Kun'ichi Miyazawa

Processing of Carbon Nanotube Reinforced Aluminum Composite

Carbon nanotube reinforced aluminum (Al) composites were produced by hot-press and hot-extrusion methods. The interfacial structure between the carbon nanotube and Al was examined using a transmission electron microscope (TEM), and the mechanical properties were measured by a tensile test. TEM observations have shown that the nanotubes in the composites are not damaged during the composite preparation and that no reaction products at the nanotube/Al interface are visible after annealing for 24 h at 983 K. The strength of the composites is only slightly affected by the annealing time at 873 K, while that of the pure Al produced in a similar powder metallurgy process significantly decreases with time. These studies are considered to yield experimental information valuable for producing high performance composites.

C 60 Nanowhiskers Formed by the Liquid–liquid Interfacial Precipitation Method

Fine needlelike crystals of C 6 0 have been formed by a liquid-liquid interfacial precipitation method which uses an interface of the concentrated toluene solution of C 6 0 /isopropyl alcohol. The needlelike crystals of C 6 0 with a diameter of submicrons (C 6 0 nanowhiskers) were found to be single crystalline and composed of thin slabs with a thickness of about 10 nm. The intermolecular distance of the C 6 0 nanowhiskers was found to be shortened along the growth axis as compared with the pristine C 6 0 crystals, indicating a formation of strong bonding between C 6 0 molecules. The C 6 0 nanowhiskers are assumed to be polymerized via the 2 + 2 cycloaddition in the close-packed [110] c direction.

Synthesis of semicrystallized mesoporous TiO2 thin films using triblock copolymer templates

Abstract Self-assembled mesoporous TiO 2 thin films have been synthesized by sol-gel method using amphiphilic triblock copolymer as a template under acidic conditions. The samples were characterized by small angle X-ray diffractometry (SAXRD), thermogravimetry–differential thermal analysis (TG-DTA), transmission electron microscopy (TEM), N 2 adsorption and field emission scanning electron microscopy (FE-SEM). The structural characteristic of mesoporous TiO 2 thin films strongly depends on the pH values of precursor solution, heat treatment conditions, and the condensation of templates. It has been proven that the framework of obtained films consisted of TiO 2 nanocrystallites.

In-situ observed deformation of carbon nanotubes

Abstract Carbon nanotubes have a whisker-like structure so an extremely high strength and lack of plasticity are generally predicted. In-situ observations made by transmission electron microscopy, however, prove that carbon nanotubes bend plastically at room temperature. The bending process at the atomic level is suggested by a molecular mechanics calculation: a nanotube deforms elastically until certain critical curvature is attained; then the atomic bonding in the stressed side changes from a graphite-like bonding state to a diamond-like state.

Room-temperature synthesis of crystalline barium titanate thin films by high-concentration sol–gel method

We have succeeded in single-step synthesis of polycrystalline BaTiO3 thin film on glass substrate with the thickness of 500 nm at 50°C by newly established sol–gel method starting from high-concentration Ba- and Ti-alkoxide precursor solutions. The film was in good quality with a crack-free, smooth surface. The key process of crystallization of BaTiO3 at low temperature was the aging of gel film in a mist of water and alcohol in a sealed cell. The water mist may slow hydrolysis and the alcohol mist may stabilize the reactive Ti-alkoxide to associate the reaction rate with that of Ba-alkoxide. Both effects may lead the alkoxides to crystallize into BaTiO3 perovskite instead of being hydrolyzed separately. The dried and fired films showed optical transmission spectra in the wavelength range of 350–2600 nm with sharp absorption edge at 350 nm and the refractive index n=2.0 in the visible light region was estimated from the interference fringes.

