稀土低温高浓度渗碳表面渗层的微观组织

在周期作业气体渗碳炉中采用稀土低温高浓度渗碳新工艺,于860～880℃、高炉气碳势下渗碳,可获得较理想的渗碳组织,即过共析区的碳化物呈细小颗粒状弥散分布,基底为隐晶马氏体,奥氏体发生再结晶细化至12～14级。共析区的微观组织与传统工艺无明显区别。本文还探讨了颗粒状碳化物的形成过程与机制。     

稀土元素在钢的化学热处理中作用机理研究

根据稀土元素在化学热处理中的作用，研究稀土元素渗入到钢表层的扩渗机制和在化学热处理中的活化催渗机理。在８６０℃稀土碳氮共渗过程中，稀土的扩散系数为１．０６×１０￣（－１４）ｍ￣２／ｓ。     

稀土对20Mn钢等温相变及组织形态的影响

研究了不同稀土含量对20Mn钢等温相变及组织形态的影响。随钢中稀土含量的增加,先共析铁素体析出的孕育期缩短,完成珠光体相变所需时间延长;针状铁素体量减少直至消失;珠光体片间距变密且相对转变量减少;粒状贝氏体中碳化物易于偏聚。稀土减小原奥氏体晶界能和相界面能,稀土原子偏聚在相界面上阻碍碳原子的扩散,以及可能形成高熔点稀土碳化物而减少奥氏体中碳的固溶量,是产生上述结果的主要原因。     

稀土离子在多孔阳离子交换剂内的扩散动力学

研究了稀土离子在Amberlyst15、D001、XN1010多孔树脂内的自扩散。结果表明,扩散过程遵循二级分散扩散机制。用粒内扩散方程求算了有效粒内扩散系数e,将e分解为树脂孔道扩散系数p及树脂固相扩散系数s,p与该离子在外部溶液中的自扩散系数相近,而s接近于与实验用的多孔树脂交联度相同的凝胶树脂内的自扩散系数值。     

非平衡热力学在界面传递过程中的应用

21世纪以来，随着各学科之间的交叉渗透，化学工程的研究对象越来越复杂，界面传递对多相化工过程的影响越来越显示出它的重要性，传统的传递模型已经很难对界面复杂动态的传递行为进行定量描述．本文应用线性非平衡态热力学理论，对传统物质传递模型进行描述，分析界面传递过程速率，强化的三个因素：界面传质系数K、传递截面积A、界面化学位梯度△u．以含钾化合物作为模型体系，基于非平衡热力学原理建立了描述和预测固一液界面处介质传递速率的模型，并建立了描述其溶解速率的通用模型和测定钾离子动力学数据的实验方法，通过分析探讨了多相过程速率强化的途径．     

微合金钢中稀土钒复合作用的研究

稀土在钒微合金钢中有一定的固溶量,并可达10^-5-10^-4(质量分数）数量级,稀土降低碳氮化钒完全溶解的温度,阻止奥氏体中钒的应变诱导析出,在铁素体区稀土促进碳氮化钒析出,并细化沉淀相,钒和稀土复合微合金化有更强的推迟形变奥氏体动态再结晶,抑制奥氏体晶粒长大和细化晶粒的作用。     

稀土对碳氮共渗过程的活化催渗及微合金化研究

研究了在碳氮共渗过程中加入稀土元素对钢的碳氮共渗动力学过程、金相组织和性能的影响。稀土可使20号钢、20CrMnTi、20CrMnMo等渗碳钢的扩渗速度提高15～20％,提高表面渗层碳氮含量,明显改善表层碳氮化合物颗粒尺寸和分布。应用于齿轮,可使疲劳寿命提高12％。稀土镧作为共渗组元,渗入钢表面,不仅改善夹杂物形貌和分布,净化晶界,并对钢表面进行了微合金化,从而改善了钢的性能。     

稀土对管线钢中碳化物溶解与析出行为的影响

以X80管线钢为研究对象,研究了稀土对含铌钢奥氏体化与析出行为的影响。利用热力学固溶度积公式,计算了铌碳化物的溶解温度;借助显微组织观察与硬度测试,对比分析了稀土对高温下奥氏体晶粒粗化及不同温度淬火回火后硬度的影响;通过热模拟实验并利用透射电镜,研究了稀土对实验钢在热变形过程中铌碳氮化物析出行为的作用机制。结果表明:稀土元素的加入降低了碳氮化物的固溶温度,促进了Nb(C,N)等第二相粒子的固溶,稀土能够促进热变形过程中Nb(C,N)的析出,从而提高铌元素的析出强化效果。     

