6–8 mass% Y2O3 stabilized ZrO2 (6–8YSZ) thermal barrier coatings (TBCs) are widely applied to protect the hot ends of gas turbines in large navy ships. In this work, the 8YSZ TBCs were prepared by air plasma spraying technique, and their microstructure and phase composition were investigated. The hot corrosion mechanism of YSZ TBCs in molten salts consisting of 80% Na2SO4?+?20% NaCl at 900 °C was comprehensively analyzed. The results showed that the corrosion product Y2(SO4)3 was formed due to the reaction between Na2SO4 media and the stabilizer Y2O3. As the result of the depletion of Y2O3 phase, the transformation from the tetragonal phase to monoclinic phase of ZrO2 could not been totally inhibited, which consequently induced the 4–6 vol.% expansion and more cracks of YSZ TBCs. Meanwhile, the cracks could work as transfer paths for oxygen and molten salts. The kinetic analysis on hot corrosion also showed that more reaction products (from 2 to 8.1 mg cm?1) were generated from 20 to 60 h due to more cracks generated by molten salts and oxygen infiltrating. More thermal grown oxides generated between ceramic layer, bonding layer and substrate, and the volume expansion caused by phase transition, increased the stresses in the coatings. Consequently, the peeling-off failure of 8YSZ TBCs could happen.
Highly dispersed Ni/SBA-15 catalysts were prepared via template extraction with varying different extraction times (Ni/S-x, x = 0.5, 3.5, 6.5 h) for methane reforming with carbon dioxide. Based on the various characterization results and initial activity evaluation, Ni/S-3.5 h catalyst showed the best catalytic performance. Compared with the catalyst prepared via template calcination (Ni-S), Ni/S-3.5 h catalyst held steady with CH4 and CO2 conversions while those of the Ni-S catalyst respectively decreased by 15 and 11% during the long-term stability test at 700 °C for 50 h. As TEM and TG–DSC results confirmed, Ni particles in spent Ni/S-3.5 h catalyst stayed well-dispersed with size slightly increasing from an initial 3.9–4.1 nm and nearly no carbon deposition was observed. On the contrary, Ni-S catalyst was subjected to sintered metal particles (increased from 11.6 to 18 nm) and formed carbon fibers. The prominent resistance to sintering and coking over stable Ni/S-3.5 h catalyst was attributed to the high dispersion and strengthened metal-support interaction induced via the residual in situ templates. 相似文献
Under ‘open-flask’ and mild conditions, arenes condense smoothly with aromatic aldehydes in the presence of catalytic amount of FeCl3. The reaction tolerated a variety of substitutions and functional groups. This method provides a facile and direct access to symmetrical and unsymmetrical triarylmethane derivatives. 相似文献
The effect of Mg and C contents on TC in MgCN3, and structure and superconductivity of MgCNi3-xCox were studied. It is found that the excess of Mg and C in initial material mixture is favorable to improvement inTc and helps to obtain single-phase samples. For preparing MgCNi3 superconductor, the optimum composition of starting materials is MgC1.45Ni3 with excess of Mg (20 wt.%) of the stoichiometric composition. In gCNi3-xCox system, a continuous solid solution is formed, lattice parameter decreases slightly andTc decreases obviously with increasingx. A suppression of superconductivity is observed due to the substitution of Co (Mn) for Ni. The suppression effect is smaller for the substitution of Co than that of Mn 相似文献