061 nm
| LattConst_b = 0.5506 nm
| LattConst_c = 0.2952 nm
| LattConst_alpha =
| LattConst_beta =
| LattConst_gamma =
| LattConst_ref =
| LattConst_Comment =
| UnitCellVolume =
| UnitCellFormulas = 4
| Coordination =
| MolShape =
| OrbitalHybridisation =
}}
|Section8={{Chembox Hazards
| MainHazards =
| FlashPt =
| AutoignitionPt =
}}
}}
Iron boride refers to various inorganic compounds with the formula FexBy.Haynes, William M. Handbook of Chemistry and Physics (91 edition.). 2010, Boca Raton, Florida: CRC Press. {{ISBN|978-1439820773}} Two main iron borides are FeB and Fe2B. Some iron borides possess useful properties such as magnetism, electrical conductivity, corrosion resistance and extreme hardness. Some iron borides have found use as hardening coatings for iron. Iron borides have properties of ceramics such as high hardness, and properties of metal properties, such as thermal conductivity and electrical conductivity. Boride coatings on iron are superior mechanical, frictional, and anti-corrosive.{{cite web|title=Boriding / Boronizing (DHB)|url=http://www.ibccoatings.com/boriding-boronizing-dhb|website=IBC Coating Technologies|accessdate=17 November 2014}} Iron monoboride (FeB) is a grey powder that is insoluble in water. FeB is harder than Fe2B, but is more brittle and more easily fractured upon impact.
Formation
=Thermochemical Formation=
Iron borides can be formed by thermochemically reacting boron rich compounds on an iron surface to form a mixture of iron borides, in a process known as boriding. There are a number of ways of forming boride coatings, including gas boriding, molten salt boriding, and pack boriding.{{cite journal|last1=Keddam|first1=M|last2=Chentouf|first2=SM|title=A diffusion model for describing the bilayer growth (FeB/Fe2B) during the iron powder-pack boriding|journal=Appl. Surf. Sci.|date=2005|volume=252|issue=2|pages=393–399|doi=10.1016/j.apsusc.2005.01.016|bibcode=2005ApSS..252..393K}} Typically carbon tetraboride (B4C) or crystalline boron, is sintered on the iron surface in a tetrafluoroborate flux to form the coatings.
The boron atoms diffuse into the iron substrate between 1023 and 1373 K. They first form layers of Fe2B and then form layers of FeB.The range of compounds and compositions formed depends on the reaction conditions including temperature and surrounding environment.
Bulk FeB can be formed by simple reaction between iron and boron in a high-temperature inert gas furnace{{Cite journal|last1=Natu|first1=Varun|last2=Kota|first2=Sankalp S.|last3=Barsoum|first3=Michel W.|date=February 2020|title=X-ray photoelectron spectroscopy of the MAB phases, MoAlB, M2AlB2 (M = Cr, Fe), Cr3AlB4 and their binary monoborides|journal=Journal of the European Ceramic Society|language=en|volume=40|issue=2|pages=305–314|doi=10.1016/j.jeurceramsoc.2019.09.040|s2cid=204301968|doi-access=free}} or in a microwave.{{Cite journal|last1=Bocarsly|first1=Joshua D.|last2=Levin|first2=Emily E.|last3=Humphrey|first3=Samuel A.|last4=Faske|first4=Tom|last5=Donner|first5=Wolfgang|last6=Wilson|first6=Stephen D.|last7=Seshadri|first7=Ram|date=2019-07-09|title=Magnetostructural Coupling Drives Magnetocaloric Behavior: The Case of MnB versus FeB|journal=Chemistry of Materials|language=en|volume=31|issue=13|pages=4873–4881|doi=10.1021/acs.chemmater.9b01476|s2cid=197109775|issn=0897-4756|url=https://escholarship.org/uc/item/45j3v65k}}
=Synthesis=
Iron boride nanoparticles have been formed by reducing iron boride salts in highly coordinating solvents using sodium borohydride. They have also been prepared by reducing iron salts using sodium borohydride:{{cite journal |author=Alyoshin, V.G.|title=Investigation of Composition and Chemical State of Elements in Iron Boride by the Method of X-Ray Photoelectron Spectroscopy. |journal=Journal of Solid State Chemistry|volume= 38 |issue=1 |year=1981 |pages=105–111|doi=10.1016/0022-4596(81)90478-3|bibcode=1981JSSCh..38..105A }}
:4 FeSO4 + 8 NaBH4 +18 H2O → 2 Fe2B + 6 B(OH)3 + 25 H2 + 4 Na2SO4
Structure and Properties
The structures of FeB and Fe2B were known to be interstitial in early studies. FeB is orthorhombic and Fe2B adopts body-centered tetragonal structure.{{cite journal |author1=Joshi, A.A. |author2=Hosmani, S.S. |s2cid=137130309 |title=Pack-Boronizing of AISI 4140 Steel: Boronizing Mechanism and the Role of Container Design |journal=Materials and Manufacturing Processes |volume=29 |issue=9 |pages=1062–1072 |year=2014 |doi=10.1080/10426914.2014.921705}}
=FeB=
FeB has zig-zag chains of boron atoms that are coordinated by seven iron atoms. Boron atoms have a slightly distorted mono-capped trigonal prismatic iron atom coordination and two boron atom neighbors. B-B single bond distance is 178 pm, Fe-B distance is 215–220 pm, and Fe-Fe distance is 240–272 pm. Each trigonal prism shares two rectangular faces with the nearby prisms, forming infinite prism columns.