界面流变性质对小液滴聚并过程的影响

对表面活性剂溶液中两个小液滴的聚并现象进行理论分析，并考虑相界面上质量传递对该过程的影响，得到聚并时间与界而张力和界面张力梯度、界面粘度、表面活性剂界面扩散系数、连续相和分散相的主体性质、范德华力及液滴半径的关系．     

稀土对微合金钢中碳化铌析出规律的影响

在铁素体区和奥氏体区研究了稀土对碳化铌析出动力学规律的影响。实验结果表明，在铁素体区稀土可促进碳化铌的析出，而在奥氏体区有抑制碳化铌的出的作用。用计算机进行线性拟合处理发现，稀土并不能改变碳化铌析出的动力学机制，但影响其瓜速度常数Ｋ。在６６０℃时稀土使Ｋ值增加，属于形核长大控速。在９５０℃时稀土使Ｋ值降低，属于扩散控速。表明了稀土对碳化铌要出的促进和抑制作用。     

用于聚合物溶液扩散系数计算的活度系数模型比较

用40个聚合物溶液体系的实验数据,对三个有代表性的活度系数模型用于计算联系自扩散系数和互扩散系数的热力学因子的精度进行了比较,结果表明三个模型的精度相近,误差一般在20％左右。,因而本工作揭示了聚合物溶注保由自扩散系数计算与扩散系数的一个潜在问题。即由于活度系数模型计算热力学因子误差较大所带来的较大不确定性。     

MH电极中氢扩散系数的测定及其应用

利用恒流放电法测定了金属氢化物(MH)电极中氢原子扩散系数的平均值. 通过恒电位法测定了MH电极中氢原子的扩散系数与其荷电态(SOC)的关系. 根据MH电极模型可知, 增大氢原子扩散系数或减小储氢合金粒径均能提高MH电极的快速充电性能, 并能计算出MH电极在不同的初始荷电态、不同充电倍率下, 表面氢原子浓度达到最大值所需的时间.     

Effect of Modification on the Fluid Diffusion Coefficient in Silica Nanochannels

The diffusion behavior of fluid water in nanochannels with hydroxylation of silica gel and silanization of different modified chain lengths was simulated by the equilibrium molecular dynamics method. The diffusion coefficient of fluid water was calculated by the Einstein method and the Green–Kubo method, so as to analyze the change rule between the modification degree of nanochannels and the diffusion coefficient of fluid water. The results showed that the diffusion coefficient of fluid water increased with the length of the modified chain. The average diffusion coefficient of fluid water in the hydroxylated nanochannels was 8.01% of the bulk water diffusion coefficient, and the diffusion coefficients of fluid water in the –(CH₂)₃CH₃, –(CH₂)₇CH₃, and –(CH₂)₁₁CH₃ nanochannels were 44.10%, 49.72%, and 53.80% of the diffusion coefficients of bulk water, respectively. In the above four wall characteristic models, the diffusion coefficients in the z direction were smaller than those in the other directions. However, with an increase in the silylation degree, the increased self-diffusion coefficient due to the surface effect could basically offset the decreased self-diffusion coefficient owing to the scale effect. In the four nanochannels, when the local diffusion coefficient of fluid water was in the range of 8 Å close to the wall, Dz was greater than Dxy, and beyond the range of 8 Å of the wall, the Dz was smaller than Dxy.     

Time-dependent Diffusion Coefficient and Conventional Diffusion Constant of Nanoparticles in Polymer Melts by Mode-coupling Theory (cited: 2)

Time-dependent diffusion coefficient and conventional diffusion constant are calculated and analyzed to study diffusion of nanoparticles in polymer melts. A generalized Langevin equa-tion is adopted to describe the diffusion dynamics. Mode-coupling theory is employed to calculate the memory kernel of friction. For simplicity, only microscopic terms arising from binary collision and coupling to the solvent density fluctuation are included in the formalism. The equilibrium structural information functions of the polymer nanocomposites required by mode-coupling theory are calculated on the basis of polymer reference interaction site modelwith Percus-Yevick closure. The effect of nanoparticle size and that of the polymer size are clarified explicitly. The structural functions, the friction kernel, as well as the diffusion coefficient show a rich variety with varying nanoparticle radius and polymer chain length. We find that for small nanoparticles or short chain polymers, the characteristic short time non-Markov diffusion dynamics becomes more prominent, and the diffusion coefficient takes longer time to approach asymptotically the conventional diffusion constant. This constant due to the microscopic contributions will decrease with the increase of nanoparticle size, while increase with polymer size. Furthermore, our result of diffusion constant from mode-coupling theory is compared with the value predicted from the Stokes-Einstein relation. It shows that the microscopic contributions to the diffusion constant are dominant for small nanoparticles or long chain polymers. Inversely, when nanonparticle is big, or polymer chain is short, the hydrodynamic contribution might play a significant role.     

