Hiroshi Satone

Previously, we have reported the successful preparation of a soft flocculated suspension. This is a suspension in which fine particles are well dispersed by using a polyelectrolyte dispersing agent, and then Mg²⁺ ions are added to crosslink between the dispersants adsorbed on the surfaces of the particles, so that the particles temporarily return to a liquid state with light shaking while behaving as gels at rest. In the present work we tried to apply this soft cohesive suspension as a low viscosity suspension of titanium dioxide having high versatility as a cosmetic powder. The use of globular titanium dioxide with a low yield value resulted in the successful development of a soft cohesive suspension with no precipitation or deposition of particles. In addition, when the application of this suspension in a white inkjet ink was examined, both the addition molding to a solid powder product using a piezo type cartridge and the printing experiment with a home printer using a thermal type cartridge showed the good results.

In this study, the fracture phenomenon of particle impacting with wall was directly observed using a high-speed camera. The results from the experiments indicate that the fracture behavior differs in the impact angle, and there are two types of fracture mode: one is with “Break” and the other with “Chip”. In case of low impact angle condition (less than 70°), there is only “Chip” mode. Furthermore, the effect of the particle impact angle on particle fracture phenomena was also investigated. The results of this study indicate that the particle fracture velocity almost is the same value at impact angles under 45° or higher.

The effect of terephthalic acid particle properties on particle fracture phenomena was investigated in this study. Furthermore, to evaluate the fracture characteristics in real process, the effect of the particle impact angle on particle fracture phenomena was also investigated. The results of this study indicated that: (i) the crystallite particle size correlated with the fracture stress of the particle; (ii) the crystallite particle size also showed a correlation with the critical fracture velocity and the kinetic energy of the particle; and (iii) the particle fractured more easily at impact angles under 45°.

In this study, a novel reversible control method for particle dispersion/flocculation was developed with the dual aim of preventing settling/sedimentation during storage and maintaining low viscosity in use. First, a well dispersed slurry was prepared by adding polyelectrolytes as dispersant. After preparation, multivalent cations were added to the slurry. By adding multivalent cations, the well dispersed slurry was changed to gel state because of the ionic crosslinking of polyelectrolytes adsorbing on the surface of the particles. The resultant gel was very soft and could easily be changed to liquid state by shaking. In addition, the slurry reverted back to gel state after a certain period of time. The softness of gel can be controlled by additive amount of multivalent cations. Thereby, a novel reversible control method for particle dispersion state was successfully developed.

Flame made gray titanium oxide particles which exhibit visible light absorption were successfully prepared via reduction atmospheric flame synthesis process. It was clarified that the particles have high specific surface area and are of nanometer size as a result of FE-SEM observation and specific surface area measurement. Particle properties could be varied by controlling equivalence ratio and introducing cooling gas, and the specific surface area increased as equivalence ratio increased. It was revealed that the particles are hollow for φ ＝ 1.54，1.68 and the constituent particles of shells are quite small in size. And the introducing of cooling gas affects the color of particles attributed to the oxidation degree and the specific surface increased as well. The result of XRD spectroscopy did not clearly show the generation of any magneli phases, however the peak intensity of anatase phase decreased which suggests the repression of oxidation. It was confirmed that carbon is rarely included in products and the change in color can be attributed not to carbon but to oxygen defect as a result of Raman spectrometry. Furthermore, the measurement of electric conductivity demonstrated the drastic improvement compared to stoichiometric titanium dioxide.

Centrifugal spinning of fibers with core-shell structure was tried by developing double tube nozzle spinneret. Obtained fibers were classified into three types according to fiber size. It seems plausible to infer that thin fibers are composed of only core material and thick ones are composed of only shell material. By contrast, it was clearly confirmed by observation with optical microscope that fibers have core-shell structure for medium size range around 10μm in diameter. In order to discuss the condition to obtain core-shell structured fiber, analysis based on the Hagen-Poiseuille equation focusing on the exit velocity at tip of spinneret has been conducted. As a result, relatively good agreement in exit velocity was found between core and shell materials.

When nano-sized tiny roughness is processed on a surface, the prevention of dust adhesion can be expressed by the decreasing of the van der Waals force between rugged surface and dust particle. Using nanoparticle coating on a textile, the tiny roughness can be created on a textile and the preventive effect of dust particle adhesion can be given to the cloth. This effect is applicable to working clothes etc. Generally, clothes are washed in order to remove the dirt on it, so the nanoparticle coating on a textile and the preventive effect of dust adhesion may be decreased by washing process. In order to add the functionality to the preventive effect of dust adhesion on the clothes in a practical uses, the improvement in the durability for washing is very important.<br>In this research, we confirm the preventive effect of dust adhesion and measured the effect of the number of washing on the preventive effect of dust adhesion on a textile. From our experimental results, the durability of the nanoparticle coating and the preventive effect of dust adhesion can be improved using acetalized polyvinyl alcohol treatment.

