A morphological study of the sulfurisation of digenite to covellite using reflected polarised light microscopy

摘要

Abstract A series of copper rods were reacted with sulfur vapour in evacuated glass ampoules at ～445?°C. Product materials were characterised by powder X-ray diffraction and reflected polarised light microscopy. Copper sulfurised rapidly to digenite, γ-Cu2-xS, under these conditions, whereas the subsequent sulfurisation to covellite, CuS, was notably slower, yielding texturally distinguishable inner (secondary) and outer (primary) CuS regions. A two-stage partial sulfurisation of γ-Cu1.8S resulted in the external growth of two successive layers of primary CuS, which demonstrates decisively that covellite???besides being a p-type metal???is ionically conducting at 445?°C, although considerably less so than digenite. We infer that the growth of platy covellite crystals and their radial alignment in the primary CuS layer are a consequence of copper ion mobility being restricted to the basal plane of the covellite structure. Sulfurising a coil of copper wire at ～445?°C is an effective method for synthesising covellite. Graphical abstract Display Omitted Highlights ? CuS is ionically conducting at 445?°C although considerably less so than γ-Cu2-xS. ? Alignment of CuS crystals is attributed to Cu+ ionic conduction in CuS basal plane. ? The outer layer of CuS retards further sulfurisation of the underlying γ-Cu2-xS. ? Reacting a coil of Cu wire with sulfur is an efficient method for synthesising CuS. ]]>