氢及其同位素在溴化丁基橡胶中渗透的分子模拟

使用分子动力学(MD)和巨正则蒙特卡罗(GCMC)的方法,对H_2,D_2,T_2在溴化丁基橡胶(BIIR)中的扩散和溶解行为进行了计算模拟,运用自由体积理论探讨了气体分子在聚合物内的扩散机理,并得出气体的运动轨迹。结果表明:对氢及其同位素而言,质量越小,运动速度越快,扩散系数越大,溶解度系数比较接近,渗透系数的模拟值与实验值基本吻合,为提高材料的阻隔性能提供了一定理论基础,同时预测出硫化溴化丁基橡胶对氚水也有较好的阻隔性能。     

应用MRI研究CO2在癸烷中的扩散

应用核磁共振成像(MRI)技术可视化研究CO₂在癸烷中的扩散,在MRI系统采集图像的同时,应用双室压力衰减法（PVT法）监测压力,通过对MRI图像进行信号强度分析,可得到CO₂的无量纲浓度分布,然后基于菲克定律应用有限体积法可计算得出与扩散距离和扩散时间有关的扩散系数,并可得到任意扩散时间范围内的整体平均扩散系数,MRI方法得出的扩散平衡时间范围内的整体平均扩散系数与PVT法相比较误差为2.7%,并且与相似条件下的前人实验结论具有相同的数量级(10^–9)．根据实验结果得出,扩散系数沿扩散方向下降且随时间以指数形式降低,整体平均扩散系数随扩散时间的增加而减小．     

Ar-N2混合气体输运性质的量子力学研究

基于物理力学理论,利用量子力学的IOSA方法、Numerov相移计算法和Ar-N₂相互作用的等效势模型计算了Ar在N₂气体中的扩散系数的粘滞系数,计算值与实验值符合较好,比Giantur-co等人(GVD)计算便更接近实验值,特别是粘滞系数,在整个计算区域内基本和实验相同。     

气体分子在δ-Pu表面吸附离解行为的第一原理研究

金属钚为重要的核材料,具有活泼的化学性质,很容易与环境中的氢、氧和水汽反应发生表面腐蚀。由于有关Pu金属表面性质以及气体分子与表面相互作用的理论研究公开报道较少,且不同作者的结果存在差别,我们使用广义梯度近似（GGA）方法结合平板周期模型对气体原子分子在δ-Pu表面上吸附行为进行了计算,对吸附方式、成键过程、电荷分布等方面进行了探讨。     

激光全息干涉法测量二元气体扩散系数

依据Mach-Zehnder干涉光路搭建了数字实时激光全息干涉实验台,设计加工了适用于测量二元气体扩散系数的扩散槽本体,详细介绍了根据物光相位的变化计算二元气体扩散系数的测量原理及图像处理方法。在此基础上测量了二元气体对H_2-Air、CH_4-Air和O_2-Air在273.15 K和0.1 MPa下的扩散系数,通过与文献值的比较验证了该实验方法的准确性,为后续二元气体扩散系数测量工作奠定了坚实的基础。     

燃料电池阴极扩散层扩散特性研究

本文采用粗粒化分子动力学方法研究了燃料电池阴极扩散层的扩散特性。采用全原子方法的计算结果校验了粗粒化方法的准确性,并提出了一种定量校正方案。分析了碳纳米管气体扩散层中气体和水的扩散特性,其中气体和水的扩散存在各向异性,气体和水两者在碳纳米管中轴向的扩散系数均较低,且气体和水的轴向扩散系数也随着该分子比例的降低而进一步降低;对带缺陷气体扩散层的研究表明气体扩散层中缺陷的形态对其扩散性能有显著的影响。     

页岩气中CH4-C2H6吸附-扩散分子动力学研究

本文采用巨正则蒙特卡洛(GCMC)和分子动力学(MD)模拟方法,对比分析了不同温度、压力和孔径对二元气体(CH4-C2H6)在K-伊利石中的吸附-扩散的影响。结果表明,在低压条件下,K-伊利石对C2H6的吸附能力大于CH4,C2H6优先吸附在K-伊利石孔隙表面。热力学因子随着孔径的增加而减小,C2H6的热力学因子大于CH4.气体的自扩散和MS扩散系数、传递扩散系数随着温度的增加而增加。在较高的压力条件下,C2H6传递扩散系数随温度增加而降低。随着压力的增加,CH4和C2H6的自扩散能力均降低,CH4的MS扩散系数和传递扩散系数整体上趋于降低。CH4的自扩散过程更容易发生,但C2H6互扩散能力更强。     

