Editing Metal (section)

==Categories==
Metals can be categorised by their composition, physical or chemical properties. Categories described in the subsections below include [[ferrous metallurgy|ferrous]] and [[non-ferrous metals|non-ferrous]] metals; brittle metals and [[refractory metal]]s; white metals; [[heavy metals|heavy]] and [[light metal|light]] metals; [[base metal|base]], [[noble metal|noble]], and [[precious metal|precious]] metals as well as both metallic [[#Ceramic metals|ceramics]] and [[#Polymer metals|polymers]].

===Ferrous and non-ferrous metals===
{{Main|Ferrous metallurgy|Non-ferrous metal}}
The term "ferrous" is derived from the [[Latin language|Latin]] word meaning "containing iron". This can include pure iron, such as [[wrought iron]], or an alloy such as [[steel]]. Ferrous metals are often [[magnetism|magnetic]], but not exclusively. Non-ferrous metals and alloys lack appreciable amounts of iron.

===Brittle elemental metal===
While nearly all elemental metals are malleable or ductile, a few—beryllium, chromium, manganese, gallium, and bismuth—are brittle.<ref>{{cite book |title=Structure–Property Relations in Nonferrous Metals |last1=Russell |first1=A. M. |last2=Lee |first2=K. L. |year=2005 |publisher=John Wiley & Sons |location=Hoboken, NJ |isbn=978-0-471-64952-6 |pages=passim |bibcode=2005srnm.book.....R}}</ref> Arsenic and antimony, if admitted as metals, are brittle. Low values of the ratio of bulk [[elastic modulus]] to [[shear modulus]] ([[Pugh's criterion]]) are indicative of intrinsic brittleness.<ref>{{Cite journal |last1=Senkov |first1=O. N. |last2=Miracle |first2=D. B. |date=2021-02-25 |title=Generalization of intrinsic ductile-to-brittle criteria by Pugh and Pettifor for materials with a cubic crystal structure |journal=Scientific Reports |language=en |volume=11 |issue=1 |page=4531 |doi=10.1038/s41598-021-83953-z |issn=2045-2322 |pmc=7907099 |pmid=33633140|bibcode=2021NatSR..11.4531S }}</ref> A material is brittle if it is hard for dislocations to move, which is often associated with large [[Burgers vector]]s and only a limited number of slip planes.<ref>{{Cite book |url=https://linkinghub.elsevier.com/retrieve/pii/B9780750646819X50007 |title=Introduction to Dislocations |date=2001 |publisher=Elsevier |isbn=978-0-7506-4681-9 |language=en |doi=10.1016/b978-0-7506-4681-9.x5000-7}}</ref>

===Refractory metal===
{{Main|Refractory metal}}
A refractory metal is a metal that is very resistant to heat and wear. Which metals belong to this category varies; the most common definition includes niobium, molybdenum, tantalum, tungsten, and rhenium as well as their alloys. They all have melting points above 2000&nbsp;°C, and a high [[hardness]] at room temperature. Several compounds such as titanium nitride are also described as refractory metals.
<gallery widths="165" heights="165">
File:Niobium crystals and 1cm3 cube.jpg|Niobium crystals and a 1&nbsp;cm<sup>3</sup> [[anodizing|anodized]] niobium cube for comparison
File:Macro Photographs of 3D Print of NASA Meatball - Made out of GRX-810, an Oxide Dispersion Strengthened (ODS) High Temperature Alloy (GRC-2023-C-02309).jpg|3D print of NASA meatball, made out of GRX-810, an oxide dispersion strengthened high temperature alloy
File:Rhenium single crystal bar and 1cm3 cube.jpg|Rhenium single crystal, a remelted bar, and a 1&nbsp;cm<sup>3</sup> rhenium cube for comparison
File:Titanium nitride TiN.jpg|Titanium nitride powder
</gallery>

