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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Mechanical properties of unidirectional laminated hybrid SiC–Nextel™ 720 fiber-reinforced oxide matrix composites fabricated by a novel precursor infiltration and pyrolysis method
Lixia Yang,Bofeng Zhong,Jiahao Liao,Peixuan Ouyang,Zhaofeng Chen,Fei Wang,Lirong Luo,Zongde Kou +7 more
TL;DR: In this article, the effect of annealing atmosphere (Ar and air) at 1200°C on the mechanical properties and failure mechanism of the composites was investigated, and it was shown that the presence of a considerable amount of residual carbon in the Ar-annealed composite effectively weakened the fiber/matrix interface by reducing the residual radial compressive stress and the interfacial coefficient of friction.
Journal ArticleDOI
Decoration of anatase-graphene nanocomposites on extruded nano-porous mullite based support for dye degradation under solar irradiation in a dynamic system: Photocatalytic activity and mechanical characterization
Shiva Salem,Paria Kazemi +1 more
TL;DR: In this article, an anatase-graphene-based photocatalytic composite was used for wastewater treatment under solar irradiation, which needs considering the facile decoration, mechanical reliability and economy.
Journal ArticleDOI
Novel process for synthesizing fused mullite from titanium-rich medium/low grade or waste bauxite
TL;DR: In this paper , the authors introduced a novel process to efficiently utilize medium/low-grade or waste bauxite, which is usually rich in iron oxide (total iron oxide content ≥ 8%) or titanium dioxide (titanium dioxide content ≥ 5%).
Journal ArticleDOI
SOL-GEL synthesis of mullite coatings
Rishabh Chaturvedi,Anas Islam +1 more
TL;DR: In this article, an effort was put together to create a mullite upon SIC EBC substrate utilizing sol-gel creation, which was done through X-ray diffraction (XRD) as well as Scanning Electron Microscopy (SEM).
Journal ArticleDOI
Effect of Silicon Source (Fly Ash, Silica Dust, Gangue) on the Preparation of Porous Mullite Ceramics from Aluminum Dross
TL;DR: In this article , a solid-phase sintering process with aluminum dross and different silicon sources (fly ash, silica dust, and gangue) was used to construct a porosity, density, and compressive strength of porous mullite ceramics.
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.