Abstract The effects of Fe 2 O 3 on phase evolution, density, microstructural development, and mechanical properties of mullite ceramics from kaolin and alumina were systematically studied. X‐ray diffraction results suggested that the ceramics consisted of mullite, sillimanite, and corundum, in the sintering range of 1450°C–1580°C. However, as the sintering was raised to 1580°C, mullite is the main phase with a content of 94%, and the corundum phase content is 5.9%. Simultaneously, high‐temperature sintering had a positive effect on the densification of the mullite ceramics, where both the bulk density and flexural strength could be optimized by adjusting the content of Fe 2 O 3 . It was found that 6 wt% Fe 2 O 3 was optimal for the formation of rod‐shaped mullite after sintering at 1550°C for 3 h. The sample's maximum bulk density was 2.84 g/cm 3 , with a flexural strength of 112 MPa. Meanwhile, rod‐shaped mullite grains with an aspect ratio of ~9 were formed. As a result, a dense network structure was developed, thus leading to mullite ceramics with excellent mechanical properties. The effect of Fe 2 O 3 on the properties might be attributed to the fact that Al 3+ ions in the [AlO 6 ] octahedron were replaced by Fe 3+ ions, resulting in lattice distortion.
Understanding the effect of frother on bubble entraining coal particles is an important guidance for regulating coal flotation behavior. The bubble properties and the flow field surrounding the bubble were investigated using the particle image velocimetry (PIV) technique. The bubble equivalent diameter, bubble deformation rate, and low-velocity zone area reduced as the frother concentration increased due to a decrease in surface tension with rising frother concentration. The oscillation of the bubble and low-velocity zone were subsequently analyzed. As the frother concentration increased, the oscillation frequency of the bubble and low-velocity zone gradually decreased until it approached a critical concentration of 1.6 10-4 mol/L, after which it tended to stabilize. The oscillation amplitude of the bubble and low-velocity zone slightly varied with the frother concentration but increased as the distance from the bubble increased. The coal particle trajectories and entrainment phenomenon under the effect of frother were explored via the high-speed motion capture equipment. Three typical trajectories—Escape, Offset entrainment, and Entrainment—were used to describe the coal particles' behavior around the trailing vortex zone. The predictive model of coal particle entrainment probability influenced by frothers was established. Our findings might provide an insightful insight into the evolution of mineral flotation technology.
The recognition of lumpish coal and gangue of different coal sorts was conducted using X-ray technique. Gas coal, fat coal and coking coal were used in this study, and the ash content was found to roughly increase linearly with the density independently of coal sort. Al2O3, SiO2, Fe2O3 and SO3 were detected to be the major oxides for the increase in ash content as the density increased. The gray value of coal was larger than that of gangue and decreased with the increase in thickness and density independently of coal sort and energy zone. The gray value in the high energy zone was found to overlap with that in the low energy zone. Material attribute value (R) was applied for estimating the accuracy of the recognition, and the highest accuracy was given at R = 1.3.
Abstract Using extreme high speed laser cladding technology, 316L coating was prepared on 45 steel shaft. The microstructure of the coating was observed by scanning electron microscope (SEM), and the wear resistance and corrosion resistance of the coating were tested. The results show that the coating prepared by the extreme high speed laser cladding technology has high surface flatness, no obvious cracks, voids and other defects, high density, good combination with the substrate, and fine grains. The middle and lower crystal grains are dendritic, which grows perpendicularly to the surface preferentially, and no obvious secondary dendrites are seen. The size of the dendrites in the lower part of the coating gradually decreases from the bottom to the top of the molten pool, and the top layer transforms to equiaxed grains. The dilution rate is 4.4%. The fine-grain strengthening mechanism improves the wear resistance of the coating, and the wear resistance is increased by about 31.8%. The wear mechanism is mainly abrasive wear. A stable chromium-rich oxide film is formed on the surface of the coating, and its corrosion resistance is greatly improved, but this film will be destroyed by highly concentration of Cl - .
A series of samples including leaf-like and rod-like rutile TiO2 nanoparticles with various facets exposed on the surface, parallelepiped-shaped anatase nanoparticles with [111] vertical facet exposed on the surface, irregular anatase nanoparticles, microsized six-point star-like anatase aggregates, and almond-like brookite aggregates had been hydrothermally synthesized from lepidocrocite-type layered titanate nanosheets. A systematical investigation was established to uncover the phase transition and morphological evolution from nanosheets to TiO2 polymorphs, and a phase diagram was determined by adjusting the synthesis parameters of the pH value and temperature. Two kinds of mechanisms composed of the dissolution-deposition process following Ostwald's ripening mechanism and the in situ topochemical conversion process following Ostwald's step rule had been proposed based on the time-dependent hydrothermal experiments. Briefly, the formation of the single-crystalline rutile phase appeared only at high temperatures with very low pH values, and similarly, the brookite phase strictly formed at high temperatures with a very high pH value. Nevertheless, the anatase phase could moderately appear in a wide range of temperatures and pH values. In addition, the single-crystalline rutile adopted a leaf-like morphology at low temperatures with high pH values and a rod-like morphology at high temperatures with low pH values, while the morphological evolution of anatase particles proceeded from irregular to parallelepiped-shaped and finally to six-point star-like morphology, and the crystal size was reduced from 1000 to 5 nm with decreasing pH values. Meanwhile, with the prolongation of the hydrothermal time, the layered titanate nanosheets first dissolved into the amorphous state and further converted into small anatase nanoparticles and finally to rutile or anatase nanoparticles based on the dissolution-deposition process, or the {010}-faceted layered titanate structure first converted into the [111]-vertical faceted anatase nanosheets by the topochemical transformation reaction and then split into the [111]-vertical faceted anatase nanoparticles. More importantly, the mesoporous [111]-vertical faceted anatase nanoparticles exhibited enhanced photocatalytic performance compared to that of Degussa P25, which was ascribed to its superior electronic band structure and effective charge separation. The systematical investigation in this work would be significant for consummating the preparation of the TiO2 polymorphs from layered titanate nanosheets and provided some reference values and guide schemes for the preparation of TiO2 nanoparticles with outstanding photocatalytic performance.
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