===White metal===
{{Main|White metal}}
A [[white metal]] is any of a range of white-colored alloys with relatively low melting points used mainly for decorative purposes.<ref>{{Cite web |date=2019-04-17 |title=Belmont Metals - White Metals |url=https://www.belmontmetals.com/product-category/white-metals/ |access-date=2024-07-08 |website=Belmont Metals |language=en-US}}</ref><ref>{{Cite web |last=Roden |first=Arabella |date=2019-11-04 |title=A closer look at the world of white metals |url=https://www.jewellermagazine.com/Article2/8576/A-closer-look-at-the-world-of-white-metals |access-date=2024-07-08 |website=jewellermagazine.com}}</ref> In Britain, the fine art trade uses the term "white metal" in auction catalogues to describe foreign silver items which do not carry British Assay Office marks,<ref>{{Cite book |url=https://www.assayofficelondon.co.uk/media/1818/2128-hallmarking-guide-pressready_oct2016.pdf |title=Practical guidance in relation to the hallmarking act 1973 |publisher=Assay offices of Great Britain}}</ref> but which are nonetheless understood to be silver and are priced accordingly.

===Heavy and light metals===
{{Main|Heavy metals|Light metals}}
A heavy metal is any relatively dense metal, either single element or multielement.<ref>{{cite book |url=https://books.google.com/books?id=GXYT3JKBm9EC&q=%C2%A0%C2%A0A+heavy+metal+is+any+relatively+dense+metal+or+metalloid&pg=PA3 |title=Metal contamination |date=2006 |publisher=Editions Quae |isbn=978-2-7592-0011-5 |language=en}}</ref> [[Magnesium]], [[aluminium]] and [[titanium]] alloys are light metals of significant commercial importance.<ref>Brandes EA & Brook GB (eds) 1998, ''Light Metals Handbook,'' Butterworth Heinemann, Oxford, {{ISBN|0-7506-3625-4}}, p.&nbsp;viii</ref> Their densities of 1.7, 2.7 and 4.5 g/cm<sup>3</sup> range from 19 to 56% of the densities of other structural metals,<ref>Polmear I 2006, ''Light Alloys: From Traditional Alloys to Nanocrystals,'' 4th ed., Butterworth Heinemann, Oxford, {{ISBN|0-7506-6371-5}}, p.&nbsp;1</ref> such as [[iron]] (7.9) and [[copper]] (8.9) and their alloys.

===Base, noble, and precious metals===
{{main|Base metal|noble metal|precious metal}}
The term ''base metal'' refers to a metal that is easily [[oxidation|oxidized]] or [[corrosion|corroded]], such as reacting easily with dilute [[hydrochloric acid]] (HCl) to form a metal chloride and [[hydrogen]]. The term is normally used for the elements, and examples include iron, [[nickel]], [[lead]], and zinc. Copper is considered a base metal as it is oxidized relatively easily, although it does not react with HCl.

[[File:Rhodium powder pressed melted.jpg|thumb|[[Rhodium]], a [[noble metal]], shown here as 1&nbsp;g of powder, a 1&nbsp;g pressed cylinder, and a 1&nbsp;g pellet|alt=Rhodium powder, a rhodium cylinder, and a rhodium pellet in a row]]
The term [[noble metal]] (also for elements) is commonly used in opposition to ''base metal''. Noble metals are less reactive, resistant to [[corrosion]] or [[oxidation]],<ref>{{cite book |url=https://books.google.com/books?id=Tiv9Ba4dDI4C&q=Noble+metals+are+metals+that+are+resistant+to+corrosion+or+oxidation&pg=PA267 |title=Chemical Oxidation Applications for Industrial Wastewaters |last1=Tunay |first1=Olcay |last2=Kabdasli |first2=Isik |last3=Arslan-Alaton |first3=Idil |last4=Olmez-Hanci |first4=Tugba |date=2010 |publisher=IWA Publishing |isbn=978-1-84339-307-8 |language=en}}</ref> unlike most [[base metal]]s. They tend to be precious metals, often due to perceived rarity. Examples include gold, platinum, silver, [[rhodium]], iridium, and palladium.

