Measurements of electrical and thermal properties with growth rate,alloying elements and temperature in the Al–Si–X alloys

In this work, effect of alloying elements (X = Cu, Co, Ni, Sb and Bi) and growth rates on the microstructure, physical properties (electrical resistivity, enthalpy and specific heat) of the directionally solidified Al–Si eutectic alloy have been investigated. Al–12.6Si–2X (wt. %) samples were prepared using metals of 99.99% high purity in the vacuum atmosphere. These alloys were directionally solidified under constant temperature gradient, G (7.80 K/mm) and different growth rates, V (8.3–166.0 μm/s). Flake spacing (λ) and electrical resistivity (ρ) were measured from the solidified samples. The variation of electrical resistivity with temperature in the range of 300–500 K for alloying elements in the Al–Si eutectic cast alloy was also measured. The enthalpy of fusion (ΔH) and specific heat (C_p) for the same alloy were determined by a differential scanning calorimeter from the heating curve during the transformation from solid to liquid.     

制备工艺条件对泡沫镍电阻率的影响

本文探讨了不同的工艺条件对有机多孔体电沉积法所制泡沫镍电阻率的影响。发现两种导电化处理结果相差很大，化学镀镍所得产品的电阻率明显高于浸涂石墨基导电胶所得产品。而去除有机体的热处理，先在空气中短时间预烧再还原烧结，比直接在还原气氛中热解烧结所得产品的电阻率有所降低。     

连续铸造铜单晶的力学性能和电阻率

采用自制水平单晶连铸设备制备铜单晶， 并对铜单晶的力学性能和电阻率进行了测试分析。结果表明，铜单晶与多晶铸棒比，抗拉强度降低２０ ．８５ ％ ，屈服强度降低８６ ．５４ ％ ，延伸率增加８０ ．２４ ％ ， 断面收缩率增加３９４ ．５０ ％ ； 与轧制棒比， 抗拉强度降低６５ ．９７ ％ ， 屈服强度降低９８ ．２７ ％ ， 延伸率增加２７０ ．００ ％ ， 断面收缩率增加４ ．００ ％ ； 与多晶铸棒比电阻率降低１５ ．５７ ％ ， 与定向凝固铸棒比电阻率降低４ ．２４ ％ 。因此， 连铸铜单晶具有非常优异的塑性加工性能和低电阻率     

Thermophysical Properties by a Pulse-Heating Reflectometric Technique: Niobium, 1100 to 2700 K

Pulse-heating experiments were performed on niobium strips, taking the specimens from room temperature to the melting point is less than one second. The normal spectral emissivity of the strips was measured by integrating sphere reflectometry, and, simultaneously, experimental data (radiance temperature, current, voltage drop) for thermophysical properties were collected with sub-millisecond time resolution. The normal spectral emissivity results were used to compute the true temperature of the niobium strips; the heat capacity, electrical resistivity, and hemispherical total emissivity were evaluated in the temperature range 1100 to 2700 K. The results are compared with literature data obtained in pulse-heating experiments. It is concluded that combined measurements of normal spectral emissivity and of thermophysical properties on strip specimens provide results of the same quality as obtained using tubular specimens with a blackbody. The thermophysical property results on niobium also validate the normal spectral emissivity measurements by integrating sphere reflectometry.     

Structure and electrical resistivity of the Al-carbon nanotube composites

In this paper the microstructure and the electrical resistivity of the hot-pressed Al-carbon nanotube composites have been measured. The results show that there is A1C or A1C₂ phases in the structure, the electrical resistivity of the samples with carbon nanotubes at room temperature is slightly higher than that of the samples without carbon nanotubes. There is an abrupt drop of the electrical resistivity of the Al-carbon nanotube composites at about 80 K, which is similar to the superconducting transition.     

