Editing Graphite (section)

==Natural ==
===Occurrence===
Graphite occurs in [[metamorphic rock]]s as a result of the [[reduction (chemistry)|reduction]] of [[Sedimentary rock|sedimentary]] carbon compounds during [[metamorphism]]. It also occurs in [[igneous rock]]s and in [[meteorite]]s.<ref name=HBM/> [[Mineral|Minerals]] associated with graphite include [[quartz]], [[calcite]], [[mica]]s and [[tourmaline]]. The principal export sources of mined graphite are, in order of tonnage, [[China]], [[Mexico]], [[Canada]], [[Brazil]], and [[Madagascar]].<ref name="MineralsDatabase">{{cite web
  | title = Graphite
  | work = Minerals Database
  | publisher = Minerals Education Coalition
  | date = 2018
  | url = https://mineralseducationcoalition.org/minerals-database/graphite/
  | access-date = 9 December 2018}}</ref> Significant unexploited graphite resources also exist in [[Colombia]]'s [[Cordillera Central (Colombia)|Cordillera Central]] in the form of graphite-bearing [[schist]]s.<ref>{{Cite journal |title=Is the Central Cordillera of Colombia a potential source of graphite?: Implications for the energy transition in Colombia |journal=[[Andean Geology]] |url=http://www.andeangeology.cl/index.php/revista1/article/view/V51n2-3728/html |last1=Bustamante |first1=C. |issue=2 |volume=51 |pages=413–420 |last2=Cardona |first2=A. |date=2024 |doi=10.5027/andgeoV51n2-3728|doi-access=free |bibcode=2024AndGe..51..413B }}</ref>

In [[meteorite]]s, graphite occurs with [[troilite]] and [[silicate mineral]]s.<ref name=HBM/> Small graphitic crystals in [[meteoritic iron]] are called [[cliftonite]].<ref name=Brit/> Some microscopic grains have distinctive [[Isotope|isotopic]] compositions, indicating that they were formed before the [[Solar System]].<ref>{{cite book |last1=Lugaro |first1=Maria |author-link1=Maria Lugaro |title=Stardust From Meteorites: An Introduction To Presolar Grains |date=2005 |publisher=World Scientific |isbn=9789814481373 |pages=14, 154–157}}</ref> They are one of about 12 known types of minerals that predate the Solar System and have also been detected in [[molecular cloud]]s. These minerals were formed in the [[ejecta]] when [[supernova]]e exploded or low to intermediate-sized stars expelled their outer envelopes late in their lives. Graphite may be the second or third oldest mineral in the Universe.<ref>{{cite journal |last1=Hazen |first1=R. M. |last2=Downs |first2=R. T. |last3=Kah |first3=L. |last4=Sverjensky |first4=D. |title=Carbon Mineral Evolution |journal=Reviews in Mineralogy and Geochemistry |date=13 February 2013 |volume=75 |issue=1 |pages=79–107 |doi=10.2138/rmg.2013.75.4 |bibcode=2013RvMG...75...79H }}</ref><ref>{{cite journal |last1=McCoy |first1=T. J. |title=Mineralogical Evolution of Meteorites |journal=Elements |date=22 February 2010 |volume=6 |issue=1 |pages=19–23 |doi=10.2113/gselements.6.1.19|bibcode=2010Eleme...6...19M }}</ref>

===Structure===
Graphite consists of sheets of trigonal planar carbon.<ref>{{cite book |last1=Delhaes |first1=Pierre |chapter=Polymorphism of carbon |editor-last1=Delhaes |editor-first1=Pierre |title=Graphite and precursors |date=2000 |publisher=Gordon & Breach |isbn=9789056992286|pages=1–24}}</ref><ref>{{cite book |last1=Pierson |first1=Hugh O. |title=Handbook of carbon, graphite, diamond, and fullerenes : properties, processing, and applications |date=2012 |publisher=Noyes Publications |isbn=9780815517399 |pages=40–41}}</ref> The individual layers are called [[graphene]]. In each layer, each carbon atom is bonded to three other atoms forming a continuous layer of sp<sup>2</sup> bonded carbon hexagons, like a [[honeycomb lattice]] with a bond length of 0.142&nbsp;nm, and the distance between planes is 0.335&nbsp;nm.<ref>{{cite book |title= Graphite and Precursors |author= Delhaes, P. |publisher= CRC Press |year= 2001 |url= https://books.google.com/books?id=7p2pgNOWPbEC&pg=PA146 |isbn= 978-90-5699-228-6}}</ref> Bonding between layers is relatively weak [[van der Waals force|van der Waals bonds]], which allows the graphene-like layers to be easily separated and to glide past each other.<ref>{{cite journal |last1=Chung |first1=D. D. L. |title=Review Graphite |journal=Journal of Materials Science |date=2002 |volume=37 |issue=8 |pages=1475–1489 |doi=10.1023/A:1014915307738 |s2cid=189839788 }}</ref> Electrical conductivity perpendicular to the layers is consequently about 1000 times lower.<ref>{{Cite book |last=Pierson |first=Hugh O. |url=https://www.worldcat.org/oclc/49708274 |title=Handbook of carbon, graphite, diamond, and fullerenes : properties, processing, and applications |date=1993 |publisher=Noyes Publications |isbn=0-8155-1739-4 |location=Park Ridge, N.J. |oclc=49708274}}</ref>

