SiC/M-Al金属间化合物界面固相反应研究进展

SiC/M(M=Ti,Ni,Fe)-Al金属间化合物界面固相反应的研究是材料科学领域内一个重要的理论研究课题。SiC/M-Al界面固相反应及界面状态决定着SiC/M-Al固相扩散焊接件及SiC/M-Al基复合材料的力学性能和使用性能。文章就近年来SiC/M-Al界面固相反应的研究成果进行综述,包括反应热力学与相平衡分析,反应层的组成与结构以及反应动力学与反应微观机制;并就目前研究的不足以及如何改进提出了一些看法。     

溶剂对热力学平衡性质的影响

综合讨论了溶剂对热力学平衡性质影响的新尺度－转移自由能，以及在化学热力学方面的应用。结果表明，溶剂对热力学平平衡性质的影响主要是静电作用力所致。     

CPA方程结合RG理论计算甲醇、水、氨的性质

醇类、水、氨等流体在工业上有着广泛的应用,但由于氢键作用形成分子缔合,使用简单状态方程难以精确描述其热力学性质;而在近临界区,由于浓度涨落的长程关联,使其描述则更为困难。该文在CPA(cubic plus association)状态方程的基础上,用重整化群理论修正Helmholtz自由能来考虑涨落的影响,计算了甲醇、水和氨在近临界和远离临界点区域的p-ρ-T性质。结果表明:该方法显著改善了临界参数和近临界区的气液相平衡数据的描述情况,在单相区的预测精度也较高,适用于缔合流体热力学性质的研究。     

空化初生的热力学影响研究

从非平衡态热力学理论出发,建立了有相变发生时球形气核与围流液体之间能量流和物质流的方程式．在此基础上,确定了自由气核空化初生的条件,并结合气泡动力学对此进行了深入的讨论,提出了判断满足空化初生条件的标准     

光激发引起的菌紫质人工膜系统界面自由能

应用界面双层模型和界面固有化学势的概念 ,对菌紫质人工膜系统C(N)端界面受光激发所引起的界面自由能变化进行了初步的探讨 ,导出了bR相、C或N端界面能的一般表达式 ,及三类具体的菌紫质人工膜系统 (液 bR 液 ,固 bR 固 ,液 bR 固 )界面自由能的表达式 .可以看出 ,光照下的bR人工膜系统界面自由能的变化 ,不仅与物质组分相关 ,还与跨膜电势相联系 .据此 ,在一定范围内提高bR膜系统溶液的温度、pH值 ,以及降低跨膜电压 ,都将减少界面自由能 ,从而对系统的光驱质子泵过程产生影响 .本文研究仅局限于光照的影响 ,暂不涉及体系相结构变化的情形 .     

Generic mechanism for generating a liquid-liquid phase transition

Recent experimental results indicate that phosphorus--a single-component system--can have a high-density liquid (HDL) and a low-density liquid (LDL) phase. A first-order transition between two liquids of different densities is consistent with experimental data for a variety of materials, including single-component systems such as water, silica and carbon. Molecular dynamics simulations of very specific models for supercooled water, liquid carbon and supercooled silica predict a LDL-HDL critical point, but a coherent and general interpretation of the LDL-HDL transition is lacking. Here we show that the presence of a LDL and a HDL can be directly related to an interaction potential with an attractive part and two characteristic short-range repulsive distances. This kind of interaction is common to other single-component materials in the liquid state (in particular, liquid metals), and such potentials are often used to describe systems that exhibit a density anomaly. However, our results show that the LDL and HDL phases can occur in systems with no density anomaly. Our results therefore present an experimental challenge to uncover a liquid-liquid transition in systems like liquid metals, regardless of the presence of a density anomaly.     