FeB single crystal is taken by bond domains. Bond domains are parallel to the axis of easy magnetization and perpendicular to the axis of hard magnetization. The structure of closing domains is described as "rows and zigzags of asterisks". Its bond domains possess a distinguished direction in orientation of the boundaries of major domains with rhombic shape of closing domains.
FeB is a soft ferromagnetic compound that becomes paramagnetic above ~325 °C (617 °F). In air, FeB powders begins to react with the ambient oxygen above 300 °C, though bulk FeB materials are expected to be stable in air to much higher temperatures.{{Cite journal|last1=Carbucicchio|first1=M.|last2=Reverberi|first2=R.|last3=Palobarini|first3=G.|last4=Sambogna|first4=G.|s2cid=93768377|date=March 1989|title=On the early stages of oxidation of iron borides|journal=Hyperfine Interactions|language=en|volume=46|issue=1–4|pages=473–479|doi=10.1007/BF02398233|bibcode=1989HyInt..46..473C|issn=0304-3843}} FeB is an extremely hard compound (15-22 GPa as measured by Vickers indentation), but is not sought after on borided steels because FeB layers are brittle and prone to spalling off the steel or iron.{{Cite book|chapter=Boriding (Boronizing) of Metals[1]|date=2013|url=https://dl.asminternational.org/books/book/18/chapter/277836/boriding-boronizing-of-metals-1|work=Steel Heat Treating Fundamentals and Processes|pages=709–724|editor-last=Dossett|editor-first=Jon L.|publisher=ASM International|language=en|doi=10.31399/asm.hb.v04a.a0005772|isbn=978-1-62708-165-8|access-date=2020-03-08|editor2-last=Totten|editor2-first=George E.|title=Boriding (Boronizing) of Metals[1]}}
=Fe<sub>2</sub>B=
Fe2B contains single boron atoms in square anti-prismatic iron atom coordination. Boron atoms are separated from each other and the shortest B-B distance is 213 pm. Fe-B distance is 218 pm and Fe-Fe distance is 240–272 pm.{{cite journal |author1=Kapfenberger, C. |author2=Albert, B. |author3=Pottgen, R. |author4=Huppertz, H. |s2cid=94924114 |title=Structure refinements of iron borides Fe2B and FeB |journal=Z. Kristallogr. |year=2006|volume=221 |issue=5–7 |page=477 |doi=10.1524/zkri.2006.221.5-7.477|bibcode=2006ZK....221..477K }}
Fe2B is a ferromagnetic compound that becomes paramagnetic at temperatures above 742 °C (1368 °F).{{Cite journal|last=Shigematsu|first=Toshihiko|date=1975-11-15|title=Mössbauer and Structural Studies on (Fe 1- x Mn x ) 2 B|journal=Journal of the Physical Society of Japan|language=en|volume=39|issue=5|pages=1233–1238|doi=10.1143/JPSJ.39.1233|bibcode=1975JPSJ...39.1233S|issn=0031-9015}} In air, Fe2B powders begin to react with the ambient oxygen above 400 °C. The high hardness of Fe2B (18.7 GPa or 1907 HV as measured by Vickers indentation){{Cite journal|last1=Ma|first1=Shengqiang|last2=Huang|first2=Zhifu|last3=Xing|first3=Jiandong|last4=Liu|first4=Guangzhu|last5=He|first5=Yaling|last6=Fu|first6=Hanguang|last7=Wang|first7=Yong|last8=Li|first8=Yefei|last9=Yi|first9=Dawei|date=2015-01-28|title=Effect of crystal orientation on microstructure and properties of bulk Fe 2 B intermetallic|url=https://www.cambridge.org/core/product/identifier/S0884291414003835/type/journal_article|journal=Journal of Materials Research|language=en|volume=30|issue=2|pages=257–265|doi=10.1557/jmr.2014.383|bibcode=2015JMatR..30..257M|s2cid=138979673 |issn=0884-2914|url-access=subscription}} is why homogeneous Fe2B layers are formed on top of iron or steel by boriding to make them more wear resistant.{{cite book |chapter=Wear and Galling Resistance of Borided (Boronized) Metal Surfaces |date=2017 |chapter-url=https://dl.asminternational.org/books/book/50/chapter/632564/wear-and-galling-resistance-of-borided-boronized |title=Friction, Lubrication, and Wear Technology |pages=653–660 |editor-last=Totten |editor-first=George E. |publisher=ASM International |language=en |doi=10.31399/asm.hb.v18.a0006420 |isbn=978-1-62708-192-4 |access-date=2020-03-08}}
=FeB<sub>4</sub>=
{{main|Iron tetraboride}}
Applications
Boriding, also called boronizing, is often used to improve abrasion resistance, corrosion resistance, wear resistance, and oxidation resistance. It is used in oil and gas refinery, chemical extraction, automotive, agricultural, stamping, textile extrusion and injection molding industries.
Iron based coatings recently gained attention for their mechanical, frictional, and corrosion resistant properties. As compared to the ceramic or cermet type of materials people have used before, iron based materials are relatively inexpensive, less strategic, and can be produced economically by various thermal methods with ease of fabrication and machining.{{cite journal|last1=Zhdanova|first1=O.V.|last2=Lyakhova|first2=M.B.|last3=Pastushenkov|first3=Y.G.|s2cid=136585232|title=Magnetic Properties and Domain Structure of FeB Single Crystals|journal=Met. Sci. Heat Treat.|date=May 2013|volume=55|issue=1–2|pages=68–72|doi=10.1007/s11041-013-9581-0|bibcode=2013MSHT...55...68Z}}