JunIchiro Tsubaki

Effect of particle shape on the particle size distribution measured with commercial equipment

Abstract The present paper describes the results of a round robin that has been performed to investigate the influence of particle shape on particle-size distributions measured with commercial particle-size analyzers. The commercial equipment based on the five kinds of measuring principle such as electrical sensing zone, laser diffraction and scattering, X-ray sedimentation, photosedimentation, and light-obscuration methods have been employed for analyzing blocky, flaky and rod-like ceramic particles. It is demonstrated that the particle shape has a strong influence on the particle-size distribution measured by the laser diffraction and scattering and by photosedimentation. The size range of rod-like particles is particularly wide when these methods are applied. It is also shown that the particle-size distributions of anisotropic samples measured by photosedimentation has a tendency to be remarkably scattered in the coarse-size range.

Process conditions on the preparation of supported microporous SiO2 membranes by sol-gel modification techniques

The formation process is described of supported microporous membranes, prepared by modification of α-alumina supports with colloidal silica sols. The sols were prepared by acid catalyzed hydrolysis of tetraethylorthosilicate (TEOS), using different molar ratios of H2O/TEOS and of HNO3/TEOS. Membrane composites with multiple separation layers were synthesized by a conventional dip-coating method, in which process multiple layers with interconnected pores were formed by sequentially dipping a support in sol solutions in descending order of sol size. Emphasis is given to the parameters of dipping process such as dipping time and the number of dipping procedures applied, and to the preparation conditions of silica sols, in order to identify the main factor governing performance of processed membranes. It has been found that the modification procedure using several sols with different sol size is effective for preparing a multiple separation layer through which a percolation system of pores is successfully formed. The proposed process has made it possible to prepare membranes with CO2 permeation rates on the order of 10−3 cm3(STP) cm−2 s−1 cmHg−1, which is one to two orders of magnitude higher than those previously possible by sol-gel techniques. The ideal CO2N2 selectivities, determined from single-component gas permeation experiments, are 4.2 for high-quality membranes.

A proposed new characterization of particle shape and its application

Abstract In order to identify particles morphologically nine new shape indices, using three kinds of powder particles which include circularity and elongation as reltionships between characteristic diameters, have been defined. Shape indices have been examined on their numerical lines. The nine shape indices were divided into three groups which characterize the concavities and/or convexities of a particle, mainly characterize slimless and do not characterize specific shape. Shape identification has been tried on two kinds of diagrams which were obtained by combining shape indices of different character. Particle shape without surface texture is characterized on the diagrams and it is also suggested that morphological identification of powder particles is possible with statistical treatment.

Theoretical analysis of the tensile strength of a powder bed

Abstract The authors have proposed an experimental equation which correlates the tensile strength of a powder bed measured by split cell methods with the porosity of a powder bed. In this report, the authors discuss the relationships between the porosity and the pre-compressive stress and also between the tensile strength and the pre-compressive stress. As the results of this discussion, the physical base of the proposed experimental equation is proved theoretically. Furthermore, it has also been proved that the pre-compression of a powder bed brings not only the decrease of the porosity but also the increase of compressive force at the contact point of particles, and therefore the increase of tensile strength by increasing the-compression force cannot be explained simply by the change of the porosity, and then another factor, such as the compressive force at the contact point, must be considered.

Slurry characterization by hydrostatic pressure measurement — analysis based on apparent weight flux ratio

Abstract The flocculation degree of a dense slurry was evaluated by hydrostatic pressure measurement. In order to discuss the relationship between the results obtained from the hydrostatic pressure measurement and the final packing fraction of a sediment, the ratio of apparent weight flux of the depositing particle to that of the settling particle, U b / U u was introduced. It was shown that the final packing fraction of the sediment increased with U b / U u . In addition, the value of U b / U u was theoretically estimated when the particles were well dispersed and hindered settling occurred, and the estimated value was compared with the experimental value in order to discuss the settling behavior in detail.

Characterized microstructure of porous Si3N4 compacts prepared using the pyrolysis of polysilazane

Abstract The present paper describes the feasibility of controlling pore sizes of porous-fired Si 3 N 4 compacts prepared using the pyrolysis of polysilazane, for developing a Si 3 N 4 membrane manufacturing technique. Attention has been paid to the microstructure of these compacts in order to identify the main parameter governing the evolution of polysilazane-to-ceramic direct conversion. A volumetric shrinkage, stemming from the pyrolysis of polysilazane and the following crystallization of pyrolyzed polysilazane, have been shown to be of prime interest in the control of pore-size determination. A porosity of ∼35% was achieved in the fabrication of compacts, the pore-size distribution of which was controlled in the range 1–1000 nm, with polysilazane additions of 80–200 vol%. Also demonstrated was the effect of firing temperature on pore-size distribution. The bending strength of the processed specimens was equivalent to that of Vycor glass, indicating the feasibility of an application in the preparation of microstructured membrane system.

Experimental analysis of sample preparation conditions for particle size measurement

Abstract The influence of deagglomeration on an agglomerated sample, the dispersion media for a non-oxide sample, and the measuring conditions for a mixed sample on the particle size distribution are investigated in the present paper. It is found that deagglomeration is effective for dispersing an agglomerated powder well, regardless of the type and output power of the ultrasonic disrupters used. Ethanol is a useful dispersion medium for achieving stable measurements of non-oxide samples. In the measurement of a mixed sample, the measured distributions by X-ray sedimentation do not coincide with the distribution calculated from the weight ratio for each original sample. However, they coincide with the modified distribution from the X-ray absorption ratio for each original sample, because the cumulative mass % in this measuring principle is determined on the basis of the relationship between the X-ray transmittance ratio and the suspension concentration, depending on the sample materials.

The Identification of Particles Using Diagrams and Distributions of Shape Indices

Abstract Using five kinds of real powder paricles, we obtained their shape indices from their pictures, attempted to identify the powder particles morphologically and studied the distribution functions of particle shapes and their relationships. The results were indicated as the follwing. It is possible to identify powder particles on the diagrams of the shape indices. The distributions of the shape indices are expressed by some distribution functions. The sample material and the particle size of sample particles affect the distribution of the shape indices in a different way. The distributions of two characteristic diameters and the distribution of shape index defined by ratio of these diameters are accurately connected by an equation.

An attrition test with a sieve shaker for evaluating granule strength

The purpose of this study is to establish a method for evaluation of the strength of fragile granules such as ferric oxide granules produced by spray pyrolysis from an acid solution of a metallic salt. To examine if they have enough strength to maintain their shape throughout the handling process, and at the same time, enough weakness to break down easily during a specifically designated processing. An attrition test using a Ro-Tap sieve shaker, which is usually used for particle size analysis, was employed. An attrition rate equation was derived from the attrition mechanism of granules on a sieve; a method for the evaluation of strength based on the attrition equation is presented.

Attrition testing of granules with a tapping sieve

Granules produced to overcome powder handling difficulties must retain their shape during storage or transport but, on the other hand, be easily broken down during designated process. Commonly, granule properties have been evaluated for several properties such as flowability, bulk density, and so forth; however, shape retention and fragility have not yet been evaluated. This study examines whether fragility can be evaluated with attrition tests. We carried out attrition tests with a tapping device on ferric oxide granules and followed the progression of the attrition with time. The attrition mechanism was expressed with an attrition-rate equation with two constants. We showed that these two constants are useful for characterizing the attrition of the granules used in the experiments.