Thermophysical Property Measurements of Liquid Gadolinium by Containerless Methods

Thermophysical properties of liquid gadolinium were measured using non-contact diagnostic techniques with an electrostatic levitator. Over the 1585 K to 1920 K temperature range, the density can be expressed as ρ(T) = 7.41 × 10³ − 0.46 (T − T _m) (kg · m⁻³) where T _m = 1585 K, yielding a volume expansion coefficient of 6.2 × 10⁻⁵ K⁻¹. In addition, the surface tension data can be fitted as γ(T) = 8.22 × 10² − 0.097(T − T _m)(10⁻³ N · m⁻¹) over the 1613 K to 1803 K span and the viscosity as η(T) = 1.7exp[1.4 × 10⁴/(RT)](10⁻³ Pa · s) over the same temperature range.     

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.     

Physical Properties of AZ91D Measured Using the Draining Crucible Method: Effect of SF<Subscript>6</Subscript>

The draining crucible (DC) technique was used for measurements on AZ91D under Ar and SF₆. The DC technique is a new method developed to simultaneously measure the physical properties of fluids, the density, surface tension, and viscosity. Based on the relationship between the height of a metal in a crucible and the outgoing flow rate, a multi-variable regression is used to calculate the values of these fluid properties. Experiments performed with AZ91D at temperatures from 923 K to 1173 K indicate that under argon, the surface tension (N · m⁻¹) and density (kg · m⁻³) are [0.63 − 2.13 × 10⁻⁴ (T − T _L)] and [1656 − 0.158 (T − T _L)], respectively. The viscosity (Pa · s) has been determined to be [1.455 × 10⁻³ − 1.209 × 10⁻⁵ (T − T _L)] over the temperature range from 921 K to 967 K superheat. Above 967 K, the viscosity of the alloy under argon seems to be constant at (2.66 × 10⁻⁴ ± 8.67 × 10⁻⁵) Pa · s. SF₆ reduces the surface tension of AZ91D.     

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.     

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.     

Non-contact measurements of thermophysical properties of niobium at high temperature

Four thermophysical properties of both solid and liquid niobium have been measured using the vacuum version of the electrostatic levitation furnace developed by the National Space Development Agency of Japan. These properties are the density, the thermal expansion coefficient, the constant pressure heat capacity, and the hemispherical total emissivity. For the first time, we report these thermophysical quantities of niobium in its solid as well as in liquid state over a wide temperature range, including the undercooled state. Over the 2340 K to 2900 K temperature span, the density of the liquid can be expressed as _L (T) = 7.95 × 10³ – 0.23 (T – T _m)(kg · m^–3) with T _m = 2742 K, yielding a volume expansion coefficient _L(T) = 2.89 × 10^–5 (K^–1). Similarly, over the 1500 K to 2740 K temperature range, the density of the solid can be expressed as _s(T) = 8.26 × 10³ – 0.14(T – T _m)(kg · m^–3), giving a volume expansion coefficient _s(T) = 1.69 × 10^–5 (K^–1). The constant pressure heat capacity of the liquid phase could be estimated as C _PL(T) = 40.6 + 1.45 × 10^–3 (T – T _m) (J · mol^–1 · K^–1) if the hemispherical total emissivity of the liquid phase remains constant at 0.25 over the temperature range. Over the 1500 K to 2740 K temperature span, the hemispherical total emissivity of the solid phase could be rendered as _TS(T) = 0.23 + 5.81 × 10^–5 (T – T _m). The enthalpy of fusion has also been calculated as 29.1 kJ · mol^–1.     

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.     

Preparation, characterization and conductivity studies of Li3?2xAl2?xSbx(PO4)3

New NASICON type materials of composition, Li_3−2x Al_2−x Sb _x (PO₄)₃ (x = 0·6 to 1·4), have been prepared and characterized by powder XRD and IR. D.C. conductivities were measured in the temperature range 300–573 K by a two-probe method. Impedance studies were carried out in the frequency region 10²−10⁶ Hz as a function of temperature (300–573 K). An Arrhenius behaviour is observed for all compositions by d.c. conductivity and the Cole-Cole plots obtained from impedance data do not show any spikes on the lower frequency side indicating negligible electrode effects. A maximum conductivity of 4·5 × 10⁻⁶ S cm⁻¹ at 573 K was obtained for x = 0·8 of the Li_3−2x Al_2−x Sb _x (PO₄)₃ system.     