电解质对浓悬浮液中胶体颗粒扩散特性的影响

本文利用相位调制光纤低相干动态光散射装置, 研究了不同物质量浓度下电解质 (NaCl及 BaCl₂) 对浓悬浮液中聚苯乙烯胶体颗粒扩散特性的影响. 实验结果表明, 当电解质浓度低于0.01 mol/L 时, 恒温条件下浓悬浮液中聚苯乙烯胶体颗粒扩散系数随电解质离子浓度以及离子化合价的增大而增大, 实验测量得到的扩散系数与Stern模型所得到的扩散系数符合较好. 关键词： 测量 电解质 浓悬浮液 低相干动态光散射     

聚合物分子与官能化纳米管相互作用及扩散特性的分子动力学模拟

用全原子分子动力学方法研究典型聚合物分子（PE，PEO和PP）与碳纳米管（CNT）及官能化碳纳米管（FCNT）界面的相互作用及扩散特性.动力学模拟显示：—CH₃官能团具有减弱CNT与PE和PP的相互作用，但是，—CH₃官能化后的CNT与PEO之间确有增强作用.分析含氧官能团（—OH和—COOH）官能化的CNT与PE，PEO和PP的相互作用，可知含氧官能团的确具有增强表面相互作用的功能，而且含氧原子越多，相互作用就越强.此外，—CH₃，—OH，—COOH官能化后的CNT与PE，PP和PEO体系的总能量均减少，而且能量满足—COOH < —OH < —CH₃.分析非键相互作用势（库仑能和范德瓦尔斯能），可知库伦相互作用是增强界面相互作用的主要作用能.官能化后的CNT/PE，CNT/PEO，CNT/PP体系的扩散系数都明显减小，且扩散系数大小满足—COOH < —OH < —CH₃.     

大锥角锥形床内颗粒横向混合的实验研究

在900 mm×200 mm×800 mm的冷模试验台上,试验研究了带气体入口直段的大锥角锥形床内示踪颗粒的横向扩散过程,系统考察了床料粒径dp、过余速度u—u_(mff)、静止床层高度h和气体入口直段宽度δ对床内示踪颗粒横向扩散系数D_(sr)的影响。结果表明:在大锥角锥形床中,横向混合试验持续时间间隔对示踪颗粒横向扩散系数的计算结果影响较大;示踪颗粒的横向扩散系数D_(sr),随着床料粒径dp的增大而减小,随着过余速度u—u_(mff)静止床层高度h和气体入口段宽度δ的增大而增大。     

Molecular dynamics simulation of gas diffusion behavior in polyethylene terephthalate/aluminium/polyethylene interface

Molecular dynamics (MD) simulations were performed to estimate the diffusion coefficients of O₂ and H₂O molecules in polyethylene terephthalate/aluminum/polyethylene interface at the temperature of 298 K. It came out that the diffusion coefficient of gasses in the interface is smaller than that of a single polymer, and the diffusion coefficients compare well with experimental data as well as previously published work. Furthermore, the diffusion coefficients of H₂O molecules in the interface are preferable to that of O₂ molecules. Interestingly, the largest diffusion coefficient was detected in the polyethylene terephthalate/aluminum(1 0 0)/polyethylene interface, while the smallest value of the diffusion coefficients was found in the polyethylene terephthalate/aluminum(1 1 1)/polyethylene interface. Calculation and analysis of the interaction between aluminum and polymers indicated that the interaction of polymer/aluminum(1 1 0) has the most interface strength, and crystal density of the metal surface has a definite effect on the planar interface energy. What’s more, the figure of gas molecule concentration is further resulted that the interface make contribution to adsorption of gas molecules. Moreover, the diffusion is belonging to the Einstein diffusion in the multilayer materials, and this work provides some key clues to improve the performance of polymer materials.     

Redox reactions and inward cationic diffusion in glasses caused by CO and H2 gases

We find that inward diffusion of network-modifying cations can occur in an iron-containing silicate glass when it is heat-treated in CO/CO₂ (98/2 v/v) or H₂/N₂ (1/99 v/v) gases at temperatures around the glass transition temperature. The inward diffusion is caused by the reduction of ferric to ferrous ions and this diffusion leads to formation of a silica-rich surface layer with a thickness of 200–600 nm. The diffusion coefficients of the network-modifying divalent cations are calculated and they are different for the glasses treated in the CO and H₂ gases. At the applied partial pressures of CO and H₂, the H₂-bearing gas creates the silica-rich layer more effectively than the CO-bearing gas. The layer increases the hardness and chemical durability of the glass due to the silica network structure in the surface layer.     