Factors affecting the electrical resistivity of soybean oil methyl ester

Factors affecting the electrical resistivity of soybean oil methyl ester (which is important in some industrial applications) were investigated by the addition of polar constituents [free fatty acids (FFA), water, phospholipids, monoglyceride, sterol, tocopherol, peroxides, and β-carotene] to aluminapurified soybean oil methyl ester (APSBOMe). Investigation of measuring conditions showed that reproducible results were obtained when the potential was greater than 25 V, and the charging time was greater than 10 s. The resistivity of APSBOMe increased logarithmically as temperature decreased linearly. FFA had little effect on resistivity. Saturation with water lowered the resistivity of APSBOMe much more than that of alumina-purified soybean oil (APSBO). Phospholipids reduced the resistivity significantly when added to dry ester, but the addition of water affected the resistivity of the samples containing phospholipids only slightly. Monoglyceride, sterol, tocopherol, and hydroperoxide affected the resistivity of dry methyl ester similarly, but only monoglyceride showed a significant synergistic effect with water. Diacylperoxide and β-carotene had little effect on the resistivity of the ester.     

Thermophysical properties of some key solids: An update

In 1985, the CODATA Bulletin published a Report of its Task Group on Thermophysical Properties of Solids which analyzed available data on, and gave recommended values for, the heat capacity of Cu, Fe, W, and Al₂O₃, the thermal expansion of Cu, Si, W, and Al₂O₃, the electrical resistivity of Cu, Fe, Pt, and W, the thermal conductivity of Al, Cu, Fe, and W, and the absolute thermopower of Pb, Cu, Pt, and W. The analysts for the different properties were R. B. Castanet, S. J. Collocott, P. D. Desai, C. Y. Ho, J. G. Hust, R. B. Roberts, C. A. Swenson, and G. K. White. The present paper is an updated version of the earlier report and includes more recent data which change some of the recommended values. notably the heat capacity of Cu and W and the thermal expansion of Si and W.     

High-temperature,high-pressure thermophysical measurements on liquid zinc

Wire-shaped zinc samples were resistively volume heated as part of a fast-capacitor discharge circuit. Time-resolved measurements with submicrosecond resolution of the current through the specimen, the voltage drop across it, and the thermal expansion of the specimen as a function of time allow determination of the enthalpy, electrical resistivity, and density at different temperatures up to superheated liquid states of zinc far above the normal boiling point. High static pressures, up to 3800 bar of the ambient medium water, were used. An estimate of the critical pressure for zinc is given by investigations of the stability of the sample with a framing CCD camera, taking pictures of different samples varying the ambient static pressure. The critical volume and the critical temperature are obtained by means of an extrapolation of measured data at different pressures.Paper presented at the Fourth International Workshop on Subsecond Thermophysics, June 27–29, 1995, Köln, Germany.     

PREPARATION OF AMORPHOUS Ti-Pd ALLOYS AND THEIR PHYSICAL PROPERTIES

The amorphous Ti_(l_x)Pd_x alloys within a wider composition range of 0.25相似文献   

Fast transient thermophysical measurements at Livermore

The development of the Isobaric Expansion Experiment at Lawrence Livermore National Laboratory is described. Rod samples are self-heated by current from a capacitor bank while current and sample voltage, sample cross section, and temperature are measured continuously as functions of time. The system allows nearly complete thermodynamic characterization of a material along an isobar in a single shot. The pressure of the isobar is determined by containing the sample in argon gas at a predetermined ambient pressure. Correlation of the measured quantities allows elimination of time as a common parameter. Quantities corresponding to a given time are taken to refer to a single equilibrium state. Temperature stagnation and volume and resistivity changes during phase transitions may be seen and allow the heat of transformation and the slope of the phase line in theP, T plane to be determined. Other derived quantities are specific heatc _p, volume-corrected electrical resistivity, and bulk thermal expansion coefficient. A special advantage of the technique is that all quantities are measured on the same sample in a single experiment. The short time duration of the measurements allows access to a temperature range beyond that available to slower methods.Paper presented at the First Workshop on Subsecond Thermophysics, June 20–21, 1988, Gaithersburg, Maryland, U.S.A.