Gas-evaporation synthesis of metalofullerene:La@C82 was conducted by a direct current arc evaporation of C/La2O3 composite electrode in a rotating chamber in which the thermal convection of helium buffer gas was significantly reduced. The La@C82 content in the soot under the gas pressure of 0.2-0.3 atm was enhanced by the reduction of the thermal convection. However, on the yield of C60 synthesized as a by-product of La@C82, the thermal convection had no significant effect at high gas pressure condition, where prominent effect of the thermal convection was observed on the yield of C60 synthesized from a pure carbon vapor. This result suggested that the lanthanum and oxygen atoms in the carbon vapor affected significantly the formation process of C60 as well as La@C82, resulting in a change of the macroscopic effect of thermal convection.
As new functional carbon material, carbon clusters such as fullerenes, carbon nanotubes (CNTs) and carbon capsules are very attractive, and efficient and high-quality production of carbon clusters is an important research target. In production of these carbon clusters by the arc-discharge method under Sub-atmospheric pressure, gravity (heat-convection) strongly influences on the production. Under gravity-free condition, the diffusion speed of carbon molecules becomes very low, and the reaction time of the clusters under hot-gas atmosphere could be much larger (the cooling rate is much lower) . Here, the effects of micro-gravity in the parabolic-flight experiment of production of carbon nanotubes, fullerenes and carbon nano-capsules are presented.
Diamond synthesis under microgravity environment with parabolic flights by DAS and rocket by JAXA was reported. Gaseous species on the reaction chamber were detected and analyzed with OES (optical emission spectroscopy), under terrestrial gravity environment and microgravity environment, and we expected that synthesized diamond particles might have some deferent morphology compare with terrestrial conditions. Unfortunately, this particular launch was not retrieved, so we don't have our diamond samples for confirm SEM and Raman spectra.Key wards: Diamond, Space Utilization, OES(optical emission spectroscopy)
Synthesis of bulk materials in the short-duration microgravity of the AIST's 10m drop tower have been studied. The unidirectional cooling apparatus combined with rapid cooling system was developed for the short-duration microgravity experiments. Congruent melt materials were focus to the experimental target. CdTe with a few mm-sized grains were obtained from the melt in the microgravity experiment. The cooling profile explains obvious undercooling with released latent heat. When some of impurities were added into the melt, well-oriented needle like structures were grown. Well-oriented structures are useful for improving material functions. Zn4Sb3, with oriented grains obtained in the microgravity experiment had 50% higher thermoelectrical properties in the perpendicular direction of cooling direction than that in the parallel direction of cooling direction.
We have succeeded in growing homogeneous InGaAs single crystals by the traveling liquidus-zone (TLZ) method. In the TLZ growth, crystallographic orientation of grown crystals indicates anomalous feature. That is, crystallographicaxis of terminal grown parts orients to feeds’ direction, not to seeds’ direction. This research aims at specifying the factor of such unique crystallization. Quenching experiments were performed to analyze composition and crystallographic orientation at the initial state of the TLZ growth process. As a result, a single crystal of slender InGaAs was grown in the narrow gap between the feed GaAs and the wall of the BN crucible. We conclude that this slender InGaAs single crystal is the trigger of the single crystallization. Besides, we suggest that the slender InGaAs single crystal is not dissolved in the TLZ growth process and platy InGaAs single crystals which take over the feeds’ orientation are grown.
The paper describes the methods to grow homogeneous ternary alloy semiconductor bulk crystals. InxGa1-xSb bulk crystal was grown on a GaSb seed under a constant temperature gradient using a GaSb(seed)/InSb/GaSb(feed) sandwich sample. A GaSb feed was dissolved into the InGaSb solution to supply GaSb component during the growth. The temperature gradient in the solution was estimated from the indium composition profile of the grown crystal using the InSb-GaSb pseudo binary phase diagram. In order to measure growth rate, tellurium impurity striations were intentionally introduced into the crystal by thermal pulse technique. The growth rate gradually increased to the constant value and then rapidly decreased. Nearly homogeneous In0.03Ga0.97Sb within the fluctuation of 0.005 was grown by cooling the sample at the optimized value estimated from the temperature gradient and the growth rate. The method was applied to grow homogeneous InxGa1-xSb ternary alloy bulk crystal on an InSb seed. The nearly homogeneous In0.8Ga0.2Sb and In0.6Ga0.4Sb crystals within the fluctuation of 0.05 were grown by decreasing the temperature with an optimized cooling rate of 0.77 ˚C/h and 0.33 ˚C/h, respectively.
The functional materials of Si-Ge alloy and B-FeSi2 were prepared by using the combination of the short-duration microgravity, such as drop tower and drop tube, and rapid solidification. When the sample was melted on the ground, the melt seemed to be uniform because of strong thermal convection. The sample solidified in microgravity was uniform because of rapid solidification in maintaining uniformity of the melt. In contrast, the melt solidified on the ground seemed to segregate due to argon gas pressure because of the large difference of specific gravity of the constituent elements. This heterogeneous microstructure and composition of the sample solidified on the ground was caused by a heterogeneous melt. The sintered sample with high performance and thin film with single phase were prepared by using these uniform samples.
