共查询到20条相似文献,搜索用时 31 毫秒
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The results reported here, showing the effect of a non-continuous degassing sequence on the Al-20Si-3Cu-1 Mg powder, are a complement of previous work concerning the continuous degassing of the same powder. The degassing experiments were carried out, under high vacuum, in the temperature range 20 to 550 °C in a horizontal furnace heated at a uniform heating rate of 2.5 °C min–1. The partial pressures of the released gases were monitored and analysed during the heating phase by a computerized Edwards EQ80F residual gas analyser (RGA). RGA measurements indicate that water and hydrogen are the main degassing products. A complete degassing can only be achieved if the sample is heated up to a temperature where the chemical reactions are finished in the applied time. Thermodynamical equations alone are not enough to explain the kinetics of degassing of aluminium powders. The diffusion of aluminium through its surface oxide layer (Al2O3), described by the self-diffusion of aluminium, can explain to a large extent the kinetics of degassing aluminium powders. 相似文献
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Gerhard Zilly 《真空研究与实践》2000,12(3):180-183
The efficient and economical degassing of oxygen from water under vacuum will be shown at two examples (water treatment for district heating and production of ultra pure water). 相似文献
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The solution of the diffusion equation is taken as a foundation of the theory of gas-metal interaction in high vacuum. The boundary conditions are formulated from the analysis of the gas balance equations on a metal surface and in a gas volume. The boundary conditions are generally non-linear but in some important cases linearization is permissible. In this way it is possible to obtain analytical expressions for the instantaneous gas flow on electron- and photon-induced desorption, low temperature thermal desorption and gettering at a constant pressure. By means of these formulae one can generalize the experimental data of various authors and calculate the kinetics of such processes as the outgassing of an electron collector, the gas desorption by synchrotron radiation in a vacuum chamber of electron or positron colliding-beam storage-rings, the degassing of an ultra-high vacuum system, the gas sorption by barium and titanium, etc. 相似文献
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Hydrogen is a harmful gas element that is appreciably soluble in aluminum and its alloys. Removal of hydrogen from molten aluminum has been one of the most important tasks in aluminum melt processing. In this paper, a patented degassing process, which is based on principle of vacuum metallurgy, is proposed. A porous head that connects a vacuum system is immersed in the molten aluminum. The vacuum is created within the porous head and the dissolved hydrogen will diffuse unidirectionally towards the porous head according to Sievert's law. In this way, the hydrogen in the molten aluminum can be removed. The Fick's diffusion equation is used to explain hydrogen transfer in the molten aluminum. RPT experiments are carried out to evaluate the effectiveness of the new degassing process. The experiments indicate that the hydrogen content can be dramatically reduced by use of this process. 相似文献
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N. J. van der Heijden P. Khosropanah J. van der Kuur M. L. Ridder 《Journal of Low Temperature Physics》2014,176(3-4):370-375
Controlling the critical temperature ( \(T_{C}\) ) of Ti/Au bilayers is vital in the development of practical TES detectors. Previously empirical studies have been done on aging effects in Ti/Au and other superconducting bilayers but no link with theory has been made. Here we attempt to explain the change in \(T_{C}\) with a diffusion mechanism. The change in \(T_{C}\) has been measured for a set of Ti/Au bilayer samples that have been given a variety of bake-out treatments, where we found a trend that can be partly explained by an inter-diffusion mechanism. With an empirical model based on diffusion a safe zone can be defined as a region of bake-out treatments, where the \(T_{C}\) is not affected beyond the requirements. This will shine light on the bake-out and the storage condition boundaries of these detectors. 相似文献
