偏晶溶液相分离过程的实时观测研究

为了揭示自由落体条件下偏晶合金壳核组织的形成机制，基于相似性原理设计了一种环形温度场，对丁二腈-52.6mol%H₂O偏晶溶液的相分离过程进行了实时观测. 发现在两个不混溶液相的分离过程中，富水相液滴经历了“析出→迁移→凝并→聚集"运动过程，最终形成以富水相为中心的两层壳核组织. 同时测定了液滴的运动速率，并对Marangoni迁移速率进行了理论计算，两者能够较好地符合. 由此证实了在偏晶溶液的相分离过程中，第二液相主要是在温度梯度的驱动下产生Marangoni迁移. 这一实验直观地再现了落管无容器处理过程中液滴内部的相分离过程. 关键词： 相分离 偏晶溶液 Marangoni迁移 微重力     

超高压接触变质过程中元素迁移的SRXRF研究

采用独特的样品组装方法,实验模拟超高压榴辉岩相接触变质条件,研究斜长角闪岩-CaCO₃(－H₂O)体系在超高压变质作用条件下元素的迁移特性.对经接触变质后的岩石样品进行SRXRF研究,表明压力增加不利于Ca,Sr,Fe的扩散迁移,而温度的作用则不如压力明显.超高压变质条件下Sr的迁移性比Ca,Fe要高,Sr与Ca将发生分离,而Fe的迁移特性与Ca相似;而H₂O的参与将大大促进各元素的迁移速率,其作用远远超过同样为地球内部主要流体组份的CO₂.     

声悬浮条件下黏性液滴的扇谐振荡规律研究

采用单轴式声悬浮方法研究了黏度μ =0.94-75.65 mPa·s的甘油-水溶液液滴的扇谐振荡规律. 发现一定阶数的振荡模式存在一定的临界黏度μ_c, 只有当μ < μ_c时, 该阶扇谐振荡才能被激发. 实验测定了声场调制幅度η = 0.23 时, l =2-9 阶扇谐振荡的临界黏度, 发现ln μ_c与l近似呈线性递减关系. 采用参数共振理论分析了黏性液滴的扇谐振荡过程, 发现激发扇谐振荡的液滴赤道半径扰动阈值h_c正比于液滴黏度μ, 并随l增大而增大, 因此扇谐振荡难以在高黏度和高阶模式下发生. 实验还发现, 各阶扇谐振荡的振幅和共振频率宽度随液滴黏度增大而减小, 黏度对液滴本征频率无明显影响.     

基于约束非平衡溶剂化理论的对硝基苯胺π-π*光谱移动 (cited: 1)

采用共沉淀法制备不同组分类水滑石前驱体Co-M-Al和Co-M-Ce-Al (M=Zn, Ni, Cu)复合氧化物催化剂催化分解N₂O. 结果表明,Co-M-Al系列氧化物催化剂的催化活性Co-Ni-Al系列>Co-Zn-Al系列>Co-Cu-Al系列;CeO₂添加使得催化剂催化活性进一步提高,N₂O分解温度T₅₀和T₉₀均下降80 oC;继续负载碱金属K也使氧化物催化剂催化活性提高,N₂O分解温度T₅₀和T₉₀下降约50 oC.     

OH+C2H3F的反应机理及产物支化比反应的理论研究

本文对HOC₂H₃F可能解离通道的势能面进行从头算CCSD(T)/CBS//B3LYP/6-311G(d,p)计算,同时对速率常数进行Rice-Ramsperger-Kassel-Marcus计算. 生成主要产物CH₂CHO+HF最有利的反应途径是OHC₂H₃F→i2→TS14→i6→TS9→i3→TS3→CH₂CHO+HF,其中速率决定步骤是HF通过TS11从CO桥接位置解离,能量比反应物高3.8 kcal/mol. 借助中间态TS14,F原子从C_α迁移到C_β位置生成CH₂O+CH₂F,然后通过中间态TS16,H从O迁移到C_α位置;通过中间态TS5,C-C键断裂生成产物,其能量比反应物低1.8 kcal/mol,比TS11低4.0 kcal/mol.     

硫酸催化乙二醛气体相水化反应机理和速率常数理论计算研究

采用M06-2X和CCSD(T)高阶量化计算和传统过渡态理论研究硫酸催化乙二醛气体相水化反应.对HCOCHO+H₂O, HCOCHO+H₂O+H₂O, HCOCHO+H₂O+H₂O, HCOCHO+H₂O...H₂SO₄和HCOCHO+H₂O+H₂SO₄五个路径的反应机理和速率常数进行了研究.计算结果表明硫酸具有较强的催化能力,能显著减小乙二醛水化反应的能垒,在CCSD(T)/6-311++G(3df,3pd)//M06-2X/6-311++G(3df,3pd)理论水平,当硫酸分子参与乙二醛水化反应时,反应能垒从37.15 kcal/mol减少至7.08 kcal/mol.在室温条件下,硫酸催化乙二醛水化反应的反应速率1.34×10^-11 cm³/(molecule.s),是等量水分子参与乙二醛水化反应的速率的10¹²倍,大于乙二醛与OH自由基反应的反应速率1.10×10^-11 cm³/(molecule.s).这表明大气条件下,硫酸催化乙二醛水化反应可以发生,同乙二醛与OH自由基反应相竞争.     