Temperature dependence of liquid Si (l-Si) density has been interested from view point of both industrial applications and condensed matter sciences. These are due to that Si has an unusual property at melting. When Si crystals melt, unlike other metals, their volume expands about 10 percent. Therefore l-Si has been interested from atomic structure, thus the density and the structure of supercooled l-Si have been measured by using some levitation technique, electromagnetic levitation (EML), electrostatic levitation (ESL) and conical-nozzle gas levitation (CNL) technique. Using ESL technique, the results of temperature dependence of l-Si density showed quadratic temperature dependence. On the other hand, quadratic temperature dependence of l-Si density has not been confirmed in the results of measurements using EML technique, because the results of EML technique had large variation in temperature dependence. The existing the maximum density in undercooled regions expected from the first principle molecular dynamics (FPMD) simulations. We performed the precise measurements of density of supercooled l-Si using EML technique with static magnetic fields and also performed structure analysis of l-Si by x-ray diffraction combined with the FPMD. The observed density of supercooled l-Si density and the FPMD results shows good agreement in the temperature range from 1450K to 1800K. The structure of supercooled l-Si was also good agreement between experiments and FPMD simulations. Based on these results, we discuss about the existence of density maximum in supercooled l-Si which is well known in water (H2O) at 4°C.
The Nd-Fe and Nd-Fe-Al alloys were containerlessly solidified by using two types of drop-tubes: short and long ones, the free fall lengths of which are 3 m and 26 m, respectively. The diameters of as-dropped samples formed by using these short and long drop-tubes are ranged 100-1000 and 100-2300 mms, respectively. The coercivities of the as-dropped Nd-Fe-Al samples formed in the long drop-tube increased with decrease of the diameters, but in the samples with diameters less than the critical one, the coercivities decreased whereas the saturation of the magnetization increased. The reason for this phenomenon is ascribed to the formation of soft magnetic phases such as an amorphous phase due to the high cooling rates. In Nd-Fe alloys, on the other hand, all of the as-dropped samples exhibited hard magnetic properties, Hc = 4.6 kOe. The microstructures of the as-dropped 90Nd-10Fe samples consisted of primary a-Nd and the included metastable phases. In as-dropped 70Nd-30Fe samples with diameters of 212-300 mms, the microstructure consisted of primary metastable phases and fine a-Nd. Considering the previous experimental results using the gas-jet electromagnetic levitator, it can be concluded that the high coercivities of the as-dropped Nd-Fe samples are attributed to this fine metastable phase and a-Nd. Key Words: Containerless process, Short drop tube, Microgravity, Size effect, Non-equilibrium solidification.
8Nd_2Dy_85Fe_5B droplets were containerlessly solidified using a 26m drop tube. The substitution of Dy for Nd in the 10Nd_85Fe_5B sample suppressed the formation of the a-Fe phase and promoted the crystallization of theRE2Fe17Bx metastable phase. The sample with a diameter range of 1200uM to 1500uM mainly consisted of the RE2Fe17Bx metastable phase. The metastable phase was partially decomposed into the a-Fe and RE2Fe14B phase during the postsolidification cooling stage. When the sample washeated, the metastable phase decomposed into the a-Fe and RE2Fe14B phases at around 1140K which was 40K higher than that in the 10Nd_85Fe_5B ternary alloy. Key Words: Metastable phase, Undercooling, solidification, Nd-Fe-B magnet, Containerless processing
Giant magnetostrictive materials, Tb0.297Dy0.679Fe2, were synthesized by unidirectional solidification of a mixture of Tb0.99Fe2 and Dy0.97Fe2 alloys in microgravity with magnetic field of 0 to 0.12T. Tb0.297Dy0.679Fe2 is a mixed crystal of TbFe2 and DyFe2. Tb0.297Dy0.679Fe2 synthesized in microgravity with no magnetic field had sheet-dendrites structure with 300 (cooling direction) x 200 x 30µm (thickness) and Fe-rich layer between the sheet-dendrites growing in the cooling direction, and exhibited a tendency for crystalline orientation of ＜110＞ and ＜111＞ with the cooling direction. The magnetostriction with the cooling direction was 9000ppm at an external magnetic field of 120mT. In contrast, Tb0.297Dy0.679Fe2 synthesized by unidirectional solidification in normal gravity with no magnetic field had a dendrite structure with a 30µm diameter x 250µm length growing in the cooling direction and no preferred orientation. The magnetostriction along the cooling direction was 2000ppm at an external magnetic field of 120mT. Analysis of the solidification in microgravity with magnetic field revealed that the dendrites oriented along the cooling direction and that the tendency for crystalline orientation of ＜110＞ and ＜111＞ with the cooling direction increased with increases in the magnetic field. Examination of the solidification in normal gravity with magnetic field indicated that Tb0.297Dy0.679Fe2 consisted of sheet dendrites without orientation and revealed no preferred orientation. The magnetostriction along the cooling direction increased with increases in the magnetic field. The effects of microgravity and magnetic field on the structure and crystalline orientation were considered.
BaTi2O5 spherical glasses were prepared using a containerless processing with an aerodynamic levitation furnace. The BaTi2O5 glasses were found to demonstrate some attractive physical properties e.g., giant dielectric response accompanied with crystallizations of two metastable phases, high transparency in visible and mid-infrared region, high refractive index with low abbe number, and high solubility of rare earth ions. We attribute these properties to the unusual local structure of the BaTi2O5 glass consisted of edge- or corner- shared distorted TiO5 polyhedra. In this paper, we report recent research progress on the BaTi2O5 glasses.
A crystallization process in the early solar nebula 4.6 billion years ago has been simulated by using microgravity and levitation methods through the investigation of the formation mechanism of chondrules, which are mm-sized spherical crystals, formed from silicate melt droplets during the formation of the solar system. Although the time required for the crystallization of chondrules has been believed to be several hours to days, our results strongly suggest this crystallization time be much shorter, a few seconds. The chondrules were crystallized from large supercooled or hypercooled melts. This short-time crystallization hypnosis has been supported by numerical simulations based on shock wave model.