Identification and formation of green rust 2 as an atmospheric corrosion product of carbon steel in marine atmospheres

Abstract

Green rust 2 (GR2(SO42-)) was detected amongst the products formed on a carbon steel rod exposed to atmospheric corrosion using X-ray diffraction (XRD). The presence of green rust 2 has been related to sulphate reducing bacteria (SRB) in the sea spray. These were detected using test catch rods made out of inert material and posterior lab identification using Starkey culture. Likewise, after the exposure of said rods to sea environmental conditions, SRBs have been isolated from among the carbon steel corrosion products. The evolution of GR2(SO42-) from GR1(SO42-) was ruled out due to the tendency of this compund to produce GR2(SO42-) in the presence of sulphate ions, as is the case here. Likewise, the evolution from GR1(Cl-) has also been ruled out since in such case as this compound should be formed (it has not been detected in any of the 39 stations studied), the enormous affinity of the GRs with divalent anions (such as is the case with SO42-) as opposed to the monovalent ions (such as is the case of the Cl-) makes GR1(Cl-) transform into GR2(SO42-).