Journal ArticleDOI
Structure and properties of mullite—A review
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TLDR
Mullite has achieved outstanding importance as a material for both traditional and advanced ceramics because of its favourable thermal and mechanical properties as discussed by the authors. But it is not a suitable material for many applications.Abstract:
Mullite has achieved outstanding importance as a material for both traditional and advanced ceramics because of its favourable thermal and mechanical properties. Mullite displays various Al to Si ratios referring to the solid solution Al 4+2 x Si 2−2 x O 10− x , with x ranging between about 0.2 and 0.9 (about 55 to 90 mol% Al 2 O 3 ). Depending on the synthesis temperature and atmosphere mullite is able to incorporate a number of transition metal cations and other foreign atoms. The crystal structure of mullite is closely related to that of sillimanite, which is characterized by chains of edge-connected AlO 6 octahedra running parallel to the crystallographic c -axis. These very stiff chains are cross-linked by tetrahedral chains consisting of (Al,Si)O 4 tetrahedra. In more detail: Parallel to a the tetrahedra are linked to the relatively short more stiff Al–O(A, B) bonds, whereas parallel b they are linked parallel to the relatively long more compliant Al–O(D) bonds. In mullite some of the oxygen atoms bridging the tetrahedra are removed for charge compensation. This gives rise to the formation of oxygen vacancies and of T 3 O groups (so-called tetrahedral triclusters). The anisotropy of the bonding system of mullite has a major influence on the anisotropy of its physical properties. For example: • the highest longitudinal elastic stiffness is observed parallel c , but lower ones parallel a and especially parallel b , • the maximum of the thermal conductivity occurs parallel c , but maller ones parallel a and especially parallel b , • large thermal expansion especially parallel b , • fastest crystal growth and highest corrosion parallel c . Heat capacity and thermal expansion measurements of mullite display reversible anomalies in the temperature range between about 1000 and 1200 °C. It is believed that tetrahedral cations, bridging O atoms, and O vacancies undergo dynamical site exchange processes at high temperatures. At lower temperatures the dynamic disorder may transform to a static one. Diffraction experiments revealed that also partially ordered states may exist.read more
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Casting and sintering of a sanitaryware body containing fine fire clay (FFC)
TL;DR: In this article, the effects of casting and sintering behavior of fine fire clay at different particle sizes on sanitaryware body was investigated in a tunnel and box kiln.
Journal ArticleDOI
A Comparison of Al(OH) 3 and Mg(OH) 2 as Inorganic Porogenic Agents for Alumina
TL;DR: In this paper, particles of aluminium hydroxide (Al(OH)3) and magnesium hydroxides (Mg(OH2) of similar average size were added separately to an alumina castable (up to 67 vol.).
Journal ArticleDOI
Porous ceramics with near‐zero‐shrinkage and low thermal conductivity from hazardous secondary aluminum dross
Wenhao Li,Xiaoyan Zhang,Junjie Zhang,Hanlin Shen,Jun Lei Yang,Ying Yue Liu,Jun Lu,Shengen Zhang,Jinlong Yang +8 more
TL;DR: In this article , a simple, versatile, and low-cost approach has been proposed to realize the green utilization of secondary aluminum dross, the hazardous solid waste, namely directly sintering dry-pressed green bodies from secondary aluminium dross to fabricate porous ceramics according to high-temperature foaming process spontaneously without adding spare foaming agents.
Journal ArticleDOI
Research Progress on Oxide/Oxide Ceramic Matrix Composites
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Preparation of TaB/TaB2/mullite composites by combustion synthesis involving aluminothermic reduction of oxide precursors
Chun-Liang Yeh,W.C. Kao +1 more
TL;DR: TaB/TaB2/mullite composites were fabricated by self-sustaining combustion involving aluminothermic reduction of two oxide precursors, Ta2O5 and B2O3 as mentioned in this paper.
References
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Book
Petrogenesis of metamorphic rocks
TL;DR: In this paper, the four divisions of metamorphic grade are defined: very low grade, medium grade, high grade and low grade metamorphism, and the change from low grade to medium grade to high grade.