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《腐蚀工程科学与技术》2013,48(3):192-194
AbstractFailure analysis was conducted on two failed electronic cardsfrom the Computer Center of the Kuwait Institute for Scientific Research. The results of the elemental analysis indicated that the corrosion product film found on contact pins and soldered through holes was composed of copper and sulphur compounds. Chemical analysis of the air in the computer room indicated a high level of nitrogen oxide (up to 300 ppb), whereas other gases such as H2S and SO2 were below the detectahle limits (100 and 200 ppb respectively) of the analytical technique used. It was concluded that the initial high relative humidity ( ~ 75%) had synergised with the strongly oxidising nitrogen oxide and H2S and/or SO2 to bring about the corrosion of copper substrate in ‘bare spots’ or gaps in the soldered contacts, causing card failure. Other factors, such as galvanic coupling of the copper substrate with nickel, silver, and gold plates, and the relatively high local temperature, may have accelerated the corrosion process. A decrease in the relative humidity to the optimum value of 45% did not obviate card failure. It was concluded that efficient air filters should be utilised in the computer environment, as electronic equipment can be damaged by levels of pollutant gases 10 times lower than those cited for human safety requirements. 相似文献
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《International Journal of Cast Metals Research》2013,26(5):271-279
AbstractNine grades of pearlitic cast iron containing different graphite morphologies (from flake, compacted and spheroidal) have been studied. The parameters investigated include the graphite aspect ratio, nodularity, graphite size and modulus of elasticity. These parameters have been correlated and compared with different existing bound and model equations. It has been found that the modulus of elasticity of the graphite phase increases as the aspect ratio and nodularity of the graphite increases, i.e.flake graphite gives a lower modulus of elasticity than spheroidal graphite. The experimental values of the modulus of elasticity show good agreement to bound and model equations, although flake graphite cast irons show higher deviation from the modelled values. An equation for the correlation between the graphite modulus of elasticity and the nodularity is presented. Introducing this linear correlation into an existing model for the determination of the effective modulus of elasticity gives a continuous function, including all grades of cast irons, with a very good agreement with experimental values. The modulus of elasticity of cast irons can be accurately predicted from both bound and especially model equations, using the aspect ratio and nodularity of the contained graphite particles. The fit is improved by using a modulus of elasticity of the graphite phase that is based on the graphite morphology, considering that the modulus of elasticity of the graphite is different in the basal and prismatic planes. 相似文献
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An account is given of an investigation in which gross particles consisting of either jute or viscose rayon fibres of different lengths and diameters were spun in both secondary cellulose acetate filaments and a polyurethane elastomer in order to verify whether a significant degree of reinforcement was possible with a composite material of this type. The mechanical properties of the composite cellulose acetate fibres were studied, and it is shown that both types of filler produced a decrease in breaking extension and an increase in initial modulus with increasing filler content. The strength of the jute-filled material is also shown to increase. Similar effects on the breaking extension and initial modulus of the rayon-filled polyurethane filaments were observed, and here there was also a decrease in strength that arose from the difference in extensibility between the rayon and the polyurethane filament. 相似文献
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Studies of the Antarctic sea ice edge and ice extent from satellite and ship observations 总被引:5,自引:0,他引:5
Passive microwave-derived ice edge locations in the Antarctic are assessed against in situ observations from ships between 1989 and 2000. During the growth season (March-October), the ship data agrees with satellite data very well, with r2 values of 0.99 and 0.97 for the Bootstrap and Team algorithms, respectively. During the melt season (November-February), the agreement is not so good with the passive microwave ice edge typically 1-2° of latitude south of the observations. This is due to the low concentration and saturated nature of the ice, and the r2 values for this period are 0.92 and 0.80 for the Bootstrap and Team algorithms, respectively. Sensitivity studies show that such an offset in the summer ice edge location can cause significant errors in trend studies of the extent of sea ice cover in the Southern Ocean. The passive microwave ice concentration at the ice edge observed by ship varies greatly, averaging 14% for the Team algorithm and 19% for the Bootstrap. Comparisons between passive microwave data and SAR, Landsat and OLS data during the ice growth season show that while small-scale details in ice edge location are lost, the passive microwave data generally provide good and consistent representation of the higher resolution imagery. 相似文献
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《Materials Science & Technology》2013,29(11):1344-1348
AbstractIn this study, a 355 nm UV Nd:YAG laser is used to process silicon wafers. In order to obtain microstructures with high aspect ratio, a dual prism optical system is set up to control the cutting linewidth of the UV laser beam. During the laser beam propagation through the prisms, the two prisms are rotated with the same angular velocity, which results in the focal spot of the laser beam moving in a circular path on the silicon substrates. When the laser beam moves relative to the holder (workstation), a laser cutting process can be carried out. With this laser system, the cutting linewidth is controllable ranging from 10 μm to 1 mm by adjusting the initial phase difference in the two prisms. The experimental results show that arbitrary shaped silicon based microstructures with high aspect ratio can be fabricated by this 355 nm UV laser system, and the aspect ratio over 10 can be obtained. 相似文献
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