Oxide ceramics include alumina, zirconia, silica, aluminum silicate, magnesia and other metal oxide based materials. They are non-metallic, inorganic compounds that include oxygen, carbon, or nitrogen. Oxide ceramics have high melting points, low wear resistance, and a wide range of electrical properties. The minerals used to make these ceramic materials are crushed or ground into a fine powder that is purified by adding it to a solution and allowing a chemical precipitate to form. The precipitate is then separated from the solution and heated to form a highly pure powder. After purification, small amounts of wax are added to bind the ceramic powder. Plastics may also be added to provide pliability. The powder can then be shaped into different objects by various molding processes such as slip casting, pressure casting, injection molding, and extrusion. After oxide ceramic materials are molded, they are heated in a process known as densification to strengthen the material.
Oxide ceramics vary by maximum use temperature, thermal conductivity, modulus of rupture, modulus of elasticity, electrical resistivity, average crystal size, density, and purity. The maximum use temperature is the highest temperature to which oxide ceramic materials can be exposed without degradation. Thermal conductivity is the linear heat transfer per unit area for a given applied temperature gradient. The modulus of rupture (MOR) or cross-break strength is the maximum flexural strength that oxide ceramics can withstand before failure or fracture occurs. Young’s modulus or the modulus of elasticity is a material constant that indicates the variation of strain produced under an applied tensile load. Average crystal size measures the individual grains or crystals within the microstructure of a polycrystalline material. Density is the mass per unit of area. Purity is the percentage, by weight, of major components.
Oxide ceramics are available with a variety of special features. For example, glazes and protective coatings seal porosity, improve water or chemical resistance, and enhance joining to metals or other materials. Machinable ceramics can be machined in the green, glass, or finished state without excessive chipping. Porous ceramics have many open or closed internal pores that provide a thermal barrier. Fused materials bond individual grains or crystals together without the use of binders. Instead, these industrial ceramic materials are formed through sintering or firing, hot pressing or hipping, extrusion, fusing and casting, or deposition.
Oxide ceramics are used in a variety of applications. Examples include chemical and materials processing, electrical and high voltage power applications, radio frequency (RF) and microwave applications, and foundry and metal processing. Industrial ceramic materials are used to fabricate optical components such as lenses, windows, prisms, and optical fibers. They are also used in the manufacture of semiconductors and parts and tooling. Refractory ceramics have high melting points and are suitable for applications requiring high wear resistance, high temperature strength, electrical or thermal insulation, or other specialized characteristics. Structural components use oxide ceramic materials that have higher compressive strengths and elastic moduli than metals.