Mathematical Relationship Between Surface Emission and Diffusion Coefficients

ABSTRACT

This naver analvzes the surface emission coefficient corresponding to anv diffusion coefficient expressed as an exponential function of the concentration diffusing substance in capillary porous solids. Theoretical equations for surface emission coefficient for both sorption and desorption are presented. Procedures to derive the diffusion coefficient and to verify the corresponding surface emission coefficient are made using experimental sorption data of aspen (Populur sp.) wood. It is of interest to note that the theoretical models for diffusion and surface emission coefficients can be established and/or evaluated using the same set of experimental dara.     

Diffusion Coefficients in Crosslinked Polystyrene

Abstract

We measured the breakthrough curves for rectangular pulses of methane, ethane, and acetylene at low concentrations adsorbed on crosslinked polystyrene at 0, 25, and 30°C. The method of moments was utilized to evaluate the diffusion coefficients of the three gases based on a homogeneous-solid diffusion model.     

增钙渣和混合材与水泥比表面积的关系

根据小磨试验和生产实际推导出粒化增钙液态渣复合硅酸盐水泥强度与熟料强度、混合材掺量、比表面积之间的关系式,此式可用于水泥粉磨主要工艺参数的计算与控制.     

Oxygen Diffusion Coefficients in Alkali Silicates

Oxygen self-diffusion coefficients in molten alkali silicates were measured by the technique of heterogeneous isotopic exchange with a gaseous phase enriched in ¹⁸O. For the composition 64 wt% SiO₂-36 wt% K₂O, the diffusion coefficients from 700° to 1000°C under 100 torr O₂ pressure are described by The effect of pressure on D _O*, studied for the same composition at 900°C under O₂ pressures of 20 to 400 torr, is described by D _O*= kP _O2^{−(0.44±0.09)}. For the composition 75 wt%SiO₂-25 wt% K₂O, the diffusion coefficients from 750° to 1000°C under 100 torr O₂ pressure are described by The effect of pressure on the self-diffusion coefficients can be explained by a diffusion mechanism involving O vacancies.     

Probing Surface Chemistry Effects on Effective Diffusion Coefficients in Hierarchically Porous Media Through Multiscale Simulations

Multiscale diffusion simulations in a realistic macro-mesoporosity model of a silica-based chromatographic bed are performed to study the effect of relevant surface chemistry parameters, namely length and ligand density of surface-tethered alkyl chains, on effective mesopore and bed diffusion coefficients. Efficient linker schemes enable integration of interfacial dynamics information obtained from molecular dynamics simulations at the single-mesopore level into the hierarchical porosity and multiscale transport model.     

Surface Diffusion

Advances in instrumentation have made it possible in recent years to study the microstructure of inorganic materials at atomic resolution using the technique of high-resolution electron microscopy (HREM). Details of instrumentation have been described elsewhere [l], and applications and trends for HREM have recently been reviewed [2]. Although HREM is primarily a technique for studying bulk defects, it is increasingly also being applied in the profile-imaging mode to derive information about surfaces [3]. The high spatial resolution of the electron microscope makes it a valuable tool for the characterization of heterogeneous catalysts. This is evidenced by the growing number of studies wherein electron micrographs are being used to describe the morphology of a particular catalyst. Profile imaging is proving particularly useful in this regard for following changes in surface structure as a function of treatment conditions [4].     

Observations on Activity and Diffusion Coefficients in Na-Montmorillonite

Double-layer theory was used to obtain the distribution of electrical potential between adjacent clay particles. From this distribution, the activity coefficients of the sodium and chloride ions in the system were calculated. The calculated values were close to the observed ones. The porosity of the clay-water system was calculated from the density and concentration of clay. The calculated value was used to calculate the geometry factor. Then this factor and the diffusion coefficient of water in bulk water were used to calculate the diffusion that water would have in the clay if the water therein had its normal viscosity. Results indicated that the water in the clay was about twice as viscous as normal water. Having the geometry factor and the viscosity of the water in the system, it was possible to compute the diffusion coefficients that Na⁺ and Cl^? would have in the absence of electrical interaction with the clay. The computed values were close to those observed. To obtain closer agreement, electrical field strengths calculated by double-layer theory were used in an empirical equation relating viscosity and field strength to obtain the distribution of viscosity relative to the particle surfaces. Also, double-layer theory was used to obtain ionic distributions with respect to these surfaces. From the resulting distributions it was possible to determine, by means of appropriate equations, the ionic diffusion coefficients that should obtain in the clay system. Diffusion coefficients determined in this manner were somewhat better than those calculated without regard for electrical effects.     

Diffusion Coefficients of Electrolyte Solutions in Polymers

Abstract

An open-ended conductimetric cell has been used to determine mutual differential diffusion coefficients of electrolytes swelling in polymers. We measured diffusion coefficients of KCI and NaCl in aqueous solution, in polyurethane foam, polyvinylalcohol and polyhydroxybutyrate, POxB, commercially labelled as “Biopol.”     

