排序方式: 共有18条查询结果,搜索用时 31 毫秒
1.
Laser nitriding and laser cementation are investigated by Mössbauer spectroscopy and complementary methods. It is demonstrated how the backscattering versions of Conversion Electron and Conversion X-ray Mössbauer spectroscopy can contribute to the investigation of surface processes, like the laser-induced formation of nitrides and carbides. Additionally, the formation of semiconducting iron disilicide can be achieved by ion-beam mixing and pulsed laser irradiation of Fe/Si bilayers. The results of both processes are compared.
相似文献2.
Zinc is widely used as a protective coating material due to its corrosion resistant properties. The structure and oxidation resistance of Al and Cr mixed zinc coatings, deposited by pack cementation process, is thoroughly examined in this work. The morphology and chemical composition of the as-deposited and oxidized samples was accomplished by electron microscopy while the phase identification was performed by XRD diffraction analysis. The experimental results showed that the addition of aluminum or chromium in the pack mixture forms only Al and Cr rich phases on the surface of the specimens without affecting significantly the phase composition of the rest zinc coatings. In the case of Zn-Al coatings, the overlying layer contains high concentrations of Al together with lower amounts of zinc and iron and in Zn-Cr coatings this layer contains Cr, Fe and Zn atoms and has much smaller thickness. The presence of these additional layers promotes significantly the oxidation resistance of the zinc pack coatings and they preserve most of their initial thickness and chemical content when exposed to an aggressive environment while their oxidation mass gain was measured at low levels during the oxidation tests. 相似文献
3.
龙游石窟砂岩的泥质胶结物研究 总被引:1,自引:0,他引:1
本文通过对浙江龙游石窟砂岩的岩矿鉴定,砂岩泥质胶结物质的X-衍射定性及定量分析、扫描电镜观察、差热分析,以了解砂岩的泥质胶结特征,为石窟风化研究和保护加固研究提供科学依据。 相似文献
4.
5.
杨运来 《中国科学B辑(英文版)》1989,(5)
In this paper, firstly, the amount of collapsible space is statistically determined from the pore-size distributions of loess slices before and after collapse by using a polarizing microscope. Then, the characteristics of the structure and the copulation of loess grains are studied, and the copulations which decrease in strength upon contact with water are discovered. Lastly, by studying the joint action of external causes——a certain load and a certain moisture content——and internal conditions, the mechanism of loess collapse is advanced. 相似文献
6.
Cementation is produced by mixing a certain amount of cement with the saturated clay. The purpose of this paper is to model the cementation effect on the mechanical behavior of cement-treated clay. A micromechanical stress-strain model is developed considering explicitly the cementation at inter-cluster contacts. The inter-cluster bonding and debonding during mechanical loading are introduced in two ways: an additional cohesion in the shear sliding and a higher yield stress in normal compression. The model is used to simulate isotropic compression and undrained triaxial tests under various confining stresses on cement-treated Singapore clay with various cement contents. The applicability of the present model is evaluated through comparisons between numerical and experimental results. The evolution of local stresses and local strains in inter-cluster planes is discussed in order to explain the induced anisotropy due to debonding at contact level under the applied loads. 相似文献
7.
GaAs-玻璃粘接阴极组件热辐射放气成份质谱分析 总被引:1,自引:0,他引:1
为解决负电子亲合势GaAs光电阴极电子发射灵敏度低的问题,运用质谱计对GaAs-玻璃粘接阴极组件在高温热辐射除气时的放气成份进行了分析, 获得了GaAs电子发射层原子级表面。结果表明:组件150℃为表面放气,450℃为材料体内放气,580℃为洁净表面获得温度,大于650℃ 时GaAs发射层面有As蒸发。这说明严格控制发射层表面洁净温度,是保证制备高性能阴极灵敏度的关键。 相似文献
8.
9.
Yanqiang Qiao 《Applied Surface Science》2010,256(24):7462-454
Cr-modified silicide coatings were prepared on a Ti-Nb-Si based ultrahigh temperature alloy by Si-Cr co-deposition at 1250 °C, 1350 °C and 1400 °C for 5-20 h respectively. It was found that both coating structure and phase constituents changed significantly with increase in the co-deposition temperature and holding time. The outer layers in all coatings prepared at 1250 °C for 5-20 h consisted of (Ti,X)5Si3 (X represents Nb, Cr and Hf elements). (Ti,X)5Si4 was found as the only phase constituent in the intermediate layers in both coatings prepared at 1250 °C for 5 and 10 h, but the intermediate layers in the coatings prepared at 1250 °C for 15 and 20 h were mainly composed of (Ti,X)5Si3 phase that was derived from the decomposition of (Ti,X)5Si4 phase. In the coating prepared at 1350 °C for 5 h, single (Ti,X)5Si3 phase was found in its outmost layer, the same as that in the outer layers in the coatings prepared at 1250 °C; but in the coatings prepared at 1350 °C for 10-20 h, (Nb1.95Cr1.05)Cr2Si3 ternary phase was found in the outmost layers besides (Ti,X)5Si3 phase. In the coatings prepared at 1400 °C for 5-20 h, (Nb1.95Cr1.05)Cr2Si3 ternary phase was the single phase constituent in their outmost layers. The phase transformation (Ti,X)5Si4 → (Ti,X)5Si3 + Si occurred in the intermediate layers of the coatings prepared at 1350 and 1400 °C with prolonging co-deposition time, similar to the situation in the coatings prepared at 1250 °C for 15 and 20 h, but this transformation has been speeded up by increase in the co-deposition temperature. The transitional layers were mainly composed of (Ti,X)5Si3 phase in all coatings. The influence of co-deposition temperature on the diffusion ability of Cr atoms was greater than that of Si atoms in the Si-Cr co-deposition processes investigated. The growth of coatings obeyed inverse logarithmic laws at all three co-deposition temperatures. The Si-Cr co-deposition coating prepared at 1350 °C for 10 h showed a good oxidation resistance due to the formation of SiO2 and Nb, Cr-doped TiO2 scale after oxidation at 1250 °C for 10 h. 相似文献
10.