Measurements of thermophysical properties of liquid metals by noncontact techniques

With the advent of containerless processing techniques such as electromagnetic levitation, it is now possible to study the properties of high-temperature liquid metalsin situ by applying sophisticated noncontact diagnostics, such as pyrometry and high-speed videography. Thermophysical properties of interest are, e.g., specific heat, thermal conductivity, and viscosity. Applying containerless processing, it is also possible to undercool the melt because of the lack of container-induced nucleation sites. This gives access to a metastable region of the phase diagram. The knowledge of thermophysical data in this region is very important, because undercooling plays a major role in any solidification process. The degree of undercooling not only determines the growth velocity, but also is crucial in selecting the eventually obtained metastable solid phase. In this paper, some recent developments are surveyed relating to the noncontact measurements of emissivity, specific heat, electrical conductivity, density, surface tension, and viscosity, as well as a discussion of possible experiments in microgravity.Paper presented at the Third Workshop on Subsecond Thermophysics, September 17–18, 1992, Graz, Austria.     

Thermophysical Properties of Molten Germanium Measured by a High-Temperature Electrostatic Levitator1

Thermophysical properties of molten germanium have been measured using the high-temperature electrostatic levitator at the Jet Propulsion Laboratory. Measured properties include the density, the thermal expansivity, the hemispherical total emissivity, the constant-pressure specific heat capacity, the surface tension, and the electrical resistivity. The measured density can be expressed by _liq=5.67×10³–0.542 (T–T _m ) kg·m^–3 from 1150 to 1400 K with T _m=1211.3 K, the volume expansion coefficient by =0.9656×10^–4 K^–1, and the hemispherical total emissivity at the melting temperature by _{T, liq}(T _m)=0.17. Assuming constant _{T, liq}(T)=0.17 in the liquid range that has been investigated, the constant-pressure specific heat was evaluated as a function of temperature. The surface tension over the same temperature range can be expressed by (T)=583–0.08(T–T _m) mN·m^–1 and the temperature dependence of the electrical resistivity, when r _liq(T _m)=60·cm is used as a reference point, can be expressed by r _{e, liq}(T)=60+1.18×10^–2(T–1211.3)·cm. The thermal conductivity, which was determined from the resistivity data using the Wiedemann–Franz–Lorenz law, is given by _liq(T )=49.43+2.90×10^–2(T–T _m) W·m^–1·K^–1.     

Measurements of thermophysical properties by a stepwise heating method

An outline of the stepwise heating method for measuring thermal diffusivity and specific heat capacity of samples in both solid and liquid phases is described. The method is based on the measurement of temperature response at the surface of a solid sample when the other surface is heated in step-function. By making the best use of the characteristic points of this method, applications to samples in the liquid state, especially to high temperature melts such as molten salts, have been tried. As examples of measurement results, the thermal diffusivity, specific heat capacity, and thermal conductivity of zirconia brick and the thermal diffusivity of molten salts are shown in graphic form.Presented at the Japan-United States Joint Seminar on Thermophysical Properties, October 24–26, 1983, Tokyo, Japan.     

Noncontact Measurements of Thermophysical Properties of Molybdenum at High Temperatures

Four thermophysical properties of both solid and liquid molybdenum, namely, the density, the thermal expansion coefficient, the constant-pressure heat capacity, and the hemispherical total emissivity, are reported. These thermophysical properties were measured over a wide temperature range, including the undercooled state, using an electrostatic levitation furnace developed by the National Space Development Agency of Japan. Over the 2500 to 3000 K temperature span, the density of the liquid can be expressed as _L(T)=9.10×10³–0.60(T–T _m) (kg·m^–3), with T _m=2896 K, yielding a volume expansion coefficient _L(T)=6.6×10^–5 (K^–1). Similarly, over the 2170 to 2890 K temperature range, the density of the solid can be expressed as _S(T)=9.49×10³–0.50(T–T _m), giving a volume expansion coefficient _S(T)=5.3×10^–5. The constant pressure heat capacity of the liquid phase could be estimated as C _PL(T)=34.2+1.13×10^–3(T–T _m) (J·mol^–1·K^–1) if the hemispherical total emissivity of the liquid phase remained constant at 0.21 over the temperature interval. Over the 2050 to 2890 K temperature span, the hemispherical total emissivity of the solid phase could be expressed as _TS(T)=0.29+9.86×10^–5(T–T _m). The latent heat of fusion has also been measured as 33.6 kJ·mol^–1.     

