The effects of X-ray irradiation and temperature on the formation and stability of chemical species on enargite surfaces during XPS
By Plackowski, Chris; Hampton, Marc A.; Nguyen, Anh V. & Bruckard, Warren J.
Published in Minerals Engineering
NULL
2013
Abstract
An investigation of the species present on the surface of natural enargite and the effects of X-ray radiation on the surface after electrochemical oxidation at pH 10 has been carried out using X-ray photoelectron spectroscopy. Surface species present on fractured and polished unoxidized enargite have been compared with those present on the polished surface after oxidation at pH 10. The effect of X-ray irradiation time as a function of temperature on the forms and intensities of the photoelectron signals from the enargite surface was studied. High binding energy (BE) components and shake-ups of the Cu 2p signals, characteristic of a copper (II) hydroxide surface layer, reduced in intensity with increasing X-ray exposure time. Associated changes in the relative concentrations of surface oxygen species were also observed. Comparing a surface exposed to X-rays at 35 °C with that maintained at -135 °C, temperature was shown to significantly influence the rate of change. The observed changes were evaluated in terms of a proposed two-stage mechanism involving the dehydration of Cu(OH) to CuO, followed by photoreduction of CuO to Cu2O. The photoreduction effects of X-ray irradiation should be significantly reduced by sample cooling for consistent analysis of the enargite surface using XPS.
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