A Monte Carlo simulation method for modeling sintering and grain growth of solid grains using a three dimensional lattice was studied to analyze an effect of anisotropic surface energy (γSV) of particles on the development of porous structures in sintered materials. The changes in porosity (fV), mean grain diameter (DS), fraction of connected pores (fV,C) and contiguity of the solid phase (C) were examined in cases with three different γSV relations and initial grain diameters (DS,0). Introducing anisotropic γSV brought an increase in fV and fV,C and an decrease in DS and C, and this tendency became more marked for fine DS,0. By this simulation study, the use of the particle with anisotropic γSV was considered to have an advantage to obtain fine and stable porous structures in sintered materials.
Specimens with a molar ratio of 100ZnO-2TiO2-2CoO-2Al2O3 (hereafter, ZTCA) were heat-treated by pulse current sintering (PCS) at a sintering temperature of 1423 K for 10 min and at applied pressures of 30-80 MPa. The thermoelectric characteristics of the obtained specimens were investigated from the viewpoint of their microstructure. On the basis of the resistivity-temperature characteristics of the specimens that were obtained by sintering ZTCA at 60 and 80 MPa, the resistance of the specimens locally increased at approximately 800 K during heating and the resistance during cooling remained higher than that during heating in the thermal history (hysteresis). The local increase and the hysteresis in the resistance were not observed for the specimen sintered at the low pressure of 30 MPa, which had large crystal grains and was densified, but they were observed for those sintered at the high pressures of 60 and 80 MPa, which had fine particles and were porous. In addition, a following problem has come up, that is, the local increase in the resistance of the ZTCA specimen observed at approximately 800 K may lead to a reduction in the power factor of the thermoelectric characteristics.
A metal/ferroelectric/insulator/semiconductor Pt/SrBi2Ta2O9(SBT)/Hf-Al-O(HAO)/Si is a promising gate structure for a ferroelectric-gate transistor. Effects of adding nitrogen into the HAO were investigated. Pt/SBT/HAO(N)/Si and Pt/SBT/HAO(O)/Si were prepared by depositing the HAO in N2 and O2, respectively. Nitrogen inclusion in the HAO(N) was confirmed by secondary ion mass spectrometry (SIMS). The SIMS results also indicated that diffusions of Sr, Bi and Ta into the HAO(N) were much more suppressed than those into HAO(O). Scanning transmission electron microscope (STEM) images showed that the HAO(N) was amorphous and fine while the HAO(O) was polycrystallized and rugged. The STEM image also showed an interfacial layer (IL) between the HAO and Si, grown mainly during an annealing process at 800°C for 1h for SBT polycrystallization. The major components of the IL were Si and O. The IL thicknesses of the HAO(N) and the HAO(O) were 3.4 nm and 7.4 nm respectively. Capacitance-voltage measurements of the Pt/SBT/HAO(N)/Si showed a 0.9V memory window at ±6V gate-voltage swing, which was three times larger than the memory window of the Pt/SBT/HAO(O)/Si. We concluded that adding nitrogen into the HAO of Pt/SBT/HAO/Si was effective for obtaining a large memory window by suppressing material diffusions and the IL layer growth.
Wet-jet milling process was employed to modify the properties of Al2O3 slurry after ball milling. Particle size distribution of slurry wet-jet milled after ball milling corresponded to that of ball-milled slurry. However, the viscosity of ball-milled slurry increased rapidly with time, whereas the viscosity of the slurry wet-jet milled after ball milling was stable for long times. Al2O3 particles after ball milling yielded more OH groups on the surface. These OH groups were reduced or removed by wet-jet milling following ball milling. Moreover, wet-jet milled slurry after ball milling had lower re-flocculation properties and higher packing density of above 60% than ball-milled slurry. Hence, Al2O3 particles in slurry wet-jet milled after ball milling is packed well as compared to ones of ball-milled slurry before wet-jet milling treatment.
Mixtures of Ti and six kinds of anatase-type TiO2 which differ in adsorbed water content were mechanically alloyed by a planetary ball mill to synthesize TiO. The milled powders were investigated by powder X-ray diffractometry and scanning electron microscopy. The results showed that TiO formation was inhibited by adsorbed water. The effect of adsorbed water on the MA process will be discussed in terms of TiHx formation and local temperature rise. In addition, we also found that polymorphic transformation of TiO2 induced by ball milling was inhibited by adsorbed water.
We have ever proposed to prepare the highly functional material films by using an electrophoretic deposition (EPD) method. In this review, we have utilized the EPD process to fabricate the binder-free carbon negative electrodes for lithium ion secondary batteries; these electrodes were fabricated without mixing a binder. Powdered active materials are usually used for the electrode of lithium ion secondary batteries. The binder is used to form it as an electrode but is not concerned in charge-discharge reaction directly. Therefore, if it is not used for the electrode fabrication, it leads to high energy density of a battery. Artificial graphite powders could be deposited on the anode substrate by the EPD method. Smooth and uniform deposit could be obtained. It was shown clearly that the binder-free artificial graphite film functioned as the negative electrode for lithium ion secondary batteries. In addition, a co-deposited film consisting of activated carbon and Ketjenblack powder particles was investigated as the electrode for capacitor cells. It was found that the co-deposited film fabricated by adding polyvinylidine difluoride as a binder to the EPD bath operated successfully as it. From these results, it is concluded that the EPD method can be applied as the carbon electrode fabrication process.
Carbon nanotubes (CNT) have many interesting properties such as high thermal conductivity. Therefore, Cu/CNT composites are expected to be applied as heat sink material with good thermal properties. In this study, Cu/CNT precursor in which CNT distributed homogeneously was fabricated by colloidal process, and homogeneous distribution of CNT in Cu matrix was also observed in Cu/CNT composites sintered by spark plasma sintering (SPS). According to the analysis of gas generated from high-temperature precursor, structural defect of CNT, and oxygen content, SPS proved useful to reduce CNT's structural defects compare to conventional sintering methods. Using SPS in vacuum atmosphere, composites can be successfully formed with low temperature in short time. Existence of amorphous layer at Cu/CNT and Cu/Cu interface was observed by FETEM.
A composite of titanium phosphate-porous carbon was prepared from amino phosphate chelate resin by adsorbing Ti (IV) and carbonization at 773K and 873K. The composite had potential for adsorption and decomposition of organic compounds in water. Removal of methylene blue in the aqueous solution was conducted by a batch test with irradiation of black light. Platinum was added into the composite as promotor. Crystalline TiP2O7 and metallic Pt were found in the composite. The diameters of these crystalline particles were less than 30nm. Pt promoted gasification of the polymer chain of the chelate resin. The removal rate of methylene blue was increased by co-existing Pt. The removal rate constant k was expressed by first order kinetics. The removal rate constant per weight of Ti in the composite k' was almost constant even though Pt content was increased.
Energy collection by the methane fermentation residue attracts attention as utilization of soy sauce lees discharges one million tons a year in Japan. We prepared the activated carbon by carbonization-activation of methane fermentation residual substance after utilization of soy sauce lees. We found that the prepared activated carbon had well-developed mesoporous structure and had better adsorption performance than commercial activated carbon for the wastewater from dye house.