China clay, also called kaolin, results from the alterations of feldspars, granite, gneiss and pegmatite rocks. China clay usually carries some impurities in a small quantity such as silica, iron. magnesium, titanium, calcium, potassium, sodium oxides, mica, tourmaline, etc. The quality of china clay depends much upon the impurities present.
China clay in mainly used in ceramics, textiles, Paper, rubber, paints, cosmetics and pharmaceuticals industries. It is also used in insecticides, white cement manufacturing.
The uses and specifications of china clay in different industries are discussed below:
In rubber industry, china clay is used as filler and as a reinforcing and
stiffening agent. For these purposes, lightweight clay having a specific gravity 2.5 is tolerated. It should be of fine mesh and should be of fine mesh and should be absolutely free from copper, which is undesirable in rubber goods.
China clay is used as an extender of suspending agent in the manufacture of while paints. The BIS has not standardized any specification for this use. However, the properties like anti-setting and tinting effects, colloidal nature, softness, freedom from grit, white color and fine size are some of the qualities which make chain clay suitable for use in paint and
distemper manufacture.
Cosmetic and Pharmaceutical: There is no BIS specification. Superfine china clay is utilized for the manufacture of products like power, adhesives, surgical plaster, lotion and ointment for external use, porcelain for dental preparation. China clay for medicinal purpose must be free from lead. arsenic and other metals that the human body will not tolerate. It should have no frothing. Particle size, frothing and sedimentation volumes are the three important factors considered in the selection of china clay for pharmaceutical purpose.
China clay is used in the manufacture of disinfectant like DDT.
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