A simple and inexpensive technique to measure molecular diffusion coefficients

The experiment proposed is simple and inexpensive and provides an accurate method for measurement of the molecular diffusion coefficient, D _m. It is a novel method that has the added advantage of easily providing data at temperatures and pressures that differ significantly from ambient values. The experimental results for naphthalene in air are in excellent agreement with the experimental values of the molecular diffusion coefficient measured by other authors. Experimental measurements of mass transfer in water were also carried out for a range of the relevant parameters. The soluble spheres used in the experiments were made of either benzoic acid or 2-naphthol, and the ranges of temperatures covered were 293–333 and 293–373 K, respectively. Using the mass transfer theory presented in this work, the molecular diffusion coefficient of the two solutes was determined, and good agreement with literature values was found.     

熔盐电脱氧法中氧离子在氯化钙熔盐中的 扩散动力学研究

本文以分子模拟为基础，构建了O2-/CaCl2的全原子模型，以Born-Mayer-Huggins（BMH）势函数对体系进行描述，研究了O2-在CaCl2熔盐的扩散动力学行为。结果表明：1073 K时O2-扩散系数为2.01×10-5 cm2/s，与F.D.Ferro经验公式的计算值一致；同时发现温度与O2-的扩散系数呈正相关关系，拟合得到O2-在CaCl2熔盐中的扩散活化能为15.6 kJ/mol。在微观结构方面，由于静电吸引的作用，熔盐中Ca2+会在O2-周围形成正电配位层，并束缚了O2-的扩散；O2-从形成的Ca2+配位层中逸出需要越过的能垒约为1.7 J。本文不仅揭示了O2-在CaCl2的动力学行为，也为计算机模拟指导研究改良熔盐配方提供研究基础。     

电动势法研究富钛渣中低价钛氧化过程动力学

用固体电解质氧浓差电池测定了不同恒温及空气条件下富钛炉渣中氧分压随时间变化的关系,建立了渣中低价钛氧化过程的动力学方程,得到了熔渣中氧传输的表感化 能以及氧在熔渣中的扩散系数,并讨论了添加铁氧化物对氧化速率的影响。     

Effect of Ambient Temperature on the Electrochemical Properties of La_4MgNi_(17.5)Co_(1.5) Hydrogen Storage Alloy

The effect of different ambient temperatures on the electrochemical properties of La_4MgNi_(17.5)Co_(1.5)hydrogen storage alloy was investigated.The X-ray diffraction pattern shows that the alloy consists of LaNi5-type phase and A_5B_(19)-type(Ce_5Co_(19) + Pr_5Co_(19)) phase.With the increase of the ambient temperature,the maximum discharge capacity of the alloy electrodes increases from 353.33(283 K) to 379.25 mAh/g(308 K),and the cyclic stability(S_(100)) of the electrodes decreases from 80.19(283 K) to 52.04%(308 K) due to the acceleration of pulverization,corrosion and oxidation at higher ambient temperature.Moreover,it is found that the increase of the temperature can accelerate the diffusion rate of hydrogen in the alloy(D) and increase the exchange current density(I_0).which are beneficial for improving the activation performance and the high-rate dischargeability(HRD) of the alloy electrodes.The activation cycles of the electrodes decrease from 4(283 K) to 1(308 K),and the HRD_(900) of the electrodes sharply increases from 66.36(283 K) to 95.64%(308 K).     

DIFFUSION OF La IN LIQUID Al-Si ALLOY

The diffusion coefficients of lanthnum in liquid Al-Si alloy have been measured successfullyby the anodic chronopotentiometry. At 973K, the diffusion coefficient of lanthanum(D_(La(Al-Si))) in liquid Al-5.2wt-%Si alloy equals (0.91±0.01)×10~(-5) cm~2 s~(-1) . In the rangeof temperatures 953-1053K, the relationship between the diffusion coefficient and the tem-perature is represented by 1gD_(La(Al-Si))=-1.78×10~(-3)-4909/T. The activation energy isQ=94.00kJ·mol~(-1). Using the diffusion data of lanthanum and strontium, the effect of thediffusion of the modifier on the incubation period of modification and cooling rate has beendiscussed.     

