Copper Corrosion Caused by Ammonium Sulfate and Sodium Sulfate Particles

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We observed the corrosion process that occurs between copper and ammonium sulfate (NH4)2SO4 or sodium sulfate Na2SO4 particles above a critical relative humidity (CRH) to study copper corrosion caused by corrosive particles. We also analyzed the corrosion products that formed on the copper by using X-ray diffraction (XRD) and Raman spectroscopy. Our results can be summarized as follows. 1) The droplet formed by the deliquescence of (NH4)2SO4 above CRH was colorless at first and became pale blue after 3 hours exposure. Further exposure turned the droplet dark blue. Patina precipitation was observed after 24 hours exposure. We attributed the color change to the formation of cupric species in the droplet. 2) With Na2SO4, the droplet color remained unchanged after 24 hours exposure. However, copper corrosion started as soon as a droplet formed on the copper surface. Further exposure resulted in an enlargement of the corroded area. 3) We analyzed the corrosion products using XRD and Raman spectroscopy and found that antlerite Cu3SO4 (OH)4 formed on copper that had reacted with (NH4)2SO4. By contrast, cuprite Cu2O was formed with Na2SO4. The results show that different corrosion products were formed when different sulfate salts reacted with copper above CRH.
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