有限反常核

从一个相对论性核模型解得了有限反常核,并找到了两个临界质量数A₁=85和A₂=165,只当质量数A≥A₁时才存在束缚的反常核,当A≥A₂时反常核的第核子结合能大于正常核.当A>3310时反常核由于库伦能而变得非束缚.     

基于反应力场的分子动力学方法研究氢在钯表面的分解

基于二阶矩近似反应力场方法构建的全维度势能面研究了氢分子及其同位素分子在钯表面的分解过程.在构建势能面的过程中数据库中只包含了氢分子与钯（111）表面相互作用的相关信息,该势能面在研究氢分子在钯（100）表面上的分解过程中表现出了非常好的可转移性.结果表明,氢分子及其同位素分子在钯（111）与钯（100）表面上的分解系数S₀均随着入射能量的增加呈现非单调变化,并且通过固定分子取向的方法发现同核分子（H₂、D₂和T₂）最有利分解取向角为90°,而异核分子（HD、HT和DT）受质心偏移的影响,其最有利分解取向角向大角度偏移.     

F−(H2O)+CH3I配体交换反应动力学

本文介绍F^?(H₂O)+CH₃I→[FCH₃I]^?+H₂O在交叉分子束碰撞能量0.3∽2.6 eV的配体交换动力学成像结果. 产物的动能受到弱键结合配合物的稳定性的影响,大量水分子的内部激发不利于中间物有效的能量重新分配,随着碰撞增加,低动能受到抑制. 在0.3 eV时,内部亲核取代非常重要,为形成I^?和I^?(H₂O)的竞争性亲核取代途径提供了依据.     

液态三元Fe-Sn-Si/Ge偏晶合金相分离过程的实验和模拟研究

本文采用自由落体实验技术和格子玻尔兹曼计算方法研究了低重力条件下液态Fe-Sn-Si/Ge合金的相分离过程. 实验发现, 二种合金液滴在自由下落过程中均发生显著的液相分离, 形成了壳核和弥散组织. 当Fe-Sn-Si合金中的Si元素被等量的Ge元素替换后, 壳核组织中富Fe区和富Sn区的分布次序会发生反转. 计算表明, 在液相分离过程中冷却速率、Marangoni对流和表面偏析对壳核构型的选择和弥散组织的形成起决定性作用.     

Macrosegregation driven by movement of minor phase in (Al0.345Bi0.655)90Sn10 immiscible alloy

Formation of macrosegregation structure in (Al_0.345Bi_0.655)₉₀Sn₁₀ (mass percent, the same below) immiscible alloy was investigated by spraying its melt into silicone oil. Two kinds of typical macrosegregation structures were obtained in the dispersed alloy spheres: core/shell structure and crescent structure. Based on the estimated temperature field inside the alloy spheres, the velocities of thermal Marangoni, solutal Marangoni, and Stokes motions of the Bi-rich minor droplets were calculated. Analysis shows that surface segregation, Soret effect, thermal Marangoni motion, solutal Marangoni motion, and Stokes motion play a key role in the formation of Al/Bi–Sn core/shell structure. If the liquid alloy spheres solidify on the condition that the radius of the Bi-rich minor droplets is smaller than a critical value, it will form Al/Bi–Sn core/shell structure, while the crescent structure will be formed when the liquid alloy spheres frozen on the condition that the radius of the Bi-rich minor droplets exceeds the critical value.     

Details of Structure Formation During the Induction Period of Spinodal-Type Polymer Crystallization

An unexpected type of primary crystal nucleation is described, involving spinodal decomposition (SD) type microphase separation due to the orientation fluctuations of rigid segments prior to crystal nucleation. This type of mechanism was found by the present authors about 10 years ago, and recently, it was theoretically revealed by Olmsted et al. to be one of three types of primary crystal nucleation: the well-known homogeneous crystal nucleation directly from the liquid–crystal coexistence domain, which occurs at higher temperatures above the binodal temperature T _b , crystal nucleation after binodal microphase separation between T _b and spinodal temperature T _s , and that after SD below T _s . The detailed experimental results for the spinodal-type crystal nucleation, especially the temperature dependence of characteristic wavelength in SD, are explained as well.     

