石川 毅彦

Electrostatic levitation in vacuum prevented contamination and multibeam heating overcame sample position stability problems occurring when handling boron at high temperatures. This allowed the density determination of the liquid as well as the high temperature solid states. Over the 2275-2460 K interval, the density of the liquid and undercooled phases was measured as ρ L (T) =2.17× 103 -0.25 (T- Tm) kg m-3, where Tm is the melting temperature (2360 K). Similarly, the density of the solid phase was measured as ρ S (T) =2.11× 103 -0.09 (T- Tm) kg m-3 over the 2010-2360 K range. These data provided clear experimental evidence that boron contracts (nearly 3%) upon melting, thus settling a decade long debate. © 2005 American Institute of Physics.

Electrostatic levitation and multibeam radiative heating overcame contamination and sample position stability problems associated with handling of liquid tantalum. This approach allowed the measurements of the surface tension and the viscosity of the superheated and undercooled states of tantalum using the oscillation drop method. The measurements of the surface tension could be expressed as σ (T) =2.15× 103 -0.21 (T- Tm) mN m-1 over the 2970-3400 K interval, where Tm is the melting temperature (3290 K). The value at Tm agrees well with the scarce data appearing in the literature. Similarly, on the 3000-3400 K temperature range, the viscosity was determined as η (T) =0.0035 exp [213.3 (RT)] (mPa s). © 2005 American Institute of Physics.

Surface tension and viscosity of liquid rhenium, which have hardly been measured due to the extremely high melting temperature of rhenium, were measured using an electrostatic levitation method combined with the oscillation drop technique. Sample position instability problems caused by the photon pressure of the heating lasers and by sample evaporation were solved by modifying the electrodes design. Good sample stability allowed the measurements of the surface tension and the viscosity over wide temperature ranges including the undercooled states. Over the 2800-3600 K interval, the surface tension of rhenium was measured as σ (T) =2.71× 103 -0.23 (T- Tm), where Tm is the melting temperature, 3453 K. At Tm, the datum agrees well with the literature values. Similarly, on the same temperature range, the viscosity was determined as η (T) =0.08 exp [1.33× 105 (RT)] (mPa s). © 2004 American Institute of Physics.

BaTiO3 samples were aerodynamically levitated and laser melted under containerless conditions and quenched with a twin-roller apparatus. The microstructure of the BaTiO3 samples became more refined with increasing undercooling level prior to quenching. A two-phase microstructure consisting of perovskite BaTiO3 and hexagonal BaTiO3 was observed in the samples. The dielectric constant of the samples decreased due to the presence of hexagonal BaTiO3. The formation of the two-phase microstructure was explained by a significant release of crystallization heat during rapid solidification. Roller-quenching experiments also revealed that BaTiO3 is not easily formed into glass.

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 ρ(T) = 10.66 × 10 3 - 0.77(T -Tm)(kg·m-3) and the ratio between the isobaric heat capacity and the hemispherical total emissivity could be rendered as CP(T)/εT(T) = 132.1 + 5.5 × 10-3(T - Tm)(J·mol-1·K -1), where Tm = 1828K. The volume expansion coefficient was also determined as 7.2 × 10-5 K-1.

The analysis of oxygen-deficient hexagonal BaTiO3 single crystals, with dielectric constant ε′∼105 and loss component tan δ∼0.13 at room temperature and a linear temperature dependence of ε′ in the range 70-100 K by impedance spectroscopy analysis was presented. The two capacitors, bulk and interfacial boundary layer, were also observed. It was shown that the colossal dielectric constant was mainly dominated by the interfacial boundary layers due to Maxwell-Wagner effect. The oxygen-deficient hexagonal BaTiO3 at 663 K, the ε′ and tan δ became, respectively, 2×104 and 0.007 at room temperature.

Thermophysical properties of liquid and supercooled nickel were measured using electrostatic levitation. Over the 14201850 K temperature range, the density can be expressed asp(T) =7.89 x 10(3)-0.65(T- T-m) (kg(.)m(-3)) with melting temperature T = 1728 K. The isobaric heat capacity was estimated as C (T) =36.2 + 1.9 x 10(-3)(T-T-m) (J(.)mol(-1.)K(-1)) over the 1420-1850 K interval by assuming a constant emissivity. The volume expansion coefficient was also calculated as 8.2 x 10(-5) K-1. In addition, the surface tension can be expressed as gamma(T) = 1739-2.2 x 10(-1)(T- T-m) (10(-3) N(.)m(-1)) and the viscosity as eta(T) =0.07 exp [6.7x 10(4)/(RT)](10(-3) Pa(.)s) over the 1553 to 1963 K temperature range.

