Refractory
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224306620
2008-07-08T07:20:31Z
Ithunn
5057149
/* Refractory materials */ (sintax, interlinks)
{{otheruses1|heat resistance}}
The term '''refractory''' refers to the quality of a material to retain its strength at high [[temperature]]s. ASTM C71 defines refractories as "non metallic materials having those chemical and physical properties that made them applicable for structures, or as components of systems, that are exposed to enviroments above 1000 °F (538 °C)"<sup>1</sup>.
Refractory materials are used in linings for [[furnace]]s, [[kiln]]s, [[incinerator]]s and [[reactor]]s. They are also used to make [[crucible]]s.
== Refractory materials ==
Refractory materials must be chemically and physically stable at high temperatures. Depending on the operating environment, they need to be resistant to [[thermal shock]], be chemically [[inert]], and/or have specific values 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]]). [[Fire clay|Fireclays]] are also widely used in the manufacture of refractories.
Refractories must be chosen according to the conditions they will face. Some applications require special refractory materials. [[Zirconia]] is used when the material must withstand extremely high temperatures. [[Silicon carbide]] and [[carbon]] are two other refractory materials used in some very severe temperature conditions, but they cannot be used in contact with [[oxygen]], as they will oxidize and burn.
=== Types of refractories ===
[[Acid]]ic refractories cannot be used in a [[base (chemistry)|basic]] environment and basic refractories cannot be used in an acidic environment because they will be [[corrosion|corroded]]. Zircon, fireclay and silica are acidic, [[dolomite]] and magnesite are basic and [[alumina]], [[chromite]], silicon carbide, carbon and [[mullite]] are neutral. [[Refractory metals]] are also frequently used.
Refractory materials are used extensively in the metal industries, along with glass melting and other heat treatment operations.
There are two common forms of refractories, bricks and monolithics. Bricks (also known as [[firebrick]]) are pre-sintered forms which can hold their shape. Monolithics are loose material which can be formed into complex shapes, or sprayed into place, and have to be [[sintered]] before use. Castable refractory [[cement]] is also commonly used.
== Refractory Anchorage ==
Anti-abrasion refractory attached to pipes, chambers, etc, will require anchorage systems such as wire formed anchors or [[hexmetal]] to support the refractory linings.
== Refractory heat-up ==
Usually, refractories require special [[Refractories heat-up|heat-up techniques]] to insure that their performance will be attained as designed, and to avoid thermal shock and drying stresses until the operational status is achieved.
==References==
<sup>1</sup> ASTM Volume 15.01 Refractories; Activated Carbon, Advanced Ceramics
==See also==
*[[Furnace]]
*[[Masonry oven]]
*[[Refraction (metallurgy)]]
==External links==
* [http://www.refractoriesinstitute.org/ The Refractories Institute]
* [http://www.causeway-steel.co.uk/ Causeway Steel Products - Reafractory Anchorage Systems]
[[Category: Materials]]
[[Category: Chemical properties]]
[[Category:Refractory materials| ]]
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