The aerosol classification performance of a newly constructed rectangular jet virtual-impactor has been studied both theoretically and experimentally. It is found that the performance is well represented by potential flow calculations with modifications for the effects of the acceleration jet and flow separation at the slit. The sharpness of the classification is not as good as that of a round jet impactor, and the variable range of the cut size is smaller. In the rectangular jet impactor, however, a higher flow rate of aerosol can be treated without changing the cut size. It is also found that higher degrees of sharpness are obtained and that the cut size is variable within a certain range by introducing clean air flows as in the round jet impactor previously developed by the authors. The separation characteristic is found to be well explained by assuming perfect mixing between the aerosol flow and the clean-air flows at both ends of the rectangular jet. The maximum inertia parameter limited by the sound velocity is also discussed, and an empirical equation representing the pressure drop of the impactor is presented.

^† This report was originally printed in KAGAKU KOGAKU RONBUNSHU, 10(5), 561-567 (1984) 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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In order to determine broad ranges of particle size distribution, a new measuring method combined both light scattering and electrostatic separation-condensation nuclei is experimentally investigated. From the experiments, it is confirmed that by using a sensitive optical particle counter connected to a digital computer system, the particle size range of 10 nm to 10 µm in diameter is adequately measurable. Furthermore, using the same criteria to count the number of particles over the entire size range, this method is found to be remarkably applicable as a practical means of more accurate measurement.

^† This report was originally printed in J. Soc. Powder Technology, Japan, 23(6), 408-414 (1986) 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 submicron grinding of BaTiO₃ powder was studied by a ball mill with small alumina balls of 0.75 mmΦ to 30 mmΦ. BaTiO₃ clinker, which was obtained by calcining an equimolar mixture of TiO₂ and BaCO₃, was preground to 1.8 micron. Submicron grinding of the BaTiO₃ powder was possible by ball milling with several mmΦ balls. For a ball diameter of 2 mm, the specific surface area was maximized.
An attempt was made to represent the specific surface area in terms of volume per ball and total surface area of used balls, and the following experimental equation with a time term was obtained,
In(SS) = -0.247lnr³ - 0.738/r + 0.429 lnt + 1.57
where SS is the specific surface area, r is the ball radius, and t is time. The multiple correlation coefficient R was found to be 0.982 when calculated by computer.

^† This report was originally printed in J. Soc. Materials Science, Japan, 35(388), 54-58 (1986) 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 distribution in the combustible dust deposits placed in hot environments is described by a differential equation according to the thermal theory. The temperature profiles of the dust deposits at any time could be calculated at various ambient temperatures by solving the equation using the finite element method. Thus, the minimum ambient temperature for ignition, which is defined as the ignition temperature, and the induction time to ignition could be determined. With the cylindrical cork dust deposits, the resulting temperature distribution in the radial direction at any time, and the self-ignition temperature as well as the induction time to ignition, by varying the size of the deposit, agree well with the experimental data reported by Leuschke, except at extremely high ambient temperatures. Therefore, it is practicable to estimate the spontaneous ignition behavior of dust deposits by computer simulation.

^† This report was originally printed in J. Soc. Powder Technology, Japan, 23(5), 326-331 (1986) 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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Direct consolidation of α- and β-Si₃N₄ is conducted by the use of one-dimensional explosive shock treatment. The effect of shock pressure, phase and particle size distribution of a sample powder on the characteristics of the explosively shocked compact is examined by the measurement with X-ray diffraction (XRD), Electron spin resonance (ESR), and Infrared absorption (IR) among others. The following are the results:
1) Cracks exist in the shock compact. The apparent density and Vickers hardness increase with the increase in shock pressure. A compact of ca. 90% theoretical density is obtained.
2) Residual strain by XRD and spin density by ESR are reduced under higher shock pressures. This is considered to be attributed to the relaxation effect of high residual temperature. The shock compact of α-Si₃N₄ receives more residual strain and spin density than that of β-Si₃N₄.
3) The effect of particle size distribution of the sample powder on the characteristics of the shock compact is slight. The shock compact of larger particle size has more residual strain.
4) Metal impurities are not found except in the surface layer of the compact.
5) The solubility of the powder grinding shock compact in 1N-NaOH is higher than that of the as-received powder. This indicates that an active surface layer exists in the shock compact.
6) The tapping density of the powder grinding shock compact is much higher than that of the as-received powder.

^† This report was originally printed in J. Soc. Powder Technology, Japan, 23(4), 250-257 (1986) 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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An experiment was made to visualize the surface flow pattern of spheres in a packed bed. Spheres, the surface of which were coated with benzoic acid, were set within a packed bed and exposed to water flow for a certain period of time. The flow patterns on the surface were observed by the patterns of dissolution of benzoic acid. The patterns were compared with the results of visualizations by other workers using a different method. It was found that the present results are in good agreement with those results in terms of the location of separation lines and singular points on the surface.

^† This report was originally printed in J. Soc. Powder Technology, Japan, 22(9), 599-605 (1985) 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 report was originally printed in Monthly Semiconductor World, 8, 42-49 (1986) in Japanese, before being translated into English with the permission of the editorial committee of the Press Journal Co., Ltd., Japan.

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