共查询到19条相似文献,搜索用时 156 毫秒
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为了探索气体在固体表面高分子链中的扩散,使用分子动力学(MD)的方法,对H2,D2,T2在聚苯乙烯与金属铜(PS-Cu)界面的扩散进行了计算模拟,通过所得到气体的均方位移计算了气体在不同金属表面与聚苯乙烯界面中的扩散系数。结果显示:气体在界面的扩散系数比在聚苯乙烯本体中的扩散系数小,气体在PS-Cu(110)界面的扩散系数最大,在PS-Cu(111)界面的扩散系数最小。计算和分析了PS与金属表面的相互作用,发现其相互作用能越大,气体在此界面的扩散系数越小。同时,金属表面的晶面密度对气体在界面中的扩散也有一定的影响。 相似文献
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为了探索气体在固体表面高分子链中的扩散,使用分子动力学(MD)的方法,对H2,D2,T2在聚苯乙烯与金属铜(PS-Cu)界面的扩散进行了计算模拟,通过所得到气体的均方位移计算了气体在不同金属表面与聚苯乙烯界面中的扩散系数。结果显示:气体在界面的扩散系数比在聚苯乙烯本体中的扩散系数小,气体在PS-Cu(110)界面的扩散系数最大,在PS-Cu(111)界面的扩散系数最小。计算和分析了PS与金属表面的相互作用,发现其相互作用能越大,气体在此界面的扩散系数越小。同时,金属表面的晶面密度对气体在界面中的扩散也有一定的影响。 相似文献
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本文提出了一种测量液相扩散系数的新方法. 该方法用透明毛细管构成液相扩散池, 利用毛细管成像法特有的折射率空间分辨测量能力, 通过直接观察和记录扩散介质的等折射率薄层在毛细管中的移动规律, 基于扩散过程遵循的Fick第二定律计算出液相扩散系数. 在25 ℃下研究了丙三醇和纯水间的扩散过程, 扩散系数的测量值与全息干涉法的文献报道值之间的相对误差为4.47%, 论文同时分析了折射率测量精度和毛细管管壁黏滞力对扩散系数的影响. 用毛细管成像法测量液相扩散系数具有样品需要量少、测量速度快、系统稳定性好的特点, 为快速测定微量样品的扩散系数提供了一种有效的新方法.
关键词:
扩散系数
液体折射率
毛细管成像法 相似文献
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在激光与物质相互作用的实验中,气体靶通常由超声速喷嘴在高背压下向真空中高速喷射气体产生。激光与气体靶相互作用时确定打靶条件对整个实验有着十分重要的意义。为了得到不同实验条件下气体靶密度的分布特性,采用马赫-曾德尔干涉法测量了气体靶密度分布,获取了干涉图样。使用基于傅里叶变换的条纹处理方法测得的干涉图样,得到不同实验条件下气体分子密度的全空间分布。实验表明:用M-Z干涉仪测量超声速气体喷嘴产生的气体靶密度分布十分有效。基于傅里叶变换的条纹处理方法具有精度高、实时性好的优点,为打靶时气体靶密度的实时测量提供了可能。 相似文献
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《高压物理学报》2015,(5)
为探究在有限空间中,初始压力为0.25MPa、两处乙烯气体瞬时源在不同扩散时间下的燃爆特性,在内径200mm、高5 400mm的立式激波管中,采用上下进气方式,在强起爆条件下,测定5个不同扩散时间下3种浓度的乙烯-空气混合气体(C2H4-Air)的燃爆参数。实验结果表明,扩散时间大于1h后,3种浓度的C2H4-Air混合气体燃爆参数趋于一致。4.00%(体积分数)C2H4-Air在当前实验条件下未能达到爆轰。6.67%C2H4-Air在5个扩散时间均可达到爆轰,扩散时间为1h时的爆压、爆速分别为4.24 MPa、1 719m/s。8.89%C2H4-Air在0.08h扩散时间下只发生爆燃,扩散时间为0.5h及以上发生爆轰,扩散时间为1h时的爆压、爆速分别为4.31 MPa、1 813m/s。通过烟熏技术捕捉到6.67%、8.89%的C2H4-Air混合气体的爆轰波胞格,胞格宽度分别为8.22、14.15mm,长宽比分别为1.44、1.57。 相似文献
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本文介绍一种测定透明(或半透明)液体的扩散系数的方法。与以前所用的测量方法相比,此法具有准确度高、仪器装置和测量方法简单便于推广,以及可以在科研生产中进行现场测量而不受取样困难的限制等优点。此法亦可以用于测量气体的扩散系数。 相似文献
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提出了一种分析气泡远场干涉的理论模型。平行激光束照射到透明介质中的气泡上,折射光束与全反射光束在远场发生干涉形成内密外疏圆环状干涉条纹,推求了两平行出射光线的光程差公式和两光线之间的距离公式,分析了圆环状干涉条纹内密外疏的原因,给出了计算干涉条纹存在区域和最高干涉级的方法。通过干涉方法可以测量气泡的直径,能够用于介质深处气泡尺寸的测量。利用远场干涉对玻璃水箱、平板玻璃、玻璃棱镜中的气泡直径进行了测量,其中玻璃棱镜中气泡直径测量结果与用阿贝比长仪测量结果对比,相对差为0.9%。预期了气泡远场干涉在运动气泡尺寸、泡内气体折射率、透明光疏介质中光密介质球尺寸测量等方面的应用。 相似文献
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《光学技术》2021,47(5):565-569,581
利用气体折射率与压力之间的关系,可采用激光干涉仪对气体动态压力进行非接触测量,研究了温度对激光干涉法测量气体动态压力的影响。通过量子力学角度对气体状态方程进行维里展开,建立气体压力与折射率的模型,基于Edlen经验公式进行最新修正,探究了温度对激光干涉法测量气体动态压力的影响。结果表明,在低压范围内静态压力一定时,-20~80℃范围内温度变化与气体折射率成反比,折射率的改变量约为10~(-6)/℃,每1℃的温度变化相当于产生311.47Pa压力,温度改变对气体低压测量影响较大,应保证测量范围内温度控制优于±0.05℃,才能满足激光干涉法测量气体动态压力的要求。 相似文献
