Kimiyasu Sato

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.

Apatite formation on organic monolayers in simulated body environment

Organic monolayer films with the same functional groups as collagen were prepared by a Langmuir-Blodgett (LB) method and the LB monolayers were soaked in a simulated body fluid. Nucleation of hydroxyapatite (HA) took place on the monolayers of the carboxyl group, while no nucleation occurred on the monolayers of amino groups. From IR spectra analyses it was found that an interfacial interaction between carboxyl groups and Ca ions was important for the HA nucleation, causing the formation of HA crystals from the simulated body environment.

TiO2 Synthesis Inspired by Biomineralization: Control of Morphology, Crystal Phase, and Light-Use Efficiency in a Single Process

Hydroxyapatite is mineralized along the long axis of collagen fiber during osteogenesis. Mimicking such biomineralization has great potential to control inorganic structures and is fast becoming an important next-generation inorganic synthesis method. Inorganic matter synthesized by biomineralization can have beautiful and functional structures that cannot be created artificially. In this study, we applied biomineralization to the synthesis of the only photocatalyst in practical use today, titanium dioxide (TiO(2)). The photocatalytic activity of TiO(2) mainly relates to three properties: morphology, crystal phase, and light-use efficiency. To optimize TiO(2) morphology, we used a simple sequential peptide as an organic template. TiO(2) mineralized by a β-sheet peptide nanofiber template forms fiber-like shapes that are not observed for mineralization by peptides in the shape of random coils. To optimize TiO(2) crystal phase, we mineralized TiO(2) with the template at 400 °C to transform it into the rutile phase and at 700 °C to transform it into a mixed phase of anatase and rutile. To optimize light-use efficiency, we introduced nitrogen atoms of the peptide into the TiO(2) structure as doped elemental material during sintering. Thus, this biomineralization method enables control of inorganic morphology, crystal phase, and light-use efficiency in a single process.

Influence of emulsion on crystal growth of hydroxyapatite

The effect of an emulsion medium on the morphology and size of hydroxyapatite (HAp) nanoparticles was investigated. The HAp particles prepared in a pentaethyleneglycol dodecylether emulsion were smaller in size and in aspect ratio than those prepared from a non-emulsion. Morphological difference was also observed between the products prepared in the two systems. The edges of the HAp particles derived from the emulsion system were curved and rounded while those in the non-emulsion system were straight and truncated. These differences, deriving from the reaction media employed, indicated that a template effect of the emulsion can be utilized for controlling the size and habit of HAp nanoparticles.

Multistep Growth Mechanism of Calcium Phosphate in the Earliest Stage of Morphology-Controlled Biomineralization

We studied the effect of surface-functional-group position on precipitate morphology in the earliest stage of calcium phosphate biomineralization and determined the detailed mechanism of precipitation starting from nucleation to precipitate growth. The biomineralization template was a β-sheet peptide scaffold prepared by adsorption with carboxyl groups arranged at strict 7 Å intervals. Phosphate was then introduced. Within 10 s, highly ordered embryos of calcium phosphate were formed and confined by a peptide nanofiber pattern. They repeatedly nucleated and dissolved, with the larger embryos absorbing the smaller ones in a clear demonstration of an Ostwald-ripening-like phenomenon, then aggregated in a line pattern, and finally formed highly ordered nanofibers of amorphous calcium phosphate. This multistep growth process constitutes the earliest stage of biomineralization.

Colloidal processing, surface characterization, and sintering of nano ZrO 2 powders

Colloidally stable suspensions are required to fabricate dense samples with uniform microstructure by colloidal processing methods, which necessitate dispersion of ceramic powders in a liquid medium. Aqueous nano ZrO 2 suspensions were prepared using polyethylenimine (PEI) as a dispersant. PEI adsorption on nano ZrO 2 surfaces was promoted with increasing initial PEI content and suspension pH. Isoelectric point was shifted from pH 7 at 0 wt% PEI to pH 10.4 at 3 wt% PEI. Stable suspensions had mean particle sizes in the range of 100 to 150 nm and sedimentation rates less than0.4 mm/h, as compared to 2–5.5 μm and 10–50 mm/h for unstable suspensions. Samples with 98% relative density were fabricated after sintering at 1300 °C for 4 h from colloidally stable suspensions.

