Refractory Materials

International Standards Organization ASTM defines refractory materials as “non-metallic materials having those chemical and physical properties that make them applicable for structures, or as components of systems, that are exposed to environments above 1,000 °F”. In other words, the most remarkable feature of refractory materials is their resistance to high temperatures. They are also chemically inert and coefficient of thermal expansions. Refractory materials are used in a wide range of industries, but the iron-steel industry is probably the biggest consumer. Statistics show that at least %70 of the refractory materials ever produced are used in this sector. Furnaces, kilns, incinerators, and reactors are the main applications of refractory materials.

Which Materials Are Refractory?

Aluminum oxide, silicon oxide, and magnesium oxide are the most commonly used materials in refractories. Calcium oxide, tungsten carbide, and boron nitride are other examples of refractory materials. It is important to choose the refractory materials based on the conditions they are going to face. For example, hafnium carbide is probably the strongest refractory material against heat with a melting point of 4250 C. For this reason, it can be used in all severe temperature conditions. However, if acidic resistance is more important than the resistance to heat, alumina and silica would be a better choice.

Classification of Refractory Materials

Refractory materials are classified by their chemical composition and their method of manufacture. Classification based on chemical composition defines the nature of refractory materials and three in total: Acidic refractories, Neutral refractories, and Basic refractories. Acidic refractories are not affected by acidic materials, but they are less resistant to heat and corrosion. Basic refractories are stable against alkaline materials but they are affected by acidic ones. Lastly, Neutral refractories are the most chemically stable ones and can resist both acids and bases. It can also be said that the most commonly used form of refractory materials is fire bricks.