The Activation Energy <Emphasis Type="Italic">U</Emphasis>(<Emphasis Type="Italic">T</Emphasis>,<Emphasis Type="Italic">H</Emphasis>) in Y-based Superconductors

Based on the Arrhenius equation, a method to calculate the activation energy from the resistance transition is proposed for high temperature superconductors. This method is applied to the Y-based superconductors. The activation energy is found to be U(T,H)∼(1−T/T _c )^4.8(H/H ₀)^−3.8 of YBCO crystal, and U(T,H)∼(1−T/T _c )^3.3(H/H ₀)^−2.2 of Er doped MTG YBCO crystal, respectively. With the obtained activation energy U(T,H), the lower part of the experimental curve ρ(T,H) and its derivative can be reproduced.      

Abrupt Increase of the Absorption Coefficient of Alumina at Melting by Laser Radiation and Its Decrease at Solidification

Experimental data for the normal-hemispherical reflectivity R of remolded aluminum oxide ceramics for wavelengths of (0.488, 0.6328, 1.15, and 3.39) μm and effective (radiance) temperatures T _eff1 and T _eff2 for wavelengths of 0.55 μm and 0.72 μm were obtained in the process of rapid subsecond heating by CO₂ laser radiation in air and vacuum from room temperature to the formation of thin molten layers of 0.6 mm to 0.7 mm thickness and of subsequent rapid free cooling with solidification of the melt when the laser radiation was blocked. Experimentally and by numerical simulation of combined radiation and conduction heat transfer, the influence of the heating radiation flux on the formation of the thin melt on the surface of ceramics with an abrupt increase of T _eff1 and T _eff2 and on the signal of the spectrometer in the infrared range from 2 μm to 11 μm at melting and on its decrease at solidification were studied. The radiation heat flux varied from 500 W · cm⁻² to 2000 W · cm⁻². It is shown that the determining effect on the temperature field and on the intensity of outgoing radiation is caused by the formation of the isothermal continuous two-phase zone and the abrupt increase (decrease) of the absorption coefficient of the melt. The importance of kinetics in the abrupt change of the absorption coefficient of molten Al₂O₃ is noted.     

Density and Volume Fraction of Supercritical CO<Subscript>2</Subscript> in Pores of Native and Oxidized Aerogels

The density and volume fraction of an adsorbed phase of carbon dioxide (CO₂) in aerogels was investigated using a formalism based on independent measurements of neutron transmission and small-angle neutron scattering from fluid-saturated absorbers (Rother et al. J. Phys. Chem. C 111, 15736 (2007)). The range of excess fluid pressures (0 <  P <  8 MPa) and temperatures (T = 35°C and 80°C) corresponded to the supercritical regime above the critical temperature T _C = 31.1°C and critical density ρ _C = 0.468 g · cm⁻³ of the bulk fluid. The results demonstrate that a porous aerogel matrix works to create an adsorbed phase with liquid-like fluid densities reaching ~1.1 g · cm⁻³ and ~0.8 g · cm⁻³ at T = 35°C and 80°C, respectively. Thus, despite the fact that the density and volume fraction of the adsorbed fluid both decrease with temperature, the dense adsorbed phase is still present in the aerogel at temperatures far exceeding the T _C. Heat treatment (“oxidation”) of the aerogel at 500°C for 2 h, which removes a significant fraction of the alkyl groups from the aerogel surface, has little effect on the adsorption properties. The observed reduction of the density and volume fraction of the adsorbed CO₂ with temperature and its minor dependence on the surface modification are consistent with predictions of the pore-filling model.     

The orthobaric liquid and vapor densities of tetramethylsilane and of 2,2-dimethylpropane

The orthobaric densities of tetramethylsilane and 2,2-dimethylpropane have been measured by means of a hydrostatic density balance. For tetramethylsilane the liquid density has been determined from 289.73 K to the critical point 448.60 K and the vapor density from 353.55 K to the critical point, while for 2,2-dimethylpropane the liquid density has been measured from 290.88 K to the critical point 433.71 K and the vapor density from 349.01 K to the critical point. The results are represented well by the extended-scaling equation of Wegner with three correction terms and the critical indices α,β, andΔ ₁, obtained from renormalization-group theory. The fit is not improved by a term expressing an anomaly in the diameter using either of the exponents (1−α) or 2β. The critical density for tetramethylsilane is estimated as (0.2436±0.0001) g·cm⁻³ and that for 2,2-dimethylpropane as (0.2318±0.0001) g·cm⁻³.     

