Editing Boron nitride (section)

===Hexagonal BN===
{{Main|Synthesis of hexagonal boron nitride}}

[[Image:BNcrucible.jpg|thumb|right|Ceramic BN crucible]]
Hexagonal BN (h-BN) is the most widely used polymorph. It is a good lubricant at both low and high temperatures (up to 900&nbsp;°C, even in an oxidizing atmosphere). h-BN lubricant is particularly useful when the electrical conductivity or chemical reactivity of graphite (alternative lubricant) would be problematic. In internal combustion engines, where graphite could be oxidized and turn into carbon sludge, h-BN with its superior thermal stability can be added to engine lubricants. As with all nano-particle suspensions, Brownian-motion settlement is a problem. Settlement can clog engine oil filters, which limits solid lubricant applications in a combustion engine to automotive racing, where engine re-building is common. Since carbon has appreciable solubility in certain alloys (such as steels), which may lead to degradation of properties, BN is often superior for high temperature and/or high pressure applications. Another advantage of h-BN over graphite is that its lubricity does not require water or gas molecules trapped between the layers. Therefore, h-BN lubricants can be used in vacuum, such as space applications. The lubricating properties of fine-grained h-BN are used in [[cosmetics]], [[paint]]s, [[dental cement]]s, and [[pencil]] leads.<ref name=b1>{{cite book |author1=Greim, Jochen |author2=Schwetz, Karl A. | chapter = Boron Carbide, Boron Nitride, and Metal Borides | title = Ullmann's Encyclopedia of Industrial Chemistry | publisher = Wiley-VCH | location = Weinheim | year = 2005 | doi = 10.1002/14356007.a04_295.pub2 |isbn=978-3527306732}}</ref>

Hexagonal BN was first used in cosmetics around 1940 in [[Japan]]. Because of its high price, h-BN was abandoned for this application. Its use was revitalized in the late 1990s with the optimization h-BN production processes, and currently h-BN is used by nearly all leading producers of cosmetic products for [[Foundation (cosmetics)|foundations]], [[make-up]], [[eye shadow]]s, blushers, [[eye liner|kohl pencils]], [[lipstick]]s and other skincare products.<ref name=dkg/>

Because of its excellent thermal and chemical stability, boron nitride ceramics and coatings are used high-temperature equipment. h-BN can be included in ceramics, alloys, resins, plastics, rubbers, and other materials, giving them self-lubricating properties. Such materials are suitable for construction of e.g. [[Bearing (mechanical)|bearings]] and in steelmaking.<ref name=dkg/> Many quantum devices use multilayer h-BN as a substrate material. It can also be used as a dielectric in resistive random access memories.<ref>{{Cite journal|last1=Pan|first1=Chengbin|last2=Ji|first2=Yanfeng|last3=Xiao|first3=Na|last4=Hui|first4=Fei|last5=Tang|first5=Kechao|last6=Guo|first6=Yuzheng|last7=Xie|first7=Xiaoming|last8=Puglisi|first8=Francesco M.|last9=Larcher|first9=Luca|date=2017-01-01|title=Coexistence of Grain-Boundaries-Assisted Bipolar and Threshold Resistive Switching in Multilayer Hexagonal Boron Nitride|journal=Advanced Functional Materials|volume=27|issue=10|pages=1604811|doi=10.1002/adfm.201604811|hdl=11380/1129421|s2cid=100500198 |hdl-access=free}}</ref><ref>{{Cite book|last1=Puglisi|first1=F. M.|last2=Larcher|first2=L.|last3=Pan|first3=C.|last4=Xiao|first4=N.|last5=Shi|first5=Y.|last6=Hui|first6=F.|last7=Lanza|first7=M.|title=2016 IEEE International Electron Devices Meeting (IEDM) |chapter=2D h-BN based RRAM devices |date=2016-12-01|pages=34.8.1–34.8.4|doi=10.1109/IEDM.2016.7838544|isbn=978-1-5090-3902-9|s2cid=28059875}}</ref>

Hexagonal BN is used in [[Xerography|xerographic process]] and [[laser printer]]s as a charge leakage barrier layer of the photo drum.<ref>{{cite journal | author = Schein, L. B. | title = Electrophotography and Development Physics | journal = Physics Today | series = Springer Series in Electrophysics | volume = 14 | issue = 12 | pages = 66–68 |publisher = Springer-Verlag | location = Berlin | year = 1988 | isbn = 9780387189024 | bibcode = 1989PhT....42l..66S | doi = 10.1063/1.2811250}}</ref> In the automotive industry, h-BN mixed with a binder (boron oxide) is used for sealing [[oxygen sensor]]s, which provide feedback for adjusting fuel flow. The binder utilizes the unique temperature stability and insulating properties of h-BN.<ref name=dkg/>

Parts can be made by [[hot pressing]] from four commercial grades of h-BN. Grade HBN contains a [[boron trioxide|boron oxide]] [[binder (material)|binder]]; it is usable up to 550–850&nbsp;°C in oxidizing atmosphere and up to 1600&nbsp;°C in vacuum, but due to the boron oxide content is sensitive to water. Grade HBR uses a [[calcium borate]] binder and is usable at 1600&nbsp;°C. Grades HBC and HBT contain no binder and can be used up to 3000&nbsp;°C.<ref>{{cite book | author = Harper, Charles A. | title = Handbook of Ceramics, Glasses and Diamonds | publisher = McGraw-Hill | year = 2001 | isbn = 978-0070267121}}</ref>