Microstructure characterization of sol-gel derived PZT films

The crystallization of sol-gel derived amorphous PZT films deposited on a MgO single-crystal substrate and a SiO2 glass substrate was examined. The pyrochlore crystallites, 5 nm in size, were homogeneously nucleated in the amorphous films at 350 °C. The nucleation temperature of pyrochlore did not depend on the type of substrate. Fine pyrochlore grains were stable even during annealing at high temperatures up to 600 °C. The perovskite formation temperature was dependent on the substrate, and was about 550 °C on the MgO single-crystal substrate and about 750 °C on the SiO2 glass substrate. The perovskite was heterogeneously nucleated preferentially at the substrate-film interface. Perovskite nucleation was more difficult at the SiO2 glass-film interface than at the MgO single crystal-film interface. The ease of nucleation reflected the perovskite formation temperature. Perovskite crystals grew fairly rapidly, once they were nucleated in the films. In the multiple-coated films, the interface between successive layers of PZT films was a favourable nucleation site of perovskite, and the columnar perovskite grains passing through the interface were often developed.

Influence of hydrolysis water content on the microstructure of BaTiO3 xerogels prepared from high concentration metal alkoxide solutions

Optically clear and partially crystallized barium titanate (BaTiO3) monolithic xerogels were prepared by hydrolyzing the high concentration precursor solutions (1.1 mol/L) of metal alkoxides with water vapor to have different hydrolysis water contents (H2O/Ba-alkoxide mole ratio (rw) = 2.5–7.0). The microstructural changes of the xerogels have been studied by TEM, XRD and nitrogen adsorption/desorption analysis. The crystallite size of the xerogels was found to increase consecutively with increasing rw, while the average pore size showed no substantial increase until rw = 5.0 and it grew rapidly for rw > 5.0. The influence of rw on the microstructural development of the xerogels with heat-treatment was also discussed.

Structure and electrical properties of multilayer PZT films prepared by sol–gel processing

Abstract Multilayer PZT(Zr:Ti=52:48) films were prepared by the repeated process of spin-coating and firing at 600°C of a PZT sol with various heating rates between 20 and 200°C min −1 . Their structural and dielectric properties were examined. The multilayer film prepared with the heating rate of 50°C min −1 shows the highest dielectric constant and a smooth surface with no surface cracks. High-resolution TEM (HRTEM) observations of an as-deposited PZT film indicate nucleation of perovskite and pyrochlore crystals in the amorphous matrix. The perovskite crystals are found to form through the initial construction of {110} planes.

The diffusionless cubic-to-tetragonal phase transition in near-stoichiometric ZrO2CeO2

The diffusionless c-t transition of near-stoichiometric ZrO2ue5f8CeO2 prepared by rapid solidification process in oxygen atmosphere was examined. ZrO2ue5f8CeO2 with CeO2 content between 20 and 80 mol% are fully tetragonal and ZrO2-90 mol%CeO2 is fully cubic at room temperature. The c-t phase transition is easily completed during rapid cooling. The tetragonality of t-ZrO2 decreases linearly with increasing CeO2 content and almost disappears at a composition of about 80 mol%CeO2. The microstructure of t-ZrO2 formed by the diffusionless c-t transition in ZrO2ue5f8CeO2 is characterized by domains with anti-phase boundaries and by twins. The diffusionless c-t transition in near-stoichiometric ZrO2ue5f8CeO2 is assumed to be a second-order phase transition, as well as that in ZrO2ue5f8Y2O3 reported previously, because of the microstructural similarity between the two materials. The nature of the phase transition changes with oxygen deficiency in ZrO2ue5f8CeO2, which is generated during annealing at high temperatures and/or at low oxygen partial pressure.

The microstructure of deformed nanocrystalline Ag and Ag/Fe alloy

Structures of alloys prepared by an inert-gas condensation and compaction method and subsequently rolled were examined with interest in the deformation mechanism. The initial grain size is found to be smaller in the alloy than in the single component material, but XRD measurements indicate that a normal preferred orientation of rolling is developed in the Ag/Fe alloy slightly but not in the Ag at all. The grain growth occurs more or less but hardness is not increased by deformation in both materials. Strain contrasts along grain boundaries are observed by TEM, but tangled dislocations are found in grain interior of neither of the deformed materials. The observation has indicated that the dominant mechanism of deformation in the examined nanocrystalline materials, especially in the single component material, is considered to be grain boundary sliding accomplished by a diffusional process.