Phase separation and rapid solidification of liquid Cu<Subscript>60</Subscript>Fe<Subscript>30</Subscript>Co<Subscript>10</Subscript> ternary peritectic alloy

The metastable liquid phase separation and rapid solidification of Cu₆₀Fe₃₀Co₁₀ ternary peritectic alloy were investigated by using the drop tube technique and the differential scanning calorimetry method. It was found that the critical temperature of metastable liquid phase separation in this alloy is 1623.5 K, and the two separated liquid phases solidify as Cu(Fe,Co) and Fe(Cu,Co) solid solutions, respectively. The undercooling and cooling rate of droplets processed in the drop tube increase with the decrease of their diameters. During the drop tube processing, the structural morphologies of undercooled droplets are strongly dependent on the cooling rate. With the increase of the cooling rate, Fe(Cu,Co) spheres are refined greatly and become uniformly dispersed in the Cu-rich matrix. The calculations of Marangoni migration velocity (V _M) and Stokes motion velocity (V _S) of Fe(Cu,Co) droplets indicated that Marangoni migration contributes more to the coarsening and congregation of the minor phase during free fall. At the same undercooling, the V _M/V _S ratio increases drastically as Fe(Cu,Co) droplet size decreases. On the other hand, a larger undercooling tends to increase the V _M/V _S value for Fe(Cu,Co) droplets with the same size. Supported by the National Natural Science Foundation of China (Grant Nos. 50121101 and 50395105) and the Scientific and Technological Creative Foundation of Youth in Northwestern Polytechnical University of China (Grant No. W016223)     

Temperature dependence of Cu2O orientations in oxidation of Cu (111)/ZnO (0001) by oxygen plasma

The role of temperature on the oxidation dynamics of Cu₂O on ZnO (0001) was investigated during the oxidation of Cu (111)/ZnO (0001) by using the oxygen plasma as oxidant. A transition from single crystalline Cu₂O (111) orientation to micro-zone phase separation with multiple orientations was revealed when the oxidation temperature increased from 300 ℃ to higher. The experimental results clearly showed the effect of oxidation temperature with the assistance of oxygen plasma on changing the morphology of Cu (111) film and enhancing the lateral nucleation and migration abilities of cuprous oxides. A vertical top-down oxidation mode and a lateral migration model were proposed to explain the different nucleation and growth dynamics of the temperature-dependent oxidation process in the oxidation of Cu (111)/ZnO (0001).     

溶胶-凝胶法制备ZnO薄膜的成核-生长和失稳分解研究

采用溶胶-凝胶法在ZnWO₄单晶上制备出透明的ZnO薄膜.通过光学显微镜观察了Z nO薄膜的表面形貌.实验结果表明，ZnO薄膜的形成经历了表面成核，晶粒长大和岛的形成三 个不同的阶段.由于ZnO晶核是在非平衡条件下生长的，在生长过程中不可避免地出现了枝晶 生长和分形生长以及失稳分解. 关键词： 氧化锌薄膜 成核 枝晶生长 分形生长 失稳分解     

The Effect of Preparation Temperature on Phase Transitions of N-Isopropylacrylamide Gel

The spinodal decomposition of N-isopropylacrylamide (NIPA) gels prepared at various onset temperatures, T _on was studied by photon transmission. It was observed that the increase in turbidity is much faster in a gel prepared at higher T _on than at lower T _on values, which indicated that the NIPA-water system reaches the spinodal decomposition much faster for a gel prepared at high T _on. It is understood that a NIPA gel prepared at high T _on possesses more heterogeneities which are gained during gelation and has a low spinodal temperature, T _s. However, NIPA gels prepared at lower T _on values go to spinodal decomposition at higher T _s values.     

A Videographic Study of Dynamic Phase Separation for Immiscible Solutions under Acoustic Levitation Condition

The transparent aqueous solutions of succinonitrile(SCN) provide an effective model system to simulate the phase separation process of various advanced materials.Here we report a real-time and in-situ study of phase separation dynamics for the SCN-15%H_2O,SCN-48%H_2O and SCN-70%H_2O solutions implemented by high-speed CCD videography together with acoustic levitation technique.It is found that liquid phase separation induces an unsteady state of drop rotation under levitated conditions.The resultant centrifugal force plays the dominant role in the migration of secondary liquid globules.The most desirable homogeneously dispersive structures can only be derived from the earlier stage of phase separation,whereas three kinds of macrosegregation are always the finally stable structure patterns.The migration velocity of minor liquid phase displays the nonlinear feature owing to the variations of globule location and centrifugal force.The surface tensions and volume fractions of immiscible phases also show a conspicuous influence upon the evolution dynamics of separation morphology.     

Properties of metastable ising models evolving under the Swendsen-Wang dynamics

The behavior of the metastable nearest neighbor Ising model governed by Swendsen-Wang dynamics (SW) is investigated ind=2. The results are compared to those obtained in standard Metropolis dynamics. Both the SW and Metropolis systems are observed to decay from the metastable state via the formation of nucleating droplets. Nucleation rates are measured and found to agree with those predicted by classical nucleation theory. The growth rates of the droplets are observed to differ between the two dynamics. In addition, the dynamic critical exponentz is measured in a mean-field (Curie-Weiss) metastable Ising model at the spinodal. It is found that for SW dynamics,z=2. Since this is the same value as that obtained in the Metropolis case, this result shows that SW does not change the dynamical universality class at the spinodal.