[[Boron nitride nanosheet]]s (h-BN) can be deposited by catalytic decomposition of [[borazine]] at a temperature ~1100&nbsp;°C in a [[chemical vapor deposition]] setup, over areas up to about 10&nbsp;cm<sup>2</sup>. Owing to their hexagonal atomic structure, small lattice mismatch with graphene (~2%), and high uniformity they are used as substrates for graphene-based devices.<ref name=nn>{{cite journal|doi=10.1021/nn503140y|pmid=25094030|title=Large-Area Monolayer Hexagonal Boron Nitride on Pt Foil|journal=ACS Nano|volume=8|issue=8|pages=8520–8|year=2014|last1=Park|first1=Ji-Hoon|last2=Park|first2=Jin Cheol|last3=Yun|first3=Seok Joon|last4=Kim|first4=Hyun|last5=Luong|first5=Dinh Hoa|last6=Kim|first6=Soo Min|last7=Choi|first7=Soo Ho|last8=Yang|first8=Woochul|last9=Kong|first9=Jing|last10=Kim|first10=Ki Kang|last11=Lee|first11=Young Hee}}</ref> BN nanosheets are also excellent [[proton conductor]]s. Their high proton transport rate, combined with the high electrical resistance, may lead to applications in [[fuel cells]] and [[water electrolysis]].<ref>{{cite journal | author = Hu, S. |display-authors=etal | title = Proton transport through one-atom-thick crystals | journal = Nature | year = 2014 | volume = 516 | issue = 7530 | pages = 227–230 | doi = 10.1038/nature14015|pmid=25470058 |arxiv = 1410.8724 |bibcode = 2014Natur.516..227H |s2cid=4455321}}</ref>

h-BN has been used since the mid-2000s as a bullet and bore lubricant in precision target rifle applications as an alternative to [[molybdenum disulfide]] coating, commonly referred to as "moly". It is claimed to increase effective barrel life, increase intervals between bore cleaning and decrease the deviation in point of impact between clean bore first shots and subsequent shots.<ref>{{cite web | url = http://bulletin.accurateshooter.com/2014/09/hexagonal-boron-nitride-hbn-how-well-does-it-work/ | title = Hexagonal Boron Nitride (HBN)—How Well Does It Work? | author = <!--Staff writer(s); no by-line.--> | date = 8 September 2014 | website = AccurateShooter.com | access-date = 28 December 2015}}</ref>

h-BN is used as a release agent in molten metal and glass applications. For example, [[ZYP Coatings (company)|ZYP Coatings]] developed and currently produces a line of paintable h-BN coatings that are used by manufacturers of molten aluminium, non-ferrous metal, and glass.<ref>{{Cite web|url=http://www.colourdeverre.com/img/projects/advancedpriming.pdf|title=colourdeverre.com/img/projects/advancedpriming.pdf}}</ref> Because h-BN is nonwetting and lubricious to these molten materials, the coated surface (i.e. mold or crucible) does not stick to the material.<ref>{{Cite web|url=https://www.researchgate.net/publication/234787198|title=(PDF) Wettability, Spreading, and Interfacial Phenomena in High-Temperature Coatings}}</ref><ref>{{Cite web|url=https://hal.science/hal-02113581/document|title=Substrate Release Mechanisms for Gas Metal Arc 3-D Aluminum Metal Printing. 3D Printing &Additive Manufacturing}}</ref><ref>{{Cite web|url=https://www.researchgate.net/publication/265172365|title=(PDF) Wear properties of squeeze cast in situ Mg2Si–A380 alloy}}</ref><ref>{{Cite web|url=http://www.jwri.osaka-u.ac.jp/~dpt9/Acta(1993)BNAl.pdf|title=INTERFACIAL REACTION WETTING IN THE BORON NITRIDE/MOLTEN ALUMINUM SYSTEM}}</ref>

Exfoliated h-BN shows the ability to improved mechanical and thermal properties of polypropylene. One process used Resonant Acoustic Mixing to coat polypropylene with the h-BN. Then the h-BN was exfoliated by running the material through a high-pressure homogenizer, effectively creating nanosheets. This melt process also caused the h-BN to have a more uniform distribution through the polypropylene. Improvements were especially noted in oxidative thermal stability, enhanced oxidative induction time and reduct carbonyl index values.<ref>{{Cite journal |last=Sonker |first=Amit Kumar |last2=Tran |first2=Man Hieu |last3=Park |first3=Nathan |last4=Das |first4=Gouri Sankar |last5=Mahajan |first5=Hansa |last6=Lee |first6=Tae Hee |last7=Kim |first7=TaeYoung |date=2025-01-14 |title=Enhancement of Thermal, Mechanical, and Oxidative Properties of Polypropylene Composites with Exfoliated Hexagonal Boron Nitride Nanosheets |url=https://pubs.acs.org/doi/10.1021/acsomega.4c10677 |journal=ACS Omega |volume=10 |issue=1 |pages=1853–1861 |doi=10.1021/acsomega.4c10677 |pmc=11740118 |pmid=39829589}}</ref>