低温泵用吸附材料的研究概述

低温泵广泛应用于真空电子、半导体领域。低温泵的吸附材料对低温泵的工作性能有着重要的影响。综述了低温泵的吸附材料性能与研究现状。首先总结了吸附材料的表征方法及研究内容。然后分别叙述了分子筛、低温霜和活性炭三种低温泵主要用的吸附材料的工作性能,指出其优势和不足。最后以ITER用的低温泵为例说明低温吸附材料的应用。     

(纳米MCM-41)-CdS主-客体复合材料的制备及光学性质

以水热法制备了纳米微粒MCM-41分子筛，通过离子交换法将Cd(II)交换到分子筛中，然后采用硫代乙酰胺作硫化氢前驱体对(MCM-41)-Cd进行硫化，制备出主-客体复合材料(MCM-41)-CdS．化学分析表明，客体成功地组装到分子筛中．粉末X射线衍射结果表明，组装过程并未破坏所制备的主-客体材料中分子筛的骨架，分子筛骨架完整且结晶度仍然很高．红外光谱表明所制备材料骨架保持完好．低温N2吸附-解吸附研究表明，相对于MCM-41分子筛主体所制备的复合材料孔体积、孔尺寸及比表面积降低，表明客体在分子筛孔道内组装成功．制备的主-客体复合材料固体扩散漫反射吸收光谱相对于CdS体相呈现某些蓝移，说明客体处于分子筛孔道内，也表明分子筛主体对纳米硫化镉客体表现出明显的立体限域效应．(纳米MCM-41)-CdS及(微米MCM-41)-CdS样品呈现明显发光．     

CO探针低温原位红外光谱研究ZRP分子筛酸性位

石科院开发的高硅铝比、高活性稳定性的ZRP系列分子筛已经广泛应用在工业FCC装置上。ZRP分子筛的酸性中心主要分布在内表面(即孔道内),是催化活性和选择性的决定因素。根据ZRP的孔道特征,选取CO探针建立的低温原位红外表征方法研究不同硅铝比的ZRP系列分子筛的酸性中心的存在形式和分布状态,并与活性数据进行关联分析。结果表明2 175cm~(-1)处CO吸附特征峰为强B酸,与3 616cm~(-1)处孔内OH相对应,其缺电子特性最强,易进行反应,是研发中控制的主要因素。适当的硅铝比的ZRP分子筛具有适当数量的强B酸,其正辛烷转化率高。这为进一步开发活性高的催化剂提供了重要的信息。     

季铵型纤维素的红外光谱及对持久性有机污染物的吸附特征

文章研究了季铵型阳离子纤维素(QACC)的红外光谱和对持久性有机污染物的吸附及循环利用问题。研究了吸附工艺参数对QACC吸附容量的影响。研究了QACC对染料的吸附等温式,测定了QACC吸附染料过程的热力学参数(ΔH, ΔS, ΔG)、吸附速率常数和吸附活化能,探讨了QACC吸附机理。在近中性水溶液中,QACC对含磺酸基、羧基、羟基的水溶性芳香族有机污染物具有较大的饱和吸附容量,常见共存离子对吸附不产生影响。QACC对上述污染物的吸附既有化学吸附,也有物理吸附,而以化学吸附为主。吸附符合Langmuir等温式和一级动力学方程,吸附速率随温度升高而增大。水溶性有机污染物用0.5 mol·L-1氢氧化钠水溶液洗脱,再生后QACC可以循环利用。QACC是一种性能优良的新型功能材料,可应用于环境中持久性有机污染物的治理。     

