A new paper reports an atom probe tomography (APT) analysis of zero-valent iron (ZVI) nanofilms.

The study reveals the presence of dendritic iron oxide features that extend from a surface oxide overlayer into the ZVI bulk. The dendrites are observed by APT to be in the 5 nm x 10 nm size range, form quickly under natural atmospheric conditions and their growth into the films is, within the limit of our three-month long study, self-limiting (i.e. their initial growth appears to quickly discontinue). We hypothesize that the presence of oxidized iron dendrites over ZVI is likely to be related to the passivation processes that currently hampers the long-term use of permeable reactive barriers for enviromnmental remediation. Re-engineering based on a detailed analysis may provide a pathway to impede, halt, or even reverse the passivation process. The atomistic views also shed first light on the atmospheric corrosion process of Fe(0)-bearing engineered materials and their surfaces in the limit of low bulk impurities.