Elongated mullite crystals obtained from high temperature transformation of sillimanite

Tomba, A.G; Camerucci, M.A.; Urretavizcaya, G.; Cavalieri, A.L.; Saínz, M.A.; Caballero, A.

doi:10.1016/s0272-8842(98)00031-5

Cited by 29 publications

(17 citation statements)

References 5 publications

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“…Due to the very similar crystal structures, the elongated mullite needles have epitactical or topotactical orientation relationships with the primary phases (Pannhorst and Schneider ; Tomba et al. ; Hülsmanns et al. ).…”

Section: Discussionmentioning

confidence: 99%

Mullite in Libyan Desert Glass: Evidence for high‐temperature/low‐pressure formation

Greshake

Wirth

Fritz³

et al. 2017

Meteorit & Planetary Scien

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Libyan Desert Glass (LDG) is a SiO 2 -rich natural glass whose origin, formation mechanism, and target material are highly debated. We here report on the finding of a lensshaped whitish inclusion within LDG. The object is dominantly composed of siliceous glass and separated from the surrounding LDG by numerous cristobalite grains. Within cristobalite, several regions rich in mullite often associated with ilmenite were detected. Mineral assemblage, chemical composition, and grain morphologies suggest that mullite was formed by thermal decomposition of kaolinitic clay at atmospheric pressure and T ≥ 1600°C and also attested to high cooling rates under nonequilibrium conditions. Cristobalite contains concentric and irregular internal cracks and is intensely twinned, indicating that first crystallized b-cristobalite inverted to a-cristobalite during cooling of the SiO 2 -rich melt. The accompanied volume reduction of 4% induced the high density of defects. The whitish inclusion also contains several partly molten rutile grains evidencing that at least locally the LDG melt was at T ≥ 1800°C. Based on these observations, it is concluded that LDG was formed by high-temperature melting of kaolinitic clay-, rutile-, and ilmenite-bearing Cenozoic sandstone or sand very likely during an asteroid or comet impact onto Earth. While melting and ejection occurred at high pressures, the melt solidified quickly at atmospheric pressure.

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Section: Discussionmentioning

confidence: 99%

Mullite in Libyan Desert Glass: Evidence for high‐temperature/low‐pressure formation

Greshake

Wirth

Fritz³

et al. 2017

Meteorit & Planetary Scien

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“…The mullite ceramic phase is important in the Al 2 O 3 -SiO 2 system. The mullite phase has good mechanical and physical properties [5] such as high oxidation resistance, excellent chemical stability, good creep resistance, and low thermal conductivity [1,6,7]. In addition, porous mullite ceramic has many important uses, for example, in insulating materials, catalyst support insulation, and membrane filters for gases [8].…”

Section: Introductionmentioning

confidence: 99%

The Effect of Commercial Rice Husk Ash Additives on the Porosity, Mechanical Properties, and Microstructure of Alumina Ceramics

Ali

Hanim

Tahir

et al. 2017

Advances in Materials Science and Engineering

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A porous ceramic is made from composite materials which consist of alumina and commercial rice husk ash. This type of ceramics is obtained by mixing the commercial rice husk ash as a source of silica (SiO2) and a pore forming agent with alumina (Al2O3) powder. To obtain this type of ceramic, a solid-state technique is used with sintering at high temperature. This study also investigated the effects of the rice husk ash ratios on the mechanical properties, porosity, and microstructure. The results showed that, by increasing the content of the rice husk ash from 10 to 50 wt%, there is an increase in the porosity from 42.92% to 49.04%, while the mechanical properties decreased initially followed by an increase at 30 wt% and 50 wt%; the hardness at 20 wt% of the ash content was recorded at 101.90 HV1. When the ash content was increased to 30 wt% and 50 wt%, the hardness was raised to 150.92 HV1and 158.93 HV1, respectively. The findings also revealed that the tensile and compressive strengths experienced a decrease at 10 wt% of the ash content and after that increase at 30 wt% and 50 wt% of rice husk ash. XRD analysis found multiple phases of ceramic formation after sintering for the different rice husk ash content.

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“…Tomba and co-workers found that elongated mullite crystals are produced during the thermal decomposition of sillimanite. 17 In kyanite, elongated, fibrous mullite grains are developed at low temperatures, but their morphology changes to a tabular one with rounded edges at elevated temperatures. 18 During the thermal decomposition of andalusite single crystals, mullite single crystals develop in the interior of the andalusite parent grains, leaving an interconnected capillary network filled with a silica-rich glass.…”

Section: Introductionmentioning

confidence: 99%

“…However, the large thermal expansion displayed by the decomposition of kyanite has been used to counteract the sintering shrinkage of some refractories. 19 Dilatometric studies of large crystals of sillimanite, 17 kyanite, 18 and andalusite 7 suggest that these species may possess rather poor sintering characteristics. However, pressed compacts of attrition-milled andalusite do attain very high 2425 journal densities after sintering at 1500°C.…”

Section: Introductionmentioning

confidence: 99%

Mechanical Activation of the Decomposition and Sintering of Kyanite

Aguilar-Santillan¹,

Cuenca-Álvarez²,

Balmori‐Ramírez³

et al. 2002

Journal of the American Ceramic Society

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The influence of attrition milling on the thermal decomposition of kyanite (Al2O3·SiO2) to mullite (3Al2O3·2SiO2) and SiO2, and its subsequent sintering, was studied. A commercial kyanite was attrition‐milled for times up to 12 h. Dilatometry confirmed that as‐received unmilled kyanite decomposes between 1300° and 1435°C. The decomposition reaction is slow initially and accelerates during the later stages until about one‐half of the decomposition occurs in the last 35°C. For the attrition‐milled kyanite, the onset decomposition temperature decreases, the transformation temperature interval is reduced, and both the decomposition reaction and subsequent sintering are accelerated. A dense microstructure of fine equiaxed mullite grains in the 1 μm size range, evenly dispersed in a glassy matrix, is obtained by sintering the attrition‐milled kyanites. These results are explained in terms of the energy accumulated during attrition milling, a reduction of the milled kyanite particle size, and the presence of a liquid phase during sintering.

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Elongated mullite crystals obtained from high temperature transformation of sillimanite

Cited by 29 publications

References 5 publications

Mullite in Libyan Desert Glass: Evidence for high‐temperature/low‐pressure formation

Mullite in Libyan Desert Glass: Evidence for high‐temperature/low‐pressure formation

The Effect of Commercial Rice Husk Ash Additives on the Porosity, Mechanical Properties, and Microstructure of Alumina Ceramics

Mechanical Activation of the Decomposition and Sintering of Kyanite

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