SAPO-34分子筛的动态吸附特性实验研究

对于吸附式制冷系统而言,吸附材料的选择是系统的核心问题。对两种不同厂家的SAPO-34沸石分子筛进行了吸附特性测试。其共同特性是,温度一定时,SAPO-34分子筛的吸附量随相对湿度的增加而增大。相对湿度在40%~60%时,吸附量变化不大;而相对湿度在70%~80%时,吸附量增加较快。另一方面,由于两种SAPO-34样品的微观结构有一定差异,导致其吸附量和吸附速率也不一样。粒径较小、孔隙率较大的样品A,其吸附量比样品B大1~2倍,达到吸附饱和的时间也缩短近100分钟。此特性有利于改善吸附制冷系统的整体性能。     

利用原子层沉积技术实现有机电致发光器件的薄膜封装EI北大核心CSCD

有机电致发光器件(Organic light emitting diode,OLED)具有轻薄、便于携带、自发光、能耗低、亮度更大、柔性显示等特点,可以增加显示产品的附加值,因此被科学和产业界广泛关注。然而,OLED器件中的有机材料对空气中的水汽和氧气十分敏感,若器件在无封装保护的情况下长期在空气中存放,将会严重影响OLED的工作性能和寿命。除了选择合适的传输层材料、表面层结构和利用界面工程提高材料水氧耐受能力之外,对器件进行可靠的封装是隔绝空气中水汽和氧气侵蚀的一种有效手段。原子层沉积(Atomic layer deposition,ALD)是一种已经在实验室验证的有效薄膜沉积封装技术,由于ALD的自限制反应特性,可以在低温下沉积出厚度精确可控且均匀致密的薄膜,利用ALD沉积的薄膜往往拥有良好的机械柔性、超高的阻隔性能和光学透过率。本文将回顾原子层沉积技术的原理,分析ALD制备薄膜的水汽透过率,比较ALD在单层、有机-无机叠层薄膜封装制备上的技术优势。     

载钯分子筛修饰电极上CO吸附的原位红外反射光谱研究

制备载Ｐｄ的分子筛电极,以ＣＯ吸附为探针电化学原位ＦＴＩＲ反射光谱,首次发现限定在分子筛超笼中的纳米Ｐｄ微粒对ＣＯ的吸附具有增强红外吸收效应。     

限域Pd纳米微粒的增强红外吸收及其对电位响应速度的原位分子探针红外反射光谱研究

Y型沸石分子筛的超笼为微反应器 ,以“瓶中造船”方式合成纳米钯粒子 (nm Pd)。分别以聚氯乙烯(PVC)和Nafion(高氟化树脂 )为粘合剂 ,采用混合滴涂法和分步滴涂法制备载钯分子筛修饰电极。以CO为探针 ,用电化学原位FTIR反射光谱研究吸附态CO的红外光学性能 ,研究发现采用上述两种方法制备的载钯分子筛修饰电极具有同样的CO增强红外吸收特性和不同的电位响应速度 ,表明CO增强红外吸收特性只与钯的纳米尺度有关 ,而分子筛修饰电极的电位响应速度和电子传输能力除与分子筛本身的结构有关外 ,还受粘合剂影响。     

红外光谱法研究甲苯在HZSM-5分子筛上的扩散

采用红外光谱法研究了甲苯在两种HZSM-5分子筛上的扩散。结果表明:甲苯分子在不同颗粒大小的分子筛吸附平衡时间不同,甲苯分子首先吸附在具有硅铝桥羟基的孔道内,而当硅铝桥羟基基本占据后,才吸附在硅羟基的吸附位上,显示了硅铝桥羟基吸附较硅羟基吸附位更强;大颗粒分子筛的甲苯扩散系数显著高于小颗粒分子筛。     

基于石英晶体天平和微纳光纤的有机污染物在线监测

为了监测高功率激光驱动器中有机污染物的挥发特性以及其在光学元件表面的沉积特性,研究了基于石英晶体微量天平和微纳光纤传感器的真空腔体内有机物在线监测技术.首先测试了不同分子态污染物浓度时石英晶体天平的响应性能,然后采用视角因子等分法对微纳光纤传感器和石英晶体天平进行对比实验,模拟有机污染物在光学表面沉积的特性.实验结果表明,石英晶体天平和微纳光纤测试有机物在光学表面沉积时响应一致,均可用于高功率激光驱动器有机污染物的在线监测;当污染物面密度大于0.5×10-5g/cm2时,微纳光纤传感器有较高精度和响应速度;有机污染物浓度越高,其更容易吸附沉积在光学元件表面.     

