Ball
Clay is a highly plastic variety of clay of Kaolinite group
like China clay and fire clay, but has less refractoriness.
The chemical composition of ball clay is similar to that of
China clay, except that the ball clay contains a large proportion
of silica.
The main utility of ball clay lies in the plasticity, high bonding qualities and tensile strength. It is therefore, used in bled with non- – plastic to semi – plastics clays for obtaining requisite plasticity. It is added in various proportions for the preparation of body composition of various sanitary wares, bathtub tiles, porcelain, etc. The BIS has prescribed the following specification (IS: 4589 – 1968) for ball clay for use in the ceramic industry: - The material shall be in the form of lumps or power, free from any foreign matter and shall be highly plastic when wet. The lumps shall slake in water and from a smooth suspension when dispersed. The color of the material when fired at 1350o C shall be light gray or light cream and free from any specks or patches. Chemical
Analysis:
Separate reserves estimates of ball clay are not available and this mineral is not included in the list of minerals for the preparation of mineral inventory. The group recommends the following grade for ceramic industry for estimation of reserves of ball clay.
China Clay China clay, also called kaolin, falls under kaolinite group of clay minerals. It results from the alterations of feldspars, granite, gneiss and pegmatite rocks by hydrothermal action of aqueous solution. China clay usually carries some impurities in a small quantity such as silica, iron, magnesium, titanium, calcium, potassium, sodium oxides, mica, tourmaline, etc., which may be inherent in the parent rocks. 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: (A) Ceramics:The BIS has not standardized any specification for use of china clay in ceramic industry. However, for the manufacture of ceramic products, good quality china clay is required which should have water elasticity of 32%, shrinkage after drying should not be more than 7%, and total shrinkage after firing at a temperature of 1300o C not more than 10-14%, Grit should be low. For the manufacture of ordinary crockery and ceramic wares, presence of grit up to 2% is tolerated. But for the manufacture of high-class crockery, grit below 1% is generally preferred. In the manufacture of high-class ceramic products, the presence of lime, magnesia, iron oxides, alkalies and other impurities up to 2% is not harmful. Excess of iron, however, may color the products. Also for the manufacture of electrical switches, the iron content should be as low as possible. (B) Textile and Paper coasting: - China clay is utilized in textile industry and as a sizing and packing material. For this purpose, the clay should be white in color without tinting. Grit is the most objectionable ingredient. Oxides of magnesium and iron should be as low as possible. Dull white clay is utilized in making colored and khaki cloth. China lay is used for paper coating purpose in order to provide a smooth, even surface and to impart a glaze. Various grades of paper quality china clay of fine mash are used depending up on the quality of paper required to be manufacture. The whiteness, ink absorption, chemical inertness, uniformity of particle size and retentive properties determine the suitability of china clay for use in paper coating. BIS (IS: 505 - 1978) has standardized specifications for china clay for use in textile and paper coating industry as follows : -
(C ) Rubber: 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. The
BIS (IS: 505 – 1978) has standardized the specifications given
below:
(D)
Paints: 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. Chinaclay 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.
(F) Filler in paper: Inferior grade china clay may be used in the manufacture of brown paper, newsprint, hardboard paper and straw paperboard. The BIS (IS: 505 – 1978) have standardized the specification as given below:
G. Insecticides:
For used of china clay in other industries like white cement and refractory bricks, there is no standard specification what so ever. In case of manufactures of refractory bricks, the coarse fraction of china clay from the sedimentation tank is used. Due to lack of adequate data, no attempt could be made in the inventory as on 01.01.1985 to classify the reserves of china clay according to its end use grades. After examining the specifications standardized by BIS and the trends in the user industries, the group recommends end use classification of reserves: - (A)
Ceramic:
(B)
Textile & Paper Coating:
(C)
Rubber:
(D) Filler in Paper:
(E)
Insecticide:
The only industry in which fireclay is used is refractory industry. The I.S.I has not standardized any specification. Recently, the sub-committee on Refractory raw materials appointed by the Directorate General of Technical Development (DGTD) has recommended the following seven specifications.
In the inventory as on 01.01.1985 (as also in earlier inventories), no attempt has been made to classify the reserves according to different grades. After examining the specifications prescribed by the Sub-Committee on Refractory Raw Materials of the D. G. T. D., the group recommends the following end-use classification of reserves:
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