Nanoscale investigation of the impact of pH and orthophosphate on the corrosion of copper surfaces in water.

Advanced surface characterization techniques were used to systematically investigate either the corrosion or passivation of copper after immersion in water as impacted by pH and orthophosphate water chemistries. Atomic force microscopy, depth profiling with time-of-flight secondary ion mass spectrometry, and X-ray diffraction were used to evaluate changes in surface chemistry of copper surfaces resulting from various chemical treatments. Nanoscale differences in surface morphology are clearly evident after 6 and 24 h immersion in water samples. Orthophosphate and pH dramatically influence the evolution and progression of changes during surface corrosion. For example, in the absence of orthophosphate the surface of copper exposed to water at pH 6 had formed relatively large cubic crystals on the surface up to 400 nm in height. In the presence of orthophosphate, the morphology and growth rate of corrosion byproduct changed dramatically, and the formation of identifiable crystals diminished. These investigations provide insight into the mechanisms of surface passivation and the evolution of nanoscale mineral deposits on surfaces at very early stages of the corrosion of copper surfaces in water.