The density and the isobaric heat capacity of alumina in its liquid and undercooled states were measured using an electrostatic levitation furnace. Over the 2175 to 2435 K temperature interval, the density can be expressed as p(T) = 2.93 x 10(3)- 0.12(T - T-m) (kg.m(-3)) with T-m = 2327 K, yielding a volume expansion coefficient alpha(T) = 4.1 x 10(-5) (K-1). In addition, the isobaric heat capacity can be estimated as Cp(T) = 153.5 + 3.1 X 10(-3)(T - T-m) (J.mol(-1) .K-1) if the hemispherical total emissivity of the liquid remains constant at 0.8 over the 2120 K to 2450 K interval. The enthalpy and entropy of fusion have also been calculated respectively as 109.0 kJ.mol(-1) and 46.8 J.mol(-1).K-1.

Several thermophysical properties of liquid and supercooled ruthenium were measured using electrostatic levitation. Over the 2225-2775 K temperature interval, the density can be expressed as p(T) = 10.75 x 10(3) - 0.56(T - T-m)(kg (.) m(-3)) with T-m = 2607 K. In addition, the surface tension can be expressed as sigma(T) = 2.26 x 10(3) - 0.24(T - T-m)(mN (.) m(-1)) and the viscosity as eta(T) = 0.60 exp[4.98 x 10(4)/(RT)] (mPa (.) s) over the 2450-2725 K range. The isobaric heat capacity was estimated as C-p(T) 35.9 + 1.1 x 10(-3) (T - T-m)[(J/(mol K)] over the 2200-2750 K span by assuming a constant emissivity. The volume expansion coefficient, the enthalpy, and the entropy of fusion were also calculated as 5.2 x 10(-5) K-1, 29.2 (.) kJ (.) mol(-1), and 11.2 J/(mol K).

Transparent hexagonal BaTiO3 synthesized by containerless processing exhibits a giant dielectric constant over 100000 with a loss component tan δ of about 0.1 at room temperature. The showed weak temperature dependence in the 300 to 70 K range and then dramatically dropped by 2 orders of magnitude.

The National Space Development Agency of Japan has recently developed several electrostatic levitation furnaces and implemented new techniques and procedures for property measurement, solidification studies, and atomic structure research. In addition to the contamination-free environment for undercooled and liquid metals and semiconductors, the newly developed facilities possess the unique capabilities of handling ceramics and high vapor pressure materials, reducing processing time, and imaging high luminosity samples. These are exemplified in this paper with the successful processing of BaTiO 3. This allowed measurement of the density of high temperature solid, liquid, and undercooled phases. Furthermore, the material resulting from containerless solidification consisted of micrometer-size particles and a glass-like phase exhibiting a giant dielectric constant exceeding 100,000.

The density measurements of liquid tantalum and rhenium over wide temperature range were determined using imaging technique. A spheroid sample was levitated in a high vacuum environment using electrostatic forces via a feedback loop. The radiance temperature was measured by pyrometry at a 120 Hz acquisition rate and was calibrated to true temperature. The densities of Ta and Re were measured over temperature ranges covering both superheated and undercooled phases.

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 ρ(T) = 10.82 ×103 - 0.76(T - Tm) (kg ̇ m-3) with Tm = 2236 K, yielding a volume expansion coefficient α(T) = 7.0 × 10-5 (K-1). The isobaric heat capacity can be estimated as CP(T) = 32.2 + 1.4 × 10-3(T - Tm) (J ̇ mol-1 ̇ K-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 kJ ̇ mol-1 and 10.3 J ̇ mol-1 ̇ K-1. In addition, the surface tension can be expressed as σ(T) = 1.94 × 103 - 0.30(T - Tm) (mN ̇ m-1) and the viscosity as η(T) = 0.09 exp[6.4 × 104(RT)] (mPa ̇ s) over the 1860 to 2380K temperature range.

