A new generation of porous non-evaporable getters

The application of non-evaporable getters is increasing. In many of these applications the getters have to work at relatively low temperatures to avoid damaging internal components and their excessive degassing. At these low temperatures the bulk diffusion of the sorbed gases is normally very small (except for H₂) and therefore the active surface must be maximized. This means that large specific surfaces and porous structures have to be used. Already existing porous getters normally require activation at high temperatures (700–900°C) but in several cases this is not easy or even possible to achieve. A new generation of porous getters has therefore been prepared and studied to fulfill these requirements. The getters are based on a recently developed ZrVFe getter alloy, which is characterized by a high activity for the residual gases. The new porous getters are obtained via a sintering process between zirconium and ZrVFe alloy powders, which, however, maintains a relatively large surface area and porosity. Therefore, they combine the large specific surface and porous structure necessary for surface sorption of gases at low temperatures with the characteristics of high diffusivity, which makes possible efficient sorption also after activation at relatively low temperature (400–500°C). Besides these already remarkable properties, the getters show particularly attractive mechanical characteristics to meet the special working conditions of some tubes (vibrations, shocks, etc.). The getter performances for the main gases (H₂, CO, H₂O) are presented and discussed; the tests are performed using standard dynamic sorption techniques and the microbalance method (for H₂O). The results obtained for sorption at room temperature confirm the good performances due to the high surface area. Higher sorption temperatures (200°C, 400°C) tested show the large effects of the high diffusivity of the material used, which is responsible for the further noticeable improvement of the sorption characteristics obtained in the lower temperature ranges. These getters appear, therefore, to be a real contribution to particular problems of many vacuum devices such as special electron tubes.     

合肥光源真空室内壁镀TiZrV吸气剂薄膜的研究

TiZrV合金在180℃下加热24 h即可激活,是迄今发现的激活温度最低的非蒸散型吸气剂,已在国外一些粒子加速器得到应用。采用直流磁控溅射法,氩气作为放电气体,成功的在不锈钢管道内壁获得了TiZrV薄膜。薄膜中TiZrV之比为3:3:4左右,位于"低激活温度区"。利用三段一米长的螺线管串联所产生的磁场维持放电,完成了对三米长的波荡器真空室的镀TiZrV薄膜处理,并已安装在合肥光源储存环上,目前运行情况正常。     

真空粉末绝热容器检漏方法之探讨

以我国批量生产真空粉末绝热容器的实际情况为例,并通过数据计算分析,认为对真空粉末绝热容器可以用静态升压法考核夹层总气载,再结合分子筛的吸附作用来满足容器使用寿命的要求。目前,这种方法广泛地运用于真空粉末绝热容器制造业。     

Techniques of vacuum pumping in multi-layer insulated cryogenic vessels

The improvement in heat transfer properties obtained by use of Multi-Layer Insulation (MLI) is reviewed. The introduction of many closely spaced layers of material increases considerably the surface exposed to vacuum and flow restrictions. Experiments have been made to demonstrate that by using correct pump-down procedures the inherent difficulties can be dealt with and the improved insulation properties of MLI can be used to full advantage in laboratory cryostats which are vented and re-pumped frequently. The test apparatus, procedure and calculation are shown in detail. Test results show that the heat losses of MLI at 10⁻⁴ torr are about 10 per cent of the losses of vacuum insulation only at 10⁻⁶ torr. Heat transfer of MLI remains constant at pressures below 10⁻³ … 10⁻⁴ torr. Recommended pump down procedures are given for equipment which is occasionally vented. The importance of cleanliness during installation of MLI, of the use of heating and getter materials is demonstrated. Pump down times to 10⁻⁴ torr of 5 … 6 h after venting were easily obtained in the test system.     

Sorption of active gases by non-evaporable getter

The behaviour of St 101 getter towards the sorption of active gases like oxygen, carbon dioxide, carbon monoxide, background water vapour and nitrogen at 10 torr pressure have been studied gravimetrically at 400°C and at other temperatures. A Cahn RG Electrobalance has been used in the above studies. The sorption by St 101 getter has been compared with that of Zr powder. The sorption law and the reaction mechanism are also discussed.     

脉冲真空放电离子密度的测量

由于采用脉冲放电沉积技术能够克服连续电弧离子镀沉积时产生的液滴及负偏压放电的缺点，特别是它在镀制类金刚石薄膜中显示出来的独特性能：不含氢和硬度高，使其在薄膜沉积技术中越来越受到广大研究者的重视。为了更深入地研究薄膜的沉积工艺和薄膜性能之间的关系，迫切需要对脉冲真空放电等离子体的微观参数进行深入透彻的研究，如离子密度及其空间分布等。本文介绍了测量脉冲真空电弧离子源离子密度的方法，并采用该方法测量了脉冲真空电弧离子源离子密度及其空间分布，分析和研究了影响离子空间分布的各种参数。     

Measuring the package shipping environment in refrigerated ocean vessels

The dynamic and climatic environments inside the cargo holds of regrigerated ships carrying bananas from Central America to destinations in Europe and the United States were measured. The same environments inside individual packages of bananas were also measured for comparison. Among the variables studied were shock and vibration G-levels, temperature, humidity, and air velocity. Three different types of shipments were monitored: break-bulk, palletized, and containerized. The results show that the average G-levels are similar to those found on trailers and railcars and that the vibration levels in the packages themselves were amplified by up to as much as eight times.     

