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This paper deals with the effect of microwave energy for mullite formation from placer sillimanite. A mullite formation is seen when 60 % SiC and 5% binder are used with the composite charge material, i.e. sillimanite (60%) and Al 2 O 3 (40%). The maximum temperature of the microwave sintering furnace achieved is 1355˚C at 2450 W microwave power. A...
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... The most well-known alumino-silicate polymorphs are sillimanite (Al 2 SiO 5 ), andalusite (Al 2 SiO 5 ) and kyanite (Al 2 SiO 5 ) [7,8]. In 1928, Taylor first resolved the crystal structure of sillimanite while the cell dimensions and space group was determined by Mark and Rosband in 1926 [9,10].Sillimanite decomposes into mullite (Al 6 Si 2 O 13 ) and cristobalite (SiO 2 ) on heating between 1500 • C and 1650 • C [11,12]. The decomposition temperature may differ depending on the region of its occurrence. ...
The α-MoO3 ceramics were prepared by uniaxial pressing and sintering of MoO3 powder at 650°C and their structure, microstructure, densification and sintering and microwave dielectric properties were investigated. The sintering temperature of α-MoO3 was optimized based on the best densification and microwave dielectric properties. After sintering at 650°C the relative permittivity was found to be 6.6 and the quality factor was 41,000GHz at 11.3GHz. The full-width half-maximum of the A1g Raman mode of bulk α-MoO3 at different sintering temperatures correlated well with the Qf values. Moreover, the sintered samples showed a temperature coefficient of the resonant frequency of -25ppm/°C in the temperature range from -40 to 85°C and they exhibited a very low coefficient of thermal expansion of ±4ppm/°C. These microwave dielectric properties of α-MoO3 will be of great benefit in future MoO3 based materials and their applications.
... The most well-known alumino-silicate polymorphs are sillimanite (Al 2 SiO 5 ), andalusite (Al 2 SiO 5 ) and kyanite (Al 2 SiO 5 ) [7,8]. In 1928, Taylor first resolved the crystal structure of sillimanite while the cell dimensions and space group was determined by Mark and Rosband in 1926 [9,10].Sillimanite decomposes into mullite (Al 6 Si 2 O 13 ) and cristobalite (SiO 2 ) on heating between 1500 • C and 1650 • C [11,12]. The decomposition temperature may differ depending on the region of its occurrence. ...
The sillimanite (Al2SiO5) mineral has been sintered by conventional ceramic route and by cold sintering methods. The mineral has very poor sinterability and transformed to mullite on sintering above 1525 °C. The dielectric properties of sillimanite mineral (Al2SiO5) are investigated at radio and microwave frequency ranges. The mineral sintered at 1525 °C has low εr of 4.71 and tanδ of 0.002 at 1 MHz and at microwave frequency εr = 4.43, Qu × f = 41,800 GHz with τf = −17 ppm/°C. The sintering aid used for cold sintering Al2SiO5 is sodium chloride (NaCl). The Al2SiO5NaCl composite was cold sintered at 120 °C. XRD analysis of the composite revealed that there is no additional phase apart from Al2SiO5 and NaCl. The densification of the Al2SiO5NaCl composite was confirmed by using microstructure analysis. The Al2SiO5NaCl composite has εr of 5.37 and tanδ of 0.005 at 1 MHz whereas at microwave frequency it has εr = 4.52, Qu × f = 22,350 GHz with τf = −24 ppm/°C. The cold sintered NaCl has εr = 5.2, Qu × f = 12,000 GHz with τf = −36 ppm/°C.
... The most well-known alumino-silicate polymorphs are sillimanite (Al 2 SiO 5 ), andalusite (Al 2 SiO 5 ) and kyanite (Al 2 SiO 5 ) [7,8]. In 1928, Taylor first resolved the crystal structure of sillimanite while the cell dimensions and space group was determined by Mark and Rosband in 1926 [9,10].Sillimanite decomposes into mullite (Al 6 Si 2 O 13 ) and cristobalite (SiO 2 ) on heating between 1500 • C and 1650 • C [11,12]. The decomposition temperature may differ depending on the region of its occurrence. ...
The global strategy to reduce waste production implies development of recycling technologies and conversion of various waste into value‐added products. Fly ash is an industrial waste produced in a large amount. It comprised an aluminosilicate cenosphere, which seems perspective as a support for heterogeneous catalysts. Here we report the preparation and application of heterogeneous silver nanocatalysts deposited on cenosphere in the epoxidation reaction, a relevant process for preparation of valuable organic precursors and target chemicals. Reductive wet deposition method yields Ag nano‐dispersed coating of improved quality represented by Ag particles of about 2.7 nm on the surface of the microspheres size of 50–250 microns for catalytic synthesis of styrene‐oxide. The 0.1 mmol/g Ag/cenosphere provided best catalytic results with threefold excess of tret‐butyl hydroperoxide in acetonitrile at 80 °C. Comparison of fly ash cenosphere with other supports suggests that low porosity of microspherical support allows for an easier access of reagents to active sites of the catalyst and significantly increases the yield of epoxide and selectivity of the reaction.
Geopolymerization is the most suitable method for the valorization of mineral wastes with high contents of Si and Al oxides. Compared to Ordinary Portland Cement (OPC) materials, the geopolymers exhibit better compressive strength and thermal stability, but their flexural strength is also limited by their brittle matrix. The aim of this study is to evaluate the thermal behavior of ambient-cured fly ash-based geopolymers reinforced with recycled glass fibers in order to estimate the possibility of manufacturing precast concrete products. The thermogravimetric analysis (TGA) showed a low weight loss up to 200 ℃, followed by a much lower decrease in the 200 ℃–500 ℃ temperature range. The TA curves follow closely the trend of the Differential Thermodynamic Analysis (DTA) curves, which confirm a highly endothermic reaction in the 20 ℃–200 ℃ temperature range due to the removal of free or physically bound water. Above this temperature, small peaks corresponding to the dihydroxylation of -FeOOH or transformation of Ca(OH)2 to CaCO3 can be observed. The thermal behavior of both samples is similar, confirming that the presence of glass fibers doesn’t influence the thermal behavior of fly ash-based geopolymers.
The present paper shows a convenient and eco-friendly microwave heating method for the synthesis of fused zirconia mullite formation on combining placer sillimanite and zircon with the mixtures of alumina powder and reducing agent silicon carbide powder with lesser time. The X-ray diffraction data field-emission scanning electron microscope spectrum and scanning electron microscopy/energy-dispersive X-ray spectroscopy analyses in this paper predict that alumina is rich in mullite grains, whereas the grain boundary region becomes rich with zirconia after microwave process. The presence of small percentage of zirconia in the intragrain region reveals that mullite compound is surrounded by well-compacted zirconia. These data also reveal the presence of fused zirconia mullite phase along with crystalline SiC and monoclinic zirconia in the composites.
