Uses of refractory

Refractory materials have the following functions:

1.As an insulation layer between the heat medium and the container wall.

2.Withstand physical stress and prevent the erosion of the container wall by the heat medium.

3.Anti-corrosion.

4.Provide insulation.

Refractory materials have a variety of useful applications.In the metallurgical industry, refractory materials are used for the lining of furnaces, kilns, reactors and other containers that hold and transport heat media such as metals and slag.Refractories are also used in other high temperature applications such as fired heaters,hydrogen reformers,ammonia primary and secondary reformers, cracking furnaces, utility boilers, catalytic cracking units, air heaters and sulfur furnaces.

Classification of refractory materials

Refractories are classified in a number of ways, based on:

1.Chemical composition

2.Manufacturing method

3.Melting temperature

4.Refractoriness

5.Thermal conductivity

Based on chemical composition

• Acid refractories

  Acidic refractories are generally not affected by acidic substances, but are easily corroded by alkaline substances, so they are used together with acidic slag in acidic environments.They include substances such as silica, alumina and fireclay bricks.Well-known reagents that can etch alumina and silica are hydrofluoric acid, phosphoric acid and fluorinated gases (e.g. HF, F2). At high temperatures, acidic refractories may also react with lime and basic oxides.

• Siliceous refractories are refractories that contain more than 93% silicon oxide (SiO2).They are acidic and have high thermal shock, flux and slag resistance as well as high spalling resistance. Silica bricks are commonly used as furnace charge in the steel industry. An important property of silica brick is its ability to maintain hardness up to its melting point under high loads.Silica refractories are generally cheaper and therefore easier to handle. New technology has been developed that gives  higher strength and longer casting duration with less silica (90%) when blended with organic resins.

• Zirconia refractories are refractories mainly composed of zirconia (ZrO2). They are often used in glass furnaces because they have low thermal conductivity, are not easily wetted by molten glass, and have low reactivity with molten glass.These refractory materials can also be used in high temperature building materials.Aluminosilicate refractories are mainly composed of alumina (Al2O3) and silica (SiO2). Aluminosilicate refractories can be semi-acidic, refractory clay composites or high alumina content composites.

Alkaline refractories

Alkaline refractories are used in areas where the slag and the atmosphere are alkaline.They are stable to alkaline substances but can react with acids which is important e. g.When removing phosphorus from pig iron (see Gilchrist-Thomas process).The main raw material belongs to the reverse osmosis group, a common example of which is magnesium oxide (MgO).Other examples include dolomite and magnesite.In the first half of the 20th century, the steelmaking process used artificial periclase (roasted magnesite) as a furnace lining material.Magnesite refractories contain ≥ 85% magnesium oxide (MgO).They have high slag resistance to lime and iron-rich slags, are highly wear and corrosion resistant, and have high refractoriness under load and are commonly used in metallurgical furnaces.Dolomite refractories are mainly composed of calcium magnesium carbonate.Generally, dolomite refractories are used in converters and refining furnaces.Magnesia-chromium refractories are mainly composed of magnesium oxide (MgO) and chromium oxide (Cr2O3).These refractories have a high degree of refractoriness and high resistance to corrosive environments.