The essential properties of ceramic refractories have been discussed. Ceramics are the principal refractory materials with a wide range of applications. The properties of ceramic refractories and their chemistry and microstructure is explained.
Definition: The materials which have high melting point and have the ability to maintain their structural properties at very high temperature are known as refractories. Generally refractories are composed of ceramics.
Refractories found their application in ceramics industries, metallurgical uses and in glass making. They are used to make interior lines of kilns and furnaces.
Essential Properties of Ceramic Material used to make Refractories:
Ceramics have the properties of high melting point and chemical inertness. They exhibit high strengths due to strong chemical bonds. This makes them useful as a refractory material.
The property of chemical inertness is useful in metallurgy and glass making industry. Special techniques are applied for Machining glass to suit furnaces, where they are exposed to extremely corrosive molten materials and gases. In addition to corrosion resistance, refractories must also be resistant to abrasion and ability to withstand resistant to thermal shock. When a material is rapidly cooled from high temperatures and again brought to a higher temperature, it leads to thermal shock in the object. This leads to the contraction is the surface layers, which ultimately leads to the development of tensile stress and cracks on the surface.
A good ceramic must be a good thermal shock resistant material. This can be achieved by altering their microstructure. The microstructure of ceramic refractories is quite coarse and crude when compared traditional ceramics like porcelain, structural clay, such as bricks.
Most ceramic refractory products are quite porous. Porosity is another essential property of ceramics refractories. It means that air spaces are incorporated into the material. The presence of pores, reduce the load-bearing strength of the material. It reduces susceptibility to thermal shock of the material. The ceramic Machining of Quartz is possible as quartz itself require some amount of porosity. However, this porous structure is undesirable when a refractory material, will come into contact with corrosive substances.
Examples of Refractories:
Basic refractories include chrome, magnesia, dolomite, and other material combinations. Periclase is used to make the ceramic bricks. Periclase is produced from magnesium carbonate, MgCO3. Magnesia bricks can be chemically bonded, pitch-bonded, burned. Chrome brick are another type of basic refractory. It is made from chromium ores, which are complex solid solutions of oxide minerals including chromium and magnetite.
1. Clay Based Refractories: Fireclay, fire bricks, High alumina, alumina bricks, Mullite, silicon carbide, zircon etc.
2. Non-Clay-Based Refractories: Non-clay refractories produce almost exclusively as bricks and pressed shapes. Examples of non clay based are magnesite-chrome, fuse-cast, molds, Magnesium, aluminum, and zirconium.
3. Other Non Clay based refractories: These are produced in smaller quantities for special applications. A Few examples include graphite, forsterite (Mg2SiO4), and magnesia-alumina combination, chrome-alumina, alumina-zirconia-silica and magnesite-chrome combination.
I have explained about various important refractory material and their properties. Machining Quartz is also done due to its properties to be used as a ceramic refractory. Machining procedure of this material requires high expertise and advanced knowledge in this field.
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