Measurement of thermophysical properties by a pulse-heating method: Thoriated tungsten in the range 1200 to 3600 K

Thoriated tungsten (tungsten, 98%: thorium oxide. 2 % ) is a widely used electrode material for inert-gas arc-welding. Data for the heat capacity, electrical resistivity. and hemispherical total emissivity of this material are reported for the temperature range 1200–3600 K. A subsecond pulse-heating technique was applied to rod specimens: radiance temperature was measured by high-speed pyrometry. Literature values of the temperature dependence of the normal spectral emissivity of tungsten were used to obtain true temperatures, using the melting point of thoriated tungsten as a calibration point. Reported uncertainties for the properties are 4 % for heat capacity, 1.5 % for electrical resistivity, and 7 % for hemispherical total emissivity.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

Non-Contact Measurements of the Thermophysical Properties of Hafnium-3 Mass% Zirconium at High Temperature

Several thermophysical properties of hafnium-3 mass % zirconium, namely the density, the thermal expansion coefficient, the constant pressure heat capacity, the hemispherical total emissivity, the surface tension and the viscosity are reported. These properties were measured over wide temperature ranges, including overheated and undercooled states, using an electrostatic levitation furnace developed by the National Space Development Agency of Japan. Over the 2220 to 2875 K temperature span, the density of the liquid can be expressed as _L (T)=1.20×10⁴–0.44(T–T _m ) (kgm^–3) with T _m =2504 K, yielding a volume expansion coefficient _L (T)=3.7×10^–5 (K^–1). Similarly, over the 1950 to 2500 K span, the density of the high temperature and undercooled solid -phase can be fitted as _S (T)=1.22×10⁴–0.41(T–T _m ), giving a volume expansion coefficient _S (T)=3.4×10^–5. The constant pressure heat capacity of the liquid phase can be estimated as C _PL (T)=33.47+7.92×10^–4(T–T _m ) (Jmol^–1K^–1) if the hemispherical total emissivity of the liquid phase remains constant at 0.25 over the 2250 K to 2650 K temperature interval. Over the 1850 to 2500 K temperature span, the hemispherical total emissivity of the solid -phase can be represented as _TS (T)=0.32+4.79×10^–5(T–T _m ). The latent heat of fusion has also been measured as 15.1 kJmol^–1. In addition, the surface tension can be expressed as (T)=1.614×10³–0.100(T–T _m ) (mNm^–1) and the viscosity as h(T)=0.495 exp [48.65×10³/(RT)] (mPas) over the 2220 to 2675 K temperature range.     

Measurement of thermophysical properties of molten salts: Mixtures of alkaline carbonate salts

The purpose of this study is to develop measuring methods for the thermal diffusivity, the specific heat capacity, and the density of molten salts, as well as to measure these properties of mixtures of alkaline carbonate salts. The thermal diffusivity is measured by the stepwise heating method. The sample salt is poured into a thin container, and as a result, a three-layered cell is formed. The thermal diffusivity is obtained from the ratio of temperature rises at different times measured at the rear surface of the cell when the front surface is heated by the stepwise energy from an iodine lamp. The specific heat capacity is measured using an adiabatic scanning calorimeter. The density is measured by Archimedes' principle. Thermal conductivity is determined from the above properties. Measured samples are Li₂CO₃-K₂CO₃ (42.7–57.3, 50.0-50.0, and 62.0-38.0 mol%).Invited paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

Measurements of specific heat and electrical resistivity of austenitic stainless steel (St. 1.4970) in the range 300–1500 K by pulse calorimetry

A direct heating pulse calorimetric technique has been applied for the measurements of specific heat, electrical resistivity, and hemispherical total emissivity of austenitic stainless steel (St. 1.4970), a candidate for thermal conductivity standard reference material. The specific heat and electrical resistivity were measured in the range 300 to 1500 K, and the hemispherical total emissivity was measured in the range 1300 to 1500 K. The maximum measurement uncertainties were estimated to be 3% for specific heat, 1% for electrical resistivity, and 5% for emissivity.Paper presented at the Second Workshop on Subsecond Thermophysics, September 20–21, 1990, Torino, Italy.     

