Papers by Author: Hideaki Sano

Abstract: The purpose of incorporating CNTs into ceramic materials is to enhance the toughness of ceramic materials, in which the interface plays a key role. Due to the nanoscale of nanocomposites, however, it is not easy to acquire a direct knowledge of the interface behavior. In this research, we simulated the dynamics of CNT/SiC and branched CNT/SiC under uniaxial tensile stress using molecular dynamics method (LAMMPS). The simulation method using molecular dynamics provide an insight into designing an effectively toughened ceramic nanocomposite materials.

Abstract: Effects of carbon nanotubes (CNT) addition on mechanical properties, electric conductivity and oxidation resistance of CNT/Al₂O3-TiC composite were investigated. It was found that flexural strength, Young’s modulus and fracture toughness of the composites were improved by addition of more than 2 vol%-CNT. In the composites with more than 3 vol%-CNT, the oxidation resistance of the composite was degraded. In comparison with Al₂O3-26vol%TiC sample as TiC particle-percolated sample, the Al₂O3-12vol%TiC-3vol%CNT sample, which is not TiC particle-percolated sample, shows almost the same mechanical properties and electric conductivity, and also shows thinner oxidized region after oxidation at 1200°C due to less TiC in the composite.

Abstract: Spherical carbon nanoparticles were prepared by the polycondensation of resorcinol and formaldehyde using sol-gel method in the presence of cetyltrimethylammonium bromide (CTAB) and subsequent carbonization. Addition of carbon nanotubes (CNTs) in the precursor solution resulted in CNT/carbon porous composites. The effect of carbon nanotubes (CNTs) on the microstructure, pore structure and electrical double layer capacitance of CNT/porous carbon composites was examined based on the field emission scanning electron microscope, transmission electron microscope observation, N2 isothermal adsorption, cyclic voltammetry and charge/discharge tests. The results showed that 20% CNT addition had little effect, but 50% CNT addition significantly changed the microstructure and pore distribution, and charge/discharge properties.

Abstract: Spherical carbon nanoparticles were synthesized by sol-gel polymerization of resorcinol and formaldehyde in the presence of CTAB(cetyltrimethylammonium bromide) and subsequent carbonization at 900°C. It is found that the amount of CTAB, water and catalyst showed a significant impact on the morphology and size of carbon nanoparticles. According to the BET surface area and capacitance, the nanoparticles were divided into two groups. The carbon nanoparticles with surface area of 725-758 m2/g showed capacitance between 120-140 F/g, while those with surface area of 596-649 m2/g showed capacitance only 60-80 F/g. Difference in the pore size of 1.5 nm to 3.0 nm probably contributed to the difference of capacitance.

Abstract: B4C and SiC particle-dispersed carbon composite were fabricated from calcined pitch coke, B4C and SiC with various particle size by grinding and then pressureless sintering. During non-isothermal oxidation test up to 1400°C in air atmosphere, oxidation behavior of the C/B4C/SiC composite was clarified by means of calculation of kinetic parameters using experimental data of mass change, gas formation of CO2, and oxygen gas consumption. Amount of the matrix carbon oxidized above 800°C in the composite with SiC particle of 0.4 µm and 0.9 µm in size was less than that in the composite with SiC particle of 50 nm and 1.8 µm in size. The oxidation of the matrix carbon was shown to depend upon the formation of B2O3 glass below 800°C oxidation, and that of SiO2 glass above 800°C. The composite containing SiC with 20 nm in size was stable against oxidation above 1400°C except the temperature ranging from 900°C to 1100°C.

Abstract: Carbon nanotubes and nanofibers were synthesized at 400-800°C by a typical CVD method using SiO2, Al2O3, or MgO supported Ni or Co catalyst, and acetylene as feedstock. The effects of temperature, substrates and catalyst on the yield and structure of carbon nanotubes and nanofibers were investigated in detail. The experimental results showed that Ni based catalysts tended to form carbon nanofibers with “herringbone” structure, though for Ni/Al2O3 catalyst, the products at 800°C changed to a structure like carbon nanotube. Co based catalysts tended to form carbon nanotubes.