There are two allotropic forms called ''alpha'' ([[Hexagonal crystal family|hexagonal]]) and ''beta'' ([[Rhombohedral crystal system|rhombohedral]]), differing in terms of the stacking of the graphene layers: stacking in alpha graphite is ABA, as opposed to ABC stacking in the energetically less stable beta graphite. Rhombohedral graphite cannot occur in pure form.<ref name=Gold/> Natural graphite, or commercial natural graphite, contains 5 to 15% rhombohedral graphite<ref name=rhombo>{{Cite journal |last1=Latychevskaia |first1=Tataiana |last2=Son |first2=Seok-Kyun |last3=Yang |first3=Yaping |last4=Chancellor |first4=Dale |last5=Brown |first5=Michael |last6=Ozdemir |first6=Servet |last7=Madan |first7=Ivan |last8=Berruto |first8=Gabriele |last9=Carbone |first9=Fabrizio  |last10=Mishchenko |first10=Artem |last11=Novoselov |first11=Kostya |date=2019-08-17 |title=Stacking transition in rhombohedral graphite |journal=Frontiers of Physics |volume=14 |issue=1 |at=13608 |doi=10.1007/s11467-018-0867-y  |arxiv=1908.06284 |bibcode=2019FrPhy..1413608L |s2cid=125322808}}</ref> and this may be due to intensive milling.<ref>{{cite journal |last1=E. Fitzer |display-authors=etal|title=Recommended terminology for the description of carbon as a solid (IUPAC Recommendations 1995) |journal=Pure and Applied Chemistry |date=1995 |volume=67 |issue=3 |pages=473–506 |doi=10.1351/pac199567030473 |url=https://www.degruyter.com/document/doi/10.1351/pac199567030473/html}}</ref> The alpha form can be converted to the beta form through shear forces, and the beta form reverts to the alpha form when it is heated to 1300&nbsp;°C for four hours.<ref name=rhombo/><ref name=Gold>{{GoldBookRef |file=R05385 |title=Rhombohedral graphite}}</ref>

<gallery perrow="6">
File:Graphite ambient STM.jpg|[[Scanning tunneling microscope]] image of graphite surface
File:Graphite-layers-side-3D-balls.png|Side view of ABA layer stacking
File:Graphite-layers-top-3D-balls.png|Plane view of layer stacking
File:Graphite-unit-cell-3D-balls.png|Alpha graphite's [[unit cell]] 
</gallery>

