A New Approach to Determine External Surface and Volume of Irregularly Shaped Particles

A new approach to characterize fine particles is described that enables rapid determination of external surface area and volume. Individual particles are isolated and held in an electrodynamic balance. The particles are backlit to produce a high contrast shadow image that is projected onto a video camera detector. The resulting video signals are sent to a video imaging system that digitizes the video camera output in real time. Each video image field is reduced to a set of 20 to 30 number pairs that can be used to reconstruct the image to determine particle length, width, cross·sectional area, and perimeter. Surface areas and volumes are obtained by rotating particles using a set of directed gas jets and recording image data for successive video fields as a function of rotation angle. Particle perimeters and radii of rotation are determined for each video field and these data are numerically integrated to yield surface area and volume. Data acquisition times of less than 5 s are required for complete particle surface characterization. Data are presented for carbon spheres and irregularly shaped coal particles to demonstrate the measurement system. The methods described are an integral part of a powerful new system that enables detailed characterization of mass, density, external surface and volume of irregularly shaped particles in the 20-200· .... m diameter size range.