The Dissolution of Magnesium in Hydrochloric Acid

Abstract

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, external 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 the stirring effect of the hydrogen bubbles which are evolved.The changes in the electrode potential with the acid concentration have been shown to depend on a deposition of low overvoltage impurities (Fe, Cu, Mn, etc.) on the surface of the metal. When this condition is taken into account, the observed electrode potentials are readily explained in terms of the electrochemical theory of corrosion.The effect of external polarization (anodic 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 electrochemical 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.