Synergistic Effects of Additives on the Deposition Behavior, Throwing Power and Surface Roughness of Cu Obtained from Electrorefining Solution

Abstract

To elucidate the synergistic effects of gelatin, thiourea, and chloride ions on the deposition behavior, throwing power, and surface roughness of Cu obtained from electrorefining solutions, Cu electrodeposition was performed at a current density of 200 A·m⁻² and a charge of 5 × 10⁵ C·m⁻² in an unagitated sulfate solution containing 0.708 and 2.04 mol·dm⁻³ of CuSO₄ and H₂SO₄, respectively, at a temperature of 60°C. Gelatin and chloride ions have synergistic effects on the polarization for Cu deposition, and the polarization effect increased with each concentration. Thiourea was found to promote Cu deposition and decrease the polarization effects of gelatin and chloride ions as its concentration in the solution were increased. The throwing power and surface roughness of the deposited Cu changed depending on the concentration of the three additives. The throwing power of Cu significantly worsened with increasing concentrations of thiourea and its surface roughness decreased with decreasing concentrations of chloride ions. With increasing concentrations of gelatin, the throwing power of Cu improved and its surface roughness decreased. The correlation between the throwing power and polarization resistance of Cu deposition was observed, and the throwing power of Cu improved as its polarization resistance increased. Since the surface roughness of deposited Cu is a result of its micro deposition properties, it does not depend on polarization resistance alone. Thiourea appeared to promote Cu deposition at the concavity, and therefore, it decreased the surface roughness of the deposited copper.