Editing Refractory (section)

==Classification of refractory materials==
{{More citations needed section|date=August 2023}}
Refractories are classified in multiple ways, based on:

# Chemical composition 
# Method of manufacture 
# Size and shape
# Fusion temperature 
# Refractoriness 
# Thermal conductivity

===Chemical composition===

====Acidic refractories====
Acidic refractories are generally impervious to acidic materials but easily attacked by basic materials, and are thus used with acidic slag in acidic environments. They include substances such as [[Silicon dioxide|silica]], [[alumina]], and [[fire clay]] brick refractories. Notable reagents that can attack both alumina and silica are hydrofluoric acid, phosphoric acid, and fluorinated gases (e.g. HF, F<sub>2</sub>).<ref>{{Cite web|url = http://accuratus.com/alumox.html|title = Accuratus|date = 2013|access-date = November 22, 2014|website = Aluminum Oxide, Al2O3 Ceramic Properties}}</ref> At high temperatures, acidic refractories may also react with limes and basic oxides.

* '''Silica refractories''' are refractories containing more than 93% [[silicon oxide]] (SiO<sub>2</sub>). They are acidic, have high resistance to thermal shock, flux and slag resistance, and high spalling resistance. Silica bricks are often used in the iron and steel industry as furnace materials. An important property of silica brick is its ability to maintain hardness under high loads until its fusion point.<ref name="IspatGuru" /> Silica refractories are usually cheaper hence easily disposable. New technologies that provide higher strength and more casting duration with  less silicon oxide (90%)  when mixed with organic resins have been developed.  
* '''Zirconia refractories''' are refractories primarily composed of [[Zirconium dioxide|zirconium oxide]] (ZrO<sub>2</sub>). They are often used for glass furnaces because they have low thermal conductivity, are not easily wetted by molten glass and have low reactivity with molten glass. These refractories are also useful for applications in high temperature construction materials.
* '''Aluminosilicate refractories''' mainly consist of [[alumina]] (Al<sub>2</sub>O<sub>3</sub>) and silica (SiO<sub>2</sub>). Aluminosilicate refractories can be semiacidic, fireclay composite, or high alumina content composite.{{clarify|date=May 2020}}<ref>{{Cite book|last=Poluboiarinov|first=D. N.|title=Vysokoglinozemistye keramicheskie i ogneupornye materialy|year=1960|location=Moscow}}</ref>

====Basic refractories====
Basic refractories are used in areas where slags and atmosphere are basic. They are stable to alkaline materials but can react to acids, which is important e. g. when removing [[phosphorus]] from [[pig iron]] (see [[Gilchrist–Thomas process]]). The main raw materials belong to the RO group, of which magnesia (MgO) is a common example. Other examples include dolomite and chrome-magnesia. For the first half of the twentieth century, the steel making process used artificial [[periclase]] (roasted [[magnesite]]) as a furnace lining material.

* '''Magnesite refractories''' are composed of ≥ 85% [[magnesium oxide]] (MgO). They have high slag resistance to lime and iron-rich slags, strong abrasion and corrosion resistance, and high refractoriness under load, and are typically used in metallurgical furnaces.<ref>{{Cite web|url=https://www.termorefractories.com/products/refractory-bricks-blocks/magnesite-refractories.html|title=Magnesite Refractories|website=www.termorefractories.com|access-date=2020-03-06}}</ref>
* '''Dolomite refractories''' mainly consist of [[calcium magnesium carbonate]]. Typically, dolomite refractories are used in converter and refining furnaces.<ref>{{Cite web|url=http://www.ruizhirefractory.com/en/new/dolomite-Brick-and-Magnesite-Dolomite-Brick.html|title=Dolomite brick and magnesia dolomite brick|website=www.ruizhirefractory.com|access-date=2020-03-06}}</ref>
* '''Magnesia-chrome refractories''' mainly consist of magnesium oxide (MgO) and [[Chromium(III) oxide|chromium oxide]] (Cr<sub>2</sub>O<sub>3</sub>). These refractories have high refractoriness and have a high tolerance for corrosive environments.

