The Rate of Dissolution of Zinc and Cadmium in Chromic Chloride Solutions

Abstract

The relative potentials of the zinc-zinc ion, chromous-chromic ion systems might lead one to expect smooth progress of the reaction Zn + 2Cr +++ ~ Zn + § + 2Cr ++. However, various other reactions are possible, and the dissolution or corrosion process is complicated; it is electrochemical in nature, and, in some solutions, rapid enough to permit transport control of the rates. The dissolution rate is highly dependent on the form of chromic ion present, on pretreatment of the metal surface, in some solutions on the acidity, and, under some conditions, the main reaction is hydrogen evolution with little reduction of chromic ion.

Ionic Mass Transfer and Concentration Polarization at Rotating Electrodes

“…In studies of dissolution and corrosion rates of rotated metal rods, King and coworkers (19)(20)(21)(22) estimated the mass transfer coefficients employing King and Shack's earlier experimental finding (23), according to which "normal diffusion (or transport) control requires that rates be linear with peripheral speed above about 5000 cm/min" (22). King and Cathcart (24) indicated that the mass transfer coefficient is directly proportional to the 0.7 power of the diffusion coefficient of the reacting ionic species.…”