Rotation of a horizontal cylinder is proposed as a new method to realize effectively-reduced gravitational environment, which suppresses the convective mass transport during crystal growth from vapor. Numerical calculations were carried out in order to evaluate the effect of this method. The reduction of Sherwood number (Sh) was confirmed and a characteristic feature of this method, the transient increases of flow velocity accompanied by the transition from the boundary-layer driven regime (BLDR) to the core-driven regime (CDR), was found . Crystal growth of ZnSe by chemical vapor transport method (CVT) using iodine as a transport agent was carried out in order to demonstrate the effect. The experimental results agree with the numerical prediction, and stable growth of ZnSe singe crystal with a diameter of 1 inch was achieved.
We synthesized diamond from a graphite source in terrestrial and high gravity experiments. Diamond was deposited on silicon substrates. These deposits were characterized by scanning electron microscopy and Raman spectroscopy. The completely closed reaction chamber, which designed and manufactured at Teikyo University of Scienece and Technology, is easy to install on a centrifuge. We successfully synthesized diamond at high gravity on a large centrifuge at Clarkson University. Compared with terrestrial experiments, high gravity significantly affected the particle size and coverage. Under our experimental conditions, the crystal growth rate was increased at high gravity. This new reaction chamber is also very suitable for space experiments. Even with the limited volume and electric power available in spacecraft, we can install many of our chambers.
Experimental studies on the formation of a homogeneous spray and its ignition and combustion behaviors have been carried out by using microgravity conditions produced by a drop shaft. A rapid expansion apparatus was newly developed for the microgravity experiments. Homogeneous sprays were generated by rapid expansion of saturated fuel vapor-air mixtures. Microgravity conditions were applied to prevent the generated droplets from falling by gravity. Methanol and air were used as a fuel and an ambient gas, respectively. Telemicroscope and shadowgraphy were employed to observe the behaviors of the droplet formation and the flame propagation.
The homogeneous sprays up to about 30 µm in mean droplet diameter were generated successfully. It was experimentally shown that the mean droplet diameter, the total equivalence ratio and the ratio of liquid fuel to vapor fuel, which are important parameters for spray combustion, can be controlled independently with the rapid expansion apparatus. Two types of the flame propagating through a stationary homogeneous spray were observed under microgravity conditions.
Mega-gravity field (strong acceleration field) can realize the sedimentation of even atoms, and is expected to create a nonequilibrium crystal-chemical state in multi-component condensed matter . However, the materials science research in mega-gravity field has now remained as an unprecedented area, although the micro-gravity field has been much used in materials science. We presented a self-consistent theory of the sedimentation of atoms in condensed matter, and developed a ultracentrifuge apparatus to generate a strong acceleration field of over 1 million (1 X 106) g at high temperature . Recently, we , for the first time , succeeded in formation of the atomic concentration distributions caused by sedimentation of component atoms in an alloy. In this article, the effects on atoms, molecule and crystal, and the applications strong acceleration field are discussed on the basis of the theoretical and experimental results . The ultracentrifuge apparatus is described , and the recent mega-gravity field experiment on the Bi- Sb system alloy is shown. It is suggested that the sedimentation of atoms and the instability in molecular or crystalline state under a mega-gravity field will be used as a new materials processing, to control compositions, impurities or isotopes, to form graded structure, and to control micro-structure in solids, etc., in many fields such as metallurgy, semiconductor science, polymer science, solid state chemistry, nucleonics, etc., as well as biochemistry.
Simultaneous observation of flow patterns and surface temperature distributions was conducted in a microgravity experiment in the sounding rocket TR-IA #6 with the aim of understanding characteristics of unsteady Marangoni convection in a liquid bridge simulating a half floating zone model. The liquid bridge was 28 mm in diameter and 20 mm in length, and the temperature difference of 50 K was imposed between the heated and the cooled disks so as to achieve a super critical condition. Flow patterns visualized and measured by three-dimensional trajectories of tracer particles have revealed unsteady and complicated flow patterns exhibiting vortex-like circulation zones in the corner region near the disk edge. Time-resolved surface temperature distributions measured with an infrared camera showed intermittent surface temperature fluctuations, which were revealed to be corresponding to the passage of hot fluid lumps coming down from the heated disk. Unlike expectation, no obvious rotational motions were recognized in the three-dimensional particle trajectories or in the surface temperature distributions.
The diffusion coefficient of liquid lithium, which is expected to show large isotope effects because of its small atomic mass, was measured by the long capilary method under the microgravity due to the launch of the sixth TR-IA rocket. The detailed description is given for the procedure of the microgravity experiment for the very active element such as liquid Li. The smaller diffusion coefficient was obtained for 7Li in 6 Li compared with the case of 6Li in 7Li. These behaviours were discussed from the point of view of the hard sphere model.
In order to clarify the solidification mechanisms of Al-Ti and Al-Ti-B system alloys under microgravity conditions, experiments are carried out by using Sounding Rocket TR-lA No. 6. Different compositions of six samples are melted and solidified in the two isothermal furnaces on board the rocket. In the higher temperature furnace of 1400°C, the hyper-peritectic composition of Al-1.3%Ti alloy revealed that the primary TiAl3 crystals distributed in the melt act as nucleation sites and then form granular crystals. The hypo-peritectic alloy revealed that the TiAh and TiB2 crystals in the Al-Ti and Al-Ti-B master alloys are melted perfectly and then the large crystals form. In the lower temperature furnace of B00°C, TiAh and TiB2 crystals in the master alloy remained and they nucleated the granular crystals as if the peritectic reaction occurred.
Marangoni convection of silicon melt was studied from the viewpoint of a heat and mass transfer for a low Prandtl number liquid. Temperature measurement and flow visualization in a half-zone bridge of molten silicon were carried out in a microgravity condition using the NASDA TR-IA-6 rocket. Fourier-transformation analysis of temperature fluctuations showed several peak frequencies for the microgravity condition when a temperature difference between interfaces of the bridge was 47.0 K. On the other hand, a single peak was seen when the temperature difference was 32.5 Kin the ground-base experiment. It is thought from those analyses that the transition from non-periodic to periodic flow of the silicon Marangoni convection in a half-zone liquid bridge system exists between these conditions. With using X-ray radiography, tracer motions in the azimuthal directions were observed near the molten silicon surface. This observation indicates that the tracer motions are driven by the temperature fluctuations in the azimuthal direction.