Metal Corrosion in the Vadose Zone: Effects of Moisture Cycles and Active Evaporation Conditions

Metals buried in time-varying saturation environments often withstand wet-dry cycles and active evaporation. This study aims to identify the underlying physical processes relevant to corrosion and its severity in these extreme environmental conditions. Two experimental devices and test protocols investigate corrosion in the vadose zone in relation to (1) wet-dry cycles and (2) ion migration from host sediments into clean backfills. Corrosion characterization uses weight loss, micro-CT and photographic imaging. Experimental results and analyses highlight the importance of identifying the controlling transport mechanism to anticipate corrosion rates. Moisture cycles augment corrosion rates in comparison to static conditions due to enhanced oxygen and residuals transport, and an increased active corroding area. Metals buried in sand columns exposed to an active evaporation regime display that critical unsaturated conditions result in higher mass loss than highly saline conditions as both oxygen and air phases are connected. We demonstrate that a capillary barrier prevents clean sand contamination from native electrolytes resulting in an efficient solution to prevent corrosion of buried metals in arid climates.