基于摩擦系数的扩散模型

根据分子间摩擦系数与组分自扩散系数关系,提出一个新的互扩散系数模型。模型分为3部分：组成项、自扩散系数和化学势与组分关系。采用文献自扩散系数值,并用不同状态方程以计算化学势与组分关系,模拟1 132～1 810℃之间不同组成二氧化碳气体混合物的互扩散系数,并与实验值做了比较。结果表明采用Peng-Robinson(PR),Redlich-Kwong(RK)及Van der Waals(VdW)方程计算化学势与组分关系而得到的模拟结果优于Virial方程,且平均误差在5%之内。     

压力和温度对瓦斯扩散规律的影响研究

针对瓦斯吸附解吸法测定瓦斯扩散系数时局限于颗粒煤、无法施加围压且气体压力不能任意设定等问题,采用规则块煤结合气相色谱分析法测定瓦斯在块煤中的扩散系数,分析了不同气体压力、温度下块煤瓦斯扩散规律。实验结果表明,随着气体压力的增大,煤基质吸附气体增加且发生膨胀变形,从而孔隙减小,扩散阻力增大,扩散系数减小;随着温度的升高,气体分子运动速度增大,扩散动力增强,扩散系数变大。     

计算机模拟估算气体的扩散系数

使用计算机模拟了气体分子在背景气体中的一维扩散过程,结果显示:越靠近初始位置处,分子数密度越大;扩散时间越长,分子分布的空间范围越大;模拟的分子数越多,涨落越小;分子的方均位移与扩散时间成正比。本文的模拟方法可用来估算气体的扩散系数,对1标准大气压和15°C条件下,氩气、氢气、氮气、氧气、二氧化碳和氖气的自扩散系数,以及此条件下氢气在氧气中、氢气在氮气中、氢气在二氧化碳中和氧气在氮气中的互扩散系数进行了估算,并把估算的扩散系数和相应的扩散系数实验值作了对比,二者不但数量级符合的很好,数值也比较接近,说明估算较为成功。     

利用Aspen Plus计算和预测物质的溶解度

利用Aspen Plus计算和预测固体、液体和气体物质的溶解度。固体物质溶解度计算利用Mixer+Heater模块,液体溶解度计算利用Decanter模块,气体溶解度计算利用Flash2模块,并利用Sensitivity模块进行灵敏度分析,可得到固体和液体在不同温度下以及气体在不同温度和不同压力下的溶解度。以KCl、NaNO_3和NH_4Cl为例,计算不同温度下固体物质在水中的溶解度,计算值与文献值的平均相对偏差分别为0.47%、0.65%和0.26%:液体物质以苯为例,计算其不同温度下在水中的溶解度,计算值与文献值吻合良好:气体物质以CO_2为例,计算其在不同温度和不同压力下水中溶解度,计算结果均与文献值吻合较好。案例研究的结果表明本文建立的固体、液体和气体物质的溶解度计算方法均是可靠的,对于物性手册和文献中查不到的溶解度数值,可以通过本文提出的方法进行计算和预测,计算结果可为工业生产提供科学可靠的数据。     

二氧化锡薄膜气敏传感器对常见室内污染气体的 电阻2温度特性及机理分析

采用无机试剂(SnCl2·2H2O)为原料,用溶胶-凝胶提拉法制备了二氧化锡薄膜及相应的气敏传感器,并研究了二氧化锡薄膜气敏传感器在常见室内污染气体气氛中的电阻-温度变化关系.结果发现不同气氛下电阻-温度特性各不相同,由此可以获得被测气体的相关信息.本文还用分子轨道计算软件对四种室内污染气体的分子轨道进行了计算,并根据分子轨道能级的相对位置定性解释了二氧化锡薄膜气敏传感器在不同气氛中的电阻-温度曲线.通过对甲醛、苯、甲苯、二甲苯四种气体电阻-温度曲线的测试可以确定被测气体的种类.     

水在环氧树脂中扩散的分子动力学模拟

用分子动力学方法(MD)模拟水分子在TGDDM/DDS交联环氧树脂中的扩散,分析了温度和含水量对水在环氧聚合物中扩散系数的影响。基于Einstein公式,通过均方位移曲线计算的扩散系数表明,温度越高,水分子扩散系数越大,与文献中所给出的实验值相吻合:在含4个不同水浓度的环氧体系中,得到的水分子氧原子间的径向分布函数表明,含水量越高,存在于系统中的水越易以水分子簇形式存在。从微观上证实了模拟结果-扩散系数随水浓度的升高而增加,此结论也通过实验得到了证实。     

基于有限元模型的建筑混凝土柱屈曲承载力计算

为了解决传统混凝土承载力算法存在峰值负荷计算值误差较大的问题,本文提出基于有限元模型的建筑混凝土柱屈曲承载力计算方法.通过有限元模型,对混凝土柱进行有限元数值模拟分析,模拟其屈曲力学性能,判断混凝土柱整体抗屈曲强度,确定屈曲承载力极限时的应力-应变关系曲线,并完成曲线参数计算.此次算法与两种传统算法进行对比实验,对三组混凝土柱试件进行破坏,比较峰值负荷计算值和试验值,结果表明,此次算法减小了峰值负荷的计算误差,此次算法的屈曲承载力计算结果更为准确.     

