Research under Microgravity Environment

Creation of Industrial Technology Making Use of Microgravity Environment

Objectives of the Research

There is not gas and mass transfer by a convection under microgarvity, and it is dispersed mixture having a different specific gravity uniformly and effect of surface tension appears conspicuously. It is impossible to get such unique environment on the ground. As for means to get microgravity circumstances, there are a drop tower, a rocket, a space shuttle and so on. We study to establish a method to utilize microgravity environments to industry technology as a purpose by use of the facilities obtained short-time microgravity environments such as our 10 m drop tower and Japan Microgravity Center (JAMIC). To establish industry technologies using microgravity environments, we are studying the synthesis of functional metastable materials, the analysis of reaction and measurements of physical properties at the dynamic environment of heat transfer and the synthesis of form function controlled materials which a characteristic for microgravity environments profit is clear. As a means of experiment, we are using short-time microgravity environments for 10-5 g 10 seconds obtained by free-fall of 490 m of the underground facility of JAMIC (Kami-Sunagawa, Hokkaido) and for 10-3 g 1.2 seconds obtained by free-fall of 10 m of the HNIRI drop tower. We develop research on materials synthesis using 13 m drop tube on the basis of the results by the use of these fall towers furthermore.

　　　　　　　The HNIRI 10 m drop tower

The HNIRI 13 m drop tubes made of iron and glass

Novel Technology for Materials Creation

・Synthesis of Metastable State Material under Microgravity Environment

In solidification under non-contact processing, nucleation can be suppressed and the molten metal can be cooled below its melting point. This phenomenon is called supercooling, and solidification from a supercooled melt can produce a metastable solid phase, so called metastable state material. The supercooled state has been observed in solidification experiments using the 1.3 seconds microgravity condition at the Hokkaido National Industrial Research Institute (HNIRI). In our study, the technique of solidification in the supercooled state and production of metastable state material has been developed as a conventional material production technique. Our main activity is concerned with solidification of III-V semiconductor. For example, highly crystallized In-Sb alloy with impurity semiconductor properties can be produced by solidification from a supercooled melt under microgravity conditions. The impurity semiconduction was observed in an In-Sb with non-stoichiometric ratio, Furthermore, relative optical absorbance is 40 % larger than that of single crystal In-Sb produced in normal gravity. At present, it has been developed of the synthesis of the material for electronic devices of which properties may not appear when produced under normal gravity.

Single crystal of In-Sb semiconductor
　

・Synthesis of Shape-Controled New Materials

Under microgravity, surface tension of liquid is relatively enhanced, and liquid materials become spherical shape consequently. Furthermore, single crystal-like spherical semiconductors can be synthesized using supercooling state which is easy to occur when melt (metal, alloy, semiconductor etc.) is solidified under microgravity. Spherical semiconductor is considered to be used as a highly efficient photo-functional material and as a 3 dimensional semiconductor device with p-n junction. In our institute, synthesis of spherical semiconductor is investigated by melt-solidification technique using 13 m drop tube.

Ball-shape gerumanum sythesized by drop tube

Energy-Saving Industrial Technology

・The Research on Combustion Mechanism

The microgravity environment has the convenient futures for the research on combustion. The suppression of natural convection and the holding fuel particle in air become possible under a microgravity environment. This research aims to elucidate the mechanism of fuel combustion in boiler and engine to improve efficiency and solves the environmental problem.

・The Research on Solid Particle Combustion

The ignition and combustion behavior of pulverized coal particles are studying. The coal particle cloud was dispersed and suspended in air. The gaseous atmosphere, kinds of coals and concentration of coal particles are chosen as the parameters in experiments. The ignition behavior of coal particle and flame propagation in coal dust have been investigated.

0.03 s after ignition

0.06 s after ignition

0.09 s after ignition

　

・The Measurement of Temperature Distribution of Flame

The temperature profile in combustion flame is the important information to know the mechanism of NO_x or soot formation. The fine ceramic fiber was introduced in the flame as the sensor. The light emission from fiber was used to estimate the temperature profile of flame.

Combustion of three droplets array

The light emission from SiC fiber in flame

Precise Measurement of Thermal Properties of Materials

・Precise Measurement of Thermal Properties of Materials

In the case of measurement of thermal properties of liquid materials (semiconductor melt, water, organic solvent etc.), it is difficult to measure these values precisely on the ground due to thermal convection. In our study, thermal conductivities of liquid materials are measured precisely using short-time microgravity. In addition, surface tension and density of liquid materials are measured using microgravity. The precise thermal properties measured under microgravity are useful for standardization of industry and improvement of synthesis process of high-quality semiconductor.

Thermal conductivity measurement by transient hot disk method

・ Measurement of Wettability of Semiconductor melt

When single crystal is grown from semiconductor melt by using CZ technique, wettability of semiconductor melt against semiconductor crystal and crucible affects the pulling-up rate and the temperature control of melt, and the size and quality of grown single crystal are also affected. In our study, new analysis method of wettability using micrograivty was developed. In this method, work of adhesion of semiconductor droplet could be evaluated using the phenomenon that droplet own-weight became nearly zero under microgravity was developed.

Profile of HNIRI 　　

HNIRI Home Page