Ajay Kumar at 17:25, 24 August 2023

2023-08-24T17:25:55Z

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{{Short description|Refractory clays used in ceramics manufacturing}}
[[File:Fornello inv.3916 IF 77656.jpg|thumb|300px|Furnace in fire clay.]]
'''Fire clay''' is a range of [[refractory]] [[clay]]s used in the manufacture of [[ceramic]]s, especially [[fire brick]]. The [[United States Environmental Protection Agency]] defines fire clay very generally as a "mineral aggregate composed of hydrous silicates of aluminium (Al2O3·2SiO2·2H2O) with or without free silica."<ref>{{Cite document| title=Calciners and Dryers in Mineral Industries | type=Background Information for Proposed Standards | id=EPA-450/3-85-025a | publisher=U.S. Environmental Protection Agency | year=1985 | pages=3–48}}</ref>

==Properties==
High-grade fire clays can withstand temperatures of 1,775 °C (3,227 °F), but to be referred to as a "fire clay" the material must withstand a minimum temperature of {{convert|1515|°C|F}}.<ref name=MZ>[http://www.mineralszone.com/minerals/fire-clay.html Minerals Zone, World Mineral Exchange.] {{Webarchive|url=https://web.archive.org/web/20110714100738/http://www.mineralszone.com/minerals/fire-clay.html |date=2011-07-14 }} Retrieved 2011-6-23.</ref> Fire clays range from ''[[flint clay]]s'' to ''plastic fire clays'', but there are ''semi-flint'' and ''semi-plastic'' fire clays as well. Fire clays consist of natural [[argillaceous]] materials, mostly [[Kaolinite]] group clays, along with fine-grained [[micas]] and [[quartz]], and may also contain [[organic compound|organic]] matter and [[sulphur]] compounds.

Fire clay is resistant to high temperatures, having [[fusion point]]s higher than {{convert|1,600|°C|F}}; therefore it is suitable for lining [[Metallurgical furnace|furnace]]s, as fire brick, and for manufacture of utensils used in the [[metalworking]] industries, such as [[crucible]]s, [[saggar]]s, [[retort]]s and [[glassware]]. Its stability during firing in the [[kiln]] means that it can be used to make complex items of pottery such as pipes and sanitary ware.

==Chemical composition==
The chemical composition typical for fire clays are 23-34% [[aluminium oxide|Al2O3]], 50-60% [[silicon dioxide|SiO2]] and 6-27% [[loss on ignition]] together with various amounts of [[iron(III) oxide|Fe2O3]], [[Calcium oxide|CaO]], [[Magnesium oxide|MgO]], [[Potassium oxide|K2O]], [[Sodium oxide|Na2O]] and [[Titanium dioxide|TiO2]].<ref name=MZ /> Chemical analyses from two 19th-century sources, shown in table below, are somewhat lower in alumina<ref name="Thorpe1">{{cite book
| last = Thorpe
| first = Sir Thomas Edward
| title = A Dictionary of Applied Chemistry Volume I
| publisher = Longmans Green & Company, London
| year = 1890
}}</ref><ref name="King1">{{cite book
| last = King
| first = William B.
| title = King's Treatise on the Manufacture and Distribution of Coal Gas
| publisher = self
| year = 1878
}}</ref>
although a more contemporary source quotes analyses that are closer.<ref name="Shackelford1">{{cite book
| last1 = Shackelford
| first1 = James F
| title = Ceramic and glass materials: structure, properties and processing
| publisher = Springer
| page = 121
| year = 2008
}}</ref>

{| class="wikitable"
|+ Fire clay compositions
|-
! rowspan=2 |
! colspan=3 | Thorpe<ref name="Thorpe1" />
! colspan=3 | King<ref name="King1" />
! Shackelford<ref name="Shackelford1" />
|-
! Stonebridge
! Eisenberg I
! Eisenberg II
! Newcastle 1
! Newcastle 2
! Newcastle 3
! N/A
|-
| SiO2 (%)
| 65.10
| 89.8
| 64.7
| 51.1
| 47.6
| 48.6
| 58.1
|-
| Al2O3 (%)
| 22.2
| 5.40
| 24.0
| 31.4
| 29.5
| 30.2
| 23.1
|-
| MgO (%)
| 0.18
| 0.09
| 0.40
| 1.54
| 0.71
| 1.91
| 1.00
|-
| CaO(%)
| 0.14
| 0.20
| 0.37
| 1.46
| 1.34
| 1.66
| 0.08
|-
| Iron Oxides (%)
| 0.18
| 0.09
| 0.40
| 4.63
| 9.13
| 4.06
| 2.40
|-
| K2O (%)
| 0.18
| 0.61
| 2.40
| colspan=4 align=center | not given in the text
|-
|}

==Extraction==
Unlike conventional [[brick]]-making clay, some fire clays (especially flint clays) are [[mining|mined]] at depth, found as a [[seatearth]], the underclay associated with [[coal]] measures.

==References==
{{Reflist|2}}

{{Authority control}}

{{DEFAULTSORT:Fire Clay}}
[[Category:Ceramic materials]]
[[Category:Silicates]]
[[Category:Refractory materials]]
[[Category:Bricks]]
[[Category:Clay]]

Fire clay - Revision history

Ajay Kumar at 17:25, 24 August 2023