Analysis of thermodynamic functions of silicon at high temperatures

It is for the first time that the results of experimental studies of variation of the enthalpy and heat capacity of silicon are analyzed within the framework of anharmonic expansion of the Debye model with due regard for the temperature dependence of the characteristic Debye temperature θ(T) in the temperature region above room temperature up to the melting point. The calculation results in a wide range of temperatures 300 ≤T≤ 1400 K are in rather satisfactory agreement with the experimental temperature dependence of the enthalpy variation of the material. However, in the vicinity of the melting point of siliconT _m = 1690 K, the experimental points lie above the predicted curve. The additional increment of the enthalpy of silicon in the premelting region, established for the first time in this study, is interpreted within the framework of the Frenkel thermal activation model.     

Protonic conduction in Al2(SO4)3·16H2O: coulometry,transient ionic current,infrared and electrical conductivity studies

Proton transport in Al₂(SO₄)₃·16H₂O has been established using different techniques namely coulometry, transient ionic current, i.r., DTA/TGA and electrical conductivity. The possible charge carriers are H⁺ and OH⁻ generated as a result of possible electrolysis of hydrate water molecules. The mobilities of the two charge carriers are approximately 4×10⁻⁵ and 2.4×10⁻⁵cm²V⁻¹s⁻¹. The electrical conductivity shows strong dependence upon humidity and also shows a against 1/T behaviour closely related with its thermal dehydration reaction.     

Thermal Conductivity of a Simulated Fuel with Dissolved Fission Products

The thermal diffusivity of a simulated fuel with fission products forming a solid solution was measured using the laser-flash method in the temperature range from room temperature to 1673 K. The density and the grain size of the simulated fuel with the solid solutions used in the measurement were 10.49 g · cm⁻³ (96.9% of theoretical density) at room temperature and 9.5 μm, respectively. The diameter and thickness of the specimens were 10 and 1 mm, respectively. The thermal diffusivity decreased from 2.108 m² · s⁻¹ at room temperature to 0.626 m² · s⁻¹ at 1673 K. The thermal conductivity was calculated by combining the thermal diffusivity with the specific heat and density. The thermal conductivity of the simulated fuel with the dissolved fission products decreased from 4.973 W · m⁻¹ · K⁻¹ at 300 K to 2.02 W · m⁻¹ · K⁻¹ at 1673 K. The thermal conductivity of the simulated fuel was lower than that of UO₂ by 34.36% at 300 K and by 15.05% at 1673 K. The difference in the thermal conductivity between the simulated fuel and UO₂ was large at room temperature, and decreased with an increase in temperature. Paper presented at the Seventeenth European Conference on Thermophysical Properties, September 5–8, 2005, Bratislava, Slovak Republic.     

Thermophysical Property Measurements of Supercooled and Liquid Rhodium

The density, the isobaric heat capacity, the surface tension, and the viscosity of liquid rhodium were measured over wide temperature ranges, including the supercooled phase, using an electrostatic levitation furnace. Over the 1820 to 2250 K temperature span, the density can be expressed as (T)=10.82×10³–0.76(T–T _m ) (kgm^–3) with T _m =2236 K, yielding a volume expansion coefficient (T)=7.0×10^–5 (K^–1). The isobaric heat capacity can be estimated as C _P (T)=32.2+1.4×10^–3(T–T _m ) (Jmol^–1K^–1) if the hemispherical total emissivity of the liquid remains constant at 0.18 over the 1820 to 2250 K interval. The enthalpy and entropy of fusion have also been measured, respectively, as 23.0 kJmol^–1 and 10.3 Jmol^–1K^–1. In addition, the surface tension can be expressed as (T)=1.94×10³–0.30(T–T _m ) (mNm^–1) and the viscosity as (T)=0.09 exp[6.4×10⁴(RT)] (mPas) over the 1860 to 2380 K temperature range.     