分子动力学模拟聚乙烯在碳纳米管表面的扩散

通过采用分子动力学方法模拟不同链长的聚乙烯分子在单壁碳纳米管表面的扩散,探究了聚乙烯的动力学性质。研究表明随着链长的增加聚乙烯在碳纳米管表面的扩散系数减小,且二者间存在明显的标度关系。聚乙烯在碳纳米管表面扩散的扩散系数和聚乙烯吸附在碳纳米管表面的构象有关,有序结构的聚乙烯比无序结构的聚乙烯在碳纳米管表面扩散的快。此外,由于受到碳纳米管吸附作用的影响,聚乙烯分子在平行于管轴和垂直于管轴2个方向上的扩散系数不同,扩散表现各向异性。     

生物分子在Ni纳米膜表面吸附的力学特性： 分子动力学模拟

采用COMPASS力场,通过分子动力学模拟,研究了Ni纳米薄膜的弹性模量的尺寸效应,以及生物分子吸附在Ni表面对其力学性能的影响.计算结果表明,随着厚度的增大,吸附强度也在增强;Ni纳米薄膜的弹性模量随着膜厚的减小而减小.氨基酸在Ni表面的吸附能够提高其弹性模量1～2 GPa,并且表明分子的取向是重要的影响因素.     

分子模拟方法预测流体热力学性质

流体的热力学性质数据对化工过程设计具有重要意义,除实验测定外,也可采用分子模拟方法计算。为了考查分子模拟方法预测流体热力学性质的准确性和可靠性,本文以环氧乙烷为例,基于所开发的分子力学力场,综合采用分子动力学和蒙特卡罗等多种分子模拟方法,预测了环氧乙烷在较大温度范围内的气液相平衡、第二维里系数、热容、粘度系数等多种热力学性质。结果表明,采用分子模拟方法所预测的热力学性质与实验值吻合良好,所计算的环氧乙烷的液体密度、气相第二维里系数、热容和粘度系数的平均偏差分别在1%、5%、5%和10%以内。由此可见,分子模拟方法可以成为获取流体热力学性质的另1种可靠手段。     

乙烯基硅烷在聚乙烯中扩散行为的模拟计算

通过三种硅烷（A171,A172,A151）对LDPE,LLDPE,HDPE塑料试片的渗透实验,采用浸泡称重法,得到了渗透量随时间变化的曲线,利用Fick定律测得了不同温度下的扩散系数,同时采用有限差分法法,利用Visual Basic6．0语言,编制计算机程序,模拟了上述体系的扩散行为,得到的扩散系数与实测值一致。根据Arrhenius方程求得A171在HDPE,LDPE,LLDPE扩散活化能分别为38．2,24．0和22．0kJ。为硅烷接枝聚乙烯过程中硅烷浸泡时间的估算建立了快速便捷的方法。     

Atomic mobility, diffusivity and diffusion growth simulation for fcc Cu-Mn-Ni alloys

On the basis of the critically reviewed experimental diffusivities available in the literature, the atomic mobilities of Cu, Mn and Ni in fcc Cu-Mn-Ni alloys were assessed as a function of temperature and composition by means of DICTRA (DIffusion Controlled TRAnsformation) software. Comprehensive comparisons between the calculated results and the experimental data show that a good agreement is obtained for various diffusivities in binary and ternary systems, including impurity diffusion coefficients, tracer diffusion coefficients and interdiffusion coefficients. The atomic mobilities obtained can also be used to describe various diffusion phenomena for a series of binary and ternary diffusion couples, such as concentration profiles, the Kirkendall shift, the interdiffusion flux and diffusion paths.     

Diffusivities and atomic mobilities in bcc Ti-Zr-Nb alloys

Diffusion couples were prepared and annealed at 1373 K for 72 h and 1473 K for 48 h, respectively. The interdiffusion coefficients at the intersection composition were obtained using the Whittle and Green method and the ternary trace diffusion coefficients using Hall method. The experimental diffusion coefficients of Ti and Nb in bcc Ti-Zr-Nb system were assessed to develop an atomic mobility database. The calculated diffusion coefficients and composition profiles show good agreement with the experimental data.     

Assessment of diffusion mobility for the bcc phase of the Ti-Al-Cr system

Experimental diffusion data in the literature were critically assessed to develop the diffusion mobility for the bcc phase of the Ti-Al-Cr system by means of a DICTRA-type (Diffusion Controlled Transformation) diffusion modeling. Good agreements were obtained from comprehensive comparisons made between the calculated and experimental diffusion coefficients. The developed diffusion mobility was further validated by appropriate prediction of interdiffusion behavior observed from diffusion couple experiments in the literature.     

