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71.
In this work, the reactions of ethane and ethene in an oxidizing and non-oxidizing atmosphere over γ-alumina were investigated under temperature-programmed conditions, in an attempt to estimate the possible contribution and functionality of the support in the reaction pathway of ethane ODH over MoO3/Al2O3 catalysts. The results indicate that alumina contributes to the primary deep oxidation and dehydrogenation routes of ethane to COx and coke respectively, which proceed effectively over the acidic OH groups and the Al3+–O2− acidic centers. On the contrary, the formation of ethylene seems to be coupled to the presence of redox sites on the catalytic surface and requires the presence of the molybdena phase. Moreover, the redox sites of the MoOx species were found to unselectively activate the further overoxidation of the olefin to carbon oxides. Therefore, Al2O3 catalyzes the unselective primary oxidation of ethane to carbon oxides, whereas the molybdena phase is involved in the selective oxidative dehydrogenation (ODH) of ethane to ethene and the secondary overoxidation of ethene to COx. 相似文献
72.
Preparation of Titanium Nitride/Alumina Laminate Composites 总被引:2,自引:0,他引:2
Jing-Xian Zhang Zheng-Ren Huang Dong-Liang Jiang Shouhong H. Tan Zhijian Shen Mats Nygren 《Journal of the American Ceramic Society》2002,85(5):1133-1138
A preparation route for TiN/Al2 O3 laminate composites has been described. A water-based process using Al2 O3 and TiN slurries with solids contents of 40 and 35 vol%, respectively, was used to make TiN and Al2 O3 tapes. The removal of the binder was monitored by weight-loss measurements in a thermogravimetry unit. Bodies composed of Al2 O3 and TiN tapes were densified at temperatures of 1400° and 1500°C using the Spark Plasma Sintering® (SPS) technique. Densities of >98% of the theoretical densities were approached. Crack-free and almost fully densified TiN/Al2 O3 compacts were prepared by heating the burned-out green bodies to the final sintering temperature (1500°C) at a rate of 100°C/min, and with a holding time of 5–10 min, under a pressure of 75 MPa. The microstructures of the obtained compacts were studied using scanning electron microscopy. Grain sizes in the sintered Al2 O3 and TiN compacts were similar to those of the precursor powders. Hardness and indentation fracture toughness were measured at room temperature, and the monolithic compacts as well as the laminate composites exhibited anisotropic mechanical behavior; i.e., the cracks propagated much more easily in a direction parallel to the laminas than perpendicular to them. 相似文献
73.
Hyoun-Ee Kim Steven J. Zinkle William R. Allen 《Journal of the American Ceramic Society》1990,73(2):425-429
Alumina enriched in 17 O was successfully fabricated from aluminum isopropoxide and water containing the 17 O isotope. This material was necessary for an experiment to study the radiation damage expected in alumina exposed to a nuclear fusion reactor environment. The enrichment levels of specimens subjected to different preparation schedules were measured using a nuclear reaction analysis technique. Replacement of the 17 O isotope in the ceramic by atmospheric oxygen occurred readily. Therefore, successful fabrication of suitably enriched alumina specimens required that all processing steps be performed under vacuum or inertgas environments. The optimum fabrication procedure produced enriched alumina specimens of >99.5% of theoretical density, ∽10-μm grain size, and a flexural strength of 280 MPa. 相似文献
74.
During the preparation of alumina as a catalyst support from aluminium nitrates by precipitation with a NH4OH base, NO
2
⋅
radicals have been formed in the catalyst after calcination under air in the solid at different temperatures. These radicals
remained stable until a calcination temperature of 800°C. When the calcined catalyst was degassed under vacuum above 300 °C,
the NO
2
⋅
was reduced to give NO⋅ and O- species which were both tightly trapped in the solid. These latter species remained stable until vacuum treatment at 800
°C.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
75.
Molecular dynamics (MD) simulations of-Al2O3, using a pairwise additive interaction potential of Pauling's type with four different radii for aluminum atoms, were analysed in order to determine the influence of the radius on the modification of coordination numbers of A1 relative to the ideal structure, at two different temperatures of 300 and 1500 K. It is found that the best choice is the radius of penta-coordinated aluminum, reproducing structural and vibrational properties of the compound in excellent agreement with experimentally observed properties. 相似文献
76.
Phase calculation for nonequilibrium multicomponent systems is attempted using the stepwise-regression method. The experimental data (the amount and composition of glassy phase in a system of Al2 O3 –SiO2 ceramics as functions of the state of the original materials, the firing temperature, and the composition of the samples) are treated by the proposed method. The equations obtained are accurate in estimating the amount and composition of glassy phases in the system, showing that the stepwise-regression method is effective in phase calculation. 相似文献
77.
78.
79.
Stabilization of -alumina phase by silica was studied in nanocomposite (diphasic) alumina-silica gels by XRD and BET surface areas measurements. Five wt.% of silica (22 nm particles) increased the crystallization temperature of to -alumina by about 100°C from boehmite (10 nm particles) derived alumina. Stabilization of -alumina was caused by the formation of intimate contact (Al-O-Si) between components by diffusion of silica into the defect alumina structure.Also with the Department of Agronomy. 相似文献
80.