粉体の充てん構造と破断強度(<小特集>粉体小特集)

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In order to obtain the interparticle force of powder. there exists a method of measuring a tensile strength necessary to fracture the compressed powder bed. The results obtained by this method show certain fluctuation in magnitude of the tensile strength, greatly depending on packing structure of powder. Because of lack of quantitative representation on the packing structure, the powder phase has been assumed as rather homogeneous. Accordingly the cohesion force (interparticle force) is generally estimated through the following procedures ; firstly a relationship between porosity of powder and average number of contact with the nearest neighbours is established experimentally using the matters packed up irregularly from uniform sphere-particles, and then the cohesion force per one contact is assigned to individual particle dividing the macroscopic tensile strength by the total number of contact. It is, however, questionable whether or not the above assumption holds for the actual powders. In order to reconsider it, the micropore distribution of the powder samples whose porosity was artificialy controlled was measured by means of a mercury porosimeter. It was found from this experiment that a powder has a structure packing up heterogeneously of aggregations with which finer particles condensed together. A close attention was directed to a relation between tensile strength and structure of the fractured surface. For this course, two groups of powder matters were tentatively prepared which had been granulated to arbitary size from fine particles with well known size distribution, and the tensile strength of the compressed powder bed was measured both for normal powder and those granulated ones. Furthermore their fractured surface was observed by means of optical microscope. The result seemed to suggest that the fracture in the compressed powder bed caused by tensile starts from the part at which a relatively large pore resulted from the heterogeneous packing was found. Further support was given through the following experiments. As a two dimentional packing model. polystyrene pieces, which have the dimensions of 1〜5mm in size and heterogeneous shape, were floated compactly on the water and the fracture process with tensile was directly observed. It became more confident that the fracture propagates infectiously through the route where the heterogeneous packing structure is remarkable. The fact that the heterogeneity of packing within powder has a great influence on the tensile strength was also supported by the observation of the fractured surface of powders in which mica, subjected to surface treatment with hydrohobic material, was mixed in a certain ratio. From these experiments described above, it can be concluded that when Rumpf's equation is applied onto the results of tensile strength of the compressed powder bed, the interparticle force is underestimated for individual particle.
社団法人日本材料学会の論文
1980-09-15

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荒川正文
京都大学化学研究所

粉体の充てん構造と破断強度(<小特集>粉体小特集)

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