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J.H. Rohling J. Shen C. Wang J. Zhou C.E. Gu 《Applied physics. B, Lasers and optics》2007,87(2):355-362
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 相似文献
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Characterization of partially sintered ceramic powder compacts using fluorinated gas NMR imaging. 总被引:3,自引:0,他引:3
A Caprihan C F Clewett D O Kuethe E Fukushima S J Glass 《Magnetic resonance imaging》2001,19(3-4):311-317
We use nuclear magnetic resonance (NMR) imaging of C2F6 gas to characterize porosity, mean pore size, and permeability of partially sintered ceramic (Y-TZP Yttria-stabilized tetragonal-zirconia polycrystal) samples. Conventional measurements of these parameters gave porosity values from 0.18 to 0.4, mean pore sizes from 10 nm to 40 nm, and permeability from 4 nm(2) to 25 nm(2). The NMR methods are based on relaxation time measurements (T(1)) and the time dependent diffusion coefficient D(Delta). The relaxation time of C2F6 gas is longer in pores than in bulk gas and it increases as the pore sizes decrease. NMR yielded accurate porosity values after correcting for surface adsorption effects. A model for T(1) dependence on pore size that accounts for collisions between gas molecules and walls as well as surface adsorption effects is proposed. The model fits the experimental data well. Finally, the long time limit of D(Delta)/D(o), where D(o) is the bulk gas diffusion coefficient is useful for measuring tortuosity, while the short time limit was not achieved experimentally and could not be used for calculating surface-area to volume (S/V) ratios. 相似文献
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Zhang Z Ouriadov AV Willson C Balcom BJ 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2005,176(2):215-222
Gas transport across polymeric membranes is fundamental to many filtering and separation technologies. To elucidate transport mechanisms, and understand the behaviors of membrane materials, accurate measurement of transport properties is required. We report a new magnetic resonance imaging (MRI) methodology to measure membrane gas phase diffusion coefficients. The MRI challenges of low spin density and short gas phase relaxation times, especially for hydrogen gas, have been successfully overcome with a modified one-dimensional, single-point ramped imaging with T(1) enhancement, measurement. We have measured the diffusion coefficients of both hydrogen gas and sulfur-hexafluoride in a model polymeric membrane of potential interest as a gas separator in metal hydride batteries. The experimental apparatus is a modified one-dimensional diaphragm cell which permits measurement of the diffusion coefficient in experimental times of less than 1 min. The H(2) gas diffusion coefficient in the membrane was 0.54 +/- 0.01 mm(2)/s, while that of sulfur-hexafluoride was 0.14 +/- 0.01 mm(2)/s, at ambient conditions. 相似文献
