Influence of Bath Compositions and Some Operating Conditions on the Electroplating of Cobalt from Aqueous Sulphate Baths

SUMMARY

A systematic study has been made of the influence of aqueous sulphate bath constituents on the cathodic polarization curves during cobalt electrodeposition. The optimum bath composition has been established and it contains: 0.30 mol l⁻¹ CoSO₄.7 H₃0, 0.30 mol⁻¹ H₃BO₃. 0.05 mol l⁻¹ (NH₄)₂SO₄ and 0.10 mole l⁻¹ Na₂SO₄.10 H₂o. Cobalt electroplating from the optimized bath has been performed under a variety of conditions viz: pH, 1.5 to 5.3; current density, 0.2 to 2.0 A dm⁻² and temperature 25 to 53°C. Under the most suitable conditions, the optimum bath is characterized by a high cathodic efficiency (~ 99%), moderate throwing power (21.6%) and throwing index (1.47). The bath produced smooth, adherent and semibright plates characterized by a high microhardness (411.4 kgf mm⁻²) and their morphologies, as revealed by scanning electron microscopy, showed a dependence on the plating variables.