Editing Refractory (section)

==Refractory materials==

Refractory materials must be chemically and physically stable at high temperatures. Depending on the operating environment, they must be resistant to [[thermal shock]], be [[chemically inert]], and/or have specific ranges of [[thermal conductivity]] and of the coefficient of [[thermal expansion]].

The [[oxide]]s of [[aluminium]] ([[alumina]]), [[silicon]] ([[silica]]) and [[magnesium]] ([[magnesium oxide|magnesia]]) are the most important materials used in the manufacturing of refractories. Another oxide usually found in refractories is the oxide of [[calcium]] ([[lime (mineral)|lime]]).<ref>{{Cite book|url=https://books.google.com/books?id=QU-Qvud3OvoC&q=alumina%2C+silica+and+magnesia+are+most+important+materials+used+in+the+manufacturing+of+refractories&pg=PA141|title=Fundamentals of Modern Manufacturing: Materials, Processes, and Systems|last=Groover|first=Mikell P.|date=2010-01-07|publisher=[[John Wiley & Sons]]|isbn=9780470467008|language=en}}</ref> [[Fire clay]]s are also widely used in the manufacture of refractories.

Refractories must be chosen according to the conditions they face. Some applications require special refractory materials.<ref>{{Cite journal|last=Sonntag, Kiss, Banhidi, Weber|year=2009|title=New Kiln Furniture Solutions for Technical Ceramics|journal=Ceramic Forum International|volume=86|issue=4|pages= 29–34}}</ref> [[Zirconia]] is used when the material must withstand extremely high temperatures.<ref>{{Cite book|url=https://books.google.com/books?id=-g_hx8ROlPYC&q=Zirconia+is+used+when+the+material+must+withstand+extremely+high+temperatures&pg=PA35|title=Zirconium|last=Roza|first=Greg|date=2009|publisher=The Rosen Publishing Group|isbn=9781435850705|language=en}}</ref> [[Silicon carbide]] and [[carbon]] ([[graphite]]) are two other refractory materials used in some very severe temperature conditions, but they cannot be used in contact with [[oxygen]], as they would [[Oxidation|oxidize]] and burn.

[[Binary compounds]] such as [[tungsten carbide]] or [[boron nitride]] can be very refractory. [[Hafnium(IV) carbide|Hafnium carbide]] is the most refractory binary compound known, with a [[melting point]] of 3890&nbsp;°C.<ref>{{cite book|author=Hugh O. Pierson|title=Handbook of chemical vapor deposition (CVD): principles, technology, and applications|url=https://books.google.com/books?id=NF3W6zlN9WsC&pg=PA206|access-date=22 April 2011|year=1992|publisher=William Andrew|isbn=978-0-8155-1300-1|pages=206–}}</ref><ref>[http://periodic.lanl.gov/72.shtml Hafnium] {{Webarchive|url=https://web.archive.org/web/20170811032626/http://periodic.lanl.gov/72.shtml |date=11 August 2017 }}, Los Alamos National Laboratory</ref> The [[ternary compound]] [[tantalum hafnium carbide]] has one of the highest melting points of all known compounds (4215&nbsp;°C).<ref>{{cite book|title=McGraw-Hill encyclopedia of science and technology: an international reference work in fifteen volumes including an index|url=https://books.google.com/books?id=TjYLAQAAIAAJ|access-date=22 April 2011|year=1977|publisher=McGraw-Hill|isbn=978-0-07-079590-7|page=360}}</ref><ref>{{cite encyclopedia|title=Hafnium|url=http://www.britannica.com/EBchecked/topic/251419/hafnium|encyclopedia=Encyclopædia Britannica|publisher=[[Encyclopædia Britannica, Inc.]]|access-date=17 December 2010}}</ref>

[[Molybdenum disilicide]] has a high melting point of 2030 °C and is often used as a [[heating element]].