Thermophysical properties of several refractory metals with 4d and 5d electrons (Ti, Zr, Hf, Nb) were measured by containerless methods and compared with calculations based on the HS model. Despite of rough assumptions, the determination of packing fractions and plasma parameters, agreement between measured and calculated values is good.

The density of neodymium-doped calcium aluminate (&lt 1 mol% Nd2O3·50% CaO·50% Al2O3) liquid was measured over a wide temperature range using an electrostatic levitation furnace. The density was obtained using an UV-based imaging technique that allowed excellent illumination throughout all phases of processing, including elevated temperatures. Over the 1560-2000 K temperature range, the density could be expressed as ρ(T) = 2.83 × 103 -0.21(T - Tm) (kg·m-3) (±2%) with Tm = 1878 K, which yielded a volume coefficient of thermal expansion α(T) = 7.5 × 10-5 K-1.

Here is reported a new scheme to accurately determine the vapor pressure of undercooled, liquid, and high temperature solid materials. The method relies on an imaging technique that measures the time variation of the radius of an electrostatically levitated sample. This scheme, compared to other techniques, offers unique opportunity to explore not only the liquid above the melting point but also the undercooled states of highly reactive materials in a contamination free environment. This was exemplified in this paper with titanium. For the first time, we report the vapor pressure (Vp) of its liquid phase over a large temperature range, covering the undercooled region. Over the 1700 to 2050 K temperature range, it was measured as Log Vp(T) = 9.154 - 17978 T-1 (3%). Similarly, for high temperature solid titanium, the vapor pressure could be expressed as Log Vp(T) = 16.634 - 32960 T-1 (6%) over the 1770 to 1940 K temperature interval. From these data, the average latent heats of vaporization and sublimation were calculated respectively as 344.8 kJ/kg (8%) and 632.1 kJ/kg (6%) respectively.

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 rho(L)(T) = 1.20 x 10(4)-0.44(T-T-m) (kg.m(-3)) with T-m = 2504 K, yielding a volume expansion coefficient alpha(L)(T) = 3.7 x 10(-5) (K-1). Similarly, over the 1950 to 2500 K span, the density of the high temperature and undercooled solid beta-phase can be fitted as rho(S)(T) = 1.22 x 10(4)-0.41(T-T-m), giving a volume expansion coefficient alpha(S)(T) = 3.4 x 10(-5). The constant pressure heat capacity of the liquid phase can be estimated as C-PL(T) = 33.47 + 7.92 x 10(-4)(T-T-m) (J.mol(-1).K-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 beta-phase can be represented as epsilon(TS)(T) = 0.32 + 4.79 x 10(-5)(T-T-m). The latent heat of fusion has also been measured as 15.1 kJ.mol(-1). In addition, the surface tension can be expressed as sigma(T) = 1.614 x 10(3)-0.100(T-T-m) (mN.m(-1)) and the viscosity as h(T) = 0.495 exp [48.65 x 10(3)/(RT)] (mPa.s) over the 2220 to 2675 K temperature range.

Four thermophysical properties of both solid and liquid vanadium: the density, thermal expansion coefficient, molar heat capacity at constant pressure, and hemispherical total emissivity, are reported. These thermophysical properties were measured over a wide temperature range, including the undercooled state, with an electrostatic levitation furnace developed by the National Space Development Agency of Japan. Over the (18402240) K temperature range, the density of the liquid can be expressed as p(T)/(kg m(-3)) = 5.46 (.) 10(3) - 0.49. (T - T-fus)/K with T-fus = 2183 K, yielding a volume expansion coefficient of the liquid a(T) = 8.9 (.) 10(-5) K-1. Similarly, over the (1700-2180) K temperature range, the density of the solid can be expressed as p(T)/(kg m(-3)) = 5.72 (.) 10(3) - 0.52 (.) (T - T-fus)/K, giving a volume expansion coefficient of the solid alpha(T) = 9.1 (.) 10(-5) K-1. The molar heat capacity at constant pressure of the liquid phase can be estimated as C-p,C-m(T)/(JK(-1) mol(-1)) = 48.78 + 2.75 (.) 10(-3) (T - T-fus)/K over the (1825-2225) K temperature range if the hemispherical total emissivity of the liquid phase remains constant at 0.32 over the temperature interval. Over the (1350-2180) K temperature span, the hemispherical total emissivity of the solid phase can be expressed as epsilon(T)(T) = 0.38-2.52 (.) 10(-4 .) (T/K) + 9.90 (.) 10(-8 .) (T-2/K-2). The enthalpy of fusion has also been measured as 26.5 kJ mol(-1). (C) 2002 Published by Elsevier Science Ltd.

