The Dissolution of Magnesium in Hydrochloric Acid 1

The dissolution of magnesium in hydrochloric acid has been studied by measuring dissolution rates and electrode potentials as functions of acid concentration, rate of agitation, temperature, xternal polarization, alloy composition, and additions to the acid solution. The dissolution rate measurements offer evidence in favor of a diffusion controlled reaction. By studying the dissolution process at acid concentrations up to 1.6N it has been possible to evaluate he stirring effect of the hydrogen bubbles which are evolved. The changes in the electrode potential with the acid concentration have be n shown to depend on a deposition of low overvoltage impurities (Fe, Cu, Mn, etc.) on the sur-face of the metal. When this condition is taken into account, the observed electrode po-tentials are readily explained in terms of the electrochemical theory of corrosion. The effect of external polarization (a odie and cathodic) in reducing local action has been related to the effect of the applied emf on the rate of transfer of hydrogen ions to the surface of the metal by diffusion and migration. The results are in accord with the view that the dissolution of metals is electrochem-ical in nature, even in cases such as the dissolution of magnesium in hydrochloric acid where stationary local cells are absent, and the dissolution rate is diffusion controlled