Structure of Milled Galena (PbS) Particles as a Result of Grinding: Observations by Electron Microscopy

Abstract

We have examined galena powders with the aim of providing information about the preparation mode of such powders from ancient Egyptian burial objects. Two extreme conditions of milling have been used to prepare galena powders in the laboratory, and the resulting products have been examined using scanning electron microscopy and transmission electron microscopy (TEM). The microstructure of hand-crushed coarse particles consists mainly of dislocation tangles. Annealing at 300 °C promotes a substantial recovery of the dislocation structure with the formation of subboundaries. Energetic ball milling produces a large variety of particle sizes, from 10 nm to several micrometers, with grains containing very high dislocation densities. Although PbS is a soft plastic compound, its fragmentation occurs down to very small sizes along various fracture regimes like in many brittle materials. Comparisons are made between TEM observations and the data obtained from x-ray diffraction peak profile analysis.