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Cleaning of vacuum components for UHV and UCV applications Ultra‐clean vacuum components and assemblies are fundamental to some cutting edge high‐tech sectors like semiconductor industry, particle accelerators, and surface analytics. Exceptionally critical for these applications are particles that stick at the vacuum facing surfaces as well as desorption of water and hydrocarbons from the surfaces into the system, because this may interfere with the sensitive ultra‐high vacuum (UHV) and ultra‐clean vacuum (UCV) processes. In this contribution, some established cleaning methods and surface treatments are discussed with respect to their effect on reducing particle contamination and outgassing of water and organic compounds from stainless steel surfaces. It is clarified that the resulting cleanliness severely depends on the detailed steps during the surface treatment and subsequent cleaning. As a consequence, the discussed methods should be chosen and adapted with great care according to the specific demands of the final application area. 相似文献
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Steam jet vacuum pumps for steel degassing The vacuum steel degassing is necessary for the production of particular steel qualities. This process requires high suction capacity and robustness of the applied vacuum pumps. This leads to the preferential application of steam jet vacuum pumps. 相似文献
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Sanche L 《Radiation protection dosimetry》2002,99(1-4):57-62
It has recently been shown that 3-20 eV electron impact on vacuum-dry samples of plasmid DNA induced substantial yields of single and double strand breaks (SSBs and DSBs). These results are summarised in the present article along with those obtained from the fragmentation of elementary components (i.e. condensed H2O, bases and sugar analogues) of DNA induced by low energy electron impact under ultra high vacuum conditions. By comparing the results from these experiments, it is possible to determine fundamental mechanisms by which low energy electrons damage DNA. The decay of transient anions formed on the DNA's basic components is found to play a crucial role in producing SSBs and DSBs. Since a large portion of the energy deposited by ionising radiation first leads to the production of low energy secondary electrons, these findings provide basic knowledge necessary to understand the genotoxic effects of high energy radiation and eventually modify these effects at the molecular level. 相似文献
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To determine the effects of vacuum environment on fatigue crack propagations in a Ti–6Al–4V alloy, K-decreasing tests were conducted in air and vacuum. The fatigue crack propagation rate became slower and threshold stress intensity factor range became larger with decreasing vacuum pressure. The tendency cannot be fully explained by the crack closure. Based on fracture surface observations, granular region of a few micrometer size asperities was observed on the fracture surface only in high vacuum and ultra high vacuum. The high vacuum environment is one of the necessary conditions for the formation of the granular region, and the fraction of surface coverage of adsorbed gas on fracture surfaces relates to the phenomenon. The formation of the granular region represents the difference of the crack propagation mechanism between vacuum and air environments. A new mechanism for the formation of the granular region was proposed, and that is one of the phenomena which can explain the reduction of crack propagation rate in vacuum. 相似文献
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中国航天器真空技术的进展(一) 总被引:1,自引:0,他引:1
围绕着中国航天器真空技术在航天领域中的应用问题,综合地介绍了其技术的发展,重点突出了中国极高真空技术的发展.提出了"分子真空寿命"这一新的物理量,并以此概念推导出测量气体分子热适应系数的方法.指出了在超高和极高真空条件下压力失去了原有的物理意义,引入了"有效压力"、"入射率"、"静压"、"动压"等新概念.探索了在空间条件下真空测量中的方向性效应和理论计算与实际测量偏离问题的特殊性和复杂性.介绍了利用分子沉技术研制的极高真空装置获得了10-11Pa极限真空度,介绍了中国已建立的航天器模拟设备的现状、性能指标和主要用途.概述了中国空间材料的真空效应研究现状,指出了空间材料、活动部件的冷焊及航天器敏感表面分子污染对航天器的长寿命和可靠性的影响.展望了中国航天器真空技术的发展. 相似文献
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为使真空泵的抽气能力能最大程度适应除气过程,在选用真空泵时需考虑到搅拌气体数量、设备表面放气和设备的漏气率.随着钢液真空处理技术的发展,能保证高效率、有效地脱除钢液中的气体成为迫切的问题.由于抽出气体有灰尘,维修次数多等综合因素,应采用抽气能力大、运转可靠性强、结构简单的蒸汽喷射泵而非机械泵.但近年来,钢液真空处理真空... 相似文献
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《Materials Letters》2007,61(4-5):1246-1250
Ultrasonic degassing, an environmentally clean and cheap technique, is an efficient way of degassing in a static volume melt. Vacuum degassing has also been tested as a beneficial and clean method in producing high quality products. An experimental device which combines the vacuum degassing and ultrasonic degassing has been built. Parametric studies have been carried out to investigate the efficacy of the ultrasonic degassing of molten aluminum alloy under reduced pressure. The results indicate that a combination of these two techniques makes degassing more efficient. 相似文献