Measuring the robson angle in vacuum arcs of various length

It is established that the Robson angle, which determines the direction of motion of a cathode spot of vacuum arc in a homogeneous electric field sloped relative to the cathode, depends mostly on the inter-electrode gap width. The dependence of the Robson angle on the field slope at various gap widths has been measured for molybdenum and tungsten cathodes. The knowledge of this angle is necessary for correct choice of the optimum magnetic field configuration controlling the cathode spot dynamics in setups for vacuum-arc deposition of various coatings and in vacuum commutation devices.     

高真空多层绝热抽真空工艺研究现状与发展

通过分析影响真空度的主要因素及其影响规律,针对不同的影响因素提出了各自有利真空获取和维持的解决方案,并将各措施具体地与抽真空工艺过程控制各环节相匹配,从而制定出较为科学的现行抽真空工艺流程.通过剖析现有工艺的局限性和研究成果,对抽真空工艺的现状、发展趋势提出建议.     

The determination of volume ratios by gas depletion through multiple expansions

We present a new technique for the determination of the volume ratio of two vacuum chambers connected through a valve. The method is based on the measurement of the pressure in a chamber filled with a gas that is repeatedly depleted by expansion in a second chamber that was previously evacuated. Our calculation shows that under the reported measurement conditions, this technique has an uncertainty comparable to that obtained from the gas accumulation technique [Elliott KWT, Clapham PB.The accurate measurement of the volume ratios of vacuum vessels. NPL Report MOM 28, January 1978]. An excellent equivalence between the results obtained with this new technique and the measurements obtained by the gas accumulation technique is demonstrated.     

Activation characterization of non-evaporable Ti-Zr-V getter films by synchrotron radiation photoemission spectroscopy

The effect of activation temperature on the degree of reduction of dense and porous TiZrV films was investigated by synchrotron radiation photoemission spectroscopy. The dense and porous TiZrV films have similar composition and thickness, and their specific surface areas are 2 m²/g and 13 m²/g, respectively. Comparing the previous results of the porous TiZrV film [Chien-Cheng Li, Jow-Lay Huang, Ran-Jin Lin, Chia-Hao Chen, Ding-Fwu Lii, Thin Solid Films 515, (2006) 1121.], the degree of activation of the porous TiZrV film is lower than that of the dense TiZrV film. To complete the activation treatment of the dense and porous TiZrV films, the activation temperature must be higher than 350 °C or the activation time must be longer than 30 min.     

Application of molecular interaction volume model in vacuum distillation of Pb-based alloys

A method is presented for calculating the separation coefficients of Pb-Au and Pb-Sn alloys in vacuum distillation based on molecular interaction volume model (MIVM). A significant advantage of the model lies in its ability to predict the thermodynamic properties of liquid alloys using only binary infinite activity coefficients. The calculated results of Pb-Ag, Pb-Au, Pb-Sb, Pb-Sn and Sb-Sn show good agreement with experimental data in literature. It shows that the prediction effect of the proposed method is of better stability and reliability because the MIVM has a good physical basis.     

Evaluation of target purity using various vacuum systems

Gold targets were prepared under various conditions using both a cryo-pump and a conventional diffusion pump evaporator system. Measurements were made at the Argonne Tandem Accelerator System to determine the purity of these targets.     

Radiation and thermal effects on porous and layer structured materials as getters of radionuclides

The long term radiation and thermal effects on porous and layer structured materials that may function as getters for radionuclides have been evaluated using accelerated laboratory experiments including energetic electron, ion or neutron irradiation, as well as high-temperature thermal annealing. The materials studied include: zeolites, layered silicates (mica and smectite clays), open framework structured apatite and crystalline silicotitanate (CST) which is an important synthetic ion-exchange material for the chemical separation of high-level liquid radioactive wastes.In situ transmission electron microscopy during irradiation by energetic electrons and ions has shown that all the studied materials are susceptible to irradiation-induced amorphization. Amorphization can be induced by ionization and/or direct displacement processes. Amorphization may be preceded or accompanied with dehydration, layer spacing reduction and gas bubble formation. In the case of zeolites, CST and some layer silicates, radiation effects are significantly enhanced at higher temperatures. In fact, thermal annealing at high temperatures alone can cause complete amorphization of zeolites. Our experiments have shown that amorphization or even partial amorphization will cause a dramatic reduction (up to 95%) in ion-exchange and sorption/desorption capacities of zeolite for radionuclides, such as Cs and Sr. Because the near-field or chemical processing materials (e.g., zeolites or CST) will receive a substantial radiation dose after they have incorporated radionuclides, our results suggest that radiation effects may, in some cases, retard the release rate of sorbed or ion-exchanged radionuclides.     

