Himeji, Japan
Himeji, Japan

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Yamamoto Y.,Mikuni Color Ltd | Yamamoto Y.,Tohoku University | Kawaraya M.,Mikuni Color Ltd | Segawa H.,Tokyo University of Science | And 3 more authors.
Chemistry Letters | Year: 2011

Dispersions of TiO2 nanoparticles were prepared from titania powder (P25, Degussa) using a bead-mill method. The dispersion was controlled by the mixing time and was observed using dynamic laser-light scattering. TiO 2 screenprinting pastes were prepared from the TiO2 dispersions for application as photoelectrodes in dye-sensitized solar cells (DSSCs). The coated nanocrystalline TiO2 electrodes were evaluated using X-ray diffraction (XRD) and a haze meter. The shape and crystallinity of the TiO 2 nanoparticles were not changed, but the transparency was improved by the beadmilling process. However, aluminum contamination on the TiO2 surface was found to increase with bead-milling time. A TiO2 paste prepared from an optimized dispersion was used to fabricate a DSSC with 10% photoenergy-conversion efficiency. ©2011 The Chemical Society of Japan.

Yamamoto Y.,Mikuni Color Ltd. | Yamamoto Y.,Tohoku University | Soda R.,Tohoku University | Kano J.,Tohoku University | Saito F.,Tohoku University
International Journal of Mineral Processing | Year: 2012

A new model, an enlarged particle model, is proposed for simulating behavior of numerous tiny beads in wet beads milling using discrete element method (DEM). The enlarged particle model is assumed to be composed of several tiny beads. The behavior of enlarged particles in the stirred mill was simulated numerically using DEM. Furthermore, an experiment measuring the bead velocity in a transparent milling chamber using a high-speed camera was conducted to validate the enlarged particle model. The behaviors of 2 and 3 mm beads in the stirred mill were also simulated using DEM. The velocity distributions of beads obtained from the simulation agree well with experimental ones when choosing the adequate frictional coefficient of beads. Then the virtual frictional coefficient was introduced into the enlarged particle model. The virtual frictional coefficient was determined so that the velocity distribution of the enlarged particles agrees with the distribution obtained from experiments. The adequate virtual frictional coefficient increases with an increase in the enlarged ratio, which is determined as a volume ratio of enlarged particle to bead. The correlation between the adequate virtual frictional coefficient and the enlarged ratio was apparent. © 2012 Elsevier B.V.

Yamamoto Y.,Mikuni Color Ltd. | Yamamoto Y.,Tohoku University | Aoyama Y.,Mikuni Color Ltd. | Shimizu S.,Mikuni Color Ltd. | And 3 more authors.
International Journal of Photoenergy | Year: 2011

Titania powder (P25) was dispersed by bead-milling breakdown method, and the dispersivity of TiO 2 was controlled by adjusting the mean secondary TiO 2 particle size to 45, 56, and 75nm by changing the dispersion solvent blend ratio of ethanol and terpineol. The transparency of the coated layer increased when the particle size of TiO 2 aggregates became smaller than 100nm. Although the transparency was significantly different according to differences in the size of nanocrystallyne-TiO 2 aggregates, the resulting photovoltaic (PV) effect of a dye-sensitized solar cell (DSSC) was not significantly different between the different aggregate sizes. A double layer structure (transparent TiO 2 layer/opaque TiO 2 layer) was adopted to improve the PV effect, which resulted in an improvement of the photocurrent and conversion efficiency of 13.2 and 11.1, respectively, from that for the DSSCs with single-layered TiO 2 electrodes. Copyright © 2011 Yasuhiro Yamamoto et al.

Yamamoto Y.,Mikuni Color Ltd. | Yamamoto Y.,Tohoku University | Soda R.,Tohoku University | Kano J.,Tohoku University | Saito F.,Tohoku University
Powder Technology | Year: 2012

We investigated the dispersion of a carbon black sample by a bead mill under wet conditions and assessed the correlation of its rate constant with the bead impact energy. The carbon black used in the experiment is fine powder of less than 100. nm diameter, dispersed in solvent by a bead mill under different milling conditions. The degree of dispersion was defined by a normalized number of coarse particles of carbon black in the slurry; it was correlated with dispersion time, representing an empirical equation. As for the bead impact energy, we simulated the motion of the beads in the mill under wet conditions in different conditions using the Discrete Element Method (DEM). The impact energy of the beads was determined from the bead velocities in different conditions. Results show that the dispersion rate constant of the carbon black sample in the mill is fairly correlated with the impact energy of the beads. It is well correlated with the impact energy of the beads is based on the normal impact energy. © 2011 Elsevier B.V.

Kawaraya M.,Mikuni Color Ltd. | Shimizu S.,Mikuni Color Ltd. | Hisashi H.,Mikuni Color Ltd. | Kamiya H.,Tokyo University of Agriculture and Technology
Ceramic Transactions | Year: 2010

Oxidation states of four kinds of carbon black (CB) powders, which varied with the length of ozone oxidizing time, were determined using vacuum pyrolysis. The zeta-potential and dispersibility were determined from the median particle size, d50, measured in an aqueous suspension prepared from each oxidized CB powder. The relationship between the oxidation state of the CB and the dispersion behavior is discussed. Additionally, the effect of adding alkali species to neutralize each suspension on the zeta-potential was evaluated. The amounts of carboxyl and quinine groups of the CB increased concomitantly with ozone oxidation time. The absolute value of the zeta-potential of the CB suspension increased with the amount of oxidized groups, and the maximum value of the zeta-potential reached -71.3 mV. The high absolute value of the zeta-potential indicates good dispersibility of the CB particles in the aqueous suspension. The alkali addition influences the dispersibility, the zeta-potential, and dispersibility of the oxidized CB.

Yamamoto Y.,Mikuni Color Ltd. | Soda R.,Tohoku University | Kano J.,Tohoku University | Saito F.,Tohoku University
Particuology | Year: 2014

We applied the discrete element method (DEM) of simulation modified by an enlarged particle model to simulate bead motion in a large bead mill. The stainless-steel bead mill has inner diameter of 102 mm and mill length of 198 mm. The bead diameter and filling ratio were fixed respectively at 0.5 mm and 85%. The agitator rotational speed was changed from 1863 to 3261 rpm. The bead motion was monitored experimentally using a high-speed video camera through a transparent mill body. For the simulation, enlarged particle sizes were set as 3-6 mm in diameter. With the DEM modified by the enlarged particle model, the motion of enlarged particles in a mill was simulated. The velocity data of the simulated enlarged particles were compared with those obtained in the experiment. The simulated velocity of the enlarged particles depends on the virtual frictional coefficient in the DEM model. The optimized value of the virtual frictional coefficient can be determined by considering the accumulated mean value. Results show that the velocity of the enlarged particles simulated increases with an increase in the optimum virtual frictional coefficient, but the simulated velocity agrees well with that determined experimentally by optimizing the virtual frictional coefficient in the simulation. The computing time in the simulation decreases with increased particle size. © 2013 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences.

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