THE MECHANISM OF SILVER GRANULAR ELECTRODEPOSITS FORMATION

Granules as a possible form of metal electrodeposit call be formed dur ing deposition of metals, such deposition processes being characterize d by large exchange current density values. Because of this, zero nucl eation zones around growing grains are formed, permitting granular met al growth. In some cases of prolonged deposition, macro-crystalline de posits can be formed as well as granular ones? e.g. in the case of sil ver deposition at overpotentials lower than the critical value for den drite growth initiation. The mechanism of granular deposit growth as a final form of metal electrocrystallization is proposed. Silver boulde rs were deposited on platinum and silver substrate. At low deposition potentials, various crystallographic forms, some of them ideal or deri ved from cube-octahedron-type morphology, were obtained as a result of independent grain growth inside zones of zero nucleation. In addition to cube-octahedra, twinned and multiply twinned silver particles were also observed. The nucleation density was found (1) to increase with increasing deposition overpotential, (2) to decrease with increasing s ilver concentration, and (3) to be greater on Ag than on Pt for the sa me deposition overpotential and dendrite precursors. Increasing overpo tential leads to increase of density of twinned grains. The grain grow th at greater overpotentials from more concentrated solution is less i deal: producing a granular deposit on prolonged deposition.