Quantifying the amount of reducing substance in the corrosion products on magnesium electrodes

This brief report describes an ad hoc two-stage method for quantifying the amount of reducing substance, presumed to be magnesium hydride, found in the corrosion products on pure magnesium electrodes exposed to localised corrosion. In the first stage, the corrosion product was dissolved in a small amount (approx. 20 mL) of an aqueous solution of 200 g/L chromic (VI) trioxide (CrO ₃ ) with volumetric measurement of small amounts of H ₂ gas (1–3 mL) produced by the oxidative hydrolysis of the hydride. In the second stage, the quantity of Cr(III) ions generated from the reduction of chromic acid by the reaction with magnesium hydride in the first stage was measured by a spectrophotometric technique utilising the absorbance from Cr(III) ions at 650 nm.