Selective oxidation of Fe-30Cr at low temperatures: 743–823 K

Fe-30 Cr specimens were oxidized for 6×10²–3.6×10⁴ s at 743–823 K in pure oxygen at a pressure of 1.33×10⁴ Pa. Depth profiling of oxidized surfaces was performed with the simultaneous use of Auger electron spectroscopy (AES) and inert gas-ion (Ar⁺ or Xe⁺) sputter-etching technique. Chromium was selectively oxidized, and a chromium-depletion zone was formed in the underlying alloy. The values (10^–16–10^–15 cm² s^–1) of the interdiffusion coefficient, D, of the underlying alloy evaluated from the depth-composition profiles were compared in magnitude with the values extrapolated from lattice diffusion data of the corresponding alloy obtained at high temperature. The apparent activation energy obtained from an Arrhenius plot of the evaluated diffusion coefficient, however, was one-third of the value for the corresponding alloy at high temperatures. Discussion was made on the possible mechanism of selective oxidation at low temperatures.     

Mg-Fe-CLDH对模拟谷氨酸废水的吸附分离

采用共沉淀法合成Mg与Fe摩尔比为3：1的层状双金属氢氧化物（Mg-Fe-LDH）,然后在500℃下煅烧6 h得到煅烧双金属氢氧化物（Mg-Fe-CLDH）。分析Mg-Fe-CLDH与Mg-Fe-LDH对谷氨酸的吸附性能,研究溶液p H、谷氨酸初始浓度、共存阴离子及温度等因素对吸附效果的影响,并对其吸附过程的动力学和热力学过程进行研究。结果表明：Mg-Fe-CLDH对谷氨酸的吸附效果很好,吸附率在优化条件下达到99.9%;吸附动力学符合准一级动力学方程,平衡吸附等温线很好地符合Langmuir方程。颗粒内扩散模型能很好地描述吸附动力学过程。颗粒内扩散模型拟合结果显示,颗粒内扩散不是唯一的反应速率控制步骤。     

铜在福州地热水中的腐蚀热力学

<正> 引言 福州地区蕴藏有丰富的地热资源,在开发中需要充分考虑地热水对金属设备的腐蚀问题。本文作者拟用M.Pourbaix创立的电位-pH图,从热力学角度探讨金属在本地区地热水中的腐蚀倾向。本文取铜作为研究对象,以市区东北部GW_2井的地热水作为介质。该井水温68℃;pH7.4;水质属Cl~--SO_4~(2-)-Na~+类型,经抽样分析,含量大于1ppm的有K~+、Na~+、Ca~(2+)、Fe~(2+)、Cl~-、SO_4~(2-)、HCO_3~-、CO_3~(2-)、F~-。对金属腐蚀作用较大的为Cl~-(90.04ppmSO_4~(2-)(146.97ppm)、HCO_3~-(57.97ppm)和CO_3~(2-)(4.80ppm)。因为地热水温高于25℃,故需取高温下的热力学数据绘制出高温的E-pH图,以进行判断。我们使用BASIC语言编写铜地热水系统E-pH图的电算程序,应用APPLEⅡ微机处理数据和绘图,并测出铜在地热水中的自然腐蚀电位,讨论其腐蚀倾向。     

Surface diffusivity of atomic deuterium on Ni3（Al,Ti）（110）surface with and without boron

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氢在钢中低温扩散系数

在293K～328K的温度范围内,用Devanathan-Stachurski电池装置测定了氢在A3、08F、16MnR和20G钢中的氢渗透曲线,求得氢扩散系数与温度之间的阿仑尼乌斯方程,为监测钢在使用中氢的积累提供基本参数.      

