Ball clay, like china clay, is a variety of kaolin. It differs from china clay in having a higher
plasticity and less refractoriness. In chemical composition, ball and china clays do not differ
greatly except that the former contains a larger proportion of silica. Its name is derived from
the practice of removing it in the form of ball-like lumps from clay pits in the UK.
Verwenden
The main
utility of ball clay is its plasticity, and it is mixed with nonplastic or less plastic clays to make
them acquire the requisite plasticity. The high plasticity of ball clay is attributed to the fact
that it is fine-grained and contains a small amount of montmorillonite. Over 85% of the
particle sizes present in ball clay are of 1 μm or less in diameter. It is light to white in color
and on firing may be white buff. The pyrometric cone equivalent to ball clay hardly ever
exceeds 33. Usually the following mass fractions of ball clay are commonly used in various
types of ceramic compositions: vitreous sanitaryware 10 to 40 wt.%, chinaware 6 to 15 wt.%,
floor and wall tiles 12 to 35 wt.%, spark plug porcelain 10 to 35 wt.%, semivitreous whiteware 20 to 45 wt.%, and glass melting-pot bodies 15 to 20 wt.%. The wide use of ball clay is mainly
due to its contribution of workability, plasticity, and strength to bodies in drying. Ball clay,
on the other hand, also imparts high-drying shrinkage, which is accompanied by a tendency
toward warping, cracking, and sometimes even dunting. This undesirable property is compensated by the addition of grog.
Application
Industrial applications: Filler for paper and board, coating clays, ceramics, bone china,
hard porcelain, fine earthenware, porous wall tiles, electrical porcelain, semivitreous china,
glazes, porcelain, enamels, filler for plastics, rubbers and paints, cosmetics, insecticides,
dusting and medicine, textiles, and white cement.
