Abstract
Formation of corrosion products on zinc was investigated with in-situ Raman and FTIR when exposed to wet supercritical carbon dioxide (scCO2) and subsequent depressurization. Zinc oxide (ZnO) and smithsonite (ZnCO3) formed on zinc in scCO2. The dissolved water precipitated as liquid water in the reaction cell during depressurization. Formation of ZnO, ZnCO3 and a needle-like zinc hydroxy carbonate species on zinc was observed inside a sessile water droplet during conditions simulating the depressurization phase. Addition of oxygen accelerated the formation of the carbonate species due to higher cathodic activity that increased zinc dissolution.
Highlights
Zinc is widely used for corrosion protection in galvanized steels by providing sacrificial protection
The dark spatters indicate the early stages of corrosion on the zinc surface, which is initiated by the dissolved water in the Supercritical CO2 (scCO2) phase as no free water is present
The effect of wet scCO2 treatments on zinc surfaces was investigated with in-situ optical imaging, Raman and FTIR
Summary
Zinc is widely used for corrosion protection in galvanized steels by providing sacrificial protection. The surface of galvanized steel typically has poor adhesion to organic coatings and requires an adhesion layer that is currently obtained by chemical surface treatments of zinc within the industry [1,2]. The chemicals used in the treatments are harmful for the environment, which has led to the search of alternative methods [3,4]. Carbonates formed on zinc surfaces due to atmospheric corrosion have shown exceptional improvement in corrosion resistance of zinc, as well as better adhesion for organic coatings that are later applied [5,6,7,8,9]. Artificially grown carbonate layer produced with a scCO2-treatment method would provide advantageous surface properties as shown in our previous studies [10,11]. The present study aims to investigate in detail the interactions of zinc, CO2 and water that occur in the wet supercritical and subcritical CO2 conditions during the treatment
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