Iron oxidation at low temperature (260–500 C) in air and the effect of water vapor

The oxidation of iron has been studied at low temperatures (between 260 and 500 C) in dry air or air with 2 vol% H2O, in the framework of research on dry corrosion of nuclear waste containers during long-term interim storage. Pure iron is regarded as a model material for low-alloyed steel. Oxidation tests were performed in a thermobalance (up to 250 h) or in a laboratory furnace (up to 1000 h). The oxide scales formed were characterized using SEM-EDX, TEM, XRD, SIMS and EBSD techniques. The parabolic rate constants deduced from microbalance experiments were found to be in good agreement with the few existing values of the literature. The presence of water vapor in air was found to strongly influence the transitory stages of the kinetics. The entire structure of the oxide scale was composed of an internal duplex magnetite scale made of columnar grains and an external hematite scale made of equiaxed grains. 18O tracer experiments performed at 400 C allowed to propose a growth mechanism of the scale

Future challenges in colloid and interfacial science

This article deals with topics where I expect special future challenges, exemplifying these by experiments out of my own department. One area where I expect large progress also in view of many technical developments in the past concerns the understanding of the structure of fluid interfaces at the atomic level. It is shown by non-linear optical spectroscopies that the free water surface is ice-like and can be “liquefied” by ion adsorption. X-ray fluorescence from the interface demonstrates that ion binding is very specific which cannot be explained by existing theories. A second major area are nonequilibrium features, and one of the old and new ones here is nucleation and growth. This presentation concentrates on effects produced by ultrasound, a well-defined trigger of gas bubble formation. It exhibits high potential for chemistry at extreme conditions but with a reactor at normal conditions. It has special importance for treatment of surfaces that can be also manipulated via controlled surface energies. A third area will concern complex and smart systems with multiple functions in materials and biosciences. As next generation, I anticipate those with feedback control, and examples on this are self-repairing coatings

Hierarchically organized Li-Al-LDH nano-flakes: a low-temperature approach to seal porous anodic oxide on aluminum alloys

This work suggests a low-temperature sealing approach for tartaric–sulfuric acid (TSA) anodized AA2024 based on hierarchically organized Li–Al-layered double hydroxide (LDH) structures. The new proposed sealing is expected to be directly competitive to the standard hot water sealing (HWS) approaches because of its reduced treatment temperature and high protection efficiency. A hierarchical organization of in situ formed LDH nano-flakes across the depth length of the TSA pores, from the macrodown to the nano-size range, was observed with transmission electron microscopy (TEM). Electrochemical impedance spectroscopy (EIS) studies showed that the densely packed LDH arrangement at the porous oxide layer is directly related to the drastically improved barrier properties of TSA. Moreover, LDH flakelike structures worked as “smart” reservoirs for corrosion inhibiting vanadium species (VOx) that are released on demand upon the onset of corrosion. This was confirmed using a scanning vibrating electrode technique (SVET), giving relevant insights into the time-resolved release activity of VOx and the formation of the passivation layer on cathodic intermetallics, corroborated with EDX and analytical Raman spectroscopy. Passive and active corrosion protection was imparted to the anodic layer via new Li–Al-LDH structures with long-term protection exceeding that of standard HWS procedures.This work has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement no. 645676 project MULTISURF. Dr M. Mohedano is grateful to MICINN (Spain) for nancial support via Proyecto Retos Jovenes Investigadores MAT2015-73355-JIN. Dr S. V. Lamaka acknowledges the nancial support of Alexander von Humboldt Foundation via Experienced Researcher Grant. Dr J. Tedim thanks FCT for the researcher grant IF/00347/2013. This work was developed in the scope of the project CICECO – Aveiro Institute of Materials, POCI-01-0145-FEDER-007679 (Ref. FCT UID/CTM/50011/2013), nanced by national funds through the FCT/MEC and when applicable co-nanced by FEDER under the PT2020 Partnership Agreement. Dr D. Mata would like to thank Dr Nico Scharnagl for the Raman scientic discussions. Authors acknowledge Mr Maksim Starykevich for carrying out the GDOES analyses

The use of electrochemical techniques for the characterization of the corrosion behavior of sol-gel-coated metals

2nononenoneAndreatta, Francesco*; Fedrizzi, LorenzoAndreatta, Francesco; Fedrizzi, Lorenz