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Register a new userMechanistic insights of dissolution and mechanical breakdown of FeCO3 corrosion films
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Adriana Matamoros Veloza Dr
Publication date
2020
fields
Physics
and research's language is
English
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To understand the behavior of corrosion films on X65 C-steel under CO2 conditions is paramount to identify the formation and transformations of corrosion products. This work presents the chemical changes and mechanical effects produced by pH and flow on corrosion films through the combination of molecular techniques with imaging. Siderite, wustite and magnetite were identified as corrosion products at neutral pH, which dissolved and mechanical damaged at low pH by a 1m/s brine flow with a crystal size reduction of ~80%. In contrast, at pH 7 and 1m/s flow facilitated the removal of entire crystals from the film.
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The phase immiscibility and the excellent matching between Ag(001) and Fe(001) unit cells (mismatch 0.8 %) make Fe/Ag growth attractive in the field of low dimensionality magnetic systems. Intermixing could be drastically limited at deposition temperatures as low as 140-150 K. The film structural evolution induced by post-growth annealing presents many interesting aspects involving activated atomic exchange processes and affecting magnetic properties. Previous experiments, of He and low energy ion scattering on films deposited at 150 K, indicated the formation of a segregated Ag layer upon annealing at 550 K. Higher temperatures led to the embedding of Fe into the Ag matrix. In those experiments, information on sub-surface layers was attained by techniques mainly sensitive to the topmost layer. Here, systematic PED measurements, providing chemical selectivity and structural information for a depth of several layers, have been accompanied with a few XRD rod scans, yielding a better sensitivity to the buried interface and to the film long range order. The results of this paper allow a comparison with recent models enlightening the dissolution paths of an ultra thin metal film into a different metal, when both subsurface migration of the deposit and phase separation between substrate and deposit are favoured. The occurrence of a surfactant-like stage, in which a single layer of Ag covers the Fe film is demonstrated for films of 4-6 ML heated at 500-550 K. Evidence of a stage characterized by the formation of two Ag capping layers is also reported. As the annealing temperature was increased beyond 700 K, the surface layers closely resembled the structure of bare Ag(001) with the residual presence of subsurface Fe aggregates.
Epitaxial thin films have been utilised to investigate the radiolytic dissolution of uranium dioxide interfaces. Thin films of UO$_2$ deposited on single crystal yttria stabilised zirconia substrates have been exposed to water in the presence of a high flux, monochromatic, synchrotron x-ray source. In particular, this technique was applied to induce dissolution of three UO$_2$ thin films, grown along the principle UO$_2$ crystallographic orientations: (001), (110) and (111). Dissolution of each film was induced for 9 accumulative corrosion periods, totalling 270s, after which XRR spectra were recorded to observe the change in morphology of the films as a function of exposure time. While the (001) and (110) oriented films were found to corrode almost linearly and at comparable rates, the (111) film was found to be significantly more corrosion resistant, with no loss of UO$_2$ material being observed after the initial 90s corrosion period. These results distinctly show the effect of crystallographic orientation on the rate of x-ray induced UO$_2$ dissolution. This result may have important consequences for theoretical dissolution models, as it is evident that orientation dependence must be taken into consideration to obtain accurate predictions of the dissolution behaviour of UO$_2$.
This work addresses the early stages ($le$1000 h) of the dissolution corrosion behavior of 316L and DIN 1.4970 austenitic stainless steels in contact with oxygen-poor (C$_O$ < 10$^-$$^8$ mass%), static liquid lead-bismuth eutectic (LBE) at 500{deg}C for 600-1000 h. The objective of this study was to determine the relative early-stage resistance of the uncoated steels to dissolution corrosion and to assess the protectiveness of select candidate coatings (Cr$_2$AlC, Al$_2$O$_3$, V$_2$Al$_x$C$_y$). The simultaneous exposure of steels with intended differences in microstructure and thermomechanical state showed the effects of steel grain size, density of annealing/deformation twins, and secondary precipitates on the steel dissolution corrosion behavior. The findings of this study provide recommendations on steel manufacturing with the aim of using the steels to construct Gen-IV lead-cooled fast reactors.
Chemically inert Coatings on Havar entrance foils of the targets for [18F] production via proton irradiation of enriched water at pressurized conditions are needed to decrease the amount of ionic contaminants released from Havar. In order to find the most effective protective coatings, the Nb-based coating microstructure and barrier properties have been correlated with deposition parameters as: substrate temperature, applied bias, deposition rate and sputtering gas pressure. Aluminated quartz used as a substrate allowed us to verify the protection efficiency of the desirable coatings as diffusion barriers. Two modeling corrosion tests based on the extreme susceptibility of aluminum to liquid gallium and acid corrosion were applied. Pure Niobium coatings have been found less effective barriers than Niobium-titanium coatings. But Niobium oxide films, according to the corrosion tests performed, showed superior barrier properties. Therefore Multi-layered Niobium-Niobium oxide films have been suggested, since they combine the high thermal conductivity of Niobium with the good barrier properties of Niobium oxide.
We present the temperature- and thickness-dependent structural and morphological evolution of strain induced transformations in highly-strained epitaxial BiFeO3 films deposited on LaAlO3 (001) substrates. Using high-resolution X-ray diffraction and temperature-dependent scanning-probe-based studies we observe a complex temperature- and thickness-dependent evolution of phases in this system. A thickness-dependent transformation from a single monoclinically distorted tetragonal-like phase to a complex mixed-phase structure in films with thicknesses up to ~200 nm is the consequence of a strain-induced spinodal instability in the BiFeO3/LaAlO3 system. Additionally, a breakdown of this strain-stabilized metastable mixed-phase structure to non-epitaxial microcrystals of the parent rhombohedral structure of BiFeO3 is observed to occur at a critical thickness of ~300 nm. We further propose a mechanism for this abrupt breakdown that provides insight into the competing nature of the phases in this system.
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