Shinichi Yoda

New sample levitation initiation and imaging techniques for the processing of refractory metals with an electrostatic levitator furnace

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 (∼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 pr...

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 σ(T)=1.937×103−0.199(T−Tm) (mN·m−1) with Tm=2742 K and the viscosity as η(T)=4.50−5.62×10−3(T−Tm) (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 σ(T)=1.500×103−0.111(T−Tm) (mN·m−1) and the viscosity as η(T)=4.74−4.97 ×10−3(T−Tm) (mPa·s) where Tm=2128 K. For titanium (Tm=1943 K), these properties can be expressed, respectively, as σ(T)=1.557×103−0.156(T−Tm) (mN·m−1) and η(T)=4.42−6.67×10−3(T−Tm) (mPa·s) over the temperature range of 1750 to 2050 K.

Thermophysical properties of liquid refractory metals: Comparison between hard sphere model calculation and electrostatic levitation measurements

Thermophysical properties of molten refractory metals (titanium, zirconium, hafnium, and niobium) have been measured using a containerless method. Using an in-house developed electrostatic levitator, the density, the heat capacity, the entropy, the surface tension, and the viscosity of liquid phases have been measured over a wide temperature range. The measured data showed good agreement with theoretical calculations based on the hard sphere model.

Free surface heat loss effect on oscillatory thermocapillary flow in liquid bridges of high Prandtl number fluids

Abstract The effect of free surface heat loss on oscillatory thermocapillary flow is investigated in liquid bridges of high Prandtl number fluids. It is shown experimentally that the critical temperature difference changes by a factor of two to three by changing the air temperature relative to the cold wall temperature. In order to understand the nature and extent of the interaction between the liquid flow and the surrounding air, the heat transfer from the liquid free surface is investigated numerically for the conditions of the present experimental work. The airflow analysis shows that even when the heat loss is relatively weak (the Biot number is unity or smaller), the critical temperature difference is affected appreciably. It is shown that the heat loss effect is significant in widely conducted tests near room temperature and that the critical temperature difference is much larger than the room temperature value when the heat loss is minimized. The analysis suggests that an interaction between the surface heat loss and dynamic free surface deformation near the hot wall is responsible for the observed heat loss effect.

Hybrid electrostatic–aerodynamic levitation furnace for the high-temperature processing of oxide materials on the ground

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–50.5Al2O3 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–50.5Al2O3 mol %) using an electrostatic levitation method. The article also discusses the advantages of this facility compared with other existing instruments for the contai...

Non-contact Thermophysical Property Measurements of Liquid and Supercooled Platinum

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 ρ(T)=2.93×103-0.12(T-Tm) (kgm-3) with Tm=2327 K, yielding a volume expansion coefficient α(T)=4.1×10-5 (K-1). In addition, the isobaric heat capacity can be estimated as CP(T)=153.5+3.1×10-3(T-Tm) (Jmol-1K-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 kJmol-1 and 46.8 Jmol-1K-1.

A one-dimensional model to predict the growth conditions of InxGa1−xAs alloy crystals grown by the traveling liquidus-zone method

The traveling liquidus-zone (TLZ) method has been used effectively to grow ternary alloy single crystals of uniform composition. In this study, a one-dimensional model is presented to predict the growth conditions of this technique. It was shown that under the assumed growth conditions, the model gives accurate predictions for the growth conditions of the TLZ method including the composition of the grown crystals. Numerical results agree with those of experiments.

Microgravity experiments of flame propagation in ethanol droplet-vapor-air mixture

A basic study of spray combustion has been made with a rapid expansion apparatus that can produce monodispersed fuel droplet clouds under microgravity conditions. The effects of droplets on flame propagation were investigated for ethanol droplet-vapor-air mixtures. The pressure of the fuel droplet-vapor-air mixtures was set at 0.2 MPa for all experiments. The total equivalence ratio varied in the range of 0.6–1.6. The ratio of the liquid fuel mass to the total fuel mass varied from 0% to 60%, and the mean droplet diameter ranged from 7 to 45 μm. It was found that the flame speed of fuel droplet-vapor-air mixtures exceeded that of premixed gases of the same total equivalence ratio in two regions of the total equivalence ratio. One region exists on the fuel-lean side, the other exists on the fuel-rich side. For mixtures of 0.3 in the liquid equivalence ratio, the increase in the mean droplet diameter from 7.5 to 11 μm caused an increase in the flame speed in the region where the flame speed increases with the increase in the total equivalence ratio. In contrast, in the region where the flame speed decreases with the increase in the total equivalence ratio, an increase in the mean droplet diameter caused the flame speed to decrease. For mixtures with a mean droplet diameter of 11 μm, an increase in the liquid equivalence ratio from 0.2 to 0.3 caused an increase in the flame speed in the region where the flame speed decreases with the increase in the total equivalence ratio. For mixtures with a total equivalence ratio of 0.8 the flame speed reached its maximum value when the mean droplet diameter was about 11 μm and the liquid equivalence ratio was about 0.2.

Protein crystallization by using porous glass substrate.

The effects of a commercially available porous glass substrate (Corning Porous Glass No.7930) on the heterogeneous nucleation of proteins [hen egg-white lysozyme (HEWL), thaumatin and apoferritin] have been investigated in order to develop an improved method to facilitate the nucleation of protein crystals. It was found that the porous glass substrate could promote the nucleation at lower supersaturations. The induction time for nucleation decreased, and the crystals obtained from porous glass substrates were larger than those from normal glass substrates. Many pores and channels of 10-100 nm in diameter were observed on the porous glass surface by atomic force microscopy (AFM). It is believed that these pores and channels are crucial for facilitating the nucleation process in this work.

Noncontact density measurements of tantalum and rhenium in the liquid and undercooled states

Electrostatic levitation together with multibeam heating and ultraviolet imaging overcame contamination, imaging, and sample position stability problems associated with handling of liquid tantalum and rhenium. Here, the density [ρ(T)] of these metals is reported in the superheated and undercooled states. Over the 2760–3580 K interval, the density of tantalum was measured as ρ(T)=1.50×104−0.41(T−Tm) kg m−3, where the melting temperature Tm, was 3290 K. For rhenium, the density was determined (2700–3810 K) as ρ(T)=1.84×104−0.91(T−Tm), with Tm=3453 K. From these data, respective volume expansion coefficients of 2.7×10−5 and 4.9×10−5 K−1 were calculated. At Tm, the data agree well with the literature values.