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.
- Acidic refractoriesconsist of acidic materials like alumina (Al2O3), and silica (SiO2). They are impervious to acidic materials, but easily attacked by basic materials. Important members of this group are alumina, silica, and fireclay refractories.
- Basic refractoriesconsist of basic materials such as CaO, MgO, etc. These are impervious to basic materials, but easily attacked by acidic materials. Important members of this group are magnesite and dolomite refractories.
- Neutral refractories are made from weakly acid/basic materials such as carbon, silicon carbide (SiC), chromite (FeCr2O4) and zirconia (ZrO2).
Based on chemical composition[edit]
Acidic refractories[edit]
Acidic refractories consist of mostly acidic materials like alumina (Al2O3) and silica (SiO2). They are generally not attacked or affected by acidic materials, but easily affected by basic materials. They include substances such as 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, F2).[12] At high temperatures, acidic refractories may also react with limes and basic oxides.
Neutral refractories[edit]
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 R2O3 group. Common examples of these materials are alumina (Al2O3), chromia (Cr2O3) and carbon.
Basic refractories[edit]
These are used in areas where slags and atmosphere are basic. They are stable to alkaline materials but can react to acids. 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.
Based on method of manufacture[edit]
- 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.
Shaped[edit]
These have standard size and shapes. These may be further divided into standard shapes and special shapes. Standard shapes have dimension that are conformed by most 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 9 × 4 1⁄2 × 2 1⁄2 inches (230 × 114 × 64 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 refractories)[edit]
These are without definite form and are only given shape upon application. These types are better known as monolithic refractories. The common examples are plastic masses, Ramming masses, castables, gunning masses, fettling mix, mortars etc.
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.
Based on fusion temperature[edit]
Based on fusion temperature, (melting point) refractory materials are classified into three types.
- Normal refractory: fusion temperature of 1580 ~ 1780 °C (e.g. Fire clay)
- High refractory: fusion temperature of 1780 ~ 2000 °C (e.g. Chromite)
- Super refractory: fusion temperature of > 2000 °C (e.g. Zirconia)
Snip-it from an article by Wikipedia
