Corrosion of copper in phosphoric acid solutions

• Ya.G. Avdeev, A.K. Mitrushonkova and T.E. Andreeva

Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, 31-4, Leninsky prospect, 119071 Moscow, Russia

Abstract: Certain regularities of corrosion of metallic copper M1 in freely aerated H₃PO₄ solutions have been revealed; the media under study included solutions containing Cu(II) phosphate as a corrosion product, and Fe(III) phosphate as an additional oxidizing agent. Useful information about the possibility of chemical reactions occurring during copper corrosion in these media and the reaction products was obtained by analyzing the E–pH diagram of the Cu–H₂O–phosphate anion system. Using the data on the mass loss of metal samples in the aggressive medium, the corrosion rates of copper in H₃PO₄ solutions (20±2°C) were obtained for various exposure times of the metal in the corrosive medium and at various acid concentrations in solutions. The maximum average corrosion rate of the metal was 0.11 g/(m²∙h) in 2 M H₃PO₄ over 8 days of testing. Upon prolonged contact of copper with 2 M H₃PO₄ (12 days), the mass loss of the metal due to the corrosion was 25 g/m². The addition of Cu(II) phosphate to 2 M H₃PO₄ solution does not significantly affect the corrosion rate of metallic copper in this medium. As a result, the accumulation of Cu(II) phosphate, the product of metallic copper corrosion in this aggressive medium, does not have a noticeable effect on copper corrosion. In contrast, copper corrosion increases significantly in the presence of Fe(III) phosphate in H₃PO₄ solutions. According to the data obtained for 6 h of testing, the corrosion rate of copper in 2 M H₃PO₄ in the presence of 0.01 M Fe(III) phosphate is 6.5 times higher than without it. This effect is slightly reduced with an increase in the duration of contact between the metal samples and the acid solution, and is enhanced with an increase in the concentration of Fe(III) phosphate in the aggressive medium. This regularity should be taken into account for industrial conditions in order to prevent accelerated corrosion of copper when technological H₃PO₄ solutions, contaminated with Fe(III) phosphate, come into contact with copper equipment.

Keywords: acid corrosion, copper, phosphoric acid, copper(II) phosphate, iron(III) phosphate

Int. J. Corros. Scale Inhib., 2026, 15, no. 1, 338-350
doi: 10.17675/2305-6894-2026-15-1-17

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