The influence of deposition method on the packing uniformity of powder beds.

A number of methods of preparing powder packings have been assessed in terms of the resulting variability of local porosity. Measurement of local porosity was carried out by a gamma-ray attenuation technique. It was found that overall porosity and the distribution of local porosity were highly dependent on particle properties and deposition method. Some deposition methods tended to give rise to the alternate formation and collapse of temporary structures within a growing bed, and in such cases, relatively high variability of local porosity was detected. More uniform packings could be formed by deposition of powder in even layers. In many cases, a significant relationship between local porosity and position within a packing was established, the central areas generally being of lowest porosity. This was true of packings both of high and low overall variability of porosity.