Time Dependent Effects in Surface Tension Measurements of an Industrial Fe‐alloy

The surface tension of an industrial FeC‐alloy containing Si, Mn and S in the few atomic per cent range was measured by the oscillating drop method in ground based electromagnetic levitation and under reduced gravity conditions on board a parabolic flight. The results from the parabolic flight exhibited a large variation between different heating cycles and a discrepancy with the ground based experiments with regard to the value of the surface tension at the liquidus temperature and the temperature coefficient. The variation of the surface tension temperature coefficient is interpreted as resulting from the loss of volatile surface active components such as S and Si in subsequent heating cycles. The results demonstrate the importance of the time scale of the measurement and ambient atmosphere for surface tension measurements of industrial alloys containing volatile surface active components. For comparison with the experimental values the surface tension and segregation were modelled using different models. As a result of the analysis, the surface tension as a function of temperature best representing the starting industrial alloy is obtained as σ(T) = 1.52–1.53 10^‐4 (T–1752K) Nm^‐1.     

磁悬浮球实验系统的模糊控制仿真

该文介绍磁悬浮球实验系统的结构与工作原理，根据模糊控制技术，设计了一个二维模糊控制器，在实验的基础上，确定了输入输出变量的范围，并对变量进行了模糊化，根据小球的物理运动规律，建立了模糊控制规则，在Matlab/Simulink环境下进行了仿真，并进行了实际控制实验，实验表明，所设计的模糊控制器具有很强的鲁棒性。     

Observations of the Effects of Oxide Skins on the Oscillations of Electromagnetically Levitated Metal Droplets

The surface tensions of liquid metals can be derived from measurements of the natural oscillation frequencies of levitated drops through the Rayleigh relation, In general, during terrestrial measurements, a spectrum consisting of three to five dominant oscillation frequencies (in the range of 30 to 60 Hz) are found, rather than the single one predicted by Rayleigh, due to deformation of the drop shape by gravity and the supporting magnetic field. Cummings and Blackburn have derived a correction factor to align the measured frequencies with the Rayleigh frequency, which has been shown to hold through micro-gravity experiments by Egry et al., for the majority of metals that have a liquid surface. Work at the NPL on more complex, commercial alloys has found that, in some cases, oscillation frequencies may be split into more complex spectra exhibiting seven to nine oscillation frequencies. This has been attributed to formations of oxide from the metal collecting on the surface of the droplet. Observations of the frequency spectra and high speed video images of the levitated drops are discussed.     

磁悬浮转子微陀螺的微细加工工艺研究

介绍了磁悬浮转子微陀螺的工作原理及有关的微细加工工艺。磁悬浮转子微陀螺的平面线圈是采用光刻、电镀及溅射等微细加工方法来实现的,微转子的加工有冲压、蒸铝沉积等方法,其中冲压能得到质量较好的微转子;上壳体采用体硅腐蚀来制作。初步的实验表明该方案是行之有效的。     

Surface Tension Measurements on CMSX-4 Superalloy by the Drop-Weight and Oscillating-Drop Methods

The surface tension of the CMSX-4^®reg; superalloy has been determined by the drop-weight and oscillating-drop methods which are well adapted to reactive materials. The recommended values are 1.59 J·m^–2 for the surface tension at the liquidus temperature and –0.14× 10^–3 J·m^–2· K^–1 for the temperature coefficient. A conclusion of the present work is that the interpretation of surface tension measurements performed on a complex alloy generally requires additional work to be performed on simpler associated binary or ternary systems, as well as some support from solidification experiments.     

Density and Thermal Expansion of Liquid Au-Cu Alloys

The density of liquid Cu-Au alloys is measured using the technique of electromagnetic levitation, which entails producing a shadow image of the sample. The shadow is recorded by a digital CCD-camera, and the volume of the sample is calculated by an image processing algorithm. The density and thermal expansion of several alloys and the pure elements copper and gold are investigated at various temperatures above their melting points. In addition, the densities are also investigated as a function of the gold concentration at constant temperature. The measured values agree with literature data and with predictions obtained by molecular dynamics. It was found from data analysis that the ideal solution model applies.     

Surface Tension and Density of Oxygen-Free Liquid Aluminum at High Temperature

New values of densities and surface tensions of liquid aluminum obtained in the range 1600 to 2360 K by contactless techniques in neutral gases are reported. Conditions for oxygen-free aluminum are fulfilled which allow determination of the surface tension of aluminum. Extrapolation to the melting point, T _m = 933 K, confirms the value of (T = 933K) = 1.05 N m^–1.     

电动悬浮型磁悬浮列车悬浮与导向技术剖析

基于场－路相结合的分析方法,通过计算机辅助分析和仿真,深入系统地剖析了ＥＤＳ型磁浮列车最新的悬浮、导向系统。揭示了由交叉连接“８”字形零磁通线圈与超导磁体组成的系统的理论研究与工程应用价值的内涵,从而满足了高速磁浮列车悬浮、导向功能的工程需求。     

Density and Thermal Conductivity Measurements for Silicon Melt by Electromagnetic Levitation under a Static Magnetic Field

The density and thermal conductivity of a high-purity silicon melt were measured over a wide temperature range including the undercooled regime by non-contact techniques accompanied with electromagnetic levitation (EML) under a homogeneous and static magnetic field. The maximum undercooling of 320 K for silicon was controlled by the residual impurity in the specimen, not by the melt motion or by contamination of the material. The temperature dependence of the measured density showed a linear relation for temperature as: ρ(T) = 2.51 × 10³−0.271(T−T _m) kg · m⁻³ for 1367 K < T < 1767 K, where T _m is the melting point of silicon. A periodic heating method with a CO₂ laser was adopted for the thermal conductivity measurement of the silicon melt. The measured thermal conductivity of the melt agreed roughly with values estimated by a Wiedemann–Franz law.