基于能量耗散的应力引起的土体各向异性模型

从热力学定律出发,介绍了土体受力变形过程中能量耗散函数的合理表达形式,据此导出耗散应力空间中的屈服函数及流动法则.分析迁移应力,确定了真实应力空间中的屈服函数,并采用旋转硬化规律考虑应力引起的土体各向异性.这种模型以自由能函数和耗散函数为基础进行整体构造,自动满足热力学第二定律,不需要引入其他假定.提出了利用弹塑性本构模型计算三轴试验曲线的方法.采用遗传优化算法拟合了某土料三轴排水剪切试验结果,确定了模型参数.用得到的模型参数计算绘出其他固结应力下三轴排水剪切曲线,并与实测曲线比较,验证了模型的有效性.     

冶金热力学计算软件的开发

在冶金热力学研究中,一般会碰到很多热力学数据及其计算分析,为快速精确地进行热力学计算,利用VC＋＋语言的计算功能,研制了基于数据库信息的冶金热力学计算软件。软件数据库中存储了冶金研究中常用物质的热力学性质参数供用户使用并且该数据库可根据用户的需求进行扩充。用户可利用数据库中热力学数据进行冶金过程反应的热力学计算,得到如反应吉布斯自由能、反应热及反应平衡常数等基本热力学参数并将计算结果生成数据文件作为绘图软件的输入。     

不可逆过程中自由能减小率的计算

基于非平衡系统的局域平衡假设,对有物质输运的不可逆过程的自由能流密度与局域自由能减小率进行了计算和讨论,为用辅助热力学函数研究不可逆过程进行的速率问题提供有益的参考.     

CALPHAD modeling of molar volume

Databases concerning basic physical properties of materials, such as molar volume, density, thermal expansion coefficient, elastic constants, thermal conduc- tivity, etc., are essential parts of the underlying knowledge for materials design. While thermodynamic databases provide chemical driving forces and phase equilibrium data, physical property databases provide essential physical parameters, such as volume, lattice constant, lattice misfit, elastic energy, interfacial energy, etc., for phase transfor- mation and microstructure simulations. Combined with thermodynamic databases, physical property databases established on the basis of the calculation of phase diagram （CALPHAD） method can be used to calculate physical properties together with phase equilibria, phase fractions, phase compositions, and thermodynamic properties for multi-component and multi-phase material systems and for the constituent phases. In this paper, we will discuss in detail various volume models based on the CALPHAD method which are capable of describing experimental data in a wide range from cryogenic temperatures to melting points, from the atmospheric pressure to high pressures for pure substances as well as multi-component and multi- phase materials.     

Atomic phase diagram

Based on the Thomas-Fermi-Dirac-Cheng model, atomic phase diagram or electron density versus atomic radius diagram describing the interaction properties of atoms of different kinds in equilibrium state is developed. Atomic phase diagram is established based on the two-atoms model. Besides atomic radius, electron density and continuity condition for electron density on interfaces between atoms, the lever law of atomic phase diagram involving other physical parameters is taken into account, such as the binding energy, for the sake of simplicity.     

再论经典连续统力学基本定律和均衡方程体系

指出了经典连续统场论中惯用的热动力学基本定律的不完整性．提出了经典热力连续统力学的新的热静力学和热动力学的第一和第二基本定律．由它们可以自然地和同时推导出热静力学的所有平衡方程和熵不等式及热动力学所有均衡方程和熵率不等式．     

元系统热力学及其对铁电和超导等系统的应用

发展了一种元系统的热力学,用微分拓扑的方法,仅从热力学第一定律出发,就证明了元系统的热力学温度函数和熵函数的存在性,导出元系统的热力学基本方程,其结果可推广到平衡态和非平衡态的宏观系统。文中也讨论了元系统热力学应用于铁电、超导等系统的热力学的可能性。     

Bridging properties of the debonded interface with frictional sliding

A theoretical model simulating the properties of frictional bridging is presented and relatively perfect stress solutions for the fiber and matrix are obtained. Based on the energy equilibrium in the process of interfacial debonding, an expression for the energy release rate G is derived to explore the interfacial fracture properties. By introducing an interfacial debonding criterion G≥Γ_i, a method for determining the critical debond length is proposed and the bridging constitutive relationship is also obtained. Numerical calculations are conducted for the fiber-reinforced composite SCS-6/T_i-6Al-4V and the results are also compared with those obtained by using other existing models.     