Pressure dependence of the mutual diffusion coefficients of the binary systems N2 + Ar, N2 + O2, O2 + Ar and Ar + Kr at 300 and 323 K

The Loschmidt technique has been used to measure the pressure dependence at two temperatures of the binary diffusion coefficients of the systems N₂-Ar, N₂-O₂, O₂-Ar and Ar-Kr; gas mixtures were analysed with a mass spectrometer. The results for the first three systems indicate that the first term of the Thorne-Enskog theory for moderately dense gases is not adequate to describe binary diffusion in these systems. Because the quantity (n$\text{D}$₁₂) is a linear function of the number density in all cases, higher order terms need not be considered.     

Determination of binary diffusion coefficients of gases using photothermal deflection technique

A photothermal deflection (PD) technique was applied to measure the binary diffusion coefficients of various gases (CO₂–N₂, CO₂–O₂, N₂–He, O₂–He, and CO₂–He). With an in-house-made Loschmidt diffusion cell, a transverse PD system was employed to measure the time-resolved PD signal associated with the variation of the thermal diffusivity and the temperature coefficient of the refractive index of the gas mixture during the diffusion. The concentration evolution of the gas mixture was deduced from the PD amplitude and phase signals based on our diffraction PD model and was processed using two mass-diffusion models explored in this work for both short- and long-time diffusions to find the diffusion coefficient. An optical fiber oxygen sensor was also used to measure the concentration changes of the mixtures with oxygen. Experimental results demonstrated that the binary diffusion coefficients precisely measured with the PD technique were in agreement with the literature values. Moreover, the PD technique can measure the diffusion coefficients of various gas mixtures with both short- and long-time diffusions. In contrast, the oxygen sensor is only suitable for the long-time diffusion measurements of the gas mixtures with oxygen. PACS 78.20.Nv; 51.20.+d     

Diffusion cooling in neon,argon, and krypton afterglow plasmas

Measurements are reported of ambipolar diffusion coefficients as determined from ion density loss rates, and of electron temperatures determined using the single Langmuir probe technique, in afterglow plasmas of spectroscopically pure neon, argon and krypton. In each gas there was a critical pressure,p _{0 c} , above which the product of the ambipolar diffusion coefficient,D _a , and the reduced gas pressure,p ₀, was pressure independent and above which the electron temperature was found to cool asymptotically to the gas temperature. For pressures belowp _{0 c} ,D _a p ₀ decreased with decreasing pressure, and the electron temperature cooled asymptotically to a steady equilibrium value,T _eq, below the gas temperature, this equilibrium value itself decreasing with decreasing gas pressure. These results clearly show that diffusion cooling of electrons was taking place at these low gas pressures. A detailed study of the krypton afterglow showed that the values ofD _a p ₀ andT _eq for a given gas pressure were related in a manner predicted by simple diffusion theory. During the course of these measurements values for the zero field mobilities of Ne⁺, Ar⁺ and Kr⁺ ions in their parent gases were obtained and are also reported.     

Oxide Materials for Development of Integrated Gas Sensors—A Comprehensive Review

In the recent past a great deal of research efforts were directed toward the development of miniaturized gas-sensing devices, particularly for toxic gas detection and for pollution monitoring. Though various techniques are available for gas detection, solid state metal oxides offer a wide spectrum of materials and their sensitivities for different gaseous species, making it a better choice over other options. In this article a critical parameter analysis of different metal oxides that are known to be sensitive to various gaseous species are thoroughly examined. This includes phase of the oxide, sensing gaseous species, operating temperature range, and physical form of the material for the development of integrated gas sensors. The oxides that are covered in this study include oxides of aluminum, bismuth, cadmium, cerium, chromium, cobalt, copper, gallium, indium, iron, manganese, molybdenum, nickel, niobium, ruthenium, tantalum, tin, titanium, tungsten, vanadium, zinc, zirconium, and the mixed or multi-component metal oxides. They cover gases such as CO, CO₂, CH₄, C₂H₅OH, C₃H₈, H₂, H₂S, NH₃, NO, NO₂, O₂, O₃, SO₂, acetone, dimethylamine (DMA), humidity, liquid petroleum gas (LPG), petrol, trimethylamine (TMA), smoke, and many others. Both doped and undoped oxides are analyzed for the compatibility with silicon processing conditions and hybrid microcircuit fabrication techniques. In silicon processing conditions, they are further analyzed for the suitability for simple silicon surfaces, silicon-on-insulator (SOI) surfaces, and micromachined silicon geometries for different operating temperatures. Discussion on gas-sensing properties of each material and its applications are described in the text in alphabetical order of the elemental oxides. Further, the gas-sensing properties like sensitivity, detection limits, operating temperature, and so on are summarized in tables al ong with relevant references. The figures incorporated in the present review are primarily based on discussions and data in tables. However, these figures provide a qualitative comparison and present a pictorial view to examine suitability of a material for a particular application. From the known parameters, the present study clearly indicates the suitability of certain materials and the gases that they cover for the development of integrated micro gas sensors. A clear picture has been brought out for the development of silicon-based processing technology. Various parameters are discussed for the selection of these materials, to examine their suitability and practical problems that are being associated. Etching of these metal oxides and the reliability of devices are also discussed.     

