Calcined China Clay (Calcined Kaolin)

Mineral Formula PH Color Bulk Density (Kg/Lit)
Calcined Clay Al2O3·2SiO2·2H2O 5-7 White 0.300 – 0.350

What is Calcined Kaolin?

Calcined Kaolin or Calcined Clay is also called as Metakaolin or Chamotte. It is an an anhydrous aluminium silicate, a white powdered non-plastic material). It is produced when raw kaolin or more popularly known as Clay or China Clay is fired enough to reduce its crystalline water content via a process known as Calcination.

The Chemical formula for Calcined Kaolin is Al2O3·2SiO2·2H2O

The HS code for Calcined Kaolin is 2507

The CAS number of Calcined Kaolin is 15123-81-6

Calcined kaolin uses/Calcined kaolin application:

Synthetic zeolite:

New uses of china clay are in the manufacture of synthetic zeolites. Calcined clay is used as a source of alumina and silica to produce synthetic zeolites. Synthetic zeolites are used in the refineries and petrochemical industries as molecular sieves. This use is becoming widely used.


Paint Extender:

Calcined Kaolin is used as a functional extender in paint. Calcined kaolin has proven to be an excellent extender for titanium dioxide (white) pigment in paint. This is because Kaolin is chemically inert, has high covering power, gives desirable flow properties and reduces the amount of expensive pigments required. Its hardness also improves physical durability of the paint film and its burnish resistance.

Quality & Specifications of Calcined China Clay

Product Name Calcined Kaolin 
Appearance White Micronised Powder
Application Paint, Paper And Rubber, PVC Cables
Physical Parameters
Powder Brightness (%) ISO  Greater than 90.00 %
Water Panel Color Shade On Glass Plate Pure White
Bulk Density (Kg/ Lit) 0.300 – 0.350
Ph (of 10 % solution) 5 – 7
Yellow Index 2 – 3
Oil Absorption (ml / 100gm) 55 – 65
Specific Gravity 2.5 – 2.7
Moisture Content (105°C / 1Hrs) Less than 0.50 %
Dispersion Ability Very Good
Hand Filling Smoothness Smooth
% of TiO2 Replacement 15 % Min.
Hiding / Covering Ability Very Good
Chemical Composition
%SiO2 50 – 52
% Al2O3 42 – 44

What is the process of Calcination?

Calcination is a thermal process that causes raw clay to transform to other amorphous or crystalline phases. The phase transformations that occur during calcination are the dehydroxylization of kaolinite to metakaolinite at about 500°C and crystallization of metakaolinite into mullite above 1,000°C. Calcination increases the brightness of kaolin by burning off organic matter and structures the clay into aggregates.

The practical definition of Calcination is heating raw clay until all its free water evaporates, all organic contamination is burned off, and all lattice-bound water is driven off.

Calcination is most commonly performed in rotary kiln also known as a calciner.

The calcination process increases whiteness and hardness of the Clay, improves its electrical properties, and alters the size and shape of the kaolin particles.Calcination makes the powder whiter and more chemical inert.

How does Calcination Change Clay or China Clay or Kaolin?

  1. Removes Free Moisture: Between 100°C – 150°C
  2. Dehydroxylation: Removal of chemically bound moisture. This happens between 400°C to 600°C and the product is known as metakaolin. Metakaolin has applications in cement, rubber, cables & ultramarine blue.
  3. Exothermic recrystallization: Between 925°C – 1050°C Metakaolin transforms to the Spinel Phase. The spinel phase is used mainly for paint applications as an extender for TiO2; it also has a few applications for paper, ceramics, polymer and rubber industries.
  4. Mullite Formation – At temperatures beyond 1050°C crystals of Mulltie begin to form. The mullite phase finds its way into the ceramic industry.

Calcined kaolin

Ashok Mineral Enterprises offers Calcined kaolin also known as Calcined Clay which is an anhydrous clay, thermally structured aluminum silicate, formed by heating ultra-fine natural kaolin at a very high heat which is used for application in industries such as paint, rubber, paper and ceramic.

Calcined Kaolin price

Ashok Mineral Enterprises offers Calcined Clay for various industries including the Paint & Coatings industry. For any further details on grades available, Price and offers please contact us.


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