液态结构与性质关系Ⅰ——Mg熔体的运动黏度及与熔体微观结构的关系

采用坩埚扭摆振动法测量Mg熔体的运动黏度,得到935—1190 K温度区间高精度的黏度-温度关系曲线v(T),发现升温和降温过程中Mg熔体的黏度随温度变化呈指数规律单调递增(减),没有发生异常变化和滞后现象.同时,利用液态结构中原子集团演变行为的物理模型,计算得出该温度区间Mg熔体的主要结构信息参数——原子集团尺寸-温度关系曲线d(T);通过对实验和计算数据的综合分析,发现Mg熔体的运动黏度和原子集团尺寸均为温度的单值函数,且二者之间存在线性的函数关 关键词： 金属熔体 结构与黏度相关性 原子集团演变 线性关系     

Ni-15%Mo合金熔体热物理性质的Monte Carlo模拟

采用EAM势对6×6×6的Ni-15%Mo合金熔体进行Monte Carlo模拟,通过对不同温度下获得的NVT系统的平衡态统计分析得出Ni-15%Mo合金熔体在过冷态和过热态时的热物理性质.通过构造系统生成新表面,表面张力做功使系统能量发生改变,从而得到液态表面张力的模拟结果.Ni-15%Mo合金熔体的表面张力在1500—2000 K的温度范围内,随温度的变化规律为σ=1.918-1.130×10^-3（T-T_m） N/m 关键词： Monte Carlo模拟 表面张力 比热 Ni-15%Mo合金     

壁面材质和温度场对熔融硅润湿角的影响

本文建立了毛细模型, 采用微流动两相流水平集法计算了熔融态硅液与壁面的润湿角, 以人造金刚石作为壁面材料的计算结果与实验结果进行比较, 验证了该模型和计算方法的正确性. 在此基础上, 分别选用碳化硅、石墨和人造金刚石作为壁面材料, 探讨了不同壁面材料表面张力和壁面黏附力对润湿角的影响规律. 结果发现, 相同温度下的毛细力作用使得熔融硅液出现起伏上升现象; 润湿角均有不同程度的减小然后增大, 最终趋于稳定; 初始阶段, 由于气/熔融硅液表面张力与气/壁面表面张力之差变化较大, 液面起伏波动较大; 随后趋于稳定上升. 同时发现石墨作为壁面材料时, 以上变化更易趋于稳定. 该研究为熔体中生长晶体硅获得更稳定的生长环境提供了理论依据.     

表面光散射法正十六烷高温热物理性质研究

为拓展高温下流体黏度和表面张力的测量,改进了原有的表面光散射实验系统,将实验的温度区间拓展至570K,改进后的系统在整个温区内测量黏度和表面张力的扩展不确定度分别为2%和1%(k=2)。利用新的实验系统研究了正十六烷在353~547 K温度范围内的黏度和表面张力,并利用实验数据分别拟合了温度倒数多项式和van der Waals方程,在全温度范围内实验值与方程的偏差均在1%之内。在较宽的温度范围内获得的正十六烷的高精度黏度和表面张力数据和方程,可以作为参考数据和方程,用于相关仪器的标定和检验。     

液态Sn的粘度及其熔体微观结构的变化

通过对液态Sn的粘度的系统测量和分析,借助DTA-TG综合热分析方法,研究了金属熔体Sn的粘度随温度变化的规律和熔体微观结构的变化.结果表明,Sn熔体的粘度随温度的变化呈明显的不连续性,根据粘度的变化可以将熔体状态分为高温区、中温区和低温区,各温区间存在粘度突变温度点.在突变温度点处,金属熔体Sn可能发生了微观结构的变化.?     

溅射Al对AlN的“润湿”与钎焊

由于润湿性不佳, 难以实现金属钎料对陶瓷的无过渡层直接钎焊, 本文在研究了溅射Al薄膜对AlN的“润湿”作用的基础上, 通过磁控溅射的方法在AlN表面沉积Al基薄膜作为钎料, 在真空条件下对AlN陶瓷进行了直接钎焊. 采用高景深光学显微镜、扫描电子显微镜和X射线能量分散谱表征了钎焊接头和剪切断口的组织及形貌. 结果表明, 高能量溅射Al粒子对AlN的撞击可以形成只有850 ℃以上高温才可获得的Al-N化学键, 实现Al对AlN的“润湿”, 使Al基薄膜钎料能够在较低的温度(≥ 510 ℃)对AlN直接钎焊. 此方法获得的Al/AlN接头的剪切强度达到104 MPa, 含3.8 at.% Cu的Al合金钎料接头强度可进一步提高到165 MPa, 它们的剪切断裂都产生于钎缝金属之中; 增加钎料中的Cu含量至9.1 at.%后, Cu在钎缝与陶瓷界面的偏聚使接头的剪切强度降低为95 MPa. Al-20 at.% Ge合金可以将钎焊温度降低至510 ℃, 但Ge在钎缝与陶瓷界面的偏聚使接头在48 MPa发生断裂.     

