The parameters of impact sound between two particles are discussed to measure the particle size and velocity of colliding particles by the analysis of that impact sound. The radiation mechanism of the impact sound is considered theoretically, and the pressure waveform of the sound is estimated on the basis of the radiation mechanism. The calculation of pressure waveform takes account of the reflection of the impact sound from the surface of the colliding spherical particle. The estimated waveform agrees well with the measured one.
The parameters of impact sound related closely to the particle size and impact velocity between particles.
The results show that it is possible to measure the particle size and velocity of flowing particles by the analysis of flow noise.

^† This report was originally printed in J. Soc. Powder Technology, Japan. 24(10), 655-663 (1987) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Powder Technology, Japan.

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This paper describes an experimental investigation of the charge acquired by a single particle when striking a metal plate. The particle was projected from a pneumatic gun onto the metal plate. The initial charge carried on the particle before impact and impact charge were measured under various conditions of impact velocity, ν_ο (7∼18 m/s) and angle, θ (0º∼60º).
The charge transfer is dependent not only on the impact conditions but also on the initial charge of the particle. The impact charge almost proportionally decreases with an increase in the initial charge. There is a particular value of this charge which results in no net transfer and which is independent on the impact conditions. This special point can be utilized to estimate the effective work function of insulating particles.
While a larger impact velocity leads to a larger charge transfer because in the increase of the contact area, the data cannot be arranged with the maximum contact area derived from the normal component of the impact velocity, ν_οcosθ. A much larger enhancement of the charge transfer is caused by the tangential component of velocity, ν_οsinθ. This fact is extremely different from the previous works (Refs. 2 and 4) which describe that the tangential component had no effect on the charge transfer by collision.

^† This report was originally printed in J. Soc. Powder Technology, Japan. 24(12), 765-770 (1987) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Powder Technology, Japan.

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The relationship between the average coordination number and void fraction in a randomly packed system of uniform-sized spheres was investigated by four different kinds of computer simulated results to judge whether or not the coordination number could be uniquely estimated from the voidage. The relationship between the coordination number and voidage depends on the type of the computer simulation program used and our research results showed clearly that the coordination number cannot be uniquely estimated from the void fraction. These computer simulated results were compared with the calculated results using some empirical or model equations which have already been reported in the literature. The model equations by Gotoh and Suzuki et al. and the empirical equations by Sunada et al. and Nagao were found to be in fairly good agreement with some of our simulated results.

^† This report was originally printed in J. Soc. Powder Technology, Japan. 25(4), 204-208 (1988) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Powder Technology, Japan.

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To clarify the mechanism and characteristics of planetary ball milling, batch grinding experiments were carried out under various conditions. The motion of the balls in the mill was observed and analyzed by using multi stroboscope photography connected to an image analyzer, and the contact force on the mill wall by the balls was measured using a pressure sensor.
The surging phenomenon of the balls in the mill was confirmed by the photographic analysis. Based on this result, it is predicted that the grinding mechanism in the planetary ball mill consists of compressive, abrasive and shear stress of the balls, which is believed to be effective in producing very fine particles.
About thirty percent of ball filling of the mill was found to be the optimum. This was explained by an analysis of the motion of the balls and the measurement of the contact force.
It was found that the grinding limit is greatly dependent on ball size. An experimental equation expressing the relationship between the finest average size of the ground product and the ball size is also given in this article.

^† This report was originally printed in J. Soc. Powder Technology, Japan, 25(5), 297-302 (1988) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Powder Technology, Japan.

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Roller mills have come to be actively used for the fine grinding of solids. In this paper, the compressive crushing of powder beds was carried out to study a roller mill. The effect of the applied load, the mass of feed and the particle size on the probability of crushing and on the crushing resistance were studied. The sample used was quartz. The following results were obtained:
1) When the applied load was constant, the deformation of the powder bed increased with the increase in the mass of feed and particle size.
2) The probability of crushing increased with the increase in the applied load, but the rate of increase of the probability gradually decreased.
3) The mass of the feed with a low crushing resistance was observed, and it had a certain range. This range narrowed with the decrease in the particle size.
4) The crushing resistance increased with the decrease in the particle size.

^† This report was originally printed in J. Soc. Powder Technology, Japan, 25(5), 292-296 (1988) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Powder Technology, Japan.

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The wet grinding characteristics of CWM (Coal Water Mixture) at high concentrations was investigated by conducting batch preparation tests using a laboratory-scale ball mill.
Although the grindability became worse with the increase in the slurry concentration, it was found possible to prepare CWM of 65∼75% by use of the proper dispersant. The improvement of grindability was caused by the improved movement of balls owing to the decrease in the apparent viscosity at low shear rates. The grindability greatly changed with the coal type. The difference of grindability among coal types was mainly due to the difference in the flocculation force.

^† This report was originally printed in KAGAKU KOGAKU RONBUNSHU, 14(2), 155-160 (1988) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Chemical Engineers, Japan.