In [[alchemy]] and [[numismatics]], the term base metal is contrasted with [[precious metal]], that is, those of high economic value.<ref>{{cite book |url=https://books.google.com/books?id=dWMqaOTqSqcC&q=A+precious+metal+rare+metal+of+high+economic+value&pg=PA203 |title=Earth's Natural Resources |last=Walther |first=John V. |date=2013 |publisher=Jones & Bartlett Publishers |isbn=978-1-4496-3234-2 |language=en}}</ref> Most coins today are made of base metals with [[fiat currency|low intrinsic value]]; in the past, coins frequently derived their value primarily from their [[precious metal]] content; [[gold]], [[silver]], [[platinum]], and [[palladium]] each have an [[ISO 4217]] currency code. Currently they have industrial uses such as platinum and palladium in [[catalytic converters]], are used in [[jewellery]] and also a role as investments and a [[store of value]].<ref>{{cite book |url=https://books.google.com/books?id=qaBmBgAAQBAJ&q=The+demand+for+precious+metals+is+driven+not+only+by+their+practical+use%2C+but+also+by+their+role+as+investments+and+a+store+of+value&pg=PA105 |title=The Art of RF (Riba-Free) Islamic Banking and Finance: Tools and Techniques for Community-Based Banking |last=Abdul-Rahman |first=Yahia |date=2014 |publisher=John Wiley & Sons |isbn=978-1-118-77096-2 |language=en}}</ref> Palladium and platinum, as of summer 2024, were valued at slightly less than half the price of gold, while silver is substantially less expensive.

===Valve metals===
{{Main|Valve metals}}
In electrochemistry, a valve metal is a metal which passes current in only one direction due to the formation of any insulating oxide later.<ref>{{Cite journal |last1=Yasuda |first1=Kouji |last2=Macak |first2=Jan M. |last3=Berger |first3=Steffen |last4=Ghicov |first4=Andrei |last5=Schmuki |first5=Patrik |date=2007 |title=Mechanistic Aspects of the Self-Organization Process for Oxide Nanotube Formation on Valve Metals |url=https://iopscience.iop.org/article/10.1149/1.2749091 |journal=Journal of the Electrochemical Society |language=en |volume=154 |issue=9 |pages=C472 |doi=10.1149/1.2749091|bibcode=2007JElS..154C.472Y }}</ref>

=== Metallic ceramics ===
[[File:Titanium nitride coating 90.jpg|thumb|TiN coated drill bit]]
There are many ceramic compounds which have metallic electrical conduction, but are not simple combinations of metallic elements. (They are not the same as [[cermet]]s which are composites of a non-conducting ceramic and a conducting metal.) One set, the transition metal nitrides has significant ionic character to the bonding, so can be classified as both ceramics and metals.<ref name="Stampfl-2001" /> They have partially filled states at the Fermi level<ref name="Stampfl-2001" /> so are good thermal and electrical conductors, and there is often significant charge transfer from the transition metal atoms to the nitrogen.<ref name="Stampfl-2001" /> However, unlike most elemental metals, ceramic metals are often not particularly ductile. Their uses are widespread, for instance [[titanium nitride]] finds use in orthopedic devices<ref>{{Cite journal |last1=van Hove |first1=Ruud P. |last2=Sierevelt |first2=Inger N. |last3=van Royen |first3=Barend J. |last4=Nolte |first4=Peter A. |date=2015 |title=Titanium-Nitride Coating of Orthopaedic Implants: A Review of the Literature |journal=BioMed Research International |language=en |volume=2015 |pages=1–9 |doi=10.1155/2015/485975 |doi-access=free |issn=2314-6133 |pmc=4637053 |pmid=26583113}}</ref> and as a wear resistant coating.<ref>{{Cite journal |last1=Santecchia |first1=Eleonora |last2=Hamouda |first2=A. M. S. |last3=Musharavati |first3=Farayi |last4=Zalnezhad |first4=Erfan |last5=Cabibbo |first5=Marcello |last6=Spigarelli |first6=Stefano |date=2015 |title=Wear resistance investigation of titanium nitride-based coatings |url=https://www.sciencedirect.com/science/article/pii/S0272884215009116 |journal=Ceramics International |volume=41 |issue=9, Part A |pages=10349–10379 |doi=10.1016/j.ceramint.2015.04.152 |issn=0272-8842}}</ref> In many cases their utility depends upon there being effective deposition methods so they can be used as thin film coatings.<ref>{{Cite journal |last=Matthews |first=A. |date=1985 |title=Titanium Nitride PVD Coating Technology |url=http://journals.sagepub.com/doi/10.1179/sur.1985.1.2.93 |journal=Surface Engineering |language=en |volume=1 |issue=2 |pages=93–104 |doi=10.1179/sur.1985.1.2.93 |issn=0267-0844}}</ref>

