Hideaki Nagai

Thermally conductive composite films of hexagonal boron nitride and polyimide with affinity-enhanced interfaces

Thermally conductive ceramic/plastic composite materials are needed in various industries for thermal management. The present work aimed at creating composite films of hexagonal boron nitride (h-BN) particles and polyimide. A thermal conductivity of 7 W m−1 K−1 was achieved at solids loading of 60 vol% with flexibility maintained.

Effective-Time of Pulsed Photothermal Heating for Polycrystalline Nucleation of Perovskite Oxide Films from an Amorphous Matrix

For making a photoinduced crystal growth method more universal, we have investigated the key parameters for polycrystalline nucleation from an amorphous matrix of LaMnO3 with focus on the pulsed photothermal heating time under excimer laser irradiation. We have clearly demonstrated that effective annealing time (teff) was very important for the crystallization under the excimer laser irradiation. The teff is defined as the time in which the temperature at the film surface increases over the effective annealing temperature for the crystallization of LaMnO3. The threshold of the teff value for initial crystal nucleation was evaluated to be approximately 60 ns for this material.

A Thermoelectric Zintl Phase Na2+xGa2+xSn4–x with Disordered Na Atoms in Helical Tunnels

A polycrystalline sample of Na2+x Ga2+x Sn4-x with x = 0.19 has low thermal conductivities of 0.56 and 0.58 W m(-1) K(-1) due to static and dynamic positional disorder of Na atoms in the crystal structure and dimensionless figures of merit (ZT values) values of 0.98 and 1.28 at 295 and 340 K, respectively. The performance is comparable to those of commercial Bi2 Te3 -based materials.

Thermal effusivity measurements of insulating liquids using microsized hot strip probes

A method based on the pulse transient hot strip (PTHS) technique is developed for studies of thermal effusivity of insulating liquids only requiring a drop-size sample. The original technique is here extended to single-sided measurements of liquids with a known solid background, using a probe calibrated against a liquid reference medium. Tests were made on water and silicone oils of varying viscosity (5–3000 CS). The microsized probes produce results in agreement with macroscopic bulk data, without any influence from natural convection. It is proposed that relative errors from both radiation and convection are significantly reduced when shortening the experimental time scale by several orders of magnitude. An error analysis is included, presenting design criteria to optimize measurement sensitivity and accuracy.

Characterization of Anisotropic and Irregularly-Shaped Materials by High-Sensitive Thermal Conductivity Measurements

In modern thermal analysis and design involving thermal transport in solid components it is necessary to apply different modeling of the thermal heat flow in bulk material and across solid surface interfaces either in shape of a layer or a solid-solid interface. Similar differences occur when applying different measurement techniques. Some techniques have been developed specifically for the purpose of performing measurements of bulk properties by removing the influence from thermal contact resistance between the measurement probe and the sample material. Thermal conductivity measurements on metal and ceramic objects of various geometries such as thin bars, thin sheets as well as coatings or layers are here described when using the Transient Plane Source technique. A summary overview of the recent developments of this technique, including its ability to be applied in measurement situations covering a wide range of length and time scales, is also presented. Structural changes in anisotropy can be recorded with high sensitivity by comparative measurements. The technique may be applied in situations requiring non-destructive testing, e.g. samples of particular geometry used for mechanical or tensile testing.

Ultrahigh temperature vibration sensors using aluminum nitride thin films and W∕Ru multilayer electrodes

Ultrahigh temperature vibration sensors have been fabricated from highly c-axis-oriented aluminum nitride (AlN) thin films and tungsten/ruthenium (W∕Ru) multilayer bottom electrodes. These films and electrodes were prepared by radio-frequency magnetron sputtering on zirconium oxide (ZrO2) substrates, such as AlN∕W∕Ru∕ZrO2. The vibration sensors resisted the heat treatment of 1450°C for 1h in argon, and after that, peeling and cracks were not observed in the sensor surface. The “tough” behavior of the vibration sensors in the high temperature is probably attributed to the chemical composition change of the W∕Ru multilayer bottom electrodes to Ru60W40 and Ru15W85 solid solutions that prevent chemical reactions and relax thermal stress.

Synthesis of Si–Ge Alloy by Rapid Cooling in Short-Duration Microgravity

We solidified Si–Ge alloys by rapid cooling in short-duration microgravity. When the Si–Ge melt was solidified by contact with the copper chill block (cooling rate; 100 K/s), the samples solidified in microgravity and on the ground had large grains (about 0.2 mm diameter), and were segregated. When we splat-solidified Si–Ge melt on the copper chill block by using argon gas pressure (4×105 Pa), the solidified sample contained less Ge than the starting material because of the heterogeneity of the Ge component in the melt. When we splat-solidified the Si–Ge melt in microgravity, we obtained a layer with a fine structure (less than 1 µm diameter) on the side contacting the copper chill block because of the high cooling rate (>5000 K/s). A 100-µm-thick layer with fine structure was obtained by doping with P; this layer was much thicker than that in the nondoped sample. The thermal conductivity of the sample splat-solidified in microgravity was lower than that of the arc-melted sample.

Life Cycle Assessment and Long Term CO 2 Reduction Estimation of Ultra Lightweight Vehicles Using CFRP

Japanese annual oil consumption is about 300 GL (giga liter) and energy related CO 2 emission is about 300 MtC (mega ton carbon). Among them, transport vehicles consume one third of the oil, 100 GL/year, and emit 20 percent of the CO 2, 61 MtC/year. Then, the substitution of carbon fiber reinforced plastics (CFRP) for the structural mate rial of transport vehicle is quite effective in lightening, fuel efficiency and hence the mitigation of glob al warming. In this paper, life cycle CO 2 emission and energy consumption of the ultra lightweight automobile us ing CFRP are presented first. Then, the effect of lightweight and fuel cell automobiles on the mitigation of global oil consumption and CO 2 emission is estimated under the assumption of Asian motorization.

Diamagnetic Anisotropy Detected by a Magnetic Oscillation in Drop Tube without Suspending Crystals with Fiber

A method designed to detect magnetic anisotropy Δχ with high sensitivity is improved considerably using microgravity. Oscillation of a magnetically stable axis of a crystal with respect to a magnetic field is observed in the improved method. A fiber that suspends the sample in a horizontal field in conventional methods is omitted using microgravity produced in a drop capsule; in previous methods, the restoration force of the fiber was the standard for measuring Δχ. Oscillations of ordinary diamagnetic materials such as apophyllite, calcite, KH2PO4, gypsum, Rochelle salt and urea were achieved at a field intensity of 1.30 T. Biotite and graphite oscillated at 0.0126 T; a small magnetic torque of 4 ×10-10 Nm was detected for the two materials.

EFFECT OF HEAT TREATMENT ON THE STRUCTURE OF SiC−Si3N4 COMPOSITE ULTRAFINE POWDER

Effect of heat treatment on the structure of SiC−Si3N4 composite ultrafine powder was studied. SiC-Si3N4 composite ultrafine powder synthesized by laser-induced gas-phase reaction was heat-treated at various temperatures below 1773 K in 99% Ar+1% H2 gas mixture. The change of the structure was studied by chemical analysis, x-ray diffraction (XRD), and transmission electron microscope (TEM). The structure of the powder did not change significantly in lattice constant, particle size, and composition by the treatment up to 1573 K. The structure of the powder changed drastically by the treatment above 1673 K. The broad XRD pattern due to β-Si for the original powder changed to the four phases of β-SiC, Si and α, β-Si3N4 by the treatment at 1773 K, accompanied by large increases in particle size and lattice parameter, and decreases in nitrogen content and specific surface area.