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Kaolin

What is Kaolin?

Kaolin rock

Kaolin, or ‘china clay’ as it is commonly called, is a hydrated aluminum silicate crystalline mineral formed over many millions of years by the hydrothermal decomposition of granite rocks. Hydrous kaolin is characterized by its fine particle size, plate-like or lamellar particle shape and chemical inertness. Metakaolin is manufactured by the calcination of kaolin to form an amorphous pozzolanic  white mineral additive for use in cement based products.

Calcined Kaolin is an anhydrous aluminum silicate produced by heating ultrafine natural kaolin to high temperatures in a kiln. The calcination process increases whiteness and hardness, improves electrical properties, and alters the size and shape of the kaolin particles.

Geology

Kaolin is formed when the anhydrous aluminum silicates found in feldspathic rocks, like granite, are altered by weathering or hydrothermal processes. The process which converted the hard granite into the soft matrix found in kaolin pits is known as ‘kaolinization’. The quartz and mica of the granite remain relatively unchanged whilst the feldspar is transformed into kaolinite. Smectite may also form in small quantities in some deposits. The refining and processing of the fine fraction of the kaolinized granite yields predominantly kaolinite with minor amounts of mica, feldspar, traces of quartz and, depending on the origin, organic substances and/or heavy minerals.

Physical properties

SEM photograph kaolin
  • High brightness
  • Non abrasive
  • Naturally fine particles
  • Refractory, remains white after calcination
  • Weak conductivity (heat and electricity)
  • Hydrophilic and easily dispersed in water
  • Adhesives & Sealants
  • Ceramics
  • Construction
  • Cosmetics
  • Paints & Coatings
  • Paper & Board
  • Plastic Film
  • Rubber
  • Adhesives & Sealants

    In adhesives & sealants, kaolin gives good barrier effect and rheology control.
    Controlling rheology can influence the speed at which adhesive can be applied which is important in high speed paper laminating processes.

  • Ceramics

    Kaolin is a majority component for the ceramics industry, where its high fusion temperature and white firing characteristics make it particularly suitable for the manufacture of sanitaryware, tableware, wall and floor tiles and refractories.

    Kaolin for sanitaryware
  • Construction

    • In the construction industry, kaolin, metakaolin and calcined kaolin are used to improve the mechanical properties, porosity and appearance of various types of concrete and cement.
    • Kaolin provides an excellent alumina source for the production of fiberglass.
    Learn more
  • Cosmetics

    Kaolin is prized in face creams, facemasks and make up where it provides superior sebum and impurities absorption and acts as a texturizing, matting and mattifying agent. It is an ideal natural opacifying agent in gels and shampoos.

    Learn more
    Shampoo bottle
  • Paints & Coatings

    Used in decorative paints, it is an excellent natural opacifier and partial replacement for titanium dioxide in paint formulations.

    kaolin for decorative paints
  • Paper & Board

    In papermaking and fibre based packaging, kaolin imparts gloss, smoothness, printability and improved barrier performance.

  • Plastic Film

    Calcined kaolin is used extensively as an antiblock additive in plastic films and as an infrared barrier additive in plastic films for agricultural and greenhouse applications.

  • Rubber

    In rubber, kaolin helps regulate curing rates, improving consistency and tear resistance. It enhances electrical properties by absorbing polymerization by-products and improves permanent set and processability.
     

    kaolin in rubber

For more information, please visit Imerys Kaolin or Imerys Ceramics.

Imerys Performance Additives Kaolin locations worldwide

Click on the map for contact details of our Kaolin locations worldwide