Refractory materials are used in furnaces, kilns, incinerators, and reactors. Refractories are also used to make crucibles and moulds for casting glass and metals and for surfacing flame deflector systems for rocket launch structures. Today, the iron- and steel-industry and metal casting sectors use approximately 70% of all refractories produced.
CLASSIFICATION OF REFRACTORY MATERIALS
Refractory materials have different classifications:
1.) Based on chemical composition
Acidic Refractories - Acidic refractories consist of mostly acidic materials. They are generally not attacked or affected by acidic materials, but easily affected by basic materials.
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 R2O3 group.
Basic Refractories - These are used in areas where slags and atmosphere are basic; they are stable to alkaline materials but could react with acids. The main raw materials belong to the RO group to which magnesia (MgO) is a very common example.
2.) Based on method of manufacture – this includes 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.); and Un-formed dry refractories.
3.) Based on fusion temperature - 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); and Super refractory: fusion temperature of > 2000 °C (e.g. Zirconia).
TO SUMMARIZE
Refractories are used by the metallurgy industry in the internal linings of furnaces, kilns, reactors and other vessels for holding and transporting metal and slag. In non-metallurgical industries, the refractories are mostly installed on fired heaters, hydrogen reformers, ammonia primary and secondary reformers, cracking furnaces, incinerators, utility boilers, catalytic cracking units, coke calciner, sulfur furnaces, air heaters, ducting, stacks, etc.
Majority of these listed equipment operate under high pressure, and operating temperature can vary from very low to very high (approximately 900°F to 2900°F). The refractory materials are therefore needed to withstand temperatures over and above these temperatures. Listed below is the sample melting temperatures of key metallurgical elements where refractory application is critical.