Fluidity of methyl cellulose-contained suspensions and pastes prepared from differently milled Al2O3 powder.

The boundary factors of transition from a methyl cellulose (MC)-contained Al(2)O(3) suspension to a paste were investigated from the view points of adsorption affinity and correlation between average surface to surface separation distance between particles (SDP) and polymer size. Non-damaged and damaged particle surfaces were prepared by wet-jet milling and ball milling, respectively. The amount of MC adsorbed on the wet-jet milled Al(2)O(3) particle surface was decreased by half compared to the ball-milled one. By increasing the solids loading from 10.0 to 12.8 vol%, the MC-contained Al(2)O(3) suspension prepared from ball milling was turned into a paste. On the other hand, it prepared from wet-jet milling was not turned into a paste even if the solid loading was increased from 10.0 to 12.8 vol%. From the creep-recovery measurements, the fluidity of the wet-jet milled sample with 12.8 vol% of solids loading was estimated to be 4 times as large as that of ball-milled one. Therefore, it was found that the state of particle surface had a strong effect on the fluidity of a suspension. The polymer size estimated from the molecular weight and Flory exponent relationship was calculated to be 266 nm. The SDP of suspensions with 10.0 and 12.8 vol% solids loading was calculated to be 215 and 165 nm, respectively. With the decreasing of SDP, the effect of adsorption affinity between the particle surface and the polymer became more striking because the contact area between them was increased. Hence, there are two factors that control the transition between a suspension and a paste; one is the relationship between SDP and polymer size, and the other is the adsorption affinity between the particle surface and the polymer.

Carbon fiber/epoxy composite materials cured thermally and with microwave irradiation

In this paper, composite materials of short carbon fibers (CFs) and a thermosetting epoxy were prepared in three different ways: without curing, thermal curing, and thermal curing followed by microwave irradiation. Mechanical properties of the three kinds of CF reinforced plastic (CFRP) composites were studied to explore the effect of microwave irradiation. Microscopic study with the aid of a scanning electron microscope (SEM) was performed on fractured composite surfaces to identify the principle features of failure. Degree of polymerization of the epoxy resin in the three CFRP composites was evaluated by infrared (IR) spectroscopy. The microwave irradiated CFRP exhibited mechanically ductile behavior even though its highest degree of polymerization. Use of microwaves and resultant stronger physico-chemical linkage at the interface between CF and epoxy resin are the main feature of this study.

Hydrothermal Synthesis of Nano ZrO2 Powders

Hydrothermal synthesis of nano ZrO2 powders were carried out at a temperature range of 100 to 200°C, using zirconium solution. Formation of ZrO2 formation was accelerated with temperature and precipitation of ZrO2 took place directly from the solution. XRD analysis revealed that monoclinic ZrO2 was formed at all conditions. Crystallite size was found to range from 2.6 to 4 nm. Mean particle size increased from 93 nm at 135°C to 125 nm at 200°C after reaction time of 2 h.

Positronium Time-Of-Flight Measurements of Porous Silsesquioxane Films

Emission of ortho-positronium (o-Ps) from the surface of hydrogen-silsesquioxane (HSSQ) low-dielectric constant (low-k) films was studied with a newly developed Ps time-of-flight (TOF) measurement system. Clear TOF peaks were observed from a high porosity film (KI31), indicating its higher open porosity in comparison with the other film (YK48) with less porosity. When the incident positron energy was raised from 0.5 to 4.0 keV, o-Ps emission energy for the former film was decreased from 1.1 to 0.07 eV. This is attributed to the increased o-Ps traveling distance inside an open pore. The presence of clear TOF peaks at high incident energies suggests that the open pores in KI31 are well interconnected.