Effects of additives on the surface roughness and throwing power of copper deposited from electrorefining solutions

To elucidate the synergistic effects of gelatin, thiourea, and chloride ions on the surface roughness, throwing power, and polarization curves for Cu deposition 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 mol·dm−³ of CuSO₄ and 2.04 mol·dm−³ of H₂SO₄ at a temperature of 60C. In solutions containing all three additives (gelatin, thiourea, and chloride ions), the surface roughness of deposited Cu decreased with increasing thiourea and gelatin concentrations and decreasing chloride ions concentration. On the other hand, the throwing power of deposited Cu improved with decreasing thiourea concentration and increasing gelatin concentration in solutions containing all three additives. The throwing power of deposited Cu was significantly improved in solutions containing both gelatin and chloride ions. The polarization resistance dE/di for Cu deposition increased in solutions containing both gelatin and chloride ions, resulting in an improvement in the throwing power of Cu deposition. As small amounts of thiourea have a depolarization effect on Cu deposition, a smoothing effect is expected to result from the promotion of deposition at recesses.