A model for oxidation-driven surface segregation and transport on Pt-alloys studied by atom probe tomography

Using a purpose-built 3D atom probe, we have previously shown that exposure to oxidising gases (NO, N₂O, O₂) induces Rh surface segregation in Pt–Rh alloys, the extent of which is strongly dependent on treatment temperature, crystallographic plane and the presence of ternary alloy additions. In this paper, the segregation trends identified on three different crystallographic surfaces of Pt–Rh are analysed using thermodynamic and kinetic arguments. The segregation model we present is generic for diffusion on alloy surfaces in the presence of active gases. From it we obtain activation energies and diffusion coefficients for the processes of metal-oxide species diffusion both perpendicular to and laterally across the surface. Using these we propose a simple model for the interaction of chemically active gases with the surfaces of such alloys. Applying this understanding to sequential oxidation/reduction treatments would in principle allow improved control of the surface composition of alloy catalysts. Related applications of this model include optimisation of core–shell catalyst nanoparticles.     

Application of the diffraction theory for photothermal deflection to measurements of thermophysical and mass-diffusion properties of gases

The application of recently developed diffraction theory for cw transverse photothermal deflection spectroscopy (normal deflection only) to the measurements of thermophysical and mass-diffusion properties of gases is presented. Compared with the traditional ray-optics theory, the diffraction theory has one more term in the phase signal. This term quantitatively exhibits the probe-beam size effect on the phase signal. Experimental results demonstrated that even if the ratio of the probe-beam radius to the thermal diffusion length of a deflecting medium was as low as about 0.22, the probe-beam size effect could not be ignored when measuring the distance between the probe beam and a solid sample using the phase signal. With the measured distance, the thermal diffusivity α_g and the temperature coefficient of the refractive index dn/dT of pure gases (O₂, N₂, and CO₂) and binary gas mixtures (CO₂-O₂ and CO₂-O₂) were precisely measured, resulting in good agreement with literature values. Furthermore the measured dn/dT values of the pure gases had one more significant figure than the literature ones. The concentration dependences of α_g and dn/dT were employed for the determination of mass-diffusion coefficients of CO₂-O₂ and CO₂-N₂, and the results were consistent with literature values.     

Effect of dissolved gases in water on acoustic cavitation and bubble growth rate in 0.83 MHz megasonic of interest to wafer cleaning

Changes in the cavitation intensity of gases dissolved in water, including H₂, N₂, and Ar, have been established in studies of acoustic bubble growth rates under ultrasonic fields. Variations in the acoustic properties of dissolved gases in water affect the cavitation intensity at a high frequency (0.83 MHz) due to changes in the rectified diffusion and bubble coalescence rate. It has been proposed that acoustic bubble growth rates rapidly increase when water contains a gas, such as hydrogen faster single bubble growth due to rectified diffusion, and a higher rate of coalescence under Bjerknes forces. The change of acoustic bubble growth rate in rectified diffusion has an effect on the damping constant and diffusivity of gas at the acoustic bubble and liquid interface. It has been suggested that the coalescence reaction of bubbles under Bjerknes forces is a reaction determined by the compressibility and density of dissolved gas in water associated with sound velocity and density in acoustic bubbles. High acoustic bubble growth rates also contribute to enhanced cavitation effects in terms of dissolved gas in water. On the other hand, when Ar gas dissolves into water under ultrasound field, cavitation behavior was reduced remarkably due to its lower acoustic bubble growth rate. It is shown that change of cavitation intensity in various dissolved gases were verified through cleaning experiments in the single type of cleaning tool such as particle removal and pattern damage based on numerically calculated acoustic bubble growth rates.     

Determination of kinetic transport coefficients for ions in air as functions of electric field and temperature

A method for determining the kinetic coefficients of ion transfer in gases, viz., mobility K and longitudinal (D _L) and transverse (D _T) diffusion coefficients, as functions of the electric field E and gas temperature T is described. The method is based on the measurement of the increments to the ion mobility coefficients as functions of the electric field at a parametrically specified temperature. The kinetic transport coefficients K(E, T) and D _{L, T}(E, T) are determined for positive ions of aniline, pyridine, benzene, orthotoluidine, dimethyl methyl phosphonate, N-methyl aniline, N,N-dimethyl aniline, N,N-diethyl aniline, and diphenyl amine (DPA) formed as a result of β-ionization in air.