蛋白质在离子交换吸附剂颗粒中的扩散系数

采用以化学势梯度作为扩散推动力的Maxwell-Stephan扩散方程（MS方程）,结合平行扩散模型,对阴离子吸附剂Q-SepharoseFF吸附牛血清白蛋白（BSA）的动态试验数据进行了模拟,拟舍得到了BSA的表面扩散和孔扩散系数。研究表明表面扩散系数随pH降低、盐浓度增加而增大;孔扩散系数随pH增加、盐浓度降低而增加,随蛋白质初始浓度增加而减小。在表面扩散不容忽视且为非线性吸附的条件下采用Fick定律时得到的表面扩散系数是蛋白质浓度的函数,且大于根据MS方程得到的表面扩散系数。     

混凝土孔结构及其分形维数与氯离子扩散性能的关系

氯离子扩散系数是研究海洋环境下混凝土结构耐久性的重要参数之一。通过开展不同水胶比混凝土的压汞试验和盐雾扩散试验,研究了混凝土内部孔隙率、孔径分布及临界孔径对氯离子扩散系数的影响规律。结合Menger海绵体模型,建立孔体积分形维数与氯离子扩散系数的关系。结果表明:孔隙率和临界孔径与无量纲化氯离子扩散系数的相关性很高,可作为反映混凝土氯离子扩散性能的重要参数;通过数学分析计算得到的孔表面分形维数分布在2.56~3.86之间,孔体积分形维数分布在2.85~2.98之间;基于压汞法和分形理论计算得到的孔体积分形维数可以作为评价氯离子扩散系数的指标,在孔径小于10 nm、10～100 nm、100～1 000 nm以及大于1 000 nm四类区间,氯离子扩散系数随孔体积分形维数的增加而下降。     

多组分液体混合物扩散系数及其计算

实际分离的混合物大多数为多组分体系,因此,开展多组分传质过程的理论和实验研究具有重要的实际意义。多组分传质过程涉及Fick扩散系数和axwell-Stefan扩散系数的计算。本文阐述Fick扩散系数和Maxwell-Stefan扩散系数的意义和相互关系,以及多组分液体体系扩散系数的计算。     

挥发性有机物在土壤多孔介质中的有效扩散系数的研究

采用土柱扩散实验研究了挥发性有机物在土壤多孔介质中的有效扩散系数.根据多孔介质为干燥和含水体系将挥发性有机物分为保守性和非保守性两种类型的扩散组分,分别采用不同的迁移方程描述.对三氯乙烯和苯在砂土体系的研究表明,利用土柱扩散实验测定挥发性有机物的有效扩散系数的方法可靠,同时表明采用经验模型描述非保守性组分的扩散时应考虑适用范围.     

异戊二烯在聚苯乙烯高分子膜中的扩散系数测定

为了探讨在反应挤出过程中异戊二烯在聚苯乙烯中的扩散传递机理,采用石英弹簧法测定了298.15K、308.15K和318.15K下异戊二烯在聚苯乙烯膜中的吸收动力学曲线。探讨了温度、压力、分子量对扩散吸收的影响,并对实验结果进行了关联。结果表明异戊二烯在聚苯乙烯膜中的扩散吸收呈S型吸收,由吸收曲线获得了平均扩散系数和平衡溶解度。     

含醇溶液中分子扩散系数的分子模拟

利用分子动力学(MD)模拟验证了含醇溶液的无限稀释扩散系数模型和不同浓度溶液的扩散系数模型.选用的溶质分别为甲醇、乙醇、丙醇、异丙醇、正丁醇和甘油,温度为293.15K,压力为0.1MPa.计算结果表明:Dullien和Asfour方程适用于计算甲醇和乙醇溶液的扩散系数DAB;而对于其它醇溶液的扩散系数,Leffler和Cullinan方程较适用.     

邻二甲苯在醋酸中扩散系数的测定

利用金属膜池并用氯化钾水溶液标定了膜池常数。用已有可靠文献值的乙酸水溶液验证了装置的可靠性。测定了298．15～323．15K不同温度下邻二甲苯在醋酸中的积分扩散系数,还分别给出了微分扩散系数与邻二甲苯浓度的关联式。结果表明在相同温度下邻二甲苯在醋酸中的扩散系数随着邻二甲苯浓度的增加而减小,在同一浓度下随着温度的升高而增加。     

L-抗坏血酸水溶液扩散系数的测定

为进一步补充药类物质水溶液扩散系数的实验数据和研究相关理论模型的实用性,今制备了金属膜池,用氯化钾溶液标定了膜池常数,并用已有可靠扩散系数值的蔗糖水溶液验证了装置的可靠性.测定了298.15K到328.15K不同温度下L-抗坏血酸在水溶液中可溶解范围内不同浓度下的扩散系数.结果表明在相同温度下,L-抗坏血酸水溶液的扩散系数随着浓度的增加而减小;在同一浓度下,随着温度的升高而增加.另一方面Gordon在扩散模型基础上,关联得到一个有温度项的扩散系数半经验模型,计算结果与实验值吻合很好. 同时用精密密度计和粘度计测定了体系相应的密度和粘度,并与浓度进行了关联.