Morphological characteristics of Si₃N₄ and SiC powders for sintering were examined. Particle size of the powder was measured by four different measurement methods having different principles. The particles were observed by electron microscope, and their shape was analyzed. The following results were obtained; (1) Si₃N₄ and SiC powders, which were ground, were irregular-shaped, and the others were needle-shaped. (2) The powder contained needle-shaped particles generally builds up agglomeration, and difference in particle size measured by four types of method was found. (3) Particle size measured by light diffraction and scattering particle counter was the largest, and particle size measured by F. S. S. S. was the second largest. Particle size measured by the sedimentation method was the third, and the specific surface aera diameter measured by B. E. T. was the smallest.

View full abstract

In order to determine wide ranges of particle size distribution, a new measuring method combined both the light scattering and the electrostatic separation-condensation nuclei was experimentally investigated.
From the experiments, it was confirmed that by using a sensitive optical particle counter connected to a digital system, the size range between 10nm and 10μm in diameter was sufficiently measurable.
Furthermore, having the same counting particle number criteria in the whole size range, this method is remarkably applicable as a more accurate measurement in practice.

View full abstract

When a particle settles under centrifugal force, the direction of centrifugal force acting on the particle is in the line between the center of rotation and the particle.
Therefore, as sedimentation of particles progresses, distance between particles becomes larger and apparent concentration decreases. This change of particle concentration causes an error in particle size analysis when using the centrifugal sedimentation method. Correction of the error was made possible by solving the Volterra Integral Equation for the particle size distribution function f (k) obtained from Stokes' equation.
The change in particle concentration and the amplitude of error due to increase in the interval between particles can be estimated by assuming f (k). It was ascertained that error correction was properly made by applying the correction equation to the calculated concentration.
In addition, change in the concentration during sedimentation was measured at two different depths on the actual centrifugal particle size analyzer. As a result, as the sedimentation distance increased, the particle size didtribution tended to deviate to a larger particle size. However, by applying the correction equation for change in particle concentration, a nearly constant particle size distribution was obtained for different sedimentation distances.

View full abstract

From the view points of accuracy, simplicity and convenience in the microelectrophoretic measurement method of submicron particles by diameter, the experimental setup and the experimental are studied by means of a particle visualization system which consists of an ultramicroscope with laser light source, TV-camera and TV-monitor. By the data processing on the velocity profile of particles, the effects of observation cell performance and of the sample preparation are examined. From the experiments on iron oxide of 0.3μm in diameter by using a stirred vessel, the coagulation-dispersion process depends consistently on the zeta potential related to the pH of the liquid.

View full abstract

A new measuring method for the size distribution of fine powder has been developed by the authors, in which the change in pressure difference between two probes of different depth in a sedimentation cell, both for gravitational and centrifugal operation, is measured by a pressure sensor.
Two computation methods, the matrix and averaged height, were formulated and the results by them were compared experimentally. It was shown that the difference in the results by these two methods were not so large, and therefore the latter method was adopted as simpler and more convenient method, especially for samples with wide fine size range. Comparing the results by this method with those by other methods, it is concluded that this new measuring method is practical and promising for very fine size measurements.

View full abstract