The voidage of a powder bed is approximately related to the specific surface diameter and the major consolidation stress in a rearranged form of Gurnham's equation. The flowability of the cohesive powder, which is a ratio of the unconfined yield stress to the unit weight, is related to the specific surface diameter, the voidage, the major consolidation stress and other factors.
Estimated values of the voidage are 0.81 to 1.25 times as large as the experimental values obtained from shear tests for the 20 powders used. On the other hand, the computed results of the Flowability using both the estimated and measured results of the voidage compare favourably with the experimental results for most the 17 powders used.
Thus, the present method is applicable to the estimation of flowability for a cohesive powder having a different value of specific surface diameter.

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The most essential problem in the particle size analysis of powders including submicron particles is how to disperse the sample sufficiently. The dispersibility of a sample powder is affected by many factors, such as the method, power and time of ultrasonication, the kinds and amount of dispersant agent, the concentration and treatment of suspension, and so on.
The effect of the sample preparation condition on particle size analysis was discussed experimentally by using common advanced ceramic powders. Laser scattering and diffraction method, and the X-ray sedimentation method were used to measure the particle size distribution of dilute or concentrated suspension. The dispersibility of these suspensions were evaluated by their own zeta potential.
The following results were obtained. The dispersing state were affected by the zeta potential, the total surface area of the sample powder, and the particle diameter. The dispersibility of the submicron powders were easily changed by ultrasonication. Ultrasonicated suspension must be stirred continuously to maintain stability.

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Experimental and theoretical studies have been conducted on the effect of the surface coating ratio of a surface of modified SiO₂ particles on the measurement of contact potential difference between a powder bed and a metal. The applied potential, which is the characteristic property of the electrostatic charge, and surface coating ratio have the same mixture ratio tendency of fine to core particles. The surface coating ratio indicates the maximum value with the mixture ratio. From the photograph of a scanning electron microscope, it is found that agglomerated particles are observed on the core particle surface with the increase in the mixture ratio. The reason for the decrease in surface coating ratio with increase in the mixture ratio is the particle reentrainment effect. The experimental data agrees well with the calculated results based on the sticking coefficient of fine particle on the core particles surface.
The theoretical equation is derived for the relationship of the surface coating ratio and the mixture ratio. The change in the drained angle of repose with the mixture ratio indicates the same tendency as the relationship between applied voltage and the mixture ratio.

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The angular and radial velocities of a particle in the centrifugal force fields of a gas were experimentally and theoretically discussed. These values play a significant role in the analysis of the mechanism of separation in centrifugal classifiers and dust collectors, but they cannot be easily evaluated. The particle motion is actually different from the conventional assumption; in some cases, the angular and radial velocities actually attain only a few percentages of the usual calculated values.

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