=== Metallic polymers ===
[[File:Conducting polymers.svg|thumb|Several of the conducting polymers<ref>{{Cite journal |last1=K |first1=Namsheer |last2=Rout |first2=Chandra Sekkha |date=2021 |title=Conducting polymers: a comprehensive review on recent advances in synthesis, properties and applications |journal=RSC Advances |language=en |volume=11 |issue=10 |pages=5659–5697 |doi=10.1039/D0RA07800J|pmid=35686160 |pmc=9133880 |bibcode=2021RSCAd..11.5659K }}</ref>]]
{{Main|Conductive polymer}}{{See also|Conductive metal−organic frameworks}}
There are many polymers which have metallic electrical conduction,<ref>{{Cite journal |last1=Das |first1=Tapan K. |last2=Prusty |first2=Smita |date=2012 |title=Review on Conducting Polymers and Their Applications |url=http://www.tandfonline.com/doi/abs/10.1080/03602559.2012.710697 |journal=Polymer-Plastics Technology and Engineering |language=en |volume=51 |issue=14 |pages=1487–1500 |doi=10.1080/03602559.2012.710697 |issn=0360-2559}}</ref><ref>{{Cite journal |last=Swager |first=Timothy M. |date=2017 |title=50th Anniversary Perspective : Conducting/Semiconducting Conjugated Polymers. A Personal Perspective on the Past and the Future |url=https://pubs.acs.org/doi/10.1021/acs.macromol.7b00582 |journal=Macromolecules |language=en |volume=50 |issue=13 |pages=4867–4886 |doi=10.1021/acs.macromol.7b00582 |bibcode=2017MaMol..50.4867S |issn=0024-9297|hdl=1721.1/116306 |hdl-access=free }}</ref> typically associated with extended aromatic components such as in the polymers indicated in the Figure. The conduction of the aromatic regions is similar to that of graphite, so is highly directional.<ref>{{Cite journal |last1=Beygisangchin |first1=Mahnoush |last2=Abdul Rashid |first2=Suraya |last3=Shafie |first3=Suhaidi |last4=Sadrolhosseini |first4=Amir Reza |last5=Lim |first5=Hong Ngee |date=2021-06-18 |title=Preparations, Properties, and Applications of Polyaniline and Polyaniline Thin Films—A Review |journal=Polymers |volume=13 |issue=12 |pages=2003 |doi=10.3390/polym13122003 |doi-access=free |issn=2073-4360 |pmc=8234317 |pmid=34207392}}</ref>

=== Half metal ===
{{Main|Half-metal}}
A '''half-metal''' is any substance that acts as a [[Electrical conductor|conductor]] to [[electron]]s of one [[Spin (physics)|spin]] orientation, but as an [[Electrical insulation|insulator]] or [[semiconductor]] to those of the opposite spin. They were first described in 1983, as an explanation for the electrical properties of [[manganese]]-based [[Heusler alloy]]s.<ref>{{Cite journal |last1=de Groot |first1=R. A. |last2=Mueller |first2=F. M. |last3=Engen |first3=P. G. van |last4=Buschow |first4=K. H. J. |date=1983-06-20 |title=New Class of Materials: Half-Metallic Ferromagnets |url=https://link.aps.org/doi/10.1103/PhysRevLett.50.2024 |journal=Physical Review Letters |language=en |volume=50 |issue=25 |pages=2024–2027 |doi=10.1103/PhysRevLett.50.2024 |bibcode=1983PhRvL..50.2024D |issn=0031-9007}}</ref> Although all half-metals are [[Ferromagnetism|ferromagnetic]] (or [[Ferrimagnetism|ferrimagnetic]]), most ferromagnets are not half-metals. Many of the known examples of half-metals are [[oxide]]s, [[sulfide]]s, or [[Heusler alloy]]s.<ref>{{Cite journal |last1=Coey |first1=J. M. D. |last2=Venkatesan |first2=M. |date=2002-05-15 |title=Half-metallic ferromagnetism: Example of CrO2 (invited) |url=https://pubs.aip.org/jap/article/91/10/8345/485889/Half-metallic-ferromagnetism-Example-of-CrO2 |journal=Journal of Applied Physics |language=en |volume=91 |issue=10 |pages=8345–8350 |doi=10.1063/1.1447879 |issn=0021-8979}}</ref>

