THERMOCONVECTION-ENHANCED DEPOSITION OF COPPER

Thermal gradients and thermoconvective flow in the vicinity of the ele ctrode are shown to enhance mass transport of the electroactive specie s during reduction of copper. The transport-limited current of the cop per reduction reaction is more than doubled under conditions of positi ve and negative thermal gradient in comparison with isothermal conditi ons. Furthermore, thermal gradients affect strongly the potential depe ndence of the current. Kinetic and thermodynamic parameters for electr odeposition of copper were determined from polarization curves analyze d with Butler-Volmer, Tafel, and Levich expressions. Under isothermal conditions the exchange current density for the copper reduction react ion was found to be given by log i(0) = 7.95 - 2690T(-1) (i(0) in mA c m(-2) and T in K) under conditions of 10 mM CuSO4 in 2 M H2SO4 io (10 less than or equal to T/degrees C less than or equal to 80). The diffu sion coefficient of Cu(II) at 298 K under the same conditions was foun d to be 5.36 . 10(-6) cm(2) s(-1). Decrease of the effective thickness of the diffusion layer due to thermoconvection in the vicinity of the cathode is responsible for the effect of the gradient on transport-li mited current.