Experimental and computational study of diffusion mobilities for the bcc phase in the Fe-Al-(Si,Mn) systems

The electrical steel has attracted considerable attention due to the excellent soft magnetic properties, which can be improved by the addition of alloying elements such as Al, Si and Mn. To increase element contents, the hot-dipping and diffusion-annealing method has been developed. The method requires detailed insight on the diffusion behavior of the alloy system. In the present work, the re-assessment of the diffusion mobilities for the bcc phase (including both bcc_A2 and bcc_B2 phases) in the Fe-Al system were firstly performed based on the critical evaluation of the available experimental data. By applying the diffusion-couple method, the interdiffusion coefficients in bcc_A2 Fe-Al-Si alloys were determined and used to optimize the diffusion mobilities. The bcc_A2 Fe-Al-Mn diffusion couples were also designed to verify the diffusion mobilities. Comparison between the model-predicted and experimental diffusion data such as diffusion coefficients, concentration profiles and diffusion paths confirms the reliability of the present mobility parameters.     

Diffusion behaviors and atomic mobilities in Mg–Sc hcp and bcc alloys: Investigation via single-phase and multi-phase diffusion couples

Diffusion behaviors in Mg–Sc hcp and bcc solid solutions between 773 and 873 K were investigated using both single-phase and multi-phase diffusion couple techniques. The EPMA detected composition-distance profiles were smoothed and fitted using the error function expansion (ERFEX). The interdiffusion coefficients were extracted using Sauer–Freise integral. The interdiffusion coefficients in hcp phase showed a slightly parabolic composition dependence at the Mg-rich part and the maximum value was around 2–3 at. % Sc. However, the interdiffusion coefficients in the bcc phase monotonously decreased with the increase of solubility of Sc. The determined inter- and impurity diffusion coefficients in the hcp Mg–Sc alloys were assessed to develop the atomic mobility database, and their validity was justified by reproducing the composition profiles and diffusion fluxes obtained in this diffusion couple experiment. Meanwhile, the development of bcc atomic mobility was realized via the Maclaurin approximation, extrapolation, and optimization. The results make up for the missing data of Mg–Sc diffusion kinetics.     

Coarse-grained molecular dynamics simulation of water diffusion in the presence of carbon nanotubes

Computational modeling of the translational diffusion of water molecules in anisotropic environments entails vital relevance to understand correctly the information contained in the magnetic resonance images weighted in diffusion (DWI) and of the diffusion tensor images (DTI). In the present work we investigated the validity, strengths and weaknesses of a coarse-grained (CG) model based on the MARTINI force field to simulate water diffusion in a medium containing carbon nanotubes (CNTs) as models of anisotropic water diffusion behavior. We show that water diffusion outside the nanotubes follows Ficḱs law, while water diffusion inside the nanotubes is not described by a Ficḱs behavior. We report on the influence on water diffusion of various parameters such as length and concentration of CNTs, comparing the CG results with those obtained from the more accurate classic force field calculation, like the all-atom approach. Calculated water diffusion coefficients decreased in the presence of nanotubes in a concentration dependent manner. We also observed smaller water diffusion coefficients for longer CNTs. Using the CG methodology we were able to demonstrate anisotropic diffusion of water inside the nanotube scaffold, but we could not prove anisotropy in the surrounding medium, suggesting that grouping several water molecules in a single diffusing unit may affect the diffusional anisotropy calculated. The methodologies investigated in this work represent a first step towards the study of more complex models, including anisotropic cohorts of CNTs or even neuronal axons, with reasonable savings in computation time.     

Assessment of diffusion mobility for bcc phase of Ti–Al–Ni ternary system

The experimental diffusion coefficients of the Ti–Ni binary and Ti–Al–Ni ternary bcc phase were critically evaluated to assess the diffusion mobilities by the DICTRA-type phenomenological treatment. The calculated diffusion coefficient shows reasonable consistency with the diffusion coefficient extracted in the experiment, including the impurity and inter-diffusion coefficients in bcc Ti–Ni binary alloy and the main interdiffusion coefficient in bcc Ti–Al–Ni ternary alloy. The difference between the calculated and experimental ternary cross coefficients is within appropriate relative errors. The predicted composition profiles and diffusion paths reasonably represent the diffusion processes that occur in Ti–Ni binary and Ti–Al–Ni ternary diffusion couples, thereby validating the mobility database assessed in the present work.     

Thermodynamic assessment of the Co–Cr–Fe system and atomic mobility study of its fcc phase

In the present work, the Co–Cr–Fe system was thermodynamically assessed by using the CALPHAD approach coupled with first-principles calculations and experimental data from the literature. Subsequently, the fcc Co–Cr–Fe ternary diffusion couples annealed at 1273 and 1473K were scanned by using electron probe microanalysis (EPMA) to obtain the composition profiles, from which the interdiffusion coefficients were extracted by the Whittle-Green method. Based on these interdiffusion coefficients and present thermodynamic parameters, the atomic mobilities of Co, Cr, and Fe in the fcc Co–Cr–Fe alloys were assessed by means of DICTRA software. The calculated interdiffusion coefficients, composition profiles and diffusion paths of the fcc Co–Cr–Fe alloys were consistent with the experimental data, which verifies the accuracy of the assessed atomic mobilities.