含灰湿空气外掠翅片管束积灰和阻力特性实验研究

本文针对以褐煤预干燥乏气为代表的含灰含湿气体余热回收问题,采用含灰湿空气模拟真实干燥乏气/烟气,搭建了混合气体外掠圆形翅片管束对流冷凝实验系统,获得了灰分浓度、水蒸气质量分数、主流气体入口温度等因素对其积灰和阻力特性的影响规律.实验结果表明,阻力系数随着灰分浓度和气体入口温度的增加而增加,随水蒸气质量分数的增加而减小,...     

Inhibition of hydrogen chemisorption on uranium surfaces by traces of water vapor

Traces of about 2% water vapor are sufficient to inhibit hydrogen dissociation and chemisorption on uranium surfaces, under low pressure exposures, at room temperature. The efficiency of the inhibition increases with temperature in the range of 200 - 400 K. The inhibition effect is also influenced by the extent of residual strain of the sample, with increasing inhibition efficiencies exhibited by a less strained surface. O₂, in contrast to H₂O, is not an inhibitor to surface adsorption and dissociation of hydrogen. Three types of mechanisms are discussed in order to account for the above inhibition effect of water. It is concluded that the most probable mechanism involves the reversible adsorption of water molecules on hydrogen dissociation sites causing their “blocking”.     

Emission of Ag2 dimers from a substrate during vacuum deposition of the mixture of silver and water vapor

The work presents calculation of Ag₂ dimers emission from the substrate into the vapor medium in case of joint deposition of silver and water vapors on ideal substrate formally modeling the crystal of water ice in terms of energy properties. It is assumed that the dimers are formed on the condensation surface as a result of random collisions of atoms at their surface migration, and the dimers emission is conditioned by thermal fluctuations of crystal lattice of water ice. The calculations based on the modified Langmuir adsorption model allowed concluding that emission of silver and water dimers takes place in the entire range of the studied water vapor pressure, binding energy of silver-water, and crystal temperature. Dynamics of emission from the beginning of deposition and dependence of dimers emission on micro-roughness of the condensate surface have been investigated. Statistical processing of results has shown that the probability of dimers emission from the condensate surface is determined not only by the value of the binding energy between the dimer and condensate but by configuration of the nearest dimer environment on the condensation surface. It has been found that there is a certain value of micro-roughness of condensation surface providing the maximal intensity of dimer emission. Dimers emission from the surfaces bordering on the flows of vapor mixtures contaminates the flows with unsuspected admixtures. The latter one makes investigation of this phenomenon important for aeromechanics of vapor and gas mixtures.     

Water vapor adsorption onto activated carbons prepared from cattle manure compost (CMC)

Activated carbons were prepared from cattle manure compost (CMC) using zinc chloride activation. The structural and surface chemical characteristics of CMC-based activated carbons were determined by N₂ adsorption-desorption and Boehm titration, respectively. The water vapor adsorption properties of the prepared activated carbons with various pore structure and surface nature were examined, and the mechanism of water adsorbed onto activated carbon was also discussed. The results show that the adsorption of water vapor on carbons begins at specific active sites at low relative humidity (RH), followed by micropore filling at medium RH through the formation of pentamer cluster of water molecules in the narrow micropores. The water vapor adsorption capacity of activated carbon is predominantly dependent on its pore volume and surface area. Although capillary condensation is not the mechanism for water adsorption onto activated carbon, water can adsorb on narrow mesopore to some extent.     

