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931.
C. R. Foschini O. Treu Filho S. A. Juiz A. G. Souza J. B. L. Oliveira E. Longo E. R. Leite C. A. Paskocimas J. A. Varela 《Journal of Materials Science》2004,39(6):1935-1941
Reactive zirconia powder was synthesized by the complexation of zirconium metal from zirconium hydroxide using a solution of 8-hydroxiquinoline. The kinetics of zirconia crystallization was followed by X-ray diffraction, scanning electron microscopy and surface area measured by the nitrogen adsorption/desorption technique. The results indicated that zirconia with a surface area as high as 100 m2/g can be obtained by this method after calcination at 500°C. Zirconia presents three polymorphic phases (monoclinic, tetragonal and cubic), which are reversibly interconversible. The cluster model Zr4O8 and Zr4O7
+2 was used for a theoretical study of the stabilization process. The ab initio RHF method was employed with the Gaussian94 program and the total energies and the energy gap of the different phases were calculated and compared with the experimental energy gap. The theoretical results show good reproducibility of the energy gap for zirconia. 相似文献
932.
933.
D. M. Van Wie D. G. Drewry Jr. D. E. King C. M. Hudson 《Journal of Materials Science》2004,39(19):5915-5924
Hypersonic flight powered by airbreathing engines offers the potential for faster response time at long ranges, and reduced cost for access-to-space. In the present paper the operating environment of typical hypersonic vehicles are discussed, including results for the radiation equilibrium wall temperature of external vehicle surfaces and the flow properties through three sample engines spanning the range of hydrocarbon-fueled Mach 4-8 flight and hydrogen-fueled flight at speeds up to Mach 17. Flow conditions at several locations through the sample engines were calculated to provide indications of the required operating flow environment. Additional system consideration such a seals, joints, vehicle integration and in-service engineering are addressed. 相似文献
934.
935.
This paper reviews our research on the electrophoretic deposition (EPD) of phosphors for the processing of monochromatic and color screens for information displays. Our investigation began with the study of the fundamentals of the EPD process for phosphors. The processing variables which enhance the adhesion strength of phosphor deposits were determined. The optical performance of phosphors deposited by EPD was shown to be not affected by the process itself nor by the conditions which enhance phosphor adhesion. Processes developed to produce high-resolution color screens by combining EPD and photolithography techniques are described. Also, a method to electrophoretically deposit phosphor in a thermo-reversible gel from mixtures of poly(butyl methacrylate) and isopropanol was examined. 相似文献
936.
Carbon Black (CB)-containing immiscible polymer blends based on high-impact polystyrene/thermoplastic polyurethane (HIPS/TPU) were studied as sensing materials for an homologous series of alcohols, including, methanol, ethanol and 1-propanol. The studied immiscible blend was designed to exhibit a double-continuity structure i.e., the CB particles form chain-like network structures within the TPU phase, which forms a continuous phase within the HIPS matrix. Extruded HIPS/TPU/CB filaments produced by a capillary rheometer process at various shear rate levels were used for the sensing experiments. All filaments displayed a selective resistance changes upon exposure to the various alcohols combined with reproducibility and recovery behaviour. An attempt is made to identify the dominant mechanisms controlling the sensing process in a CB-containing immiscible polymer blend characterized by a double-continuity structure. The distinct structure and composition of the HIPS/TPU interphase region were found to have a crucial role in the sensing mechanism, determining the selectivity of the filaments toward the studied alcohols. Additionally, the sensing performance of HIPS/TPU/CB system is compared to recent results for TPU/CB compounds, polypropylene/TPU/CB and HIPS/ethylene vinyl acetate/CB immiscible polymer blends. 相似文献
937.
938.
939.
In the gold wire bonding of aluminum in microelectronic devices the presence of aluminum oxide on the metallization surface may be expected. Electron transparent couples containing an oxide layer at the interface were heated in a TEM to determine the effects of a passivation layer on intermetallic formation. Intermetallic phases were evidenced by changes in sample appearance and their structure was determined by electron diffraction. The presence of an oxide at the interface hindered second phase formation at temperatures at which they were usually expected to form. In aluminum rich couples, the formation of the AuAl2 intermetallic was not observed to form until about 350°C with the oxide present. In a reverse configuration involving a gold rich couple, an amorphous oxide phase was observed between the Al and the advancing Au2Al front. The movement of the reaction front appeared to be controlled by surface diffusion across this phase. 相似文献
940.
The results of investigation of mechanochemical reactions in the mixtures of hydroxides and carbonates of alkaline and alkaline earth metals with zirconium oxychloride and oxynitrate are presented. It is shown that one of the features of interaction between the components is the formation of the salts of alkaline and alkaline earth metals along with X-ray amorphous zirconium-containing compound. It is demonstrated that the mechanical activation of the mixture of yttrium carbonate and zirconium oxynitrate, followed by thermal treatment of this mechanically activated mixture, results in the formation of solid solution ZrO2-Y2O3 in cubic modification. 相似文献