Kinetics and Boron Diffusion in the FeB/Fe2B Layers Formed at the Surface of Borided High-Alloy Steel

In the present study, boron diffusion in the surface layers of AISI M2 borided steels and the growth kinetics of the FeB/Fe₂B layers were estimated. The boriding of AISI M2 steel was performed according to the powder-pack method and was conducted at 1173-1323?K and at various exposure times. As a result of the boriding process, the diffusion-controlled growth of the FeB/Fe₂B layers was obtained at the surface of the high-alloy steel, and the kinetics of the growth process changed parabolically over time. The boron diffusion coefficients were estimated by solving two simultaneous equations based on the limits of the boron concentration in each layer, the boride incubation time, and the parabolic growth constant. With the proposed diffusion model, an expression, which describes the evolution of the FeB/Fe₂B layers, was obtained. Moreover, the proposed model and diverse empirical models presented in the literature provided a good fit to the experimental data obtained for 10?h of exposure and different boriding temperatures.     

Kinetics analysis of mullite formation reaction at high temperatures

A detailed kinetics analysis was performed on the mullite (3Al₂O₃·2SiO₂) formation reaction occurring at high temperatures ranging from ∼1600 to 1800°C. The counterdiffusion model of Al³⁺ and Si⁴⁺ fluxes was used to derive the kinetics equation of the mullite formation reaction. From the parabolic kinetics between the thickness of the mullite layer and time, the reaction rate constant (k) for the mullite formation was determined to be a function of the average diffusion coefficient of Si⁴⁺ ions. This kinetics equation can be used to estimate the mullite formation at any temperature. By substituting previous experimental data into the present kinetics equation, average diffusion coefficient values of Si⁴⁺ ions in the mullite layer were calculated and these values are in good agreement with the diffusion coefficient values calculated using Aksay’s interdiffusion equation for mullite formation. The activation energy values for the diffusion of the Si⁴⁺ ions were estimated to range from 730 to 780 kJ/mol, which are close to those obtained from previous diffusion and creep experiments.     

低温热处理CoN／CN软X射线多层膜的界面互扩散研究

在４７３－５２３Ｋ的低温退火条件下,通过对ＣｏＮ／ＣＮ软Ｘ射线多层膜一级调制峰强度增强的定量观测,研究了ＣｏＮ／ＣＮ软Ｘ射线多层膜的界面互扩散行为,产测得低至１０＾－２５ｍ６２ｓ＾－１的有效扩散系数。通过和Ｃｏ／Ｃ多层膜的结果相比较,发现Ｎ掺杂使ＣｏＮ／ＣＮ软Ｘ射线多层膜的界面互扩散行为明显不同于Ｃｏ／Ｃ多层膜,并具有如下特点：（１）有儿扩散系数和宏观扩散系数较小;（３）扩散激活能较大;（３）临床     

Characteristics of hot tensile deformation and microstructure evolution of twin-roll cast AZ31B magnesium alloys

High temperature tensile properties and microstructure evolutions of twin-roll-cast AZ31B magnesium alloy were investigated over a strain rate range from 10-3 to 1 s-1.It is suggested that the dominant deformation mechanism in the lower strain rate regimes is dislocation creep controlled by grain boundary diffusion at lower temperature and by lattice diffusion at higher temperatures,respectively.Furthermore,dislocation glide and twinning are dominant deformation mechanisms at higher strain-rate.The processing map,the effective diffusion coefficient and activation energy map of the alloy were established.The relations of microstructure evolutions to the transition temperature of dominant diffusion process,the activation energy platform and the occurrence of the full dynamic recrystallization with the maximum peak efficiency were analyzed.It is revealed that the optimum conditions for thermo-mechanical processing of the alloy are at a temperature range from 553 to 593 K,and a strain rate range from 7×10-3 to 2×10-3 s-1.     

Determination of isothermal sections of Ni-Cr-Nb ternary system

The isothermal sections of Ni-Cr-Nb ternary system at 1 323 K and 1 423 K were determined by means of diffusion triple and energy spectrum analysis (ESA). By analyzing the diffusion layers in the diffusion couples, the compounds forming in this system were identified. There are three similar compounds found at these two temperatures: Ni3 Nb, NiNb and NbCr2-R, and four similar three-phase regions are found : (Ni) (Cr) Ni3 Nb, Ni3Nb NbCr2-R NiNb, NbCr2-R (Cr) Ni3 Nb, NbCr2-R NiNb (Nb). The results show that no phase transformation happens between these tow temperatures. But the solid solubilities of the binary compounds at 1423 K become bigger than those at 1 323 K, especially the solid solubility of NbCr2-R. No ternary compound is observed.     

