Analysis of Galvanic Corrosion Current between an Aluminum Alloy and Stainless-Steel Exposed to an Equilibrated Droplet Electrolyte

Abstract

Measurements of galvanic corrosion between UNS S13800 and UNS A97075 in bulk and equilibrated droplet electrolytes are compared with theoretical predictions of the corrosion current using calculations of the static diffusion-limited current, the classic Cottrell equation, and chemical reaction pathway models. The droplet electrolyte experiments use disks of stainless steel embedded in the aluminum alloy but isolated from electrical contact by an epoxy ring and connected via a zero-resistance ammeter potentiostat. Discrepancies between the measured and expected corrosion current for the droplet electrolyte are analyzed and a mechanism that relies on chemical reactions in the electrolyte to form corrosion products that block ion transport and suppress further oxidation is proposed. Electrochemical impedance spectroscopy and mass measurements are used to monitor changing solution properties in the equilibration of the droplet with the temperature and relative humidity environment of the atmospheric corrosion chamber.