Alumina-Mullite Composites through Interaction of Bauxite and Fly Ash
TL;DR: In this paper, an alumina-mullite composites with various mole ratios of Al2O3 and SiO2 were generated by interacting fly ash with bauxite.
Abstract: In the present investigation alumina-mullite composites with various mole ratios of Al2O3 and SiO2 were generated by interacting fly ash with bauxite. The magnitude of sintering was examined by exa...
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TL;DR: In this article, the effects of the sintering temperature, acid leaching and Al2O3/SiO2 ratio on the chemical, physical, thermal expansion properties of the samples were characterized in detail.
45 citations
11 Sep 2019
TL;DR: In this paper, the authors present a review of various mullite ceramics preparation methods that utilized a variety of industrial wastes as starting materials for the preparation of the material. But, they do not discuss the sintering temperatures and chemical additives used in the preparation and its effects.
Abstract: Some industrial wastes are shown to be useful in the production of mullite ceramics. These industrial wastes are rich in certain metal oxides such as silica (SiO2) and alumina (Al2O3). This gives wastes the potential to be used as a starting material source for mullite ceramics preparation. The purpose of this review paper is to compile and review various mullite ceramics preparation methods that utilized a variety of industrial wastes as starting materials. This review also describes the sintering temperatures and chemical additives used in the preparation and its effects. A comparison of both mechanical strength and thermal expansion of the reported mullite ceramics prepared from various industrial wastes were also addressed in this work.
30 citations
TL;DR: In this paper, the main crystal phases of calcined bauxite are corundum and mullite, appearance is layered, granular distribution, and the thermal performance is optimal, and is expected to be used for the field of high temperature solar thermal heat storage material.
Abstract: In order to further broaden the application field of calcined bauxite, using differential thermal analysis-thermo-gravimetry (DTA-TG), X-ray diffraction analysis (XRD), Scanning electron microscopy (SEM) and other testing technology to study and analysis on the high temperature performance of calcined bauxite in this paper. The results show that the main crystal phases of calcined bauxite are corundum and mullite, appearance is layered, granular distribution. Due to the thermal performance of calcined bauxite is optimal, and is expected to be used for the field of high temperature solar thermal heat storage material.
2 citations
TL;DR: In this paper, the production of high temperature structural insulator (HTSI) is discussed. But the authors do not consider the use of the EEP residue during the calcination of aluminium hydroxide in the Bayer process.
Abstract: Electrofilter powder (EP) is a residue generated in large amounts during the calcination of aluminium hydroxide in the Bayer process. The production of high temperature structural insulator (HTSI) ...
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TL;DR: In this paper, the formation of aluminum rich mullites at annealing temperatures between 700 and 1650 °C was studied and the final product at 1650°C consisted of 34 mol% of a ‘normal’ mullite with x = 0·32 and 66 mol% corundum.
Abstract: The formation of aluminum rich mullites Al4 + 2x Si2 − 2xO10 − x with x > 23 has been studied at annealing temperatures between 700 and 1650 °C. Calcination of the amorphous precursor at 700 °C yields a mullite with 88 mol% Al2O3 corresponding to an x-value of 0·809. Simultaneously, a γ-alumina phase is formed. Further increase of the annealing temperature yields an increase in the aluminum incorporation up to 92·1 mol% Al2O3 at 1000 °C derived from the refined lattice constants. This is the highest amount of Al observed so far in a mullite except the supposed end member ι-Al2O3 which, however, has not yet been established unambiguously. Above 1000 °C, the aluminum content in mullite is reduced. This is accompanied by a transformation of the spinel-type phase to a superstructure of a θ-alumina like phase. The final product at 1650 °C consists of 34 mol% of a ‘normal’ mullite with x = 0·32 and 66 mol% corundum.
101 citations
TL;DR: The kinetics, microstructural changes, and crystal structure development for crystallization of amorphous, quenched, mullite composition glass (3Al 2 O 3 ·2SiO 2 ) were studied between 900 and 1400°C as discussed by the authors.
Abstract: The kinetics, microstructural changes, and crystal structure development for crystallization of amorphous, quenched, mullite composition glass (3Al 2 O 3 ·2SiO 2 ) were studied between 900 and 1400°C. The phenomena observed were characterized using non-isothermal differential scanning calorimetry (DSC), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), powder X-ray diffraction (XRD, with both a standard laboratory diffractometer, as well as with synchrotron radiation), and Rietveld analysis. Crystallization of amorphous mullite was observed to occur in two steps. The activation energy for crystallization was 892 kJ/mol for the first step and 1333 kJ/mol for the second step. From the amorphous state, the first phase(s) to crystallize were alumina-rich, pseudotetragonal mullite (∼70 mol% Al 2 O 3 ). These crystals were highly strained and contained numerous nanometer scale inclusions. With increasing temperature, the crystals were observed to incorporate increasing amounts of SiO 2 , and approach the equilibrium orthorhombic structure. By 1400°C the pseudotetragonal to orthorhombic transition was complete, the strain was eliminated, most of the inclusions had been assimilated, there was ∼67% reduction in grain size, and the crystals had attained the composition of the initial, bulk glass (∼60 mol% Al 2 O 3 ).
66 citations
TL;DR: The sintering behavior of mullite-alumina composites containing 68 to 90 wt% of Al2O3 synthesized by a solgel method was studied in this paper.
29 citations
TL;DR: In this paper, a combination of commercially available silica and alumina precursors (fumed silica nanopowders and a boehmite sol) have been used to prepare mullite ceramics using colloidal processing and transient viscous sintering.
16 citations
TL;DR: In this article, reaction-bonded alumina was fabricated using standard powder preparation methods and the low-pressure injection molding (LPIM) forming technique, followed by reaction sintering.
Abstract: Reaction-bonded alumina was fabricated using standard powder preparation methods and the low-pressure injection moulding (LPIM) forming technique, followed by reaction sintering. The feasibility of LPIM was investigated in terms of the compounding ability of a highly agglomerated mechanically alloyed powder in a non-polar organic vehicle, and the microstructural homogeneity and resulting reliability of sintered LPIM parts. The green density of LPIM parts after debinding, roughly corresponding to the solids loading in the LPIM feedstock, was in the range of fractional density achieved by dry pressing, although the powder packing and aluminium particle deformation during forming were not the same. LPIM forming and debinding induced microstructural inhomogeneities (i.e. larger voids due to trapped air and density fluctuations) which were reflected in a slightly lower Weibull modulus, while the average strength did not differ significantly from the values obtained with dry pressed samples. The microstructure and mechanical properties of sintered parts were also related to the purity of the starting powders. The presence of impurities in the starting aluminium powder resulted in a somewhat coarser microstructure, characterized by a broader Al2O3 grain-size distribution, as well as in the presence of a thin glassy phase on the grain boundaries and in partial destabilization of dispersed tetragonal (Y2O3-stabilized) ZrO2 particles. In spite of a less favourable microstructure, the room-temperature strength and Weibull modulus were still comparable to those obtained from high-purity starting powder.
14 citations