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 sigma(T) = 1.937x10(3) - 0.199(T-T-m) (mN.m(-1)) with T-m = 2742 K and the viscosity as eta(T) = 4.50-5.62x10(-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 sigma(T) = 1.500x10(3)-0.111(T-T-m) (mN.m(-1)) and the viscosity as eta(T) = 4.74-4.97 x10(-3)(T-T-m) (mPa.s) where T-m=2128 K. For titanium (T-m=1943 K), these properties can be expressed, respectively, as sigma(T)=1.557x10(3)-0.156(T-T-m) (mN.m(-1)) and eta(T) = 4.42-6.67x10(-3)(T-T-m) (mPa.s) over the temperature range of 1750 to 2050 K.

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 rho(L)(T)=9.10x10(3)-0.60(T-T-m) (kg.m(-3)), with T-m=2896 K, yielding a volume expansion coefficient alpha(L)(T)=6.6x10(-5) (K-1). Similarly, over the 2170 to 2890 K temperature range, the density of the solid can be expressed as rho(S)(T)=9.49x10(3)-0.50(T-T-m),giving a volume expansion coefficient alpha(S)(T)=5.3x10(-5). The constant pressure heat capacity of the liquid phase could be estimated as C-PL(T)=34.2+1.13x10(-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 epsilon(TS)(T)=0.29+9.86x10(-5)(T-T-m). The latent heat of fusion has also been measured as 33.6 kJ.mol(-1).

Containerless solidification of undercooled Nd<FONT SIZE="-1">₂</FONT>Fe<FONT SIZE="-1">₁₄</FONT>B was investigated using the electrostatic levitation furnace developed by the National Space Development Agency of Japan. Spherical samples with diameters close to 2 mm were laser melted and radiatively cooled in vacuum at rates between 100 K/s and 50 K/s. Two recalescence peaks were observed in the cooling curves. They were respectively attributed to phase segregation of primary Fe and solidification of the Nd<FONT SIZE="-1">₂</FONT>Fe<FONT SIZE="-1">₁₄</FONT>B (φ) phase. The sample that solidified with the higher undercooling level showed a more refined microstructure and a higher saturation magnetization than that solidified with the lower undercooling level.

Binary Al<FONT SIZE="-1">₂</FONT>O<FONT SIZE="-1">₃</FONT>:CaO glasses containing 36-50 mole% Al<FONT SIZE="-1">₂</FONT>O<FONT SIZE="-1">₃</FONT> were synthesized by containerless processing of liquids in nitrogen using aerodynamic and a pressurized electrostatic-aerodynamic levitator. The critical cooling rate for glass formation R<FONT SIZE="-1">_C</FONT> under containerless conditions was ca. 70 K/s. The Vickers hardness of the glasses was 775-785; and the infrared transmission extended to approximately 5500 nm. The work function of the 36 mole% Al<FONT SIZE="-1">₂</FONT>O<FONT SIZE="-1">₃</FONT> composition was 3.7 eV at 1100 K.

From 1997, the National Space Development Agency of Japan (NASDA) metastable research team has studied containerless materials processing to establish undercooled and nucleation processing techniques for oxides and high-melting-temperature metals as a preparation for flying the electrostatic levitation furnace on the International Space Station. This crucible-less facility allows samples to be deeply undercooled while avoiding nucleation on the sample surface. It allows not only precise measurements of the thermophysical properties of molten sample, but also permits material processing from the undercooled state. Of the four levitation techniques (acoustic, electromagnetic, electrostatic, aerodynamic), NASDA has concentrated on the development of an electrostatic levitation system, both for use in the ISS and for fundamental research on the ground. A promising containerless experiment of a ceramic oxide using the electrostatic containerless furnace under the microgravity condition offered by a sounding rocket (TR-IA No. 7) was also carried out in 1998 and is addressed in this paper. A novel aerodynamic levitation system was developed to adopt the drop tube which gave smooth cooling curves for molten Y3Al5O12 (YAG) sample. © 2002 Elsevier Science B.V.

