Mullite


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Related to Mullite: kyanite, corundum, cordierite

mullite

[′mə‚līt]
(mineralogy)
Al6Si2O13 An orthorhombic mineral consisting of an aluminum silicate that is resistant to corrosion and heat; used as a refractory. Also known as porcelainite.

Mullite

 

a mineral from the silicate class, with a chemical composition that varies from Al6Si2O13 to Al4SiO8 (or from 3A12O3 • 2SiO2iO2 to 2Al2O3 • SiO2). Its structure is similar to that of sillimanite; however, mullite differs significantly in the irregularity of the Si and Al atoms. Mullite occurs in small prisms of the orthorhombic system. It has a hardness of 6–7 on Mohs’ scale and a density of 3,030 kg/m3; it melts at a temperature of about 1,810°C. Pure mullite is colorless; it is pinkish or bluish as a result of admixtures of iron or titanium oxides and exhibits pleochroism. Mullite is the only compound of Al2O3 and SiO2 that is stable at high temperatures.

Mullite is rarely found in nature. It was discovered in partially fused clayey enclosures in Quaternary lava on the island of Mull in Scotland. Mullite is an important component of such man-made industrial products as porcelain and fireclay (alumina-containing refractory). It is formed by heating kaolinite to 950°C and by heating such alumina silicates as andalusite, sillimanite, and kyanite at temperatures ranging from 1,300–1,550°C. Fused mullite refractory is obtained in electric furnaces from a mixture consisting of bauxite, alumina, kaolin, coke, and other substances.

References in periodicals archive ?
mullite mass for stuffing knots of the tundish of the caster-3 345.
As with the mullite, the fused silica was heated to 2,012F (1,100C) and broken down with a hammer.
The bands characterizing the [Al.sup.IV]-O stretching vibrations of the mullite tetrahedron at 732 [cm.sup.-1] and 910 [cm.sup.-1] disappeared.
It is evident that there is a strong recrystallization from 1150[grados]C, especially the formation of cristobalite and mullite. This fact explains many of the results obtained for technological properties, as in the case of water absorption and firing shrinkage.
Mullite fiber has been coated with zirconia and then used in the toughening of mullite ceramic composites.
For our measurement system, there is thermal resistant material (mullite) along the round of the heat plate to make the absorber insulated with high temperature.
If the chemical and mineral composition of the two materials (clay and biosolids) are observed, enough aluminum-silicate phases are detected to, at high temperatures (higher than 1000[degrees]C), potentially form phases such as corundum or mullite, which are very stable and hard ceramic products (compact).
Chemically and mineralogically, fly ash is principally a vitreous aluminosilicate, containing various levels of alkalies, alkaline earths, transition metals, and some precipitated crystalline mullite (3[Al.sub.2][O.sub.3] x 2Si[O.sub.2]), the proportions of which depend on the coal composition and processing [57, 58].
This produces an amorphous, highly pozzolanic state, whereas overheating can cause sintering, to form the dead burnt, non-reactive refractory, called mullite. Metakaolin reacts with Ca[(OH).sub.2], produces calcium silicate hydrate (CSH) gel at ambient temperature.
The DSC curves show endothermic and exothermic reactions during calcination, such as desorption of surface water (H2O), dehydroxy lation (structural OH-groups) and the transformation to mullite and cristobalite, with resultant temperature effects of dehydroxylation and polymorphic transformation strongly dependent on kaolinite structural order (Ece et al., 2003; Ekosse, 2008).
Among specific topics are the effect of a blowing agent on cell morphology and acoustic absorption in natural rubber foam, the surface investigation of laser-glazed mullite thin films of yttria-stabilized zirconia coatings, predicting the ultraviolet spectrum of single-stranded DNA, a reliable homemade tissue culture protocol for <Dendrobium/> orchid cultivation, heating energy briquettes from cashew nut shell, and constructing and evaluating instructional packages on vector quantity.
The solid inclusions were identified as mullite and spinel using a Renishaw inVia Raman microscope.