====Neutral refractories====
These are used in areas where slags and atmosphere are either acidic or basic and are chemically stable to both acids and bases. The main raw materials belong to, but are not confined to, the R<sub>2</sub>O<sub>3</sub> group. Common examples of these materials are [[Aluminum oxide|alumina]] (Al<sub>2</sub>O<sub>3</sub>), [[Chromium(III) oxide|chromia]] (Cr<sub>2</sub>O<sub>3</sub>) and carbon.<ref name="IspatGuru" />

* '''Carbon graphite refractories''' mainly consist of [[Graphite|carbon]]. These refractories are often used in highly reducing environments, and their properties of high refractoriness allow them excellent thermal stability and resistance to slags.
* '''Chromite refractories''' are composed of sintered magnesia and chromia. They have constant volume at high temperatures, high refractoriness, and high resistance to slags.<ref>{{Cite web|url=https://termorefractories.com/products/refractory-bricks-blocks/chromite-refractories.html|title=Chromite Refractories|website=termorefractories.com|access-date=2020-03-06}}</ref>
* '''Alumina refractories''' are composed of ≥ 50% alumina (Al<sub>2</sub>O<sub>3</sub>).

===Method of manufacture===
#Dry press process
#Fused cast
#Hand molded
#Formed (normal, fired or chemically bonded)
#Un-formed (monolithic-plastic, ramming and gunning mass, castables, mortars, dry vibrating cements.)
#Un-formed dry refractories.

===Size and shape===
Refractory objects are manufactured in standard shapes and special shapes. Standard shapes have dimensions that conform to conventions used by  refractory manufacturers and are generally applicable to kilns or furnaces of the same types. Standard shapes are usually bricks that have a standard dimension of {{cvt|9|x|4.5|x|2.5|in|mm}} and this dimension is called a "one brick equivalent". "Brick equivalents" are used in estimating how many refractory bricks it takes to make an installation into an industrial furnace. There are ranges of standard shapes of different sizes manufactured to produce walls, roofs, arches, tubes and circular apertures etc. Special shapes are specifically made for specific locations within furnaces and for particular kilns or furnaces. Special shapes are usually less dense and therefore less hard wearing than standard shapes.

====Unshaped (monolithic)====
These are without prescribed form and are only given shape upon application. These types are known as monolithic refractories. Common examples include plastic masses, [[ramming masses]], castables, gunning masses, fettling mix, and mortars.

Dry vibration linings often used in [[induction furnace]] linings are also monolithic, and sold and transported as a dry powder, usually with a magnesia/alumina composition with additions of other chemicals for altering specific properties. They are also finding more applications in blast furnace linings, although this use is still rare.

===Fusion temperature===
Refractory materials are classified into three types based on [[fusion temperature]] (melting point).

*'''Normal refractories''' have a fusion temperature of 1580{{ndash}}1780&nbsp;°C (e.g. fire clay)
*'''High refractories''' have a fusion temperature of 1780{{ndash}}2000&nbsp;°C (e.g. chromite)
*'''Super refractories''' have a fusion temperature of > 2000&nbsp;°C (e.g. zirconia)

===Refractoriness===
Refractoriness is the property of a refractory's multiphase to reach a specific softening degree at high temperature without load, and is measured with a [[pyrometric cone]] equivalent (PCE) test. Refractories are classified as:<ref name="IspatGuru" />

* '''Super duty:''' PCE value of 33–38
* '''High duty:''' PCE value of 30–33
* '''Intermediate duty''': PCE value of 28–30
* '''Low duty''': PCE value of 19–28

===Thermal conductivity===
Refractories may be classified by [[thermal conductivity]] as either conducting, nonconducting, or insulating. Examples of conducting refractories are [[silicon carbide]] (SiC) and [[zirconium carbide]] (ZrC), whereas examples of nonconducting refractories are silica and alumina. Insulating refractories include [[calcium silicate]] materials, [[Kaolinite|kaolin]], and zirconia.

Insulating refractories are used to reduce the rate of heat loss through furnace walls. These refractories have low thermal conductivity due to a high degree of porosity, with a desired porous structure of small, uniform pores evenly distributed throughout the refractory brick in order to minimize thermal conductivity. Insulating refractories can be further classified into four types:<ref name="IspatGuru" />

# '''Heat-resistant''' insulating materials with application temperatures ≤ 1100&nbsp;°C
# '''Refractory''' insulating materials with application temperatures ≤ 1400&nbsp;°C
# '''High refractory''' insulating materials with application temperatures ≤ 1700&nbsp;°C
# '''Ultra-high refractory''' insulating materials with application temperatures ≤ 2000&nbsp;°C