is part of our natural world. Its uses are multiple and diversified.
Kaolin’s whiteness and plasticity make it extremely suitable for
its extensive use as a filler, extender, ceramic raw material and pigment.
It is also an important raw material to refractory, and to catalyst,
cement and fibre glass industries.
Kaolin is used in many applications. It is a unique industrial mineral,
which remains chemically inert over a relatively wide pH range and it
offers excellent covering when used as a pigment or extender in coated
films and filling applications. In addition, it is soft and non-abrasive
and has a low conductivity of heat and electricity.
two largest applications of kaolin are the coating of paper to hide
the pulp strands and the production of high grade ceramic products.
It is also used in many other industrial processes:
in Paper: In this industry, kaolin is used both as a filler
in the bulk of the paper and to coat its surface. Kaolin's whiteness,
opacity, large surface area and low abrasivity make it an ideal raw
material for paper production. Its use allows a reduction in the amount
of expensive wood pulp required, enhances the optical properties of
the paper and improves its printing characteristics. When used as a
coating on the surface of the paper, kaolin's whiteness improves paper
brightness and opacity, whilst the size and the shape of the individual
kaolin particles give the gloss and printed paper quality required for
many different kinds of paper. Examples include papers for magazines
and brochures, art paper, cartons and boxes etc.
Kaolin in Ceramics: Kaolin converts to mullite and
glass when fired to temperatures exceeding 1000° C. It is used in
formulations described as white wares, which consists
of tableware, sanitary ware, and wall and floor tiles. It provides strength
and plasticity in the shaping of these products and reduces the amount
of pyroplastic deformation in the process of firing. In tableware, in
addition to the strength and plastic qualities, it is essential to the
achievement of high fired whiteness. This is because it contains a low
content of colouring elements such as iron and titanium.
For sanitaryware, the product is formed by casting (either in plaster,
or resin moulds under pressure). Kaolin contributes the rheological
properties that enables the casting slip to flow and drain after the
cast formation. The cast pieces are relatively heavy and the kaolin
must be strong to withstand the weight and retain the shape before the
pieces enter the kiln.
Fillers: When kaolin is used as a pigment, it is divided
broadly into filler- and paper coating grade clays based on their brightness
and viscosity. Its main properties, especially its whiteness or near
whiteness, make it very suitable as a filler or pigment. In addition,
it remains inert over a wide PH range, is nonabrasive, has a low heat
and electrical conductivity and offers brightness and opacity.
Paint: In its hydrous or calcined forms, kaolin can
improve the optical, mechanical and rheological properties of a paint.
Calcined kaolins are widely used in satin and matt paints where they
can deliver increased opacity, whiteness and scrub resistance. Kaolin
is particularly useful as a partial replacement for TiO2 pigment.
Rubber: Kaolin adds strength, abrasion resistance and
rigidity to rubber. Calcined kaolin in particular, with or without a
chemical surface treatment, finds extensive use in high value thermoplastic
elastomers for a variety of applications and in rubber insulation on
high voltage power lines.
Plastics: Kaolin is used in plastics to provide smooth
surfaces, dimensional stability and resistance to chemical attack, to
conceal fibre reinforcement patterns and to reduce shrinkage and cracking
during polymer compounding and shape forming. It is also used as a rheological
modifier and functional filler, in which capacity it is used to improve
mechanical, electrical and thermal properties. A major application is
in PVC cables where its main function is to improve electrical p r o
p e r ties. Other important applications include specialty films where
they impart anti-blocking or infrared absorption characteristics. Chemically
treated, calcined kaolins is one of the major additives used in the
manufacture of automotive parts based on engineering thermoplastics.
Refractories: Refractories are produced from natural
materials, combinations of compounds and minerals, such as kaolin, which
are used to build structures
subjected to high temperatures, ranging from simple to sophisticated
products, e.g. from fireplace brick linings to re-entry heat shields
for the space shuttle. In industry,
they are used to line boilers and furnaces, ladles, stills, kilns and
Fiberglasss : The fibreglass which is used as a strengthener
in a multitude of applications requires the use of kaolin for its manufacture.
Kaolin allows for the strengthening of the fibres integrated into the
material. It also improves the integration of fibres in products requiring
strengthened plastics: cars, boats and marine
products, sporting goods and recreation products, aviation and aerospace
products, circuit board manufacturing, fibreglass insulation, fibreglass
air filters, fibreglass tanks and pipes, corrosion resistant fibreglass
products, fibreglass building and construction products, etc.