金刚石与钛的原子热压扩散行为的分子动力学模拟

应用分子动力学方法模拟了金刚石与钛在热压扩散过程中的原子扩散行为,模拟了不同扩散温度下金刚石与钛界面的原子扩散过程,得到了界面的原子浓度分布、扩散速度以及模拟扩散系数值;采用热压扩散法在金刚石表面镀覆钛层并测量界面的扩散带宽度。研究结果表明：在热压扩散过程中C原子的扩散速度大于Ti原子;随着扩散温度的升高,原子存在低速和快速两个扩散阶段。通过热压扩散的分子动力学模拟对模拟的扩散系数进行数据拟合,能够确定C和Ti原子的扩散因子和扩散激活能,从而简单、有效地确定原子的扩散系数计算公式。金刚石与钛扩散带宽度的计算值与实测值相近,应用分子动力学方法获得的原子扩散系数公式是可行的。     

VOLUMETRIC MASS TRANSFER COEFFICIENT BETWEEN SLAG AND METAL IN COMBINED BLOWING CONVERTER

The effects of operation parameters of combined blowing converter on the volumetric mass transfer coefficient between slag and steel are studied with a cold model with water simulating steel, oil simulating slag and benzoic acid as the transferred substance between water and oil.The results show that, with lance level of 2.1m and the top blowing rate of 25000Nm^3/h, the volumetric mass transfer coefficient changes most significantly when the bottom blowing rate ranges from 384 to 540Nm^3/h. The volumetric mass transfer coefficient reaches its maximum when the lance level is 2.1m, the top blowing rates is 30000NmS/h, and the bottom blowing rate is 384Nm^3/h with tuyeres located symmetrically at 0.66D of the converter bottom.     

电场激活合成Mg2Si的热电性能研究

用Mg粉和Si粉通过电场激活加压辅助法（Field-activated and Pressure-assisted Synthesis,FAPAS）,在1073 K、50 MPa条件下快速实现了Mg2Si块体热电材料的一步法合成与致密化;合成过程反应物反应完全,产物的XRD曲线的Mg2Si峰型尖锐,占产物含量的99.5%。合成样品的Seebeck系数、电导率、功率因子分别在562K、773 K、600 K时达到最大值,分别为445μVK-1、54.4 Scm^-1、4.35 W/cmK^2。通过对比多种方法合成的Mg2Si热电材料的热电性能发现,FAPASA样品的功率因子比其它方法具有明显的优势。     

固-气共晶定向凝固法测定氢在金属熔体中的扩散系数

基于固-气共晶定向凝固技术和单相合金的定向凝固原理,提出一种测定氢在金属熔体中扩散系数的方法。以Cu-H2系为例,研究氩气分压和熔体过热度对氢在金属熔体中熔点处扩散系数的影响。结果显示,不同工艺参数条件下所获得的扩散系数差别很小,且采用该方法获得的氢在金属Cu熔体中温度相关的扩散系数方程与文献中采用实验方法获得的结果吻合得较好,并验证了该方法的可行性。除Cu-H2系外,还计算了氢在金属Mg、Si以及Cu-34.6%Mn合金熔点温度熔体中的扩散系数值以及温度相关的扩散系数方程。     

W热力学性质和弹性性质的第一性原理研究

使用第一性原理方法结合准谐近似理论研究了立方结构钨的热力学性质,包括平衡体积V、体弹模量B0、线膨胀系数α、熵S、振动自由能F、等压热容CP和等容热容CV随温度的变化关系。在计算体系的线膨胀系数、熵、振动自由能、等压热容和等容热容时考虑了热电子和热振动对自由能的贡献。计算结果表明：考虑热电子对自由能贡献后得到的线膨胀系数、熵、振动自由能和等压热容在0~2000 K范围内均与实验值符合较好。在得到平衡体积随温度变化的基础上,计算了钨立方结构的弹性性质,得到了弹性常数、体积模量、剪切模量和杨氏模量随温度的变化关系,所得结果与实验测量值符合较好