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The mathematical model previously developed for a ring ball mill based on specific rates of breakage, breakage distributions, and primary and secondary classification actions was further refined. In particular, empirical expressions are presented for both primary and secondary classification actions as a function of the mill and classifier geometry as well as the operating conditions. In addition, the scale-up factor with the make-up feed rate determined in a pilot-scale mill was further developed for larger mills. Model simulations based on parameters measured in the Hardgrove mill with the present classification models and scale-up factors correctly predicted the circuit behavior of industrial-scale mill systems.
Furthermore, some of the factors affecting the mill performance were investigated with the present simulation model. As a result, the feed size distribution and the total crushing load on balls were found to be the dominant factors.

^† This report was originally printed in J. Soc. Powder Technology, Japan, 25(7), 430-436 (1988) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Powder Technology, Japan.

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A statistical model of the distribution of the contact number for a binary mixture in an incompletely mixed state is introduced. The model is derived from the beta-binomial model proposed by Yoshizawa and Shindo³⁾. The mixing index based on the contact number is defined and described by only one parameter in this model.
The precision of the estimation of the mixing index, based on the contact number by coordination number sampling in an incompletely mixed state, has been derived and simulated on a computer.

^† This report was originally printed in J. Soc. Powder Technology, Japan, 24(8), 521-526 (1987) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Powder Technology, Japan.

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A slurry feed composed of water, PVA and fine particles are sprayed in droplet from into a spray dryer, with porous and spherical spray-dried products being recovered. However, the PVA binder is so hygroscopic that the strength of the products changes as the relative humidity changes.
For the purpose of clarifying this phenomenon quantitatively, the specific surface area, hygroscopic moisture content and strength of the spray-dried products are examined experimentally and theoretically.
The conclusions obtained are summarized as follows:
1. The hygroscopic moisture content of the products is estimated by the total of the moisture adsorbed on the surface of constituent fine particles covered somewhat with PVA and the moisture adsorbed by PVA itself.
2. The strength of the products is measured under various conditions of relative humidity. The measured values are compared with the results calculated from the previously derived equation. As a result, it was found that the strength of the products could be estimated very well by taking account the effect of the variation in humidity on binder strength in the derived equation.

^† This report was originally printed in J. Soc. Powder Technology, Japan, 24(9), 582-587 (1987) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Powder Technology, Japan.

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A new coagulation method which consists of two stages the generation of seed particles and growth of particles, was developed for the preparation of pellet-like particles from polymer latex.
In this report, first the mechanism of this coagulation was studied through an examination of the coagulating velocity during each stage. Then, the pellet-like particles were characterized by a SEM observation of the inside of a particle and measurement of particle properties.
As a result, experimental equations on the amount of generated seed particles and rate of growth of the particles were obtained. The phenomena in which the latex particles inside the coagulated particle are packed closely by drying and are fused homogeneously by sintering, was confirmed.

^† This report was originally printed in J. Soc. Powder Technology, Japan, 24(11), 700-706 (1987) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Powder Technology, Japan.

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The formation of Si₃N₄ whiskers from rice hulls was studied. Si₃N₄ whiskers were synthesized by nitridation of SiO₂-C system in N₂-gas flows at 1400 and 1450ºC. The shape and microstructure of the whiskers were SEM and TEM inspected. The whiskers of a cylindrical shape grew along the < 1011 > direction without any defects. The phase of the whiskers was of the a-type and their diameter and length were 0.1∼0.5 μm and 300∼1800 μm, respectively. A droplet of Fe-Si system was found at the tip of the whiskers. It is suggested that the VLS mechanism controls the growth of the whiskers.

^† This report was originally printed in Journal of the Society of Materials Science, Japan, 37(412), 65-69 (1988) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Materials Science, Japan.

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The temperature rise curve due to the natural oxidation of a coal deposit was numerically simulated for a coal bed having a ‘spherical’ geometry. The maximum temperature occurred at the center of the bed when oxygen was fully supplied within the bed and near the surface when oxygen decreased due to the process of the reaction. The rate of temperature rise was significantly affected by the activation energy and frequency factor of the coal Furthermore, the measurement of the moisture adsorbed on the oxidized coal samples showed that the loss in mass due to oxidation increased remarkably at temperatures above 120ºC. In assuming the limiting temperature in coal storage to be 120ºC, a maximum allowable amount of coal storage was estimated for various kinds of coal under the conditions of neither spontaneous combustion nor significant loss in mass.

^† This report was originally printed in J. Soc. Powder Technology, Japan, 25(7), 437-442 (1988) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Powder Technology, Japan.

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The formation of particles in starting solutions and its significance for the sol-gel processing of oxide materials are reviewed on the basis of previous works including our work. First, hydrolysis and polycondensation reactions of metal alkoxides in alcohol-water solutions are briefly discussed. Then, it is shown that powders prepared by the sol-gel method using metal alkoxides are suitable as starting powders for high performance glasses and ceramics because the particles produced are fine, monodispersed and uniform in chemical composition. It is also shown that the formation of round-shaped particles larger than, say, 10 nm in sols may lead to porous silica monoliths of plate or rod shape without occurrence of cracks during drying of the wet gel. It should be noted that crack-free gel monoliths can be sintered to monoliths of glass and ceramics. It is shown that essentially one-dimensional long-shaped particles can be produced by adjusting the composition and conditions of processing of the starting solution, which is required for fiber drawing from viscous sols in the course of sol-to-gel conversion.

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