Pattern selection induced by electroconvection in the electrodeposition of iron

The morphology of iron electrodeposit is shown to relate closely to the pH of the electrolyte solution. Macroscopically, depending on the strength of the interbranch convection, which is associated with the concentration of ${\mathrm{H}}_3{\mathrm{O}}^{+}$ in the electrolyte, the deposit morphology varies from treelike pattern to meshlike pattern and dense-branching morphology. Microscopically the deposit is ramified and dense-branching at lower concentration of ${\mathrm{H}}_3{\mathrm{O}}^{+},$ while it becomes relatively smooth and stringy at higher ${\mathrm{H}}_3{\mathrm{O}}^{+}$ concentration. The symmetry of the convective vortices on the two sides of the growing tip is observed to decide the growth behavior of the tip. We suggest that ${\mathrm{H}}_3{\mathrm{O}}^{+}$ influences the pattern formation and pattern selection in the electrodeposition of iron from ${\mathrm{FeSO}}_4$ solution by either initiating interbranch convection or changing the effective interfacial energy of the deposit and the electrolyte.