A dynamic technique for measurements of thermophysical properties at high temperatures

A technique is described for the dynamic measurement of selected thermophysical properties of electrically conducting solids in the range 1500 K to the melting temperature of the specimen. The technique is based on rapid resistive selfheating of the specimen from room temperature to any desired high temperature in less than 1 s by the passage of an electrical current pulse through it and on measuring the pertinent quantities, such as current, voltage, and temperature, with millisecond resolution. The technique was applied to the measurement of heat capacity, electrical resistivity, hemispherical total emissivity, normal spectral emissivity, thermal expansion, temperature and energy of solid-solid phase transformations, melting temperature, and heat of fusion. Two possible options for the extension of the technique to measurements above the melting temperature of the specimen are briefly discussed. These options are: (1) submillisecond heating of the specimen and performance of the measurements with microsecond resolution, and (2) performance of the experiments in a near-zero-gravity environment with millisecond resolution.Paper presented at the Japan-United States Joint Seminar on Thermophysical Properties, October 24–26, 1983, Tokyo, Japan.     

Research on thermophysical properties of fluids at the Grozny Petroleum Institute (USSR)

A brief survey is presented of the thermophysical properties of petroleum, petroleum products, hydrocarbons, and their mixtures and of other working fluids that are being investigated at the Grozny Petroleum Institute in the USSR. The properties include density, specific heat, surface tension, thermal conductivity, and viscosity. A list of references with the relevant information is included.     

静电悬浮条件下的材料典型热物理性质测量

随着对材料研究的逐渐深入,材料制备和材料分析的方法越来越重要,并且一些材料重要的物理性质是开展相关研究的基础。由于一些材料熔点高、难熔化,同时,传统手段无法避免容器壁的污染,或者无法在真空条件下进行试验避免气体的污染,或者由于实验性质原因只能测量特定的材料,这些方法很难测量材料在高温下过热过冷阶段的热物理性质。系统介绍了静电悬浮技术,这是一种新型的实现深过冷的方式,可以达到高温下对材料热物理性质进行测量的目的。静电悬浮技术使样品在两极板间悬浮,在悬浮的状态下采用激光对样品进行加热,使材料达到高温熔化,同时进行热物性的测量。对比了几种实现测量典型热物理性质的方法,了解静电悬浮的优势,并详细地介绍了静电悬浮技术对材料的熔体密度、热膨胀系数、表面张力和粘度系数以及比热的测量。     

Measurements of thermophysical properties of sodium acetate hydrate

Methods to measure the thermal conductivity, the specific heat capacity, and the heat of fusion of sodium acetate hydrate have been developed and the measured results have been reported for various concentrations and especially for various supercooling temperatures. Thermal conductivity was measured by using a probe method with a thermistor. The sensor element is very small, with a diameter of 0.5 mm and a length of 1.5 mm. Data for both the ordinary liquid and the supercooled liquid are smoothly connected to each other.     

Thermophysical Properties of Containerless Liquid Iron up to 2500 K

Thermophysical properties of high temperature liquid iron heated with a CO₂ laser have been determined in an aerodynamic levitation device equipped with a high-speed camera and a three-wavelength pyrometer. Characteristic curves of the free cooling and heating of the drop can be used to determine the same apparent emissivity of solid and liquid iron and to calibrate pyrometers based on the known value of the melting point of iron, i.e., 1808 K. Examination of the recalescence of undercooled liquid iron and further solidification are used to obtain the ratio of the melting enthalpy versus the heat capacity of liquid iron as . The surface tension was determined from an analysis of the vibrations of liquid drops. Results are accurately described by (mJm^–2)=(1888±31)–(0.285±0.015) (T–T _m ) between 1750 K (undercooled liquid) and 2500 K. The density of liquid iron has been deduced from the image size and the mass of the liquid iron drops.     

