Experimental investigation of the normal spectral emissivity and other thermophysical properties of pulse-heated Ni-Ti and Au-Ni alloys into the liquid phase

1. Introduction Metal working industry needs accurate thermo- physical properties of liquid metals and alloys as input data for different simulation routines to im- prove the performance of their products. Within this paper we continue the systematic investigation of the dependence of emissivity of binary alloys on the relative concentration of the constituent elements (for a previous paper see [1]). 2. Experimental method A fast ohmic pulse heating technique is applied to heat metallic wire-s…     

脉冲加热方法铌热物性参数的动态测量

提出积分球反射法脉冲加热技术测量材料热物性的方法,研制的脉冲加热瞬态热物性测量装置能同时测量铌带状试样温度范围在1100-2700K的比热容、电阻率、全波长半球发射率.装置中高速高温计测量试样的辐射温度,积分球反射计测量试样的法向光谱发射率,即可得出带状试样的真实温度.再通过测得的试样上的电压、电流等数据经计算获得其他热物性参数.对国外的标准铌试样进行了测试,所得测量数据与国外同行数据进行了比对,具有较好的一致性.实验结果表明:比热容测量不确定度为5%,全波长半球发射率测量不确定度为3.5%,电阻率的测量不确定度为3.6%,测量数据可作为航天、军事和民用领域材料应用的设计依据.     

利用积分球反射法的动态热物性测量装置研制

介绍了利用积分球反射计的脉冲加热技术测量材料热物性的一种方法和测量装置的各组成部分及工作原理。被测的带状试样被一脉冲大电流加热,利用高速高温计测量试样的辐射温度,同时利用积分球反射法获得试样的半球向光谱反射率,进而得到试样的法向光谱发射率、比热、电阻率和全波长半球发射率。该装置具有试样制备简单、测试精度高等优点。     

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.     

Thermophysical Properties and Normal Spectral Emittance of Iridium up to 3500 K

An ohmic pulse-heating experiment together with radiometry and μs-photopolarimetry is deployed at the Institute of Experimental Physics, Graz University of Technology, to obtain temperature-dependent thermophysical properties of conducting samples in the solid and molten states. This experimental setup has been used within the present work to gather data for solid and liquid iridium. Results for both thermophysical properties, as well as the normal spectral emittance obtained at a wavelength of 684.5 nm up to 3500 K are reported. The newly obtained values for iridium are presented in graphical and tabular form and compared to available literature data. The uncertainties for all reported properties are stated and it follows that, considering these expanded uncertainties, the recent data are in very good agreement with literature sources. Mutually motivated by these good results and by the scarce (if any) data available for the liquid state, the thermal conductivity and thermal diffusivity of liquid iridium are estimated by means of the Wiedemann–Franz law.     

Thermophysical properties of solid and liquid tungsten

The thermophysical properties of solid and liquid tungsten have been measured up to an enthalpy ofH = 1.4 MJ · kg^–1 using an isobaric expansion technique. These measurements give the pressure, temperature, volume, enthalpy, electrical resistivity, and sound velocity as fundamental quantities. From these, other properties may be calculated, such as specific heat at constant volume and pressure, heat of fusion, isothermal and adiabatic bulk moduli and compressibilities, and thermodynamic. Results of these calculations are presented for liquid tungsten and compared with literature values where such data exist. These data will help in understanding liquid-metal phenomenology theoretically and in the design and modeling of exploding wires, foils, and fuses.Paper presented at the First Workshop on Subsecond Thermophysics, June 20–21, 1988, Gaithersburg, Maryland, U.S.A.     

Evaporation of metals by high-density (107 A · cm−2) electrical currents

In the present work, the problem of time evolution of pressure and temperature profiles across a wire through which an electrical current with a density of the order of 10⁷ A · cm^–2 flows is solved. The correct boundary conditions for a metal surface are obtained for the case when this metal is rapidly evaporated as a result of high-power Joule heating. The pressure profile appears under these conditions due to pinch-effect and inertia of thermal expansion of the metal; the temperature profile arises because of intensive evaporation from the surface of the wire. The conditions under which a liquid metal is superheated are formulated. On the basis of the analysis of the experimental results on exploding wires, the conclusion is drawn that decay of the metastable state takes place near the binodal. It is shown that the distribution of fine dispersed vapor bubbles is strongly nonuniform across the wire and the process of expansion of the two-phase mixture is very similar to the motion of a wave.Paper presented at the Fourth International Workshop on Subsecond Thermophysics, June 27–29, 1995, Köln, Germany.     

Normal Spectral Emissivity at a Wavelength of 684.5 nm and Thermophysical Properties of Solid and Liquid Molybdenum

Polarimetric emissivity measurements adapted for a rapid pulse heating setup and recent results of normal spectral emissivity at 684.5 nm for molybdenum at melting and in the liquid phase are presented. Also reported is a complete set of thermophysical data (specific enthalpy, isobaric heat capacity, electrical resistivity, thermal conductivity, and thermal diffusivity) for molybdenum for both solid and liquid states. The results for all mentioned thermophysical properties are discussed and furthermore compared to literature values. The normal spectral emissivity and the electrical resistivity of molybdenum show opposite trends in the liquid phase, leading to the conclusion that a prediction of normal spectral emissivity at the given wavelength of 684.5 nm based on the Hagen–Rubens-relation and electrical resistivity measurements is not applicable.     

Three-Dimensional Finite-Element Analysis of High-Speed (Millisecond) Measurements

Millisecond pulse heating has become an established method to obtain accurate thermophysical property data for solid metallic materials at high temperatures. This technique is based on rapid resistive heating of a tubular- or rod-shaped specimen by an electrical current and simultaneously measuring the pertinent quantities with, at least, millisecond resolution. The temperature development during heating and subsequent cooling is usually measured by a high-speed pyrometer. For the case of a tubular specimen, the pyrometer is focused on a blackbody hole in the center part of the specimen. A three-dimensional finite-element analysis was used to investigate the limitations of the method used. A commercial program (ANSYS) was used for a highly nonlinear finite-element analysis taking into account temperature-dependent material properties as well as heat transport by radiation. Results of the simulated temperature and current density distributions are presented and discussed. Paper presented at the Seventh International Workshop on Subsecond Thermophysics, October 6-8, 2004, Orléans, France.     

Combined DSC and Pulse-Heating Measurements of Electrical Resistivity and Enthalpy of Tungsten,Niobium, and Titanium

Measurements of thermophysical properties such as enthalpy, electrical resistivity, and specific heat capacity as a function of temperature starting from the solid state into the liquid phase for W, Nb, and Ti are presented in this work. An ohmic pulse-heating technique allows measurements of enthalpy and electrical resistivity from room temperature to the end of the stable liquid phase within 60 μ s. The simultaneous optical measurement of temperature is limited by the fast pyrometers with an onset temperature of T_min = 1200–1500 K; below these temperatures, the fast pyrometers are not sensitive. A differential scanning calorimeter (DSC) is used for determination of the specific heat capacity, and also to obtain enthalpy values in the temperature range of 600–1700 K. Combining the two methods entends the range of values of electrical resistivity and enthalpy versus temperature down to 600 K. Results on the metals W, Nb, and Ti are reported and compared to literature values. This paper is a continuation of earlier work. Paper presented at the Seventh International Workshop on Subsecond Thermophysics, October 6–8, 2004, Orléans, France.