===Thermodynamics===
[[File:Carbon basic phase diagram.png|thumb|upright=1.15|Theoretically predicted [[phase diagram]] of carbon]]
The equilibrium pressure and temperature conditions for a transition between graphite and diamond is well established theoretically and experimentally. The pressure changes linearly between {{val|1.7|ul=GPa}} at {{val|0|u=K}} and {{val|12|u=GPa}} at {{val|5000|u=K}} (the diamond/graphite/liquid [[triple point]]).<ref name=Bundy>{{cite journal |last1=Bundy |first1=P. |last2=Bassett |first2=W. A. |last3=Weathers |first3=M. S. |last4=Hemley |first4=R. J. |last5=Mao |first5=H. K. |last6=Goncharov |first6=A. F. |title=The pressure-temperature phase and transformation diagram for carbon; updated through 1994 |journal=Carbon |date=1996 |volume=34 |issue=2 |pages=141–153 |doi=10.1016/0008-6223(96)00170-4|bibcode=1996Carbo..34..141B }}</ref><ref>{{cite book |first1=C. X. |last1=Wang |first2=G. W. |last2=Yang |chapter=Thermodynamic and kinetic approaches of diamond and related nanomaterials formed by laser ablation in liquid |editor-last1=Yang |editor-first1=Guowei |title=Laser ablation in liquids : principles and applications in the preparation of nanomaterials |date=2012 |publisher=Pan Stanford Pub |isbn=9789814241526 |pages=164–165}}</ref>
However, the phases have a wide region about this line where they can coexist. At [[Standard temperature and pressure|normal temperature and pressure]], {{convert|20|C|K}} and {{convert|1|atm|MPa}}, the stable phase of carbon is graphite, but diamond is [[metastable]] and its rate of conversion to graphite is negligible.<ref name=ChemThermo>{{cite book |last1=Rock |first1=Peter A. |title=Chemical Thermodynamics |date=1983 |publisher=University Science Books |isbn=9781891389320 |pages=257–260}}</ref> However, at temperatures above about {{val|4500|u=K}}, diamond rapidly converts to graphite. Rapid conversion of graphite to diamond requires pressures well above the equilibrium line: at {{val|2000|u=K}}, a pressure of {{val|35|u=GPa}} is needed.<ref name=Bundy/>

===Other properties===
[[File:Graphite-pV.svg|thumb|upright=1.15|Molar volume against pressure at room temperature]]
The [[Acoustics|acoustic]] and [[Heat|thermal]] properties of graphite are highly [[anisotropic]], since [[phonons]] propagate quickly along the tightly bound planes, but are slower to travel from one plane to another. Graphite's high thermal stability and electrical and thermal conductivity facilitate its widespread use as electrodes and refractories in high temperature material processing applications. However, in oxygen-containing atmospheres graphite readily oxidizes to form [[carbon dioxide]] at temperatures of 700&nbsp;°C and above.<ref>{{cite journal |last1=Hanaor |first1=Dorian |last2=Michelazzi |first2=Marco |last3=Chenu |first3=Jeremy |last4=Leonelli |first4=Cristina |last5=Sorrell |first5=Charles C. |title=The effects of firing conditions on the properties of electrophoretically deposited titanium dioxide films on graphite substrates |journal=Journal of the European Ceramic Society |date=December 2011 |volume=31 |issue=15 |pages=2877–2885 |doi=10.1016/j.jeurceramsoc.2011.07.007 |arxiv=1303.2757 }}</ref>

Graphite is an [[electrical conductor]], hence useful in such applications as [[arc lamp]] [[electrode]]s. It can conduct electricity due to the vast [[electron]] [[delocalization]] within the carbon layers (a phenomenon called [[aromaticity]]). These valence electrons are free to move, so are able to conduct electricity. However, the electricity is primarily conducted within the plane of the layers. The conductive properties of powdered graphite<ref>{{cite journal |last1=Deprez |first1=N. |last2=McLachlan |first2=D. S. |year=1988 |title=The analysis of the electrical conductivity of graphite conductivity of graphite powders during compaction |journal=[[Journal of Physics D: Applied Physics]] |volume=21 |issue=1 |pages=101–107 |doi=10.1088/0022-3727/21/1/015 |bibcode=1988JPhD...21..101D |s2cid=250886376 }}</ref> allow its use as pressure sensor in [[carbon microphone]]s.