It is very important to control the particle dispersion state of slurries in order to fabricate better products in wet shaping processes. Therefore it is very important to evaluate slurry characteristics to predict the product characteristics. As a result, many studies have evaluated the slurry characteristics in various ways, such as measuring apparent viscosities, gravitational settling etc. However, it has been reported that these evaluation methods do not always have a good relationship with the quality of the final products. It is thought that one of the reasons for this is the fact that the method used was inappropriate for the actual situation. Several methods useful for the material fabrication process, such as measuring apparent viscosities and gravitational settling, are explained in this paper. Furthermore, an evaluation method proposed by our group to predict in a short time the packing characteristics of a slurry by measuring the hydrostatic pressure of the slurry at the base of a settling tube is also explained.

In various industrial processes such as wet shape forming of ceramics, particles are usually applied in a slurry. In such processes, adding the appropriate amount of dispersant to the slurry is important for the production of better products. The adsorption of dispersant onto the particle surface is an important factor ; hence, many researchers have reported this phenomenon. However, few researchers have studied the effect of adsorption conformation of dispersant on dispersion stability. We investigated the effect of adsorption conformation of ammonium polycarboxylate, an adsorbed anionic polymeric dispersant with a molecular mass of 8000～10000, onto alumina. In this paper, several results of our recent research, such as the effects of additive amount of dispersant, dissolution of ion in the slurry, and effect of time at which dispersant conformation changes on dispersion stability of the slurry, are introduced.

In order to determine the preparation time for slurry in ceramic manufacturing processes, the effect of the conformation of ammonium polycarboxylate, an adsorbed anionic polymeric dispersant with a molecular weight of 8000～10000, on the dispersion stability of the slurry was investigated. The slurry preparation time was varied and the effect was investigated using and hydrostatic pressure measurement. The results of the investigation showed that the conformation of adsorbed polymers changed with time from random coil to fibril-like and that it took several days for the polymers to relax completely in the slurry. Furthermore, the dispersion state of the slurry changed with the relaxing of the conformation of adsorbed polymers. The results showed that the stretching of adsorbed polymers contributed significantly to the dispersion state of the slurry. The optimum conditions of polymers for the preparation of the slurry are also discussed.

The glass substrate is coated by the silica nanoparticle suspension using dipping or spin coat method and dried in an electric oven. The glass substrate surface is covered with nanoparticle thin layer and the transparent and tiny rugged surface can be produced on a substrate. It was experimentally confirmed to prevent dust adhesion by covering the surface of the glass substrate with nanoparticle. But the reason why the prevention of particle adhesion on nanoparticle coating substrate is not clear yet. Therefore the adhesion force between particle and substrate is measured by the centrifugal method and the relation between the adhesion force and the surface roughness is discussed from experimental and theoretical point of view. The measured and calculated results by Van der Waals force show that adhesion force decreased with the increment of the surface roughness. From the results, nanoparticle coating is very effective to prevent the dust adhesion on the substrate and the various application of nanoparticle coating can be expected.

We have developed a non-contact measuring method of mixing process in the mixer using a micro focus X-ray computer tomography. And its effectiveness was demonstrated from the experimental observation of mixing process of two kinds of particle with different X-ray transmission. The cross sectional image of particle packed bed in the cylindrical container rotation type mixer was obtained from the X-ray transmission images, and the image analysis of these cross sections was performed. From the brightness of each particle image, the particle materials can be detected and obtains the ratio of each particle on every section.<br>The degree of mixing was calculated from the measured distribution of each particle, and the effect of the separation plate in the mixer on the mixing performance of a cylindrical container rotation type mixer was studied. The actual mixing state in the mixer can be measured by non-contact, and the mixing degree in the mixing process from cross-sectional image analysis can estimate directly was shown.

In wet shaping, the amount of dispersant added to the slurry is a crucial factor in producing high-quality ceramic products. Many researchers have investigated the amount of dispersant that adsorbs to slurry particles. However, few studies have examined how the solid concentration of slurry affects the amount of adsorbed dispersant. In our previous work, we measured the amount of adsorbed dispersant at various solid concentrations and addition amounts of dispersant. In the present work, alumina particles containing magnesium as a sintering aid were used. The conformation of polyelectrolyte dispersant was changed by magnesium ions, and the adsorption isotherm showed a local maximum. In the case of laurate, some molecules remained in solution and did not adsorb to particles because of its thermal motion and few adsorbing sites. Consequently, the amount of adsorbed dispersant was affected by the diffusion of magnesium from the particles, the molecular weight of the dispersant, and the solid concentration of the slurry.

The hydrostatic pressure measurement method is one of the settling methods of a particle size distribution measurement. We measured the particle size distribution of the alumina slurries by this method and investigated the effects of the slurry concentration. However, the measured cumulative undersize is evaluated to be smaller than the true value at the high concentration because of the hindered settling. Therefore, in order to correct this phenomenon, we tried to use several equations of hindered settling suggested until now and the experimental equation. As a result, the particle size distribution of high concentration slurry can be measured without any dilution operations by using fitted experimental equation. Furthermore, the mean particle size measured by this method was closer to nominal value than the one measured by the laser diffraction method.