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Diffusion of an ideal gas in a system of small spherical heterogeneities (collective of particles and a system of small cavities in homogeneous medium) is considered. The effective diffusion coefficient is calculated using methods of multiple scattering theory. Some possible contribution to diffusion of multiple passing closed loops on the trajectory of a molecule is considered. The interest to such loops is related to constructive interference of amplitudes corresponding to two alternative ways of the loop passing (clockwise and counterclockwise). This interference always exists, irrespective to the medium disorder. In this paper, we show that the interference corrections to classical diffusion lead to appearance of low frequency macroscopic oscillations of the gas concentration and complete stagnation of the diffusion process. The latter resembles the Anderson localization of electrons in a system of impurities in an ideal lattice. 相似文献
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采用溶液 凝胶扩散共聚法成功地合成了二元体系的甲基烯酸苄酯 甲基烯酸甲酯 (BZMA MMA)层状梯度折射率板 ,折射率分布是其主要性能指标。给出了一种测量该制品折射率分布的简便实验装置和自动实现方法。该测量方法基于激光干涉的原理 ,由计算机自动跟踪干涉条纹的移动来计算梯度折射率材料的折射率分布。实验表明 ,该方法简单易行 ,具有较高的折射率测量精度 ,为科学评价自研制梯度折射率材料的性能提供了保证 相似文献
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鲜肉水分近红外漫反射方法及实验研究 总被引:2,自引:0,他引:2
研究鲜肉深层水分的快速、无损检测方法,并用于鲜肉深层水分检测仪器的研制,具有很重要的现实意义,也是市场迫切的需求。以猪鲜肉为样品,采用近红外离散式光源,应用基于稳态空间分辨方法的漫反射方式解决了检测深度问题,测量鲜肉水分含量,得到了比较好的实验结果,r均达到0.90以上。用变异系数calculation of coefficient of variability(CV)和组内相关系数intra class correlation(ICC)检验测量的可靠性,CV≤5%,ICC达到0.83,表明方法稳定可靠。 相似文献
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F. Kober B. Koenigsberg V. Belle M. Viallon J. L. Leviel A. Delon A. Ziegler M. Dcorps 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1999,138(2):308-312
It is shown that thermally polarized 3He gas can be used to measure important physical parameters and to design, test, and tune imaging sequences. The bulk values of T1, T2, and the diffusion coefficient were measured in a glass cell containing a mixture of helium-3 (0.8 bar) and oxygen (0.2 bar). They were found to be T1 = 7 s, T2 = 2.4 s, and D = 1.6 cm2 s(-1). The relaxation times T2* and T1 and the apparent diffusion coefficient of thermally polarized helium-3 gas were measured in the rat lung, and these parameters were used to design a helium-3 optimized multi-spin-echo sequence which was shown to increase the signal-to-noise ratio sufficiently to obtain the first NMR-images of thermally polarized helium-3 in the rat lung. 相似文献