Mullite, also known as porcelainite, is a rare silicate mineral formed through contact metamorphism of clay minerals. It exists in two stoichiometric forms: 3Al2O3·2SiO2 or 2Al2O3·SiO2, uniquely containing no charge-balancing cations. Mullite’s structure includes three aluminium sites: two distorted tetrahedral and one octahedral. First described in 1924 on the Isle of Mull, Scotland, mullite occurs as argillaceous inclusions in volcanic rocks there, as well as with sillimanite in tonalite at Val Sissone, Italy, and alongside emerylike rocks in Argyllshire, Scotland.
science.orgPorcellanite
Mullite (porcelainite) can be found as a constituent mineral in a type of thermally-metamorphosed rock called porcellanite.4
Use in porcelain
Mullite is present in the form of needles in porcelain.5
It is produced during various melting and firing processes, and is used as a refractory material,6 because of its high melting point of 1840 °C.7
In 2006 researchers at University College London and Cardiff University discovered that potters in the Hesse region of Germany since the late Middle Ages had used mullite in the manufacture of a type of crucible (known as Hessian crucibles), that were renowned for enabling alchemists to heat their crucibles to very high temperatures.89 The formula finally replicated in the above studies (using kaolinitic clay and then firing it at temperatures above 1100 °C) was kept a closely guarded secret by those crucible makers since the 15th century.
Mullite morphology is also important for its application. In this case, there are two common morphologies for mullite. One is a platelet shape with low aspect ratio and the second is a needle shape with high aspect ratio. If the needle shape mullite can form in a ceramic body during sintering, it has an effect on both the mechanical and physical properties by increasing the mechanical strength and thermal shock resistance. The most important condition relates to ceramic chemical composition. If the silica and alumina ratio with low basic materials such as sodium and calcium is adjusted, the needle shape mullite forms at about 1400 °C and the needles will interlock. This mechanical interlocking contributes to the high mechanical strength of porcelain.1011
Use as a catalyst
Further recent research indicates that a synthetic analogue of mullite can be an effective replacement for platinum in diesel engines for exhaust management.12
Notes
- Martinón-Torres, Marcos; Thilo Rehren; Ian C. Freestone (November 2006). "Mullite and the mystery of Hessian wares" (PDF online reproduction). Nature. 444 (7718). London: Nature Publishing Group: 437–438. Bibcode:2006Natur.444..437M. doi:10.1038/444437a. PMID 17122847. S2CID 4362496.
- Schneider, Hartmut (2005). "General Introduction". In Hartmut Schneider; Sridhar Komarneri (eds.). Mullite. Weinheim, Germany: Wiley-VCH. pp. xv–xx. ISBN 978-3-527-30974-0. OCLC 58051400.
- "Sithean Sluaigh, Strathclyde, Scotland, UK". MinDat. MinDat. Retrieved 6 November 2015.
References
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http://webmineral.com/data/Mullite.shtml Webmineral http://webmineral.com/data/Mullite.shtml ↩
http://rruff.geo.arizona.edu/doclib/hom/mullite.pdf Handbook of Mineralogy http://rruff.geo.arizona.edu/doclib/hom/mullite.pdf ↩
Fediuk, F.; Langrova, A.; Melka, K. (2003). "North Bohemian Porcellanites and their Mineral Composition: the Case of the Dobrčice Quarry, the Most Basin" (PDF). Geolines. 15: 35–43. http://geolines.gli.cas.cz/fileadmin/volumes/volume15/G15-035.pdf ↩
Kingery, W.D., ed. (1960). Ceramic Fabrication Processes. New York City: John Wiley & Sons, Inc. /wiki/New_York_City ↩
H. Schneider & S. Komarneni (2005) Mullite. Wiley, VCH, 509 pp, ISBN 3-527-30974-8 /wiki/ISBN_(identifier) ↩
Kyanite Mining Corporation (2009-10-25). "Virginia Mullite". http://www.kyanite.com/mullite.html ↩
University College London (2006-11-23). "21st Century Technology Cracks Alchemists' Secret Recipe". Science Daily. ScienceDaily LLC. Retrieved 2008-01-12. /wiki/University_College_London ↩
Martinon-Torres M.; Freestone I.C.; Hunt, A.; Rehren, T. (2005). "Mass-produced mullite crucibles in medieval Europe: Manufacture and material properties". Journal of the American Ceramic Society. 91 (6): 2071–2074. doi:10.1111/j.1551-2916.2008.02383.x. /wiki/Doi_(identifier) ↩
Hanson, Tony. "Mullite". digitalfire.com. Retrieved 2023-05-21. https://digitalfire.com/material/mullite ↩
"Vitrification Behaviour of The Porcelain Tile". Ceramics Research Co. 2012. Retrieved May 21, 2023. https://www.ceramic-research.com/articles_01.html ↩
Wang, W.; G. McCool; N. Kapur; G. Yuan; B. Shan; M. Nguyen; U. M. Graham; B. H. Davis; G. Jacobs; K. Cho; X. Hao (17 August 2012). "Mixed-Phase Oxide Catalyst Based on Mn-Mullite (Sm, Gd)Mn2O5 for NO Oxidation in Diesel Exhaust". Science. 337 (6096): 832–835. Bibcode:2012Sci...337..832W. doi:10.1126/science.1225091. PMID 22904009. S2CID 27948924. Retrieved 2012-08-16. https://www.science.org/doi/full/10.1126/science.1225091 ↩