On the Zinc and Copper Dissolution in Phosphate Solutions

• Published in: Protection of metals Vol. 39; no. 3; pp. 217 - 221
• Main Authors: Podgornova, L P, Kuznetsov, Yu I, Gavrilova, S V
• Format: Journal Article
• Language: English
• Published: New York Springer Nature B.V 01.05.2003
• Subjects: CATHODES; Copper; COPPER OXIDE; DEPOSITION; DISSOLUTION; Electrodes; PHOSPHATES; Zinc; ZINC OXIDE
• ISSN: 2070-2051; 0033-1732; 2070-206X; 1608-327X
• DOI: 10.1023/A:1023954817961

The copper and zinc dissolution in phosphate solutions is studied over wide pH range (from 4.5 to 11.7). The cathodic reaction rates are shown to depend on the pH of the solutions; they are minimum at a pH of 9.5 for zinc and 11.7 for copper. Phosphate directly participates in the cathodic process on zinc because of the reduction of phosphate to phosphite anions. Thermodynamic calculations, corroborated by electrochemical studies and analyses of the electrode surfaces by different methods, showed that zinc passivates itself by the deposition of either ZnO, Zn(OH)^sub 2^, Zn(H^sub 2^PO^sub 4^)^sub 2^, and ZnHPO^sub 4^, in the solutions of low acidity, or ZnO, Zn(OH)^sub 2^, ZnHPO^sub 4^, and Zn^sub 3^(PO^sub 4^)^sub 2^ at a pH of 9.5 to 11.7. On copper, the passive films are formed of CuH^sub 2^PO^sub 4^ and CuHPO^sub 4^ in weakly acid phosphate solutions or of CuO, Cu(OH)^sub 2^, CuHPO^sub 4^, and Cu^sub 3^(PO^sub 4^)^sub 2^ at a pH of 9.5 to 11.7.[PUBLICATION ABSTRACT]