Abstract: The effect of TiC content on oxidation behavior of the sintered WC-TiC-TaC alloys with 2 mass% TaC and different TiC amount of 3-45 mass% was investigated through oxidation tests in air at 973K in order to clarify their oxidation mechanism at high temperature. Based on the results of mass change, SEM observation, elemental map analysis and composition analysis of the samples before and after the oxidation test, it was revealed that with increasing TiC content in the alloys, mass changes from oxidation and thickness of the oxidation scale decreased. Thus, it is considered that the main component of the scales changed from WO3 to TiO2 gradually with increasing TiC content in the alloys, and oxygen diffusing through the oxidation scale to the alloys was inhibited more and more.

Abstract: The effect of oxygen addition on oxidation behavior of the β-Si3N4 ceramics with 5 mass% Y2O3 and 2 or 4 mass% Al2O3 was investigated by performing oxidation tests in air at 1300° to 1400°C and cutting performance tests. These tests were intended to clarify their ware resistance as cutting tools. The results of mass change, SEM observation and composition analysis of the specimens before and after oxidation test showed that as the Al2O3 content in the β-Si3N4 ceramics increased, mass changes resulted higher oxidation during which process pores and cracks formed due to the release of N2 gas. The values of hardness and bending strength of the specimens with relatively small amount of 2 mass% Al2O3, which formed solid solution in the Si3N4 structure [Si6-zAlzOzN8-z (z = 0.1)], showed larger than those of the specimen with 4 mass% Al2O3 (z = 0.2). The specimens group added with Al2O3 of 2 mass% (Z = 0.1) also showed high wear resistance. From this, we could conclude that the mechanical properties of β-Si3N4 ceramics depending on oxygen introduction is much effective on cutting performance improvements of the cutting performance of β-Si3N4 ceramics.

Abstract: Change in mass and gas concentration during oxidation of carbon matrix composite added with B4C and SiC particles as an inhibiter for oxidation were measured continuously and accurately using a thermogravimetric analyzer, a couple of zirconia type oxygen sensors and infrared CO-CO2 gas analyzer. Total amount of oxygen consumed, the amount of oxygen consumed for matrix carbon oxidation, the amount of oxygen incorporated in CO and CO2 gases, total oxygen consumption rate during oxidation of the composite were obtained. The amount of glass phase formed from the inhibiter and the amount of matrix carbon oxidized could be estimated from calculation of a mole balance between the total oxygen consumption and the amount of oxygen incorporated in CO and CO2 gases. Oxidation behavior and oxidation mechanism of the C-B4C-SiC composites were clarified.

Abstract: A thin film including β-silicon carbide was synthesized by a reaction of silicon monoxide gas and carbon source derived from polyimide film (PIF) at 1400°, 1500°, 1600°, 1700° and 1800°C. Formation mechanism of the SiC film was investigated thermodynamically and kinetically through the relationships among the conversion ratio of SiC, synthesis temperature and time. The formation processes were simulated based on the calculation of differential equations concerning thermodynamic and kinetic constants of 7 chemical equations. The sample obtained had a film shape similar to that of the carbon source film. The results of the time dependence curves of the conversion ratio of SiC calculated from 7 chemical equations, 14 rate constants, 2 diffusion constants, 10 chemical species and 10 differential equations are in good agreement with the experimental results of the SiC conversion ratio as a function of synthesis time. The calculation results of solving each constant suggest that the formation processes of SiC are "rate-controlled reaction at the interface" at the initial stage of the reaction, and then they gradually change to "diffusion-controlling reaction in the reacted region". In the long term synthesis, we recognized that the waste SiO with non-stoichiometric oxygen can also be used as a silicon source.