蚊子复眼的防雾原理

蚊子复眼具有超疏水性和防雾功能,主要归功于蚊子复眼具有特殊的微、纳米分级结构。建立了复眼的微、纳米分级结构模型;并从界面疏水稳定性和热力学的角度进行了分析。界面稳定性分析表明蚊子眼微米和纳米级结构可抵抗的最大压力分别为67.2 k Pa和181 k Pa,能够有效地抵御外部雾滴的润湿。对于纳米尺度的小雾滴,由于受尺度和线张力的影响,类Wenzel状态的自由能高于类Cassie状态,因此在雾化过程中总是形成类Cassie状态,并进而形成Cassie状态。由于微米结构特别的半球形状和紧密排列,能够形成锥形疏水毛细管,这一锥形毛细管能够在雾滴长大过程中将雾滴从微结构内部排出,从而实现防雾。蚊子复眼上小尺度的纳米结构是实现防雾的基础和关键。     

新型氧分子O4的理论计算研究

基于密度泛函理论的“自由团簇计算法”计算了实验上发现的新型氧分子O4的电子结构.计算了2种可能的空间结构——正方形和正四面体,分别得到了这2种结构的中性分子O4,正一价分子O 4和负一价分子O-4的基态电子结构,并根据能量最低原则确定了各自的结构参数,从而得到了O4分子2种结构的基态总能量、一价电离能及电子亲合势能.与氧原子、普通氧分子O2和臭氧分子O3的计算结果比较,显示O4分子可以以正方形结构或正四面体结构形式存在,其中正方形结构更有可能是O4分子的真实空间结构.     

单链晶体的平衡态分析

本文用统计力学的方法分析了单链晶体的平衡态．通过计算得到平衡态尺寸，平衡态尺寸与温度及单链的分子量有关．从单链晶体的热力学分析也得到了类似的平衡态尺寸表示式．比较两个结果，可从分子理论的基础上来理解单链晶体的侧表面自由能及折迭表面自由能．     

形状记忆合金本构模型的热力学框架

基于形状记忆合金(SMAs)在相交过程中的热力学势和能量耗散来建立形状记忆合金的本构模型框架，通过采用不同独立变量(应力、应变、温度和熵)的组合来选择不同的能量函数(内能、Helmhohz自由能、Gibbs自由能和焓)，用内状态变量考虑相交过程中的能量耗散，则SMAs的本构模型完全可以由热力学势及能量耗散函数来建立，实例表明其可行性.     

Simulation of phase transition process using lattice Boltzmann method

A new lattice Boltzmann model based on SC model, is proposed to describe the liquid-vapor phase transitions. The new model is validated through the simulation of the one-component phase transition process. Compared with the simulation results of van der Waals gas and the Maxwell equal-area construction, the results of the new model have a better agreement with the analytical solutions than those of SC and Zhang models. Since the obtained temperature range and the maximum density ratio in this model are expanded, and the magnitude of maximum spurious current is only between those of SC and Zhang models, it is believed that this new model has better stability than SC and Zhang models. Consequently, the application scope of this new model is expanded compared with the existing phase transition models. According to the principle of the corresponding states in engineering thermodynamics, the simulations of ammonia and water phase transition process were implemented using this new model with different equations of state. Compared with the experimental data of ammonia and water, the results show that the Peng-Robinson is the best equation of state to describe the phase transition process of ammonia and water. Especially, the simulation results of ammonia with Peng-Robinson equation of state have an excellent agreement with its experimental data. Therefore these simulation results have a significant influence on the real engineering applications.     

Ising格子流体相平衡的MonteCarlo模拟

将带空穴偏倚取样的Ｗｉｎｄｏｍ插入粒子法应用于Ｉｓｉｎｇ格子模型，求得了Ｉｓｉｎｇ格子流体在不同温度、不同密度下的剩余化学位，并通过热力学关系求得了系统的化学位、压力和压缩因子；计算了系统的内能涨落与温度的关系，并据此求得了系统在临界点附近的比热尖峰。