Determining the Diffusion Coefficient of Lithium Insertion Cathodes from GITT measurements: Theoretical Analysis for low Temperatures**

Accurate knowledge of transport properties of Li-insertion materials in application-relevant temperature ranges is of crucial importance for the targeted optimization of Li-ion batteries (LIBs). Galvanostatic intermittent titration technique (GITT) is a widely applied method to determine Li-ion diffusion coefficients of electrode materials. The well-known calculation formulas based on Weppner's and Huggins’ approach, imply a square-root time dependence of the potential during a GITT pulse. Charging the electrochemical double layer capacitance at the beginning of a GITT pulse usually takes less than one second. However, at lower temperatures down to −40 °C, the double layer charging time strongly increases due to an increase of the charge transfer resistance. The charging time can become comparable with the pulse duration, impeding the conventional GITT diffusion analysis. We propose a model to describe the potential change during a galvanostatic current pulse, which includes an initial, relatively long-lasting double layer charging, and analyze the accuracy of the lithium diffusion coefficient, derived by using the Weppner-Huggins method within a suitably chosen time interval of the pulse. Effects leading to an inaccurate determination of the diffusion coefficient are discussed and suggestions to improve GITT analyses at low temperature are derived.     

电化学阻抗法测定金属氢化物电极中氢的扩散系数

应用电化学阻抗法测定了不同荷电状态 (SOC)和不同温度下MlNi3.75Co0 .65Mn0 .4 Al0 .2 金属氢化物电极中氢的扩散系数 .结果表明 :室温下该电极中氢的扩散系数随其荷电量的增大而减小 ,SOC为 5 0 %时氢的扩散系数随温度的升高而增大 ,相应的氢扩散活化能为 35kJ/mo     

利用泰勒分析和动态涂层毛细管电泳系统快速测定蛋白质的扩散系数

以泰勒分散理论为基础, 首次采用动态涂层毛细管来准确和快速测定蛋白质分子的扩散系数.     

计时电流法测定Fe3+在离子液体BPBF4中的扩散系数

室温离子液体(简称离子液体)作为新型的反应介质和功能材料受到学术界和产业界的高度关注,正在迅速成为多学科交叉的前沿研究领域和具有良好应用前景的“绿色”高新技术,过渡金属化合物是许多重要反应的催化剂,过渡金属离子在室温离子液体中的性质是工业界关心的课题,有关过渡金属的离子液体的研究,     

锂在高有序热解石墨(HOPG)电极中的扩散系数

用循环伏安、交流阻抗和电位阶跃法研究了平板高有序热解石墨(HOPG)电极在1mol/LLiPF₆和体积比为1∶1的EC/DMC溶液中的电化学行为.结果表明,石墨的嵌锂反应仅发生在边界面上.随着嵌锂量的增加,表面SEI膜的电阻和嵌入反应的极化电阻减小.用交流阻抗谱和电位阶跃方法测定的锂在高有序热解石墨中的扩散系数一致,并随充电程度的增加而显著减小.在电极电位(vs.Li/Li⁺) 0.2～0.05V区间,扩散系数由10^-11cm²/s下降到10^-12cm²/s.     

Active layer of fuel cell electrode with polymer electrolyte: Modeling of support grains, calculation of overall cathode characteristics

The active layer of the cathode of a fuel cell with polymer electrolyte (Nafion) is considered. The optimum carbon support structure is constructed using computer simulation: its carbon “skeleton” possesses the maximum outer surface area and provides electronic conductivity of the grains, support cubes, along the three coordinate axes. Nafion is absent in the support grain, so that the grain is capable of participating only in the transport of oxygen molecules, it possesses no proton conductivity. An estimate of all parameters of an optimum support grain is provided; in particular, the value of the effective Knudsen diffusion coefficient of oxygen is established. After this, effective proton conductivity and effective Knudsen diffusion coefficient are calculated already on the whole active layer scale, according to the model of equally sized cube grains of three types. In conclusion, the overall current in the active layer of a cathode with a polymer electrolyte was calculated for the percolation cluster consisting only of Nafion grains and the Knudsen diffusion of oxygen created only by a combined gas percolation cluster consisting of void grains and all support grains. The overall current value for t = 80°C and pressure of p* = 101 kPa proved to be low, hundreds of mA/cm². The current value can apparently be increased to several A/cm² if the support grains are developed that would simultaneously possess both proton conductivity and ability to sustain oxygen diffusion.