=== Semimetal ===
{{Main|Semimetal}}
A '''semimetal''' is a material with a small energy overlap between the bottom of the [[Electrical conduction|conduction]] [[Electronic band structure|band]] and the top of the [[valence band]], but they do not overlap in [[momentum space]].<ref>{{Cite journal |last1=Zhai |first1=Enzi |last2=Liang |first2=Tianyu |last3=Liu |first3=Ruizi |last4=Cai |first4=Mingyang |last5=Li |first5=Ran |last6=Shao |first6=Qiming |last7=Su |first7=Cong |last8=Lin |first8=Yuxuan Cosmi |date=2024-08-01 |title=The rise of semi-metal electronics |url=https://www.nature.com/articles/s44287-024-00068-z |journal=Nature Reviews Electrical Engineering |language=en |volume=1 |issue=8 |pages=497–515 |doi=10.1038/s44287-024-00068-z |issn=2948-1201}}</ref> Unlike a regular metal, semimetals have charge carriers of both types (holes and electrons), although the charge carriers typically occur in much smaller numbers than in a real metal. In this respect they resemble [[degenerate semiconductor]]s. This explains why the electrical properties of semimetals are partway between those of metals and [[semiconductors]]. There are additional types, in particular [[Weyl semimetal|Weyl]] and [[Dirac semi-metal|Dirac semimetals]].<ref>{{Cite journal |last1=Armitage |first1=N. P. |last2=Mele |first2=E. J. |last3=Vishwanath |first3=Ashvin |date=2018-01-22 |title=Weyl and Dirac semimetals in three-dimensional solids |url=https://link.aps.org/doi/10.1103/RevModPhys.90.015001 |journal=Reviews of Modern Physics |language=en |volume=90 |issue=1 |page=015001 |doi=10.1103/RevModPhys.90.015001 |issn=0034-6861|arxiv=1705.01111 |bibcode=2018RvMP...90a5001A }}</ref>

The classic elemental semimetallic elements are [[arsenic]], [[antimony]], [[bismuth]], α-[[tin]] (gray tin) and [[graphite]]. There are also [[chemical compound]]s, such as [[mercury telluride]] (HgTe),<ref>{{cite journal |last=Wang |first=Yang |author2=N. Mansour |author3=A. Salem |author4=K.F. Brennan |author5=P.P. Ruden |name-list-style=amp |date=1992 |title=Theoretical study of a potential low-noise semimetal-based avalanche photodetector |journal=IEEE Journal of Quantum Electronics |volume=28 |issue=2 |pages=507–513 |bibcode=1992IJQE...28..507W |doi=10.1109/3.123280}}</ref> and some [[conductive polymers]].<ref>{{cite journal |last1=Bubnova |first1=Olga |last2=Zia |first2=Ullah Khan |last3=Wang |first3=Hui |date=2014 |title=Semi-Metallic Polymers |url=https://liu.diva-portal.org/smash/get/diva2:698183/FULLTEXT01 |journal=Nature Materials |volume=13 |issue=2 |pages=190–4 |bibcode=2014NatMa..13..190B |doi=10.1038/nmat3824 |pmid=24317188 |s2cid=205409397}}</ref>