高温金属熔体黏度突变探索

高温金属熔体的黏度是衡量液态金属动力学性质的一个重要指标,是高温金属熔体的基本物理性能之一.熔体的黏度在表征脆性系数、金属玻璃形成能力的大小和液-液相变现象方面起关键性作用.本文在介绍高温金属熔体黏度测量方法的基础上,综合评述了单质、二元和多元合金黏度随温度的变化规律和黏度突变特征,分析了黏度突变研究的物理意义,并指出高温金属熔体黏度今后研究的发展方向。     

液态结构与性质关系Ⅱ——Mg-9Al熔体的运动黏度及与熔体微观结构的关系

采用坩埚扭摆振动法测量Mg-9Al熔体的运动黏度,得到890—1190 K温区内高精度的黏度-温度关系曲线ν(T),发现升温过程中黏度随温度升高发生异常变化,当温度升高至1000—1075 K时,黏度由快速增大转变为逐渐减小,即发生转折变化;在随后的降温和第二次升温过程中,黏度随温度变化呈指数规律单调递增(减),符合Arrhenius方程式.在实验研究基础上,采用剩余键结构模型和"平均原子集团"演变行为的计算模型讨论Mg-9Al熔体的黏度与微观结构之间的相关性,结果表明:类关键词： 合金熔体 结构与黏度相关性 剩余键结构 平均原子集团模型     

纯铝熔体的微观动力学行为

利用反映原子多体相互作用的紧束缚模型及分子动力学计算机模拟技术,研究了液态金属Al的熔体结构与微观动力学行为。计算了纯金属熔体Al在不同温度下的双体分布函数,平均平方位移及速度自相关函数。模拟结果与实验结果吻合得很好,表明紧束缚模型能够描述纯铝熔体中原子间的相互作用     

悬垂液滴研究及表面张力和润湿角测定

对光滑固体表面下悬挂的液滴进行了理论分析,建立了悬垂液滴特征尺寸R和H与液滴表面张力σL和固液界面润湿角θ之间的关系式,计算发现对于特定的ρ,σL,θ值,液滴质量m与固液界面润湿半径R、液滴高度H满足特殊的曲线关系.利用此关系可以同时测量液滴的表面张力σL以及固液界面间的润湿角θ.     

Theoretical assessment on mixing properties of liquid Tl–Na alloys

Thermodynamic and structural properties of mixing of molten Tl–Na alloys at 673 K have been investigated using quasi-chemical model. To understand the mixing behaviour in more detail, emphasis is placed on the role of interaction energy term, and viscosity and surface tension of the alloys have also been analysed under statistical considerations. Our study shows negative deviation from the Raoultian behaviour in the properties of Tl–Na alloy thereby indicating hetero-coordination in the Tl–Na melt at 673 K in the full range of concentration. Theoretically, computed thermodynamic data at 673 K agree very well with the corresponding experimental data. The viscosities of the alloys computed from Kaptay equation show small negative deviation and those computed from Singh and Sommer’s formulation show small positive deviation from ideal values while the Budai-Benko-Kaptay equation predicts noticeable negative deviation in Na-rich end and positive deviation in Tl-rich end of the composition. The calculations of surface tension reveal that results obtained from layered structure approach and compound formation model are in good agreement in the Na-rich side and in reasonable agreement in Tl-rich side of the composition, while those computed from Butler equation show noticeable deviations in the intermediate compositions. Both the viscosity and surface tension of liquid Tl–Na alloys increase with addition of Tl-component, viscosity having approximately linear variation with concentration. The study shows that there is non-linear variation in surface composition with bulk concentration and for most of the compositions the surface of the alloy is enriched with Na-atoms which segregate to the surface.     

The surface tension of liquid Cu-Fe-Sb alloys

The results of study on the influence of temperature and iron and antimony on the surface tension of liquid ternary Cu-Fe-Sb systems are presented. The measurements were carried out with the sessile drop method, in a broad range of the alloy additions concentration (Fe and Sb). It was demonstrated that the surface tension varies as a linear function of temperature and concentration of iron. It was also demonstrated that antimony, in examined alloys, shows the properties characteristic of a surface-active substance, significantly reducing the surface tension value. The changes of the surface tensions as a function of concentration of antimony were described with the Szyszkowski's equation. Composition of surface layer, enriched with an antimony, was determined basing on the model, which used data regarding properties of binary systems. The surface tension values of Cu-Fe-Sb systems was also computed from model and compared with experimental data. A good agreement was obtained.     