This paper describes a novel levitation furnace for the containerless structural study of superheated and undercooled materials by neutron scattering experiments. The article discusses the concept behind this electrostatic levitator and presents preliminary levitation and positioning control data of superheated and undercooled metallic samples. The paper also highlights the advantages of this facility, in particular vacuum conditions, sample position stability, long duration levitation times, and open field of view of the molten sample. Potential modifications of the apparatus for atomic structure and dynamic studies of dielectric oxides glass forming materials are also briefly addressed. (C) 2002 Elsevier Science B.V. All rights reserved.

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 rho (L) (T) = 7.95 x 10(3) - 0.23 (T - T-m)(kg . m(-3)) with T-m = 2742 K, yielding a volume expansion coefficient alpha (L)(T) = 2.89 x 10(-5) (K-1). Similarly, over the 1500 K to 2740 K temperature range, the density of the solid can be expressed as rho (s)(T) = 8.26 x 10(3) - 0.14(T - T-m)(kg . m(-3)), giving a volume expansion coefficient alpha (s)(T) = 1.69 x 10(-5) (K-1). The constant pressure heat capacity of the liquid phase could be estimated as C-PL(T) = 40.6 + 1.45 x 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 epsilon (TS)(T) = 0.23 + 5.81 x 10(-5) (T - T-m). The enthalpy of fusion has also been calculated as 29.1 kJ . mol(-1). (C) 2001 Kluwer Academic Publishers.

This article describes a hybrid electrostatic-aerodynamic levitation furnace for the containerless processing and study of oxide materials on the ground. Its operation principle relies on an aerodynamic levitator that allows sufficient electric charge to be accumulated on a sample, due to high-temperature heating, before electrostatic levitation can be effective. The article discusses the concept of this new levitator and presents the proof of the technical feasibility of electrostatically levitating and melting oxide material samples (BiFeO3, 49.5CaO-50.5Al(2)O(3) mol %) in a pressurized atmosphere. In addition, superheating-undercooling cycles can be performed while maintaining an exceptional sample positioning stability along the three directions. Moreover, we report the first vitrification of dielectric oxide material samples (49.5CaO-50.5Al(2)O(3) mol %) using an electrostatic levitation method. The article also discusses the advantages of this facility compared with other existing instruments for the containerless processing of oxide materials, in particular, with respect to molten sample position stability and hydrodynamic quietness, long duration levitation times, and open field of view of the sample. The facility is, in its current state, capable of novel glass synthesis. Moreover, it shows great promise for structural and thermophysical properties characterization and metastable phase studies when supplemented with the appropriate diagnostic tools. The demonstration of melting and vitrifying oxide material is also a corner stone for the design of a containerless research facility in microgravity. (C) 2001 American Institute of Physics.

Two new methods that substantially ease the processing and study of refractory metals, when an electrostatic levitation furnace is used, are reported. The first technique is concerned with preheating the sample on a pedestal, prior to launch, to a temperature (similar to 1500 K) at which thermionic emission dominates all other charging/discharging mechanisms that may be going on simultaneously. Launched into levitation at that temperature, the sample can be quickly heated to its molten state without encountering further charge loss problems. This procedure thus shortens substantially the time it takes to bring the samples to their final high temperature states at which their thermophysical properties can be measured. This technique can be applied to most materials whose melting temperatures are higher than their thermionic temperatures. The second technique described is an ultraviolet-based sample imaging configuration. Due to the excellent sample-background contrast it continuously provides during all phases of processing (from solid to overheated liquid sample), it allows the measurements of the density and the ratio of constant pressure heat capacity over hemispherical total emissivity of refractory metals. This method, compared with other imaging techniques, leads to more accurate density data at very high temperatures and to density temperature coefficients closer to those reported in the literature. This is exemplified in this article with zirconium and niobium liquid samples. (C) 2001 American Institute of Physics.

This paper describes the ground-based pressurized and vacuum electrostatic levitation furnaces (ELF) currently being developed by the National Space Development Agency of Japan (NASDA). It summarizes the levitation results, including that of a laser melted Mo sample, the first such result to be reported to date in the literature for an electrostatic levitator furnace, that of the rotation control of a Sn sample from an initial rest position to a bifurcated state by the help of a rotating magnetic field, and that of a laser-assisted bifurcated Zr sample. Also presented is a cooling curve for Nb taken on the 2900-1400 K temperature range that exhibits a 450 K undercooling.