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91.
K. A. Khor F. Y. C. Boey Y. Murakoshi T. Sano 《Journal of Thermal Spray Technology》1994,3(2):162-168
There has been increasing use of Al-Li alloys in the aerospace industry, due mainly to the low density and high elastic modulus
of this material. However, the problem of low ductility and fracture toughness of this material has limited its present application
to only weight- and stiffness-critical components. Development of Al-Li/ceramic composites is currently being investigated
to enhance the service capabilities of this material. The Ti-Al alloy is also of interest to aerospace-type applications,
engine components in particular, due to its attractive high-temperature properties. Preparation of fine powders by plasma
melting of composite feedstock and coatings formed by plasma spraying was carried out to examine the effect of spray parameters
on the microstructure and properties of these materials. Characterization of the powders and coatings was performed using
the scanning electron microscope and image analyzer. Examination of the plasma-sprayed powders and coatings has shown that
in the Al-Li/SiC composite there is melting of both materials to form a single composite particle. The SiC reinforcement was
in the submicron range and contributed to additional strengthening of the composite body, which was formed by a cold isostatic
press and consolidated by hot extrusion or hot forging processes. The plasma-sprayed Ti-Al powder showed four categories of
microstructures: featureless, dendritic, cellular, and martensite-like. 相似文献
92.
在保留双反星形可控整流主电路优点的同时,根据手工焊和氩弧焊的工艺特点,对控制电路作了全集成化设计。介绍了稳弧电路、同步移相电路、触发电路及外特性控制电路的设计特点,对各单元电路进行了具体的分析。 相似文献
93.
激光诱导二甲基二乙氧基硅烷气相合成碳化硅超细粉 总被引:1,自引:0,他引:1
本工作首次采用有机硅试剂二甲基二乙氧基硅烷为反应物,进行了激光导气相反应,制备出平均粒径为40nm的非晶SiC粉末,粉末中C/Si比随反应气流量的变化而变化。非晶SiC粉末在1873K,氮气中退火1h后转变为β-SiC及α-SiC,同时,粉末中部分氧杂质及自由碳脱出粉末。 相似文献
94.
甲基偶氮四唑热稳定性和热分解机理的量子化学研究 总被引:2,自引:0,他引:2
采用量子化学方法全优化计算了1—甲基—5—偶氮四唑(1—MAT)和2—甲基—5—偶氮四唑(2—MAT)热分解反应位能曲线,探讨了热稳定性和分解机理。热分解活化能计算值分别为245.9,183.2k/mo1,静态分子结构和动态分解性质都显示出1—MAT比2—MAT有更好的热稳定性。裂解优先以开环方式发生。 相似文献
95.
Manuel Belmonte Vitor A. Silva Antonio José Fernandes Florinda Costa Rui Silva 《Journal of the American Ceramic Society》2003,86(5):749-754
The efficiency of different surface pretreatments (four standard chemical etchings and four diamond powder abrasive procedures) on silicon nitride (Si3 N4 ) substrates for chemical vapor deposition (CVD) of diamond has been systematically investigated. Blank Si3 N4 samples were polished with colloidal silica (∼0.25 μm). Diamond nucleation and growth runs were conducted in a microwave plasma chemical vapor deposition apparatus for 10 min and 6 h, respectively. Superior results concerning nucleation density ( N d ∼ 1010 cm−2 after 10 min), film uniformity, and grain size (below 2 μm after 6 h) were obtained for the mechanically microflawed samples, revealing that chemical etchings (hot and cold strong acids, molten base or CF4 plasma) are not crucial for good CVD diamond quality on Si3 N4 . 相似文献
96.
Silicon Nitride Derived from an Organometallic Polymeric Precursor: Preparation and Characterization 总被引:1,自引:0,他引:1
Wayde R. Schmidt Vijay Sukumar William J. Hurley Jr. Roberto Garcia Robert H. Doremus Leonard V. Interrante Gary M. Renlund 《Journal of the American Ceramic Society》1990,73(8):2412-2418
Partially crystalline Si3 N4 , with nanosized crystals and a specific surface area greater than 200 m2 /g, is obtained by pyrolysis of a commercially available vinylic polysilane in a stream of anhydrous NH3 to 1000°C. This polymer does not contain N initially. Crystallization to high-purity α-Si3 N4 proceeds with additional heating above 1400°C under N2 . The changes in crystallinity, powder morphology, infrared spectra, and elemental compositions, for samples annealed from 1000° to 1600°C under N2 , are consistent with an amorphous-to-crystalline transformation. Although macroscopic consolidation and local densification occur at 1400°C, volatilization and accompanying weight loss limit bulk densification. The effect of temperature on specific surface area is examined and related to the sintering process. These results are applicable to pyrolysis, decomposition, and crystallization studies of ceramics synthesized by polymeric precursor routes. 相似文献
97.
Bordiga S. Ugliengo P. Damin A. Lamberti C. Spoto G. Zecchina A. Spanò G. Buzzoni R. Dalloro L. Rivetti F. 《Topics in Catalysis》2001,15(1):43-52
Defective silicalite, an efficient and selective catalyst in the gas phase Beckmann rearrangement reaction, has been characterised by infrared spectroscopy and by molecular modelling techniques. We report a detailed IR study on the effect of outgassing treatments at increasing temperature on silanols bands and on framework modes. The effect of a temperature decrease up to 100 K (during the IR measurement) on the H-bonding interactions has also been investigated. The interaction of silanols with mesitylene, a probe molecule which cannot penetrate the channels, has been studied in order to distinguish between internal and external OH groups. Molecular mechanics and ab initio methods have also been used to model the structure and the vibrational features of a properly designed nest in order to support the assignments of the IR spectrum. 相似文献
98.
99.
100.
Irina Tsarenko Sang Park Honghua Du Woo Y. Lee 《Journal of the American Ceramic Society》2003,86(9):1622-1624
A 25 nm thick α-alumina layer was deposited on a turbine-grade silicon nitride by sol-gel dip coating and subsequent heat treatment in air at 1200°C. This layer had a nanometer grain structure. Silicon nitride protected by this thin layer showed a significant improvement in oxidation resistance over its uncoated counterpart after 200 cyclic exposures in air at 1250°C. The oxide layer grown on the coated silicon nitride also exhibited superior surface morphology, compared with the uncoated silicon nitride. 相似文献