Effects of γ-radiation versus H2O2 on carbon steel corrosion

Periodic aggregation patterns of oxide particles on corroding metals: chemical waves due to solution feedback processes

Chemical waves that produce periodic patterns are common occurrences in nature. The underlying processes involved have been studied in many disciplines of science, but rarely reported in the chemistry of corrosion. In this study of carbon steel corrosion, iron oxide crystals are observed to deposit in concentric wave patterns or in discrete bands, known as Liesegang patterns. We demonstrate that oxide growth in these patterns is preceded by the formation of a hydrogel network, which consists of a semi-stationary phase of loosely connected metal-hydroxide colloids and a mobile phase of solution saturated with metal cations. Once the hydrogel network covers the metal surface, a metal cation produced by corrosion reactions at the metal surface must diffuse through the layer into the bulk solution. While diffusing through the porous network, the metal cation undergoes adsorption-precipitation as metal-hydroxide colloids which later can dissolve back into the solution. When the kinetics of precipitation and dissolution of the metal cation can be effectively coupled with the transport flux of the dissolved metal cation, the precipitation-dissolution-diffusion cycles can be sustained over time which can lead to periodic aggregation patterns of metal-hydroxide colloids at a specific time. We also establish that for transition metal cations the precipitation-dissolution-diffusion process can couple with reversible redox reactions between the soluble and less soluble metal cations, which can affect the overall transport of banded aggregates of metal-hydroxide colloids and the growth and transformation of metal-hydroxides into crystalline oxides. If systemic feedback between different elementary processes is sustained over long durations, iron-oxide crystals of different chemical compositions and shapes aggregate in Liesegang patterns. This work demonstrates unequivocally that non-uniform deposition of metal oxides during corrosion can occur via strongly coupled solution reactions and transport processes, and not simply as a result of metallurgical non-uniformity and/or localized solution environments.

137Cs and 90Sr in surface waters of the Sea of Japan: Variations and the Fukushima Dai-ichi Nuclear Power Plant accident impact

⁹⁰Sr and ¹³⁷Cs activity concentrations in surface waters of the Sea of Japan (SOJ) decreased during the period of 1993-2010 with effective half-lives of 18 and 15 y, respectively. The longer effective half-life of ⁹⁰Sr in the SOJ may suggest a surplus of ⁹⁰Sr to SOJ surface waters, however, no clear evidence of possible ⁹⁰Sr source has been found. After the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident, temporal variations of ¹³⁷Cs in the surface water of the SOJ have changed, while ⁹⁰Sr variations followed the pre-accident trends. The ⁹⁰Sr/¹³⁷Cs ratios reveal that increases of ¹³⁷Cs due to the FDNPP accident continued in surface waters of the SOJ until 2016.

Effect of defects on reaction of NiO surface with Pb-contained solution

In order to understand the role of defects in chemical reactions, we used two types of samples, which are molecular beam epitaxy (MBE) grown NiO(001) film on Mg(001) substrate as the defect free NiO prototype and NiO grown on Ni(110) single crystal as the one with defects. In-situ observations for oxide-liquid interfacial structure and surface morphology were performed for both samples in water and Pb-contained solution using high-resolution X-ray reflectivity and atomic force microscopy. For the MBE grown NiO, no significant changes were detected in the high-resolution X-ray reflectivity data with monotonic increase in roughness. Meanwhile, in the case of native grown NiO on Ni(110), significant changes in both the morphology and atomistic structure at the interface were observed when immersed in water and Pb-contained solution. Our results provide simple and direct experimental evidence of the role of the defects in chemical reaction of oxide surfaces with both water and Pb-contained solution.