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In a wet supercritical carbon dioxide atmosphere, carbon dioxide is dissolved into water and causes corrosion of zinc-coated steel. The first corrosion products appeared in singular nano-scale initiation sites, which gradually grew in number and size and ultimately covered the whole surface. Zinc hydroxy carbonate was detected as a rapidly forming needle-like corrosion product, which prevailed at short exposure times (from minutes to hours). A prolonged exposure caused conversion of zinc hydroxy carbonate to anhydrous zinc carbonate with high crystallinity and a stable, dense layer was formed on zinc. The chemical transition from zinc hydroxy carbonate to anhydrous carbonate was reported for the first time and is in the light of current literature unique for wet scCO2 atmosphere.