Oxygen-deficient hexagonal BaTiO3 single crystals were grown by a pressurized electrostatic levitation furnace. The hexagonal BaTiO3 exhibited a giant dielectric constant (ε’) at room temperature and a weak temperature dependence of ε’ in the range from 70 K to 300 K. Annealing the hexagonal BaTiO3 in air atmosphere in order to control the amount of the oxygen deficiencies improved the dielectric properties. These results suggest that the oxygen-deficient hexagonal BaTiO3 is expected as a candidate for technological application.
When the viscosity of liquid materials is measured by the oscillation drop method, it is assumed that no exernal field is present and that the oscillation is damprd only by the viscosity of the sample. In real exoeriments, some external forces are applied to the sample in order to levitate and maintain the sample position. In the case of electrostatic levitation, huge electric fields and a feedback loop are necessary to levitate a sample in 1-G. Until now, the effect of the electric field on the viscosity measurement has not been verified. In this study, viscosity measurements with sifferent sample size are conducted using a ground based electrostatic (ESL) to investigate possible effects. The experimental results clearly show that an additional damping, associated with the levitatiing electrical field, becomes more significant as sample becomes larger.
The arc-in-liquid method is a simple and inexpensive route for synthesis of the carbon nanotubes, and other related nano-materiales. In this study, we report the effects of gravity on the synthesis of carbon nano-materials by means of arcin-water nethod. The strong heat convection caused by the arc plasma is suppressed under microgravity conditions. Therefore, the boiling flow behavior and temperature distribution in the bubble at the arc plasma have been stabilized in microgravity. As a result, flow and thermal conditions in the bubble by gravity-control bring about a significant influence on the formation of carbon nano-materiales.
We precisely analyzed the surface tension and the viscosity of Ni-Al and Ti-Al melts by the oscillation drop method including droplets rotation effects. Under microgravity conditions, beat-like radius variations due to drop method were pbserved on the oscillating droplets in electromagnetic levitation (EML) experiments. The beat-like radius variation prevents to evaluate the surface tension and the viscosity, thus we need to solve the problem about droplet rotation for obtaining the correct surface tension and viscosity. From this purpose, we performed numerically simulation of three-dimensional droplet shap with rotation, surface oscillation by the surface tension and its damping by the viscosity. From the simulation result, we proposed analytical technique to exaluate surface tension and viscosity from the beat-like radius variations of surface oscillating dloplet with rotations. We applied the technique into the oscillating drop date of Ni-Al and Ti-Al melts obtained by EML experiments using TEMPUS under microgravity conditions on board parabolic flights. As a result, it was confirmed that the surface tension snd viscosity were precisely determined even undersroplet rotating conditions.
We have developed a new crystal growth method named the traveling liquidus-zone (TLZ) method and found that the TLZ method is promising for growing compositionally uniform alloy crystals such as In0.3Ga0.7As and Si0.5Ge0.5. Our one-dimensional TLZ growth model predicts precisely the sample translation rate for growing homogeneous alloy crystals when the mass transport during the crystal growth is diffusion-limited. If convection occurs in a melt, control of the mass transport gets difficult and compositional uniformity is deteriorated. Then, we investigated the effect of convection during the crystal growth of InxGa1-xAs (x: 0.1～0.3) experimentally. We also tried to suppress convection in a melt by reducing the melt thickness in platy crystals terrestrially. Here, we report on experimental results performed for inves-tigating effect of convection in the TLZ growth method.
Solid 4He is grown in the superfluid, and its growth rate becomes enormously high at low temperature. The equilibrium crystal shape is sensitive to the gravity due to this enormously fast growth rate. The true crystal shape should be studied under the microgravity environment. The present study is the basic research aimed at the experiment in the space. The main result presented here is a new finding of the very fast growth rate ofc-facet driven by the acoustic wave and observed with the fast video camera. The new mechanism of the facet growth is presented to explain the experimental result. Some possible experiments with respect to the crystal shape of 4He are also presented to be performed on the jetplane.
Atomic oxygen concentrator is developed in order to achieve acceleration tests of atomic oxygen exposures in low Earth orbit (LEO). A ``mufti ring-type'' atomic oxygen concentrator is designed with a computer simulation using the Hard Cube Model. It is made clear that the theoretical concentration factor of atomic oxygen is expected to be 64, however the experimental value is restricted to be approximately 9. The primary factor for limiting the concentration factor is considered to be a gas build-up near the focal point. In the ground test using a laser detonation source like this study, which gives an intense atomic oxygen beam pulse within 30 μs, the concentration factor is limited by the recombination reaction of atomic oxygen in the beam pulse. However, this is not a case in the real LEO space environment. It is expected that the ``multiple ring-type'' concentrator can be expected the concentration factor over 40 in LEO.
To produce high-quality materials, a large number of studies have been carried out for the solidification and melting processes of metals and semiconductors in both terrestrial and space environments. This paper aims to describe a series of experiment on the effect of the thermocapillary convection upon the directional solidification in a liquid layer with the free surface in case of stationary and growing solid-liquid interface (SLI). If no free surface exists, the SLI is vertical and straight. On the other hand, with the free surface, the SLI is inclined against the wall-normal direction due to the thermocapillary convection. It is also found that even if the growth rate of the SLI at the free and bottom surfaces is equal, a distinct difference is observed in the solidification morphology between the both surfaces. At the top surface, we found a cellular morphology with a secondary perturbation, which was not observed in experiments hitherto.