Unlike other minerals, Mullite (3Al2O3 .2SiO2) occurs only rarely in nature and is primarily synthesized by calcining kyanite, bauxite or alumina/kaolin mixtures. The word mullite is derived from the Isle of Mull off the English coast, where the only naturally occurring deposits of mullite has been found. Find out why mullite is so popular in high-temperature refractories in a number of different applications. Click To Tweet

What is Mullite?

Mullite has an extremely high melting temperature of 1840 C, so it has excellent electrical insulation and hot load-bearing properties. It resists most corrosive environments and is very low in magnetic iron, making it ideal for steel and glass applications. 

Pro Tip: Mullite performs well in high-temperature applications, and experiences exceptional volume stability, making it a popular choice in refractories.

Mullite Properties

  • Excellent high-temperature strength
  • Good thermal shock resistance
  • Volume Stable
  • Resistance to chemical attack; excellent stability in acid metal slags and is insoluble in most acids
  • High creep resistance
  • Resistance to oxidation and attack by furnace atmospheres
  • Resistance to abrasion
  • Good electrical resistivity

Top Industries That Use Mullite-Based Refractories

  • Steel: The steel industry is the largest consumer of mullite refractories, where high creep resistance and thermal shock resistance are crucial.  The main use of mullite-based products is in blast stove bricks. Many refractories in the steel industry have varying amounts of mullite based components in them. Refractories such as MAFTEC™ are made with mullite fibers, which make them so ideal for high-temperature use.
  • Glass: The glass industry uses mullite refractories in burner blocks, ports and checker bricks as well as in the upper portion of the tanks where glass is melted. The properties outlined above are what make mullite highly prized by the glass industry.
  • Ceramics: Mullite is commonly used the ceramic industry mostly in kiln furniture items such as kiln setter slabs and posts for supporting ceramic ware during firing.

Mullite: An Excellent Choice For Refractories

Don’t know how to get to The Isle of Mull? Lucky for you, synthetic mullite is easily accessible. It has excellent high-temperature properties with improved thermal shock and thermal stress resistance owing to the low thermal expansion, good strength and interlocking grain structure. 

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