Editing Refractory (section)

===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>).