Gravimetric Measurement of Hydrogen Evolution on Magnesium

The aim of this work is to study the suitability and limitations of a new gravimetric hydrogen evolution (HE) collection method for corrosion rate determination on pure Mg. This method, originally developed by Curioni [1], is based on the real-time weight measurement of the H2 produced during dissolution and exhibits a higher accuracy level as well as better collection efficiency than the traditional volumetric method. The gravimetric HE collection method overcomes some of the limitations exhibited by the traditional volumetric HE method, where hydrogen gas tends to accumulate at the walls of the funnel and the burette, leading to a lower determination of the amount of H2 produced and thus, an underestimation of the HE rate. The gravimetric HE collection method also exhibits good suitability for the study of Mg alloys with high corrosion resistance and for short experimental times, where the low levels of H2 produced prevents reliable measurements of the amount of gas evolved by the volumetric HE collection method. The gravimetric HE collection method is also applicable for dynamic measurements, i.e. potentiodynamic and galvanodynamic polarizations. The gravimetric method was evaluated for the study of anodic HE on pure Mg (also termed Negative Difference Effect (NDE)), which is characteristic of Mg and its alloys when they are forced to dissolve at anodic potentials from the E corr. Possible artifacts and experimental limitations of the gravimetric experimental method will be discussed. [1] M. Curioni, The behaviour of magnesium during free corrosion and potentiodynamic polarization investigated by real-time hydrogen measurement and optical imaging, Electrochim. Acta 120 (2014) 284-292.