Room temperature adsorption of water by aluminum thin films

Thin films of aluminum were prepared under ultra-high vacuum conditions in order to investigate the low temperature, low pressure adsorption of water vapor by the aluminum. The kinetics of the water vapor-aluminium reaction have been found to be essentially different than the oxygen-aluminum reaction previously reported. In contrast to the “dry” oxygen uptake kinetics, a plot of the sticking coefficient of H₂O versus the total weight gain of the film indicates that the sticking coefficient of H₂O passes through a maximum. As a result of the present mass adsorption measurements of water by fresh aluminum surfaces and Huber and Kirk's previous contact potential studies of an oxidized aluminum surface upon exposure to water vapor, a model is suggested, based on the simultaneous lateral growth of oxide nuclei and first order adsorption of water dipoles on the growing oxide nuclei surfaces. The model quantitatively describes the kinetics of the mass adsorption of water and also predicts the contact potential behavior of a fresh aluminum surface upon exposure to water vapor. A sticking coefficient of approximately 0.05 is indicated for H₂O on bare aluminum while 0.11 corresponds to the sticking coefficient of water dipoles on the oxide nuclei surfaces.     

低密度SiO2气凝胶的结构与吸附特性研究

 低密度SiO₂气凝胶是一种新型纳米多孔材料,它不仅可作为惯性约束聚变的低温冷冻靶,还可作为HTO蒸汽的吸附剂用于放射性物质的环境监测。用SEM、TEM、BET、孔径分布等测试方法对低密度SiO₂气凝胶的微结构进行了研究;分别以水和苯作为吸附介质, 用吸附天平对其吸附特性进行了测试,并用BET吸附理论对其吸附结果进行了解释。     

94K低温下和室温下GaN基MSM紫外光探测器性能的比较

在采用MOCVD技术生长的GaN膜上制备出MSM紫外光探测器，分别在室温下和94K低温下，测量了探测器对不同光波长的响应、同一光波长下对不同偏压的响应、不同斩波频率下的响应。结果表明，在94K下响应有了很大的改善。当光波长从360nm增加到450nm时，响应下降了3个数量级，而常温下只下降两个数量级，但探测器的时间响应常数变长了。     

Molecular dynamics analysis of the substrate temperature effect on thermomechanical characteristics of vapor deposited nanofilms

Modern engineering applications are in need for technologies of nanostructures and nanofilms with controllable properties. The detection of these structures requires methods of atomic research, among which are molecular dynamics techniques, Monte-Carlo simulation, and ab initio calculation. The most efficient method to deal with systems of about several thousands of atoms is molecular dynamics simulation. We used this method to analyze the formation of nanolayers on a Cu substrate in vapor deposition of Cu atoms. It is shown that the film deposited on the substrate surface replicates the crystalline structure of the substrate. It is found that at low deposition temperatures, the deposited layer reveals a great quantity of vacancies and vacancy clusters (nanopores). It is demonstrated that increasing the substrate temperature in metal vapor deposition ensures a more perfect lattice in the nanocoating, and the cohesive energy of atoms in the nanolayer thus approximates experimental values. It is also found that the increase in substrate temperature in the process causes Young’s modulus and elastic limit to tend to the values of a perfect crystal.     

Tunable and reversible surface wettability transition of vertically aligned ZnO nanorod arrays

Vertically aligned zinc oxide (ZnO) nanorods (NRs) with different surface morphology were grown by metal organic chemical vapor deposition (MOCVD) on sapphire substrate. To study the effect of surface morphology on wettability, the contact angle (CA) of water was measured. It was demonstrated that the CA of the deposited ZnO NRs varied between 104° and 135° depending upon the surface morphology. The ZnO NRs became super-hydrophilic after ultraviolet (UV) illumination. However, the NR arrays were reconverted to their previous hydrophobic state after low temperature annealing (50 °C) in open atmosphere. Structural effect and preferential adsorption of water molecules on the defective sites of UV illuminated surface was used to explain the transition mechanism. Under the alternations of heat treatment and UV illumination, a reversible transition between hydrophobicity and super-hydrophilicity were observed.