Nanoscale Investigation of the Impact of pH and Orthophosphate on the Corrosion of Copper Surfaces in Water

Abstract

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.

Impact of pH, Dissolved Inorganic Carbon, and Polyphosphates for the Initial Stages of Water Corrosion of Copper Surfaces Investigated by AFM and NEXAFS

“…An interchange between particulate deposition and corrosive pitting was evident for surfaces treated with water at pH 6.5 (sample 4). With addition of high levels of DIC, consistent trends for surface deposits were observed as a function of pH and phosphate levels as previously reported, 8 however the morphology, thickness and composition of deposits showed subtle yet detectable differences at the nanoscale.…”

“…[3][4][5][6][7] Phosphates inhibit copper corrosion by producing a passivating film or protective scale layer on surfaces. 8,9 Orthophosphate and hexametaphosphate have been shown to reduce the soluble copper release from corrosion by-products. 10 Aminophosphonic acid has also been shown to inhibit corrosion of iron surfaces.…”

“…For example, in situ studies of corrosion inhibitors were investigated for different media using AFM. [12][13][14][15][16] Surface studies with AFM have been used to investigate corrosion of materials such as copper, 8,[17][18][19][20] steel, 21,22 iron 23,24 and silver. 25 Studies with AFM provide 3D topographic information for a wide range of surface materials with micron to nanometer resolution.…”

“…[27][28][29][30][31] Previously, we studied the effects of phosphates as a function of pH for mitigating the corrosion of copper. 8 Essentially, the previous report provides control experiments as a baseline for designing further studies of different water parameters. In the new studies to be disclosed in this article, we have designed experiments to study the effects of pH and polyphosphate levels combined with much higher levels of DIC.…”

Nanoscale surface characterization of aqueous copper corrosion: Effects of immersion interval and orthophosphate concentration

“…The thickness, porosity and ability of the passivating layer to conduct ions are properties that affect the progression of corrosion [10][11][12]. Studies have shown that the transformation of cuprous oxide to a more thermodynamically stable and less soluble Page 5 of 38 A c c e p t e d M a n u s c r i p t 3 material upon exposure to water can be attributed to changes in pH, alkalinity and the presence of certain anions, including sulfate and chloride [13,14].…”