Sol-gel derived Bi 2 Ti 2 O 7 ceramic powders have been prepared from methoxyethoxides of bismuth and titanium (molar ratio of Ti/Bi = 1.23 and water/alkoxides = 1.31). The Bi 2 Ti 2 O 7 phase was stable at a low temperature (700 • C), but it then transformed into mixed phases of Bi 4 Ti

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An investigation of the effect of alumina particles on the sintering behavior of a carbonyl iron powder compact was carried out in this study. Two different-sized alumina, 0.05 and 0.4 m, were added to the iron compact at amounts up to 1.2 wt pct. When 0.4 m alumina particles were added, no sintering enhancement was observed. But, in contrast to previous results reported in literature, the addition of 0.1 to 0.2 wt pct of 0.05 m alumina particles was found to improve the densification. With 0.1 wt pct, the sintered density increased from 7.25 to 7.40 g/cm 3 after the compact was sintered at 1350 ЊC for 1 hour in hydrogen. Dilatometric curves showed that alumina impeded the early-stage sintering of iron in the ␣ phase, but improved densification in the ␥ phase at high temperatures. These results, along with microstructural analysis, suggested that alumina particles exhibit dual roles; their physical presence blocks the diffusion of iron atoms, thus causing inhibition of sintering, while their grainboundary pinning effect prevents exaggerated grain growth of iron and helps densification. It follows that, depending upon the amount and size of the alumina powders, either an increase or decrease in the final sintered density can be obtained.

Configuring TiO2 into bicontinuous mesostructures greatly improves its photocatalytic efficiency. This is often ascribed to the expanded surface area. Yet, whether mesostructuring modulates TiO2's electronic structure and how that contributes to the improvement are rarely discussed. Here, we employed spectroscopic and density functional theory approaches to address the question. It is found that the improved efficacy could arise from an expansion in surface area and elevation in density of states, both of which might collectively lead to the observed reduction in charge-carrier recombination.Doping or structuring it into porous formats, with or without templates, is a common strategy to address issues arising from the relatively wide band gap (~3.2 eV) and high chargecarrier recombination rate of titanium oxide (TiO2) [1,2], a popular metal-oxide semiconductor of low cost, nontoxicity, and high abundance [3][4][5]. The structuring approaches that involve templates enable a high degree of control over pore size, pore shape, pore spatial arrangement, and specific surface area 𝐴 ! for porous TiO2; some approaches even produce porous TiO2 featuring pores in the periodic mesostructures of bicontinous cubic phases [2]. The

An investigation of the effect of heating rates on the densification behavior of carbonyl iron powder compacts, particularly on the exaggerated grain growth during the a-c phase transformation, was carried out in this study. Compacts heated at 1200°C/min and then sintered for 90 minutes at 1200°C attained 7.14 g/cm 3 , while those heated at 10°C/min reached only 6.61 g/cm 3 . Dilatometer curves using heating rates of 2°C/min, 5°C/min, 10°C/min, 30°C/min, and 90°C/min demonstrate that 90°C/min yields the highest sintered density. The microstructure analysis shows that high heating rates inhibit exaggerated grain growth during the phase transformation by keeping the interparticle neck size small and pinning the grain boundaries. This explanation is supported by the calculation that shows that the energy barrier preventing the grain boundary from breaking away from the neck is reduced hyperbolically as the neck size and the amount of shrinkage increase. The high heating rate, however, shows little beneficial effect for materials that have no allotropic phase transformation or have less drastic grain growth during heating, such as nickel and copper. Thus, bypassing the low temperatures to suppress the surface diffusion mechanism, which does not contribute to densification, is ruled out as the main reason for the enhanced densification of carbonyl iron powders.