Non-Contact Measurements of Surface Tension and Viscosity of Niobium, Zirconium, and Titanium Using an Electrostatic Levitation Furnace

The surface tension and viscosity of liquid niobium, zirconium, and titanium have been determined by the oscillation drop technique using a vacuum electrostatic levitation furnace. These properties are reported over wide temperature ranges, covering both superheated and undercooled liquid. For niobium, the surface tension can be expressed as (T)=1.937×10³–0.199(T–T _m) (mN·m^–1) with T _m=2742 K and the viscosity as (T)=4.50–5.62×10^–3(T–T _m) (mPa·s), over the 2320 to 2915 K temperature range. Similarly, over the 1800 to 2400 K temperature range, the surface tension of zirconium is represented as (T)=1.500×10³–0.111(T–T _m) (mN·m^–1) and the viscosity as (T)=4.74–4.97 ×10^–3(T–T _m) (mPa·s) where T _m=2128 K. For titanium (T _m=1943 K), these properties can be expressed, respectively, as (T)=1.557×10³–0.156(T–T _m) (mN·m^–1) and (T)=4.42–6.67×10^–3(T–T _m) (mPa·s) over the temperature range of 1750 to 2050 K.     

Synthesis and characterization of Al2?xScx(WO4)3 ceramics for low-expansion infrared-transmitting windows

A low thermal-expansion material was synthesized with potential application in thermal-shock-resistant infrared-transmitting windows. The material is derived from a solid solution of Al₂(WO₄)₃, which has positive thermal expansion, and Sc₂(WO₄)₃ with a negative thermal expansion. An optimum composition of Al_0.5Sc_1.5(WO₄)₃ was identified by synthesizing solid solutions, Al_2−x Sc _x (WO₄)₃, by a solid-state route with compositions ranging from x = 0 to 2.0. A single orthorhombic phase was obtained at all compositions. A composition corresponding to x = 1.5 had a low coefficient of thermal expansion of −0.15 × 10⁻⁶/°C in the temperature range 25–700 °C. A low temperature solution combustion process was developed for this optimum composition, resulting in a single-phase powder with a surface area of ~14 m²/g and average particle size (as determined from surface area) of 92 nm. The powder was consolidated by slip-casting, sintering, and hot-isostatic pressing into visibly translucent disks with a peak in-line transmittance of 73 % at 2300 cm⁻¹. Significant infrared absorption in a 1-mm-thick disk of this material begins near 2200 cm⁻¹ and features three absorptions arising from 2-phonon transitions at 2002, 1847, and 1676 cm⁻¹. The infrared and Raman spectra are interpreted in terms of 1-, 2-, and 3-phonon vibrational transitions.     

In situ observation of the relaxation of conductivity in γ-irradiated <Emphasis Type="Italic">n</Emphasis>-type silicon under the action of ultrasound pulses

Reversible change of the electric conductivity σ_US in a temperature range of T = 110–180 K has been observed for the first time in gamma-irradiated and partly annealed (280°C) floating-zone grown silicon (n-Si-Fz) under the action of pulsed ultrasound (longitudinal wave) at a frequency of 6–10 MHz, intensity up to 4 × 10³ W/m², and pulse duration within 10⁻⁵–10⁻³ s. It is established that the temperature dependences of the parameters of acoustic-wave-induced change of σ_US (increase time, τ _i ; decay time, τ _d ) obey the Arrhenius law. Experimental τ _{i, d} (T) curves have been used to determine the corresponding activation energies (E _i ≈ 0.09 eV, E _d ≈ 0.13 eV) and preexponential factors (τ _i ⁰ ≈ 4 × 10⁻⁸ s, τ _d ⁰ ≈ 10⁻⁹ s). The observed phenomenon is interpreted as an acoustic-wave-induced transition between the states of a metastable structural defect.     

Containerless Property Measurements of Liquid Palladium

Some thermophysical properties of liquid and supercooled palladium were measured using containerless techniques. Over the 1640–1875 K temperature interval, the density could be expressed as (T)=10.66× 10³ –0.77(T–T_m)(kg·m^–3) and the ratio between the isobaric heat capacity and the hemispherical total emissivity could be rendered as (J·mol^–1·K^–1), where T_m=1828 K. The volume expansion coefficient was also determined as 7.2 × 10^–5 K^–1.