Introduction

MICROSCOPY is the most definite method of particle size analysis, because individual particles are observed and measured. However, optical and electron microscopy also afford the opportunity for particle shape analysis. Particle shape, like particle size, is a primary powder characteristic that must be considered when determining the optimum utilization of a P/M material. Behavioral characteristics of a metal powder, such as flow rate, apparent density, compressibility, and sinterability, are all influenced by particle shape and size.

This article briefly reviews the common methods of optical and electron microscopy for image analysis of particle size distributions and particle shape characterization. Image analysis of particle size distribution is a very precise quantitative practice, while particle shape analysis is more qualitative in nature. Advancements in qualitative shape analysis are based on the use of the scanning electron microscope for determination of particle shape. In addition to its high magnification capability, this device produces an image with a three-dimensional appearance. Because of its advantages, scanning electron microscopy (SEM) has replaced optical microscopy to a large extent in the area of shape and topographical analyses of metal powders.

Quantitative shape analysis has posed numerous difficulties. However, with the advent of advanced computers and graphics systems, interest in quantitative analysis has increased. Through the use of optical and scanning electron microscopy, qualitative descriptors have been developed to label different particle shapes. As computational technology advanced, mathematical algorithms were written to describe particle shape. Fourier analysis and fractal geometry are two mathematical disciplines that are being applied to describe particle shape. Because of the computational intensity of these disciplines, most of the work has been confined to a two-dimensional space. The current challenge is to develop three-dimensional modeling programs that can accurately describe the shape of irregularly shaped particles.

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