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Extremely rare in its natural form, mullite is artificially produced for industry by melting or firing various alumino-silicates. The outstanding thermo-mechanical properties and stability of the resulting synthetic mullite make it a key component in many refractory and foundry.



World’s leading producer of calcined products for the refractory industry
Fused and sintered mullite and fused zirconia mullite solutions for foundry coatings and investment castings
Melting point of mullite


Although mullite exists as a natural mineral, occurrences in nature are extremely rare. 

Industry relies on synthetic mullites which are achieved by melting or ‘calcining’ various alumino-silicates such as kaolin, clays, rarely andalusite or fine silica and alumina to high temperatures. 

One of the best natural sources of mullite is kaolin (as kaolinic clays).. It is ideal for the production of refractories such as fired or unfired bricks, castables and plastic mixes.

Sintered mullite and fused mullite is primarily used for the production of refractories and the casting of steel and titanium alloys.

An aerial view of Andersonville site (USA)
Mullite does not exist in great quantity in a natural state. It is produced by heating of kaolin (or clays) that transform into mullite with formulation
2O3∙ 2SiO2.


  • Good creep resistance
  • Low thermal expansion
  • Low thermal conductivity
  • Good chemical stability
  • Excellent thermo-mechanical stability
  • Excellent thermal shock resistance
  • Low porosity
  • Comparatively lightweight
  • Oxidation resistance


Imerys calcined mullites are recognized as the global benchmark. They are produced from clays mined from the South Georgia kaolin belt in the US, and blended to obtain chemistries between 45% and 70% alumina. 

Our Technology Center in Lyon (France) and our Tianjin laboratory (China) feature an extensive range of minerals processing, testing and analysis tools focused on high resistance materials.


For refractory applications, Imerys high-duty, high-alumina mullites make excellent refractory product for bricks and castable due to high refractoriness, strong stability and high temperature behaviour. In this application, Mullite is well known under the brand Mulcoa.

In investment casting foundry, Imerys mullite is used under Mulgrain name. Mulgrain is used in Shell used to receive the metal. Mulgrain is ideal for preventing metal-mold reaction as well as thermal shock and cracking in finished foundry parts due to their excellent refractoriness and low thermal expansion. 

Mullites are excellent binders for refractory bricks.

Mullite is  an excellent aggregate for refractory bricks.

Imerys offers an extensive portfolio of high-quality calcined minerals with different functional properties, making it a privileged partner for the refractories and ceramics industry.



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