Effect of Pressure on the Reflectance of Compacted Powders

Abstract

The spectral reflectance of compacted powders is modified significantly by compaction. Two opposing effects may occur depending upon the opacity of the material. Transparent particles, such as white oxides, undergo a large decrease in reflectance with increasing pressure. The applied pressure decreases the distance between the particles and thereby decreases the fraction of light totally internally reflected. Opaque particles, such as metals and dark nonoxide compounds, undergo an increase in reflectance with increasing pressure. In this case, the surface density is increased, resulting in less trapping of incident light. Theoretical calculations of the reflectance of powders usually ignore the extent of compaction, and are therefore inadequate.