Graphite and graphite powder are valued in industrial applications for their self-lubricating and dry [[lubricant|lubricating]] properties. However, the use of graphite is limited by its tendency to facilitate [[pitting corrosion]] in some [[stainless steel]],<ref>[http://steel.keytometals.com/Articles/Art160.htm Galvanic Corrosion] {{Webarchive |url=https://web.archive.org/web/20090310033053/http://steel.keytometals.com/Articles/Art160.htm |date=2009-03-10 }}. keytometals.com</ref><ref>{{cite web |url= http://metals.lincdigital.com.au/files/ASM_Tech_Notes/TN7-0506-Galvanic%20Corrosion.pdf |archive-url= https://web.archive.org/web/20090227143601/http://metals.lincdigital.com.au/files/ASM_Tech_Notes/TN7-0506-Galvanic%20Corrosion.pdf |archive-date= 2009-02-27 |title= ASM Tech Notes – TN7-0506 – Galvanic Corrosion |work= Atlas Specialty Metals}}</ref> and to promote [[galvanic corrosion]] between dissimilar metals (due to its electrical conductivity). It is also corrosive to aluminium in the presence of moisture. For this reason, the [[US Air Force]] banned its use as a lubricant in aluminium aircraft,<ref>Jones, Rick (USAF-Retired) [http://www.graflex.org/speed-graphic/lubricants.html Better Lubricants than Graphite]. graflex.org</ref> and discouraged its use in aluminium-containing automatic weapons.<ref>{{cite web |url = http://gojackarmy.blogspot.com/2005/09/weapons-lubricant-in-desert.html  |archive-url = https://web.archive.org/web/20071015045426/http://gojackarmy.blogspot.com/2005/09/weapons-lubricant-in-desert.html |archive-date = 2007-10-15 |date = September 16, 2005 |title = Weapons Lubricant in the Desert |access-date = 2009-06-06}}</ref> Even graphite [[pencil]] marks on aluminium parts may facilitate corrosion.<ref>{{cite web |url = http://7faq.com/owbase/ow.asp?GoodEngineeringPractice%2FCorrosion |title = Good Engineering Practice/Corrosion |publisher = Lotus Seven Club |date = 9 April 2003 |archive-url = https://web.archive.org/web/20090916035828/http://7faq.com/owbase/ow.asp?GoodEngineeringPractice%2FCorrosion |archive-date = 16 September 2009}}</ref> Another high-temperature lubricant, [[boron nitride|hexagonal boron nitride]], has the same molecular structure as graphite. It is sometimes called ''white graphite'', due to its similar properties.

When a large number of crystallographic defects bind its planes together, graphite loses its lubrication properties and becomes what is known as [[pyrolytic graphite]]. It is also highly anisotropic, and [[diamagnetic]], thus it will float in mid-air above a strong magnet. (If it is made in a fluidized bed at 1000–1300&nbsp;°C then it is isotropic turbostratic, and is used in blood-contacting devices like mechanical heart valves and is called [[pyrolytic carbon]], and is not diamagnetic. Pyrolytic graphite and pyrolytic carbon are often confused but are very different materials.<ref>{{cite book |last1=Marsh |first1=Harry |last2=Reinoso |first2=Francisco Rodríguez |title=Activated carbon |date=2007 |publisher=Elsevier |isbn=9780080455969 |pages=497–498 |edition=1st}}</ref>)

For a long time graphite has been considered to be hydrophobic. However, recent studies using highly ordered pyrolytic graphite have shown that freshly clean graphite is hydrophilic ([[contact angle]] of 70° approximately), and it becomes hydrophobic (contact angle of 95° approximately) due to airborne pollutants (hydrocarbons) present in the atmosphere.<ref name=":1">{{cite journal |last1=Martinez-Martin |first1=David |last2=Longuinhos |first2=Raphael |last3=Izquierdo |first3=Jesus G. |last4=Marele |first4=Antonela |last5=Alexandre |first5=Simone S. |last6=Jaafar |first6=Miriam |last7=Gómez-Rodríguez |first7=Jose M. |last8=Bañares |first8=Luis |last9=Soler |first9=Jose M. |last10=Gomez-Herrero |first10=Julio |title=Atmospheric contaminants on graphitic surfaces |journal=Carbon |date=September 2013 |volume=61 |pages=33–39 |doi=10.1016/j.carbon.2013.04.056 |bibcode=2013Carbo..61...33M }}</ref><ref>{{cite journal |last1=Li |first1=Zhiting |last2=Wang |first2=Yongjin |last3=Kozbial |first3=Andrew |last4=Shenoy |first4=Ganesh |last5=Zhou |first5=Feng |last6=McGinley |first6=Rebecca |last7=Ireland |first7=Patrick |last8=Morganstein |first8=Brittni |last9=Kunkel |first9=Alyssa |last10=Surwade |first10=Sumedh P. |last11=Li |first11=Lei |last12=Liu |first12=Haitao |title=Effect of airborne contaminants on the wettability of supported graphene and graphite |journal=Nature Materials |date=October 2013 |volume=12 |issue=10 |pages=925–931 |doi=10.1038/nmat3709 |pmid=23872731 |bibcode=2013NatMa..12..925L }}</ref> Those contaminants also alter the electric equipotential surface of graphite by creating domains with potential differences of up to 200 mV as measured with [[Kelvin probe force microscope|kelvin probe force microscopy]].<ref name=":1" /> Such contaminants can be desorbed by increasing the temperature of graphite to approximately 50&nbsp;°C or higher.<ref name=":1" />

Natural and crystalline graphites are not often used in pure form as structural materials, due to their shear-planes, brittleness, and inconsistent mechanical properties.