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| China Clay, which falls under the Kaolinite
group of clays is formed by weathering or hydrothermal
alteration of felspathic rocks. It has the general formula
A12, (Si205) (OH)4. It is a hydrated alumino-silicate
having sheet structure. Free Silica (grit) is the most
undesirable impurity and is removed during processing
by levigation, sedimentation or air-separation. |
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| Some of the basic features of this mineral
are low cost, high brightness, fine particle size, platelet
shape and hydrophilic surface chemistry |
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| It is one of the essential raw materials
in the ceramic industry. A small quantity is used in white
cement, cosmetics, pharmaceuticals, abrasives, insecticides
and ultramarine blue. It is also used in the manufacture
of fine porcelain. The modern production method is a three-part
process. First, the earth overlying the clay is removed,
and a high-pressure water jet is fired at the quarry face,
liberating the clay. The clay must then be sifted and
refined to remove impurities before finally being dried
to reduce its moisture content.
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| Key to Identification |
Silica
|
SiO2 |
48 % |
| Alumina |
Al203 |
35 % to 40 % |
| Ferric Oxide |
Fe2O3 |
0.5% |
| Titanium Dioxide |
TiO2 |
0.75% |
| Magnaous Oxide |
MnO |
Traces |
| Calcium Oxide |
CaO |
Nil |
| Magnesium Oxide |
MgO |
0.70% |
| Sodium Oxide |
Na2O |
0.39% |
| Pottasium Oxide |
K2O |
0.30% |
| Loss on Ignition |
L.O.I |
13 % |
| Bulk Density (after
50 tabs ) |
0.75
gm/cc |
| pH of 10 % Solution |
8 |
| Whiteness by reflection
compared with MgO taken as 100 % |
75
% to 90 % |
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