Industrial Ceramics

Ceramics are inorganic, non-metallic materials formed due to heat. The American Society for Testing and Materials (ASTM) defines a ceramic article as, “an article having a glazed or unglazed body of crystalline or partly crystalline structure, or of glass, which body is produced from essentially inorganic, non-metallic substances and either is formed from a molten mass which solidifies on cooling, or is formed and simultaneously or subsequently matures by the action of the heat.” Most ceramic materials are porous, hard, and brittle. Ceramics has many advantages over metal, alloys, and compounded materials.

Industrial Ceramics have very good thermal, wear, and structural properties. It provides high performance in harsh environments where there are high temperatures, and in erosive, corrosive and abrasive conditions. Due to such qualities, ceramics are widely used in industries.

Refractory materials are those, which can retain their strength even at high temperatures. Such materials are used to make crucibles and linings for kilns, furnaces, and incinerators. Usually, a material that can withstand a temperature of up to 1100° C without softening is termed as refractory material.

Some of the refractory materials commonly used in industries are:

1   Magnesia – It is a white solid mineral formed by an ionic bond between one magnesium and one oxygen atom. It is used as a basic refractory material for lining crucibles.
2   Lime – It is a naturally occurring mineral and the materials derived from it are used in various industrial applications.
3   Fire Clay – It is a specific kind of clay used in manufacturing firebricks. It has a high percentage of silicon and aluminum oxides, which makes it able to withstand temperatures of up to 1600° C. Hence it is suitable for lining furnaces.
4   Silicon Carbide – It is a ceramic compound of silicon and carbon. With a melting point of nearly 2700 ° C, and being highly chemically inert, it is widely used to make furnace parts for heating and casting metals.
5   Zirconia – It is a white crystalline oxide of zirconium, with a melting point of 2715 ° C. It is used as a refractory material, in insulation, abrasives, and ceramic glazes.

Kilns are thermally insulated chambers resembling ovens, in which controlled temperature conditions are created. They are often used in industries to burn, harden or dry materials. Kilns are an vital part of the ceramic manufacturing process, which usually requires heat treatment at high temperature. During this process, various physical and chemical reactions occur, as a result of which the materials properties are permanently changed. The composition and preparation of the clay item will determine the final characteristics, so will the temperature at which it is fired, and the glazes that are used. Part of the firing process includes sintering. This process heats the clay until the particles partially melt and bond, which creates a strong, composite mass, which has a glassy phase, and is interspersed with pores and crystalline material. Through firing, due to reduction in pore size, the material shrinks. The crystalline material formed is a matrix of mostly silicon and aluminium oxides, and is very hard and strong. However, these materials tend to be brittle.

The two broad types of kilns are:    Intermittent and Continuous.
In the intermittent kiln, the ware to be fired is loaded, and taken out after the firing and cooling of both, the ware as well as the kiln.
The continuous or tunnel kiln has a centrally heated portion where the ware to be fired is continuously fed, somewhat like a car wash system.