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71.
The early stages of corrosion of AISI 314, HK 40, and Alloy 800H have been studied in a strongly carburizing (aC=0.8), weakly oxidizing
atmosphere at 1098 K. Samples with electropolished and cold-worked surfaces were exposed for up to 400 min. at temperature, in a conventional corrosion rig or in a reaction vessel which was installed within an X-ray photoelectron spectrometer. The latter facility allowed the effects of the specimen heating rate and the rat of gas flow to be investigated. Examination of the corrosion products was accomplished with the aid of XPS, SEM, TEM, and conventional metallography. Initially, surface layers comprised of -Cr2O3, (Mn, Cr)3O4, and SiO2 formed, with layer structure, microstructure, and composition being functions of alloy composition and surface condition. Only on the cold-worked surfaces did a well-developed duplex oxide, consisting of an outer, Cr-rich oxide layer and an inner, SiO2 layer, form. In good agreement with the predicted value of 1.9 wt.%, between 1.4 and 2 wt.% Si in the alloy was required to form a complete SiO2 layer. After an incubation period, -Cr2O3 became unstable and transformed to M7C3; the carbides then grew by diffusion of metal from the alloy substrate. The presence of manganese, as (Mn, Cr)3O4, in the surface oxide influenced the mode of carbide growth, whereas the rate of carbide growth was severely suppressed by a continuous SiO2 layer which acted as a diffusion barrier both to metal and to carbon. It is argued that the SiO2 layer is most effective in reducing carburization when it is free from or contains very few structural defects. 相似文献
72.
Surface modification of spherical LiNi1/3Co 1/3 Mn1/3O2 with Al2O3 using heterogeneous nucleation process 总被引:1,自引:0,他引:1
To improve the cycle stability at high voltage and high charge/discharge rate, spherical LiNi1/3Co1/3Mn1/3O2 was coated with Al2O3 by using heterogeneous nucleation process, and the physical and electrochemical properties were studied. The SEM images show that there is a uniform coating on the modified spherical LiNi1/3Co1/3Mn1/3O2. The electrochemical tests indicate that the properties of LiNi1/3Co1/3Mn1/3O2 coated with 0.5% aluminum oxide are the best. The initial capacities are 150 and 173 mA.h/g at the rate of I C in the voltage range of 2.7-4.3 V and 2.7-4.6 V, respectively, and the discharge capacities maintain about 99% and 85% after 30 cycles, respectively. While those of the bare LiNi1/3Co1/3Mn1/3O2 are only 90% and 75%, respectively. The CV tests of LiNi1/3Co1/3Mn1/3O2 show that Al203-coating can restrain the oxide-reduction peak currents fading during the charge/discharge course. 相似文献
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主动寻位与状态记忆安装技术(InitiativeLocatingandStateMemory,简称IL&SM)是一种新型的工件安装方法。通过运用齐次坐标变换原理分析了多工序转换过程中,IL&SM箱体对工件上特征间位置精度的影响,并给出了描述工件位置误差的通用数学模型,最后通过实例说明了位置误差建模方法的应用。研究结果将为消除箱体原始误差对工件加工精度影响,从而为进一步实现误差补偿提供理论参考依据。 相似文献
75.
液态金属快速结晶的热力学驱动力 总被引:1,自引:0,他引:1
采用超高真空无容器悬浮熔炼技术使液态Fe和Ni的过冷度分别达200和235K,借助量热法测定出其比热各为48.6和40.5J·mol~(-1)·K~(-1).据此精确计算出深过冷Fe和Ni快速结晶的热力学驱动力△G_(LS),并与Turnbull模型和Dubey-Ramachandrarao模型的近似计算结果相比较,发现这两种近似模型在过冷度超过100K时均产生大于1%的偏差.进一步分析发现,△G_(LS)的计算偏差对深过冷液态金属中晶体形核率的影响极大,因此快速凝固研究中应尽可能精确计算△G_(LS). 相似文献
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Links between different stabilities of switched homogeneous systems with delays and uncertainties
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This paper addresses the links between three stabilities (attractivity, asymptotic stability, and exponential stability) of switched homogeneous systems with delays and uncertainties. A system has a certain property over a given set of switching signals if the property holds for all switching signals in . It is shown that a switched homogeneous system of degree one is exponentially stable over a given set of switching signals if it is attractive or asymptotically stable over the same set. The result is then applied to switched linear systems with delays and uncertainties. Finally, an example follows to show that ‘being over a given set of switching signals’ is necessary to guarantee the equivalence between different stabilities. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
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邓燕谊 《计算技术与自动化》2009,28(4):72-75
令T为P^n上的Caldero'n-Zygmund积分算子,由T构成的交换子的有界性已有较完善的结论,本文的目的是将之推广到一般的齐型空间。设(X,d,μ)为齐型空间,将引进齐型空间(X,d,μ)上的分数次积分变换构成的交换子Iγ^b,并证明分数次积分变换构成的交换子Iγ^b的端点估计,即砖是从L^1/γ(X)到BMO(X)有界的,从Bp^γ(X)到CMO(X)有界的。 相似文献