Effects of Sample Size on Surface-Tension Measurements of Nickel in Reduced-Gravity Parabolic Flights

Surface tensions of molten metals have been reported in the literature by application of many standard techniques: sessile-drop, maximum bubble pressure, pendant-drop, and capillary-rise methods. Great experimental care must be exercised to ensure the absence of contamination, and containerless techniques based upon the classical theory of oscillations of a liquid drop are being developed for high-precision measurements on reactive alloys. Droplet positioning and heating can be efficiently accomplished by electromagnetic levitation, although additional modes of oscillation can be excited and the fundamental oscillation mode can be shifted to higher frequencies due to asymmetries in droplet shape when experiments are performed in earth-based laboratories. These additional factors associated with 1 g experiments significantly complicate data analysis. An electromagnetic levitator has been developed at Auburn University to test containerless processing methods for characterizing the surface tension of high temperature, reactive melts. Recent oscillating drop experiments with nickel samples utilizing electromagnetic levitation in the low-g environment of NASA's KC-135 research aircraft have shown droplet oscillations in the primary mode and at the fundamental frequency. A series of experiments was performed with droplets covering a range of sizes (i.e., mass), and the largest samples exhibited the largest deviations from Rayleigh's simple theory. The smallest samples exhibited oscillatory behavior consistent with Rayleigh's simple theory. An uncertainty analysis showed that the oscillating-drop technique should provide uncertainties in surface tension of ±0.1 to 2.0percnt; depending upon the uncertainty in the mass of the sample.     

High-Temperature Properties of Liquid Boron from Contactless Techniques

The density, surface tension, and spectral and total hemispherical emissivities of liquid boron obtained with contactless diagnostics are reported for temperatures between 2360 and 3100 K. It is shown that, contrary to previous expectations, liquid boron is denser than the solid at its melting point. It is also shown that the high total emissivity of 0.36 is not consistent with that of a liquid metal as recently claimed. Finally, good agreement is found with previously reported surface tensions and spectral emissivities of liquid boron.     

Thermophysical and Thermal Optical Properties of Vanadium by Millisecond Calorimetry Between 300 and 1900 K

A variant of millisecond-resolution pulse calorimetry in use at the Institute of Nuclear Sciences Vina since 1983 involves measuring the specific heat and electrical resistivity of electrical conductors from room temperature to 2500 K and the hemispherical total emissivity and normal spectral emissivity from about 1300 K to the same maximum operating temperature. The method was applied successfully to different materials: pure metals, ferrous and nickel-base alloys, reactor materials, and refractory metals in thermal characterization of candidates for thermophysical property standard reference materials. This paper presents and discusses new data obtained in the study of thermophysical and thermal optical properties of vanadium.     

熔融硅液相浸渍法制备C/C-SiC复合材料

采用熔融硅液相浸渍法制备了C/C-SiC复合材料,反应生成的SiC主要分布在层间孔和束间孔碳基体表面,少量分布在束内孔.1600℃渗硅2 h,硅化深度约为2～4 μm.由于液态硅与碳之间的润湿性很好,在碳基体表面形成了连续的SiC层,局部有粗大的多面碳化硅颗粒生成;讨论了细晶粒连续SiC层和SiC粗晶粒形成机理.由于SiC的加入,材料的抗氧化性能得到明显改善.     

Thermophysical properties data on molten semiconductors

Thermophysical properties of molten semiconductors are reviewed. Published data for viscosity, thermal conductivity, surface tension, and other properties are presented. Several measurement methods often used for molten semiconductors are described. Recommended values of thermophysical properties are tabulated for Si, Ge, GaAs, InP, InSb, GaSb, and other compounds. This review shows that further measurements of thermophysical properties of GaAs and InP in the molten state are required. It is also indicated that a very limited amount of data on emissivity is available. Space experiments relating to thermophysical property measurements are described briefly.Nomenclature Density - C _p Specific heat - Kinematic viscosity - Dynamic viscosity= - Thermal diffusivity - Thermal conductivity=C_p - Volumetric thermal expansion coefficient - Surface tension - d/dT Temperature coefficient of surface tension - g Gravitational acceleration - T Temperature - T Temperature difference - L Characteristic dimension