Silver–zinc electrodeposition from a thiourea solution with added EDTA or HEDTA

Abstract

This paper shows the study of silver–zinc electrodeposition from a thiourea solution with added (ethylenedinitrilo)tetraacetic acid (EDTA), disodium salt and N-(2-hydroxyethyl)ethylenediaminetriacetic acid (HEDTA), trisodium salt. Voltammetric results indicated that silver–zinc alloy can be obtained applying overpotential higher than 0.495 V, in Tu solution containing 1.0 × 10 −1 mol L −1 Zn(NO 3) 2 + 2.5 × 10 −2 mol L −1 AgNO 3. This was due to silver(I) ion complexation with thiourea, which shifted the silver deposition potential to more negative value and due to silver–zinc alloy deposition, which occurred at potentials more positive than the potential to zinc deposition alone. EDTA or HEDTA did not significantly affect the silver and zinc deposition potentials, but decreased the current density for silver–zinc deposition. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) analyses of the silver–zinc deposits showed that the morphology and composition changed as a function of the conditions of deposition, viz, deposition potential ( E d), deposition charge density ( q d) and solution composition (silver, EDTA and HEDTA concentrations). EDS analysis of the deposits showed sulphur (S) incorporated into the silver–zinc deposit, while SEM images showed that this sulphur content seemed to improve the silver–zinc morphology, as did the presence of EDTA and HEDTA in the solution, which enhanced the sulphur incorporation into the silver–zinc deposit. X-ray diffraction (XRD) analysis of the silver–zinc deposit showed that it was amorphous, irrespective of its composition and morphology.