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101.
High-Temperature Active Oxidation of Chemically Vapor-Deposited Silicon Carbide in CO─CO2 Atmosphere
Takayuki Narushima Takashi Goto Yoshio Yokoyama Yasutaka Iguchi Toshio Hirai 《Journal of the American Ceramic Society》1993,76(10):2521-2524
Active oxidation behavior of CVD-SiC in CO─CO2 atmospheres was investigated using a thermogravimetric technique in the temperature range between 1823 and 1923 K. The gas pressure ratio, P CO2 / P CO , was controlled between 10−4 and 10−1 at 0.1 MPa. Active oxidation rates (mass loss rates) showed maxima at a certain value of P CO2 / P CO , ( P CO2 / P CO )* , In a P CO2 / P CO region lower than the ( P CO2 / P CO )* a carbon layer was formed on the SiC surface. In a P CO2 / P CO region higher than the ( P CO2 / P CO )* , silica particles or a porous silica layer was observed on the SiC surface. 相似文献
102.
Novel acetylene monomers containing N-phenyl-substituted carbazole (Cz) and triphenylamine (TPA) groups, namely, 3-ethynyl-9-phenylcarbazole (1) and p-(N,N-diphenylamino)phenylacetylene (2) were synthesized, and polymerized with several Rh-, W-, and Mo-based catalysts. Poly(1) and poly(2) with high number-average molecular weights (15?500-974?000) were obtained in good yields (77-97%), when [(nbd)RhCl]2-Et3N (nbd = norbornadiene) was used as a catalyst. The polymers exhibited UV-vis absorption peaks derived from the Cz and TPA moieties at 250-350 nm and polyacetylene backbone above 350 nm. The UV-vis absorption band edge wavelengths of the polymers were longer than those of the corresponding monomers. Poly(2) exhibited a UV-vis absorption peak at a longer wavelength than poly(1) did, which indicates that poly(2) has main chain conjugation longer than that of poly(1). The molecular weights and photoluminescence quantum yields of the polymers obtained by the polymerization using [(nbd)RhCl]2-Et3N were larger than those of the Rh+(nbd)[η6-C6H5B−(C6H5)3]-based counterparts. The cyclic voltammograms of the polymers indicated that they had clear electrochemical properties; the onset oxidation voltage of poly(1) was higher than those of N-alkyl-substituted Cz derivatives. The polymers showed electrochromism and changed the color from pale yellow to blue by application of voltage, presumably caused by the formation of charged polaron at the Cz and TPA moieties. The temperatures for 5% weight loss of the polymers were around 350-420 °C under air, indicating the high thermal stability. 相似文献
103.
高分辨率数码相机的出现为砂土模型试验变形场非接触量测法的研究开发提供了一条简便经济而且实用的途径,在模型试验观测面上,不再需要布置嵌入式量测标志点或描画网格,直接用数码相机在试验各阶段拍摄照片,然后对照片序列进行图像相关分析,即可得出模型试验的变形场分布。利用图像匹配技术追踪模型上点的位移,借用FEM常用的等参单元的概念进行图像校准和应变计算,采用双线性插值技术可以实现微小变形量测,并提出同时用平移和旋转搜索方法,以适应砂土模型的变形特点。精度检验试验结果表明,一个像素以下的平移量测标准方差达到0.19个像素,数值试验表明,15°旋转刚体变形量测,非旋转搜索和旋转搜索的标准方差分别为0.49和0.08个像素。最后给出一个在砂土地基承载力离心机模型试验中的应用实例,分析结果包含砂土模型位移场、最大剪应变场和体积应变场的分布图。结果表明这一方法使得砂土模型局部化变形、剪切带和渐进破坏过程的量化分析成为可能。 相似文献
104.
Takaaki Aoki Toshio Seki Satoshi Ninomiya Kazuya Ichiki Jiro Matsuo 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2009,267(8-9):1424-1427
Molecular dynamics (MD) simulations of large argon clusters impacting on silicon solid targets were performed in order to study the transient process of crater formation and sputtering. The MD simulations demonstrate that the initial momentum of incident cluster is transferred to target surface atoms through multiple collision mechanism, where the initial momentum, which is along to the surface normal before impact, is deflected to lateral direction. This momentum transfer process was analyzed by the calculation of the velocity at the crater edge (the interface between cluster and target). In the case of Ar1000 cluster impact on Si(1 0 0) target at low energy per atom less than 40 eV/atom, the maximum value of lateral velocity of the crater edge increases in proportional to the velocity of incident cluster atoms. On the other hand, the crater edge velocity saturates over 40 eV/atom of incident energy per atom. In this case, the whole of constituent cluster atoms are implanted into the target and expand in both lateral and reflective directions at the subsurface region of the target. These MD simulations demonstrated that this collisional process result in the high yield sputtering of the target atoms. 相似文献
105.