基于范德瓦尔斯表面张力模式液滴撞击疏水壁面过程的研究

液滴撞击疏水壁面过程的研究在介观流体力学和微流体作用材料科学的研究中具有重要的理论意义和工程价值. 论文在SPH方法中引入范德瓦尔斯状态方程处理液滴表面张力, 考虑流体粒子之间远程吸引, 近程排斥的内部作用力, 提出了流体粒子与疏水壁面粒子间势能函数与表面张力相结合的作用模式. 通过模拟真空条件下两个静止的等体积液滴相互融合的过程, 验证了计算模式在模拟液滴的表面张力中的有效性. 采用该模式模拟的液滴撞击疏水壁面过程, 不仅能够有效地模拟液滴撞击壁面后的变形过程, 而且清晰地模拟出液滴的回弹、腾空以及二次撞壁现象的完整过程. 模拟结果与液滴撞击疏水壁面的实验结果以及VOF模拟结果符合较好, 表明本文所提出的表面张力和疏水壁面作用力处理模式对模拟液滴撞壁过程具有实际应用价值.     

二甲基亚砜水溶液表面张力及粘度与氢键的拉曼光谱研究

利用ZL-10型全自动界面张力仪(柏金环法)和NDJ-5S型数显粘度计测量体积分数为5%～100%的二甲基亚砜(DMSO)水溶液及超纯水,得到表面张力和粘度的变化规律。用拉曼光谱仪测量不同浓度DMSO水溶液的拉曼光谱,得到体系中含氢键作用的拉曼频移变化规律。实验结果表明,DMSO水溶液的表面张力随浓度的变化受DMSO水溶液中氢键作用的影响,且与氢键强度成反相关。DMSO与水的氢键作用对粘度的影响较表面张力更为复杂,粘度随浓度的变化呈二次函数的反常现象,影响因素包含氢键强度,氢键网络结构和空间方向性多个方面。该研究探索一种利用拉曼光谱研究水溶液微观结构与宏观物理性质关系的实验方法。     

Surface and transport properties of Au-In liquid alloys

Thermodynamic quantities on Au-In liquid alloys have been used as the input data for the interaction parameter calculations in the framework of the complex formation model (CFM). Once the interaction energies are computed the surface (surface tension and surface composition) and transport properties (chemical diffusion and viscosity) as well as the microscopic functions (concentration fluctuations in the long-wavelength limit and chemical short-range order parameter) have been calculated. The concentration and temperature dependent surface tension values have been compared with our new set of experimental data, obtained by the large drop method in the temperature range of T = 1273-1493 K. The anomalous change of surface tension for some alloy compositions may be attributed to a retention of order in the Au-In melts which is similar to the atomic arrangement in solid Au-In.     

Production of Fine Particles from Melts of Metals or Highly Viscous Fluids by ultrasonic standing wave atomization

Ultrasonic standing wave atomization (USWA) is a new process capable of atomizing both high surface energy liquids and highly viscous liquids. Atomization is achieved through acoustic forces acting upon a liquid jet which is guided into the central pressure node of a standing wave field. Spherical metal powders with minimum mass median diameters of less than 15 μm have been produced from metal melts with surface tensions of about 0.5 N/m. Organic liquids with viscosities between 1 and 10 Pas have been atomized, yielding mass median diameters from 20 to 330 μm. The influence of different operating parameters on the mass median diameter of metal melts and highly viscous liquids was evaluated. Parameters which were varied were ambient gas pressure, vibration amplitude of the transducers, mass flow rate, density of liquid, viscosity of the liquid, surface tension and the outlet diameter. The powders and sprays were analyzed with laser diffraction particle sizers. The physical background of the atomization process is discussed and an equation for the prediction of the mass median diameter is derived.     

Correlation between the size-dependent melting and crystallization temperatures of metal nanoparticles

The correlation between the melting and crystallization temperatures of metal nanoparticles is investigated by means of the thermodynamic approach. Size-dependent variations in the melting temperature of aluminum, tin, and copper nanoparticles are calculated with allowance for the corresponding size dependences of surface tensions in solid and liquid phases and interfacial tension. Size-dependent variations in crystallization temperature are determined under the assumption that a certain effective surface layer (skin-layer) arises before melting.     

Surface tension measurement of liquid metal with inelastic light-scattering spectroscopy of a thermally excited capillary wave

Thermally excited capillary waves propagate everywhere on a liquid surface. The relationship between the frequency and wavelength of the capillary wave reflects the surface tension of the liquid, and the lifetime of the capillary wave reflects the shear viscosity of the liquid. By observing a capillary wave with inelastic light-scattering spectroscopy, we can obtain the surface tension and the viscosity from the frequency modulation of the light and the spectral width of the scattered light. In this study, we observed capillary waves on liquid metal using high-resolution spectroscopy, and successfully measured their properties in a non-contact manner. In the experiment, values were obtained at a frequency of about 20 kHz. The values were equivalent to those at 0 Hz, since the properties of liquid metals are constant at least in the frequency region from 0 to several tens of kilohertz.