Algorithms are presented for feature extraction of the geometrical shape of particles. The system consists of a microcomputer and an image scanner which scans the micrograph of particles and transmits the compressed image data. Methods for shape analysis are: 1) calculation of fundamental particle shape parameters (Feret diameter, area, perimeter, first moment, second moment), 2) fractal analysis, 3) opening method and 4) separation of circular primary particles from an agglomerate. The connectivity of particle boundary is recognized for five cases (continuation, termination, creation, split and merge), and the fundamental shape features are calculated according to it. The validity and accuracy of these methods are examined by comparing the calculated and theoretical shape parameters for standard figures. A new index is proposed for the description of the structuring elements number of a two-dimensional particle shape in opening analysis. These methods are applied to the shape analysis of agglomerated aerosol particles generated from an electric furnace and by the CVD method, and it is shown that the fractal dimension as a particle distribution is useful for the quantitative description of shape.
†This report was originally printed in Earozoru Kenkyu, 2(2), 117-127 (1987) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Japan Association of Aerosol Science and Technology.
This paper discusses a comparison of the data of experiments obtained by using different shear tests methods in order to examine the confidence in the results of experiments on the flow properties of a bulk solid. The angle of internal friction of dry granular materials, which has been measured by both a tri-axial shear tester and a fixed volume direct shear tester, increases with a decrease in the voidage of the specimen. Except for the extremely dense and loosely packed states, the experimental results of the angle of internal friction agree within about 3 degrees. There is however a difference of 3 to 5 degrees for a material in which the particle shape is deflective. The flowability index of cohesive powders and wet materials is expressed by a ratio of the unconfined yield strength to the bulk density. The results of experiments on the flowability index are independent of the unconfined yield and direct shear tests.
†This report was originally printed in J. Soc. Powder Technology, Japan, 23(9), 678-684 (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.
The compacting characteristic of fine particles is greatly affected by the aggregate structure of particles. Several kinds of silicon nitrides, which are different from each other in particle shape, size and bulk density, were compacted in a uniaxial direction under various conditions, and the behavior of the particles during compaction was analyzed and compared by using Cooper's equation. It was found that the difference in the kind of samples and the condition of their pretreatment resulted in considerably different behaviors during compaction, and that the apparent volume reduction rate under pressure was remarkably different at low and high pressures. The aggregate structure of each sample was estimated based on the above results together with the result of the measurement of the compaction structure of the molded bodies.
†This report was originally printed in Journal of the Society of Materials Science, Japan, 35(398), 1246-1250 (1986) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. of Materials Science, Japan.
Solid additives are widely used to control the mechanical properties of powders materials in many industries. In this paper, the measurement of the tensile strength of a powder bed with a split-cell type tester was conducted to elucidate the effect of solid additives on the mechanical properties of powders. Fused alumina powder, silica sand, limestone, lactose and potato starch were selected as the powders. Furthermore, colloidal silica was used as a solid additive. The relationship between the tensile strength and the porosity of a powder bed containing the additive was proposed to characterize the effect of additives on the mechanical properties of the powders. Furthermore, the experimental results reported by others were able to be explained by the above relationship.
†This report was originally printed in J. Soc. Powder Technology, Japan, 24(7), 455-461 (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.
The transitional torque characteristics of a particle bed have been measured by using a rotary shear tester which is basically a Couette type rheometer. The torque measured on the rotor shaft under constant operating conditions showed the maximum value to be at the initial period. It then decreased exponentially with changes in the packed state of the particle bed around the shearing surface during rotation. The magnitude of the decay coefficient k of the torque indicated some of the dynamic physical properties of the solid particles, such as flowability and surface condition. It was found that the conical rotor was suitable for the more sensitive and accurate measurement of the change in the torque. A dimensionless parameter k/NR, where NR is the rotor speed, was introduced and compared with the other flowability indices. It was experimentally shown that this parameter was more sensitive in detecting slight changes in the physical properties of the particles during mixing and coating operations. The coating processes in two different types of mixers and the coating state of the binary mixture were evaluated based on this parameter.
†This report was originally printed in J. Soc. Powder Technology, Japan, 24(7), 462-468 (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.
The velocity distribution of particles flowing in a two-dimensional mass-flow hopper under gravity was obtained for the entire region of a hopper by measuring the position of tracer particles against time. The characteristic regions of discontinuity or rapid change in velocity and flow direction were found from a detailed analysis of the velocity distribution obtained. On the other hand, an approximate calculus for the estimation of the “velocity characteristic curve” and “stress characteristic curve” (i.e., slip line) was proposed on the basis of the plasticity theory. Theoretically, discontinuity in velocity is possible across the velocity characteristic curve. It was confirmed that both the characteristic regions estimated and obtained experimentally were identical Also, it was confirmed that the slip lines appear in the flow field that developed immediately after the yield of material occurred.
†This report was originally printed in KAGAKU KOGAKU RONBUNSHU, 13(3), 340-347 (1987) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Chemical Engineers, Japan.
Two-directional stress cells which can measure the small normal and friction stress of granular materials on a wall were recently developed. With these cells, the stress distributions of granular materials (silica sand and millet grain) piled conically on a plate are measured and compared with the results of theoretical analysis. The results are as follows: 1) The maximum normal stress occurs at a distance of a quarter of the outer radius of the cone of the pile, which is about (0.7∼0.8)γH, where γ is the apparent specific gravity, and H denotes the height of cone. 2) The normal stress at the center is rather small, about (0.4∼0.6)γH. 3) The maximum frictional stress also occurs at the same position as the maximum normal stress. 4) Theoretical analysis gives a maximum normal stress of 0.5γKH(√2/K-k-√K)2/(1-kK)2 at a radius of r=H/√k(2/K-k) and a normal stress at the center of γH[1-K2(ƒ- k)(2/K-k-ƒ)/(1-kK)2]. k denotes the friction coefficient, and K denotes the friction coefficient between granular material and the surface of plate. ƒ is given by the formula (40). This agrees well with the experimental result.
†This report was originally printed in J. Soc. Powder Technology, Japan, 23(12), 850-856 (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.
This paper summarizes the authors' recent studies on properties of TiO2 and nickel powders produced by gas phase reactions in aerosol reactors. The weight-average diameter and polymorphism of TiO2 particles at temperatures lower than 1200ºC were virtually unchanged 5-cm downstream from the nozzle mouth, and the effects of the residence time of gas and the reaction temperature were not dominant. However, the mean diameter of nickel powders produced by the hydrogenation of NiCl2 at 1380ºC was close to the theory assuming instantaneous fusion of coagulated particles. The fraction of rutile was maximum at ca.1000ºC. These results imply the importance of the fusion rate of particles and the heterogeneous deposition rate from the gas phase.
Novel agglomerated crystallization techniques, i.e., neutralization and solvent change, methods, were devised in order to design phenytoin (antiepileptic), crystals so as to be directly compounded during their formulation. The proposed techniques could directly transform the fine precipitated crystals into free-flowing spherical agglomerates during crystallization. Agglomeration by neutralization and solvent change was described in terms of a random-coalescence model and a mixed model with layering, respectively. The micromeritic properties of the agglomerates, e.g. surface topography, particle density and mechanical strength, depended on the agglomeration mechanism. The consolidation of the agglomerates in the neutralization process was represented by a function of the agglomeration rate constants.