23 Aluminum Oxide

Aluminum oxide (generally referred to as alumina) is the same composition as sapphire (Al2O3), which accounts for its high hardness and durability. Alumina ceramic is produced by compacting alumina powder into a shape and firing the powder at high temperature to allow it to densify (sinter) into a solid, polycrys-talline, nonporous part. Alumina is the most mature high-technology ceramic in terms of quantity produced and variety of industrial uses. Approximately 5 million metric tons were produced in 1995 for wear, chemical, electrical, medical, and other applications. Table 2.1 lists some of the applications of alumina.

Alumina is used in these applications because of its excellent combination of properties, including high hardness and wear resistance, chemical resistance, smooth surface, reasonable strength, and moderate thermal conductivity. Table 2.2

TABLE 2.1 Production Applications of Aluminum Oxide Ceramics

Seal rings

Rotary and gate valves Pump parts and liners

Papermaking foils, suction box covers, palm guides, liners Cyclone liners

Liners in coal-handling systems

Wire drawing tooling

Thread guides in the chemicals and textile industries Chemical laboratory ware Molten metal filters, crucibles Mill liners and grinding media

Chute and conveyor liners Nozzle, pipe, and tubing liners Wear pads for any application

Spark plug insulators Sodium vapor lamp arc tubes Thermocouple protection tubes Radomes

Grinding wheels, abrasives, polishes Glass tank linings Cutting tool inserts Heat exchange media Medical applications

TABLE 2.2 Comparison of Typical Properties of Aluminum Oxide and Other Advanced Ceramic
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