SEM/EDX and AFM study of gold cementation on copper(I) sulphide
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Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences
Institute of Ceramics, Mining Academy
Publication date: 2002-01-01
Physicochem. Probl. Miner. Process. 2002;36(1):9–20
This paper is methodological in nature. The results presented here are a preliminary step towards finding an optimal method of sulphide surface preparation for systematic AFM studies of AuCl4- cementation products. This technique makes it possible to see surface topography in nanoscale. Products of AuCl4- cementation on synthetic copper (I) sulphide, Cu1.86S, were investigated by scanning electron microscopy (SEM/EDX) and atomic force microscopy (AFM). The microstructure of the sulphide surface before and after the reaction with AuCl4- was analysed. Changes in the amount and shape of the products formed on polished plates and grains of the same material were compared. The process was performed in a flow-through vessel (on the plates) or in a circulation apparatus (on grain samples), by contacting the sulphide with aqueous solution containing 1.5·10-4 mol/dm HAuCl4 and 1·10-1 mol/dm HCl. The amount of gold deposited on a grain sample was determined from AuCl4- concentration decay. The reaction progress on plates was evaluated from the intensities of the AuL line of the EDX spectra. The maximum cementation degree was found to be equal to about 80 estimated atomic layers of metallic gold deposited on the sulphide. In SEM images the products were seen as crystallites of different sizes, between 0.1μm (the lowest limit detectable by SEM with a magnification of 5000x) and about 1.5μm, randomly distributed over heterogeneous surfaces of the plates and grains. The AFM technique made it possible to see the shapes of smaller crystallites, with their growth limited to the inside of cavities or cracks formed by polishing. The average density of the crystallites observed by AFM was of the order of 10 per 1μm2 geometric surface area.