Combined DSC and Pulse-Heating Measurements of Electrical Resistivity and Enthalpy of Platinum,Iron, and Nickel

Measurements of the enthalpy, electrical resistivity, and specific heat capacity as a function of temperature starting from the solid state up into the liquid phase for Fe, Ni, and Pt are presented. Two different measurement approaches have been used within this work: an ohmic pulse-heating technique, which allows – among others – the measurement of enthalpy, specific heat capacity, and electrical resistivity up to the end of the stable liquid phase, and a differential–scanning–calorimetry technique (DSC) which enables determination of specific heat capacity from near room temperature up to 1500 K. The microsecond ohmic pulse-heating technique uses heating rates up to 10⁸ K·s^–1 and thus is a dynamic measurement, whereas the differential–scanning–calorimetry technique uses heating rates of typically 20 K·min^–1 and can be considered as a quasi-static process. Despite the different heating rates both methods give good agreement of the thermophysical data within the stated uncertainties of each experiment. Results on the metals Fe, Ni, and Pt are reported. The enthalpy and resistivity data are presented as a function of temperature and compared to literature values.     

Development of a Millisecond Pulse-Heating Apparatus

A millisecond pulse-heating apparatus is presently under development at the Harbin Institute of Technology (HIT). The design is based on systems previously developed both at NIST (U.S.A.) [1, 2] and IMGC (Italy) [3] for the measurement of several thermophysical properties with millisecond time resolution. The apparatus uses rapid resistive self-heating of a strip-shaped specimen from room temperature to a pre-chosen maximum temperature. Power is furnished by a subsecond-duration electrical current pulse through the specimen. Simultaneous measurements are carried out for several quantities. The maximum current is up to 2000 A. Experiments are performed on strip-shaped specimens with the following typical dimensions: 80 mm in length, 10 mm in width, and 1 mm in thickness. The specimen is contained in a large vacuum chamber (bigger than 300 mm in both diameter and height) whose inner wall is coated with a nonreflecting paint. A special designed high-speed pyrometer will be used to measure the temperature of the specimen through one of two quartz windows of the chamber. The heat capacity, the electrical resistivity, the total hemispherical emissivity, and normal spectral emissivity of the specimen are measured by using this apparatus for various materials.     

电流脉冲加热瞬态热物性测量技术

对国内外电流脉冲加热技术的发展状况进行了综述评价.针对获取温度方法不同,主要介绍了黑体法、积分球法和激光偏振法三种基本形式的测量系统,进而介绍了扩展参数测量装置.又较为详细地介绍了作者自己研制的测量装置和特点.最后作者展望了电流脉冲加热技术的最新研究动态和发展方向.     

A Multiwavelength Reflectometric Technique for Normal Spectral Emissivity Measurements by a Pulse-Heating Method

A new technique has been developed for the direct measurement of the normal spectral emissivity at several wavelengths in pulse-heating conditions, adding some novel features to previous versions of this type of apparatus. Pulse-heating experiments were performed on niobium strip specimens, taking the specimen from room temperature to the melting point using rapid resistive self-heating. The normal spectral emissivity was measured at three wavelengths by a multi-wavelength reflectometric technique. At the same time, the radiance temperature was measured at the same wavelengths by a high-speed pyrometer from approximately 1100 K to the melting point. Details of the method, the measurement apparatus, and the calibration technique are described. Preliminary results for the normal spectral emissivity of niobium at 633, 750, and 900 nm over a wide temperature range are presented.