Surface Roughening and Oxidation of Galena Cleavage Face in a Vacuum Furnace Under Limited Air Supply

Abstract

Surface structures of galena cleavage face heated at reduced air pressures 10⁻²–10⁻³ mm. Hg and at temperatures 100°–600°C. were studied by electron diffraction. Surface roughening commences at 350°C. with the release of sulphur in combination with oxygen. The roughened surface is bounded by the {100}_PbS facets. Extra structure due presumably to some effect of the enriched lead atoms was also observed. As to the oxidation product, epitaxially oriented lead sulphate (PbSO₄) or the suboxide (Pb₂O) crystallites were obtained at temperatures below 400°C. For the latter, the needle like external shape was deduced from the analysis of the diffraction spot. Above 400°C. randomly oriented suboxide or the yellow oxide (PbO) crystallites were observed. With the complete evaporation of the crystal at 600°C. silver powder remained as the residue.