Reduction in cooling loss due to the heat transfer from burning gas to the combustion chamber wall is very important for improving the thermal efficiency in hydrogen engines. The previous research has shown that the direct injection stratified charge can be a technique to reduce the cooling loss and improve thermal efficiency in hydrogen combustion. For effective reductions in cooling loss by the stratified charge, it is very important to know the relation between the fuel injection conditions and mixture distribution. The current research employs the laser induced breakdown spectroscopy as a method to measure the hydrogen concentration distribution in the direct injection stratified charge. Measurement of instantaneous local equivalence ratio by the method clears the characteristics of mixture formation in hydrogen direct injection stratified charge. This research also tries to actively control the mixture distribution using a split fuel injection. 相似文献
106.
Toshio Shimoo Hiroshi Takeuchi Kiyohito Okamura 《Journal of the American Ceramic Society》2001,84(3):566-570
Three types of polycarbosilane-derived SiC fibers—Nicalon, Hi-Nicalon, and Hi-Nicalon S—were exposed at temperatures of 1573–1773 K under a reduced pressure of 1.3 Pa. The thermal stability of the fibers was investigated through examinations of the gas evolution, grain growth, specific resistivity, fiber morphology, and tensile strength. The thermal decomposition of the silicon oxycarbide phase began at 1523 K; then, active oxidation of the β-SiC crystallites occurred at >1673 K. The active oxidation caused serious damage to the fiber structure, which resulted in significant degradation of the fiber strength. Hi-Nicalon had a tensile strength of ∼0.5 GPa after exposure at 1773 K, although Nicalon and Hi-Nicalon S fibers completely lost their strength, even after exposure at 1673 K. Hi-Nicalon fiber had relatively good thermal stability under reduced pressure. 相似文献
107.
The effects of seed layers on the characteristics of rf-sputtered lead zirconium titanate thin films were investigated. Prior to sputtering, PbTiO 3 seed layers (100 nm) were deposited onto the Pt/Ti/Si and Pt/Si substrates by sol-gel (spin coating) processing method. Structure-property relation was studied as functions of substrate temperature and sputtering conditions. Special efforts were given in optimizing the deposition parameters to prepare the films in the perovskite phase without post deposition annealing. Dielectric constant and loss tangent of the films were in the range 800-950 and 0.04 -0.06, respectively. Remanent polarization and coercive field were 23.1 w C/cm 2 and 75kV/cm, respectively, for the films without PbTiO 3 seed layer, where as the corresponding quantities for in situ -deposited perovskite Pb(Zr, Ti)O 3 films on PbTiO 3 seed layer were 28 w C/cm 2 and 65 kV/cm, respectively. 相似文献
108.
Stress corrosion crack growth rates of 304L stainless steel after one-directionally warm-rolled along the longitudinal (L) direction were measured in oxygenated and deoxygenated pure water at 288 °C. The fracture mode is mainly intergranular in the Transverse-longitudinal (T-L) orientation specimen, while it is occasionally intergranular in the Longitudinal-transverse (L-T) orientation specimen. The crack growth rates in the T-L orientation are higher than those in the L-T orientation in both oxygenated and deoxygenated environments, which is related to the effective cracking growth path as the result of microstructural anisotropy and applied loading direction. 相似文献
109.
Hidenori Hiramatsu Yoichi Kamihara Hiroshi Yanagi Kazushige Ueda Toshio Kamiya Masahiro Hirano Hideo Hosono 《Journal of the European Ceramic Society》2009,29(2):245-253
Optoelectronic properties and device applications of layered mixed-anion compounds such as oxychalcogenide LaCuOCh (Ch = chalcogen) and oxypnictide LaTMOPn (TM = 3d transition metal, Pn = pnicogen) are reviewed. Several distinctive functions have been found in these materials based on our original material exploration concept. Fabrication of high-quality epitaxial films of LaCuOCh leads to clarifying the excellent electrical and optical properties such as high hole mobility of 8 cm2/(V s) and heavy hole doping at >1021 cm?3 in LaCuOSe, and sharp and tunable-wavelength photoluminescence in the solid–solution systems in LaCuOCh. In addition, a room temperature operation of a light-emitting diode is demonstrated using LaCuOSe as a light-emitting layer. These results suggest that the layered oxychalcogenides have potential for light-emitting layers as well as transparent hole-injection layers in organic/inorganic light-emitting diodes. Furthermore, by extending the material system from the copper-based oxychalcogenides to isostructural compounds, transition metal-based oxypnictides LaTMOP (TM = Fe, Ni), we have found novel superconductors, LaFeOP and LaNiOP. 相似文献
110.
模态综合法是对复杂的机械进行振动解析的有效方法之一。本文将该法用于带换气扇马达的振动解析。整个马达系统分成四个子结构,用锤击试验法获得各子结构的传递函数。模态参数用曲线拟合法求得。然后用模态综合法进行综合,得到全系统的动特性。比较计算值和实验值,从而证明了这个方法的有效性。 相似文献