THE KINETICS OF COLLOIDAL DEPOSITION UNDER CONDITIONS OF CONTROLLED POTENTIAL

The kinetics of the deposition of colloidal graphite particles onto an indium tin oxide electrode have been studied under conditions of controlled mass transport in a wall jet cell. The rate of deposition is followed by measuring the intensity of the light from the evanescent wave scattered by deposited particles. The effects of varying the potential on the deposition kinetics have been studied. For potentials more positive than -400 mV, the deposition into the primary minimum is always mass transport controlled, showing a radial dependence on r- 5 4 and a dependence on the volume flow rate of V 3 4f. At more negative potentials, rather variable results are found. For some surfaces there is no deposition while for others the deposition is also mass transport controlled. Intermediate cases can be found. The intensity of the scattered light is less for particles deposited under these conditions and is less the lower the electrolyte concentration. These results are explained quantitatively by assuming that the particles are being held in the secondary minimum. The lower the electrolyte concentration, the further the secondary minimum is from the electrode surface and the lower is the intensity of the evanescent wave. For the intermediate cases kinetic analysis gives the depth of the secondary minimum. The variability of the results is discussed in terms of the roughness of the surface and the interaction of the particles with the radial velocity component. © 1990.