Electrodeposition of copper under microgravity conditions

Copper was electrodeposited from 0.9M CuSO4 aqueous solution for 8 seconds during a free fall experiment in a drop shaft. A horizontally-orientated quasi two-dimensional electrolytic cell containing a 200 mu m thick electrolyte layer fell in the shaft. Electrolysis was conducted at constant current densities and the potential difference between electrodes was monitored. A common-path microscopic interferometer was installed in the capsule. The development of diffusion layer thickness measured by the intereferometer increased with the square root of time. The transient diffusion model combined with the migration effect reasonably explained the development of diffusion layer thickness. Calculated surface concentrations corresponded with the measured time variation of potential difference between electrodes. Natural convection was evident in the ground-level experiment, even using such a shallow electrolyte layer. Under microgravity, lower-index planes preferentially grew to form a fewer number of larger grains, even though electrodeposition was conducted at 0.05 to 0.3 A cm(-2) only for 8 s.