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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

Microgravity conditions give additional benefits such as:
1.) Positioning forces for containerless processing under ?-g are much smaller than that under 1g
2.) Thermally and externally induced convection by gravity and especially, in case of containerless processing by electromagnetic levitation, electromagnetic oscilation is strongly reduced.  Furthermore, In case of drop tower experiment, there are neither additional foraces free nor perturbations against fall droplet. These may have essential impact on the microstructure formation from the liquid state;
　


・Synthesis of high performance magnetic materials

The new magnetic alloys are peritectic. They contain elements of rare earth metals, which are chemically very reactive. Processing of liquid cause, therefore problems of chemical reactions with container materials and environmental gases. There are many phases of the new magnetic materials because of peritectic reactions and intermetallic compounds.  One of the new magnetic materials is the mixture of the different type of the magnetic phases such as spring magnets containing soft and hard phase.  Therefore, it is very important to synthesize a homogeneous metallurgical structure alloy with nanometer size. The research aims to produce high performance magnetic materials. In particular, experimental techniques such as containerless processing and one-directional solidification both in the Earth laboratory as well as under microgravity conditions are utilized in overcoming difficulties in the preparation and in the improvement of advanced processing of such materials.
 

     Figure 1: Schematic diagram of container;ess prosessing apparatus for microgravity experiment

     Figure 2: Schematic diagram of unidirectional solidification apparatus for microgravity experiment
 

・Synthesis of Shape-Controled New Catalyst

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 titanium dioxide with anatase type structure is considered to be used as a highly efficient photocatalyst. In our institute, synthesis of spherical photocatalyst is investigated by melt-solidification technique using 13 m drop tube.
 

     Figure 3: Schematic diagram of container processing apparatus for synthesis of shape-controled catalyst.

     Figure 4: View of solidification and oxidation process of titan in container processing
 

・Synthesis of shape-controlled new materials

The unique phenomena, such as keeping the uniformity of liquid materials etc., can be used under microgravity circumstances, and we found that the high quality crystalline materials, such as single crystal etc., could be prepared by solidification method from molten metal under microgravity circumstances.  Many electric device are manufactured from film-like or plate-like semiconductor, then we are studying the basic and technical researches for the production of the plate-like high quality crystalline materials by melt-solidification method under microgravity circumstances.

Synthesis of plate-like high quality crystalline material by unidirectional solidification

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 NOx 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

 
 

・Development of NOx-suppressed high-efficiency combustion technology

The elimination of convection under microgravity allows fuels to be steadily combusted. As a consequence, the complicated combustion behaviors, such as soot formation, are possible to be more clearly visualized. In this research, our studies have measured the combustion rate constants and droplet temperature histories, which resulted in the insight of the droplet burning process from ignition to extinction. Based on these results, further research is being conducted to develop new combustion technologies that have not only high efficincy but also low NOx emission.
 

Precise Measurement of Thermal Properties of Materials

　　　　　　　　　　　　　　

・Precise measurement of thermal properties of materials

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

                                                                             ・The system of Hot-Disk method            ・Thermal conductivity of molten Si under μ-g and 1-g

・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 circumstances 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.  The simple measurement method of density of semiconductor melt is studied by use of its spherical shape under microgravity circumstances.
 
 

                                                                             ・Shape change of molten Ge     ・Temperature-dependence of wettability of molten Ge

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