Effect of the ion-beam-induced getters on the parameters of neutron-irradiated GaAs heterostructures

It was found that the negative influence of neutron irradiation on the parameters of Schottky-gate field-effect transistors based on epitaxial GaAs heterostructures can be markedly reduced by preliminarily implanting the heterostructures with Ar ions from the side of a substrate. The effect is explained by the farrange gettering of impurities and defects from the active transistor regions in the course of the neutron irradiation, which suppresses the formation of irradiation-induced deep energy levels.     

Preparation of yttria-stabilized zirconia nanoplatelets using vacuum roll coating

Roll-to-roll vacuum coating on moving plastic substrates and the subsequent comminuting of the film into a flake or platelet with microscale lateral and thickness dimensions is an industrially mature technology utilized to produce clean, consistent material with high throughput. In this study, we describe the novel preparation of nanoplatelets by top-down vacuum evaporation of yttria-stabilized zirconium dioxides (YSZ) on a nanoembossed, moveable substrate for the purposes of making nanoplatelets. Microscopy and particle size analysis of the resulting YSZ nanoplatelets revealed that use of the nanoembossed substrate results in significant narrowing of the particle size distribution. However, while the YSZ coatings were conformal and successfully replicated the nanopattern of the underlying substrate, the stress in the film was inadequate to fracture the film into platelets that replicated the nanometer dimensions of the underlying pattern. It was determined that this is due to the inherent fracture toughness of the nanoplatelets and the augmented adhesion forces along the increased length scale of nanoparticle contacts. The nanoplatelets were further reduced in average size and size distribution by post-processing techniques of sonication, ball milling, and centrifugation. The nanoplatelet’s stoichiometry and crystallinity were modified by manipulating the source material, deposition parameters, and post-processing steps.     

Effects of catalytic surface layer on Zr-based alloy getters for hydrogen absorption

Hydrogen sorption characteristics of Zr-based alloy getters fabricated in the forms of bulk were investigated. Non-evaporable getters (NEGs) have been widely used in vacuum devices, but thermal activation process at high temperature and high vacuum environment is inevitably required for efficient sorption rate. In order to solve this problem and improve sorption kinetics, we developed and characterized Ni-coated NEGs. Ni-coated NEGs show good gettering performance and fast sorption kinetics without any activation process, compared to conventional Zr-based NEGs. It is mainly caused by the catalytic effect of surface Ni layer. Surface Ni plays an important role as a catalyst that enables hydrogen to dissociate on surface more easily and also as a protection layer against oxidation. Consequently, Ni-coated NEGs can be easily applicable to vacuum devices because those need not go through the activation process and show fast hydrogen sorption kinetics.     

Wireless communication using detectors located inside vacuum chambers

Progress in modern vacuum technology requires an increasing number of measurements to be performed in the vacuum environment itself and in many applications data transfer outside the vacuum vessels is both difficult and expensive. This paper explores the potential of wireless technology to transmit data from and into ultra high vacuum (UHV) compatible vacuum chambers using glass viewport windows attached to normal standard flange fittings. The current tests focus in particular on Bluetooth technology, and its characteristics and limitations investigated. Signal propagation has been verified up to about 9 m and the outgassing of components shown to be insignificant in a clean metal-sealed vacuum system down to a pressure of 10⁻⁷ mbar. Some preliminary tests of noise and electromagnetic field immunity have been carried out, confirming the robustness of Bluetooth spread spectrum modulation technique. Signal data from Integrated Circuit Temperature Sensors and Photodiodes have been successfully transmitted from a vacuum chamber, proving the capability of this technology standard to handle both low and high frequency data. The future prospects and the further developments of the approach are also discussed.     

Plasmachemical synthesis of coatings using a vacuum arc discharge

In this paper we discuss the issues of applying protective coatings on the copper anodes of powerful generator tubes. As a synthesized material due to its high operational properties was chosen titanium carbide obtained by sputtering a titanium cathode in benzene vapors. Scheme of a vacuum arc device used in this work and also the technological processes for the plasmachemical synthesis of coatings on complex shape anodes are described. For a correct choice of the technological parameters it was considered a model of penetration of the plasma flux into the hollow copper anode that was verified by experiments using a setup with a variable cavity diameter. On the emission spectrum of the discharge in the process of coating deposition shown in this work were recorded spectral lines corresponding to the atoms and ions of titanium and carbon ions. We investigated the distribution of elements across the thickness of the formed coating immediately after deposition and after annealing in vacuum, also the X‐ray diffraction pattern and a microsection for the obtained titanium carbide coating are presented. As a result of the work it can be noted that the described sequence of technological processes, subject to the control of plasma flux parameters, allows obtaining a high quality protective coating on parts of complex shape.