Octadecylamine (ODA) is a well-known organic inhibitor for the corrosion protection of carbon steels. In the present study, electrochemical impedance data analysis was performed to extract physical ...parameters of the ODA thin film that formed on a P275 carbon steel surface. First, surface observations and contact angle measurements showed the steel surface modification after the ODA treatment linked to the adsorption of an organic hydrophobic thin film. X-ray photoelectron spectroscopy confirmed the presence of a very thin organic layer and revealed the presence of iron oxide/hydroxide underlying the ODA film. The impedance data analysis with a power-law distribution of resistivity in the organic film allowed the permittivity and thickness to be extracted. Finally, from the impedance results with and without ODA, the instantaneous corrosion inhibition efficiency was determined.
The direct liquid injection chemical vapor deposition (DLI-CVD) of uniform and dense zirconium oxide (ZrO2) thin films applicable as corrosion protection coatings (CPCs) is reported. We present the ...entire development chain from the rational choice and thermal evaluation of the suitable heteroleptic precursor Zr(OiPr)2(tbaoac)2 over the detailed DLI-CVD process design and finally benchmarking the CPC behavior using electrochemical impedance spectroscopy (EIS). For a thorough development of the growth process, the deposition temperature (Tdep) is varied in the range of 400 – 700 °C on Si(100) and stainless steel (AISI 304) substrates. Resulting thin films are thoroughly analyzed in terms of structure, composition, and morphology. Grazing incidence X-ray diffractometry (GIXRD) reveals an onset of crystallization at Tdep ≥ 500 °C yielding monoclinic and even cubic phase at low temperatures. At Tdep = 400 °C, isotropic growth of XRD amorphous material is shown to feature cubic crystalline domains at the interfacial region as revealed by electron diffraction. Corrosion results obtained through EIS measurements and further immersion tests revealed improved CPC characteristic for the 400 °C processed ZrO2 coatings compared to the ones deposited at Tdep ≥ 500 °C, yielding valuable insights into the correlation between growth parameter and CPC performance which are of high relevance for future exploration of CPCs.
This study presents an inventory of possible chemical reactions affecting, or having affected, the Venus surface. Fluid rock reactions are simulated using experiments under conditions close to the ...present surface. Slabs or powder of several natural and synthetic silicate material (crystalline fresh basalt, altered basalt, obsidian, pumice and basalt glass) were reacted at 475 °C in CO2-H2O-H2S-SO2-CO gas mixture. Most of the runs were carried out at roughly 90 bars with a duration of one week, some experiments having longer (one month) or shorter (one day) durations. The role of H2O content was explored through a wide range of water pressure: from dry gas for the current Venus conditions up to 590 bars (86%H2O) for early Venus (or other early terrestrial planets). The gas phase was sampled before the completion of the runs for chemical analysis of major gas components (CO, H2S, SO2) as well as trace elements possibly released by the rocks. The altered samples were examined by a suite of mineralogical and chemical techniques (scanning and transmission electron microscopy, X-ray diffraction and spectroscopy).
In dry atmosphere, the redox potential of the gas was close to the Ni/NiO buffer (−21.3 to −27.3 log fO2), thus close to the current Venus conditions. The sample alteration is tenuous and limited to surface oxidation of glasses and coating of olivine by iron oxides, as well as the general deposition of (Ca,Na)SO4 at the sample surface. The oxidation of glass is reflected in the formation of magnesioferrite under the surface and is accompanied by the release of Ca, Mg and Na into the gas phase or mineralized as sulfate at the surface. In wet atmosphere, obsidian recrystallizes into a mixture of plagioclase and amphibole while basaltic glass produced non-expandable clays minerals: chlorite-type (2:1:1) at the surface and likely celadonite (2:1) below the surface. Olivine is preserved. Using obsidian (the most alterable material) as a proxy of aluminosilicates, we discuss the surface reactions operating under supercritical conditions, and we used a shrinking-core equation for modeling the long-term reactions.
These parametric exploration offer new insights into processes having affected the surface of Venus and contribute to the discussion of open questions such as the fate of water or the lifetime of vitreous dust or fine grain material if present in the current or past Venusian environment. Longer duration experiments will provide more kinetic parameters that can be extrapolated to the geologic history of Venus.
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•Samples were altered at 475 °C, typically 1 week and 90 bars, in Venus-like gas•Only olivine and glasses show signs of oxidation/alteration•In dry gas, olivine is coated by Fe-oxides and glass is oxidized (magnesioferrite)•Ca, Na, Mg, were transferred from glass to the gas phase or mineralized as sulfate•In wet gas (early Venus) glass alteration rate is modeled by a shrinking core model
A key challenge for designing hybrid materials is the development of chemical tools to control the organization of inorganic nanoobjects at low scales, from mesoscopic (~µm) to nanometric (~nm). So ...far, the most efficient strategy to align assemblies of nanoparticles consists in a bottom-up approach by decorating block copolymer lamellae with nanoobjects. This well accomplished procedure is nonetheless limited by the thermodynamic constraints that govern copolymer assembly, the entropy of mixing as described by the Flory-Huggins solution theory supplemented by the critical influence of the volume fraction of the block components. Here we show that a completely different approach can lead to tunable 2D lamellar organization of nanoparticles with homopolymers only, on condition that few elementary rules are respected: 1) the polymer spontaneously allows a structural preorganization, 2) the polymer owns functional groups that interact with the nanoparticle surface, 3) the nanoparticles show a surface accessible for coordination.
•synthesis of few-layered-graphene/Al2O3 powders with carbon deposited as pristine FLG around α-Al2O3 grains•no manipulation of nanocarbons, simple to perform, prone to up-scaling, versatile•FLG film ...located along the grain boundaries of the submicron α-Al2O3 matrix and not dispersed as discrete particles•electrically conducting samples with a percolation threshold below 0.74 vol.% of carbon•samples stronger and similarly tough and hard than submicron α-Al2O3, showing crack-deflection and crack bridging
The chemical vapor deposition of carbon onto a commercial α-Al2O3 powder bed produces a pristine film of few-layered-graphene (FLG) uniformly covering the α-Al2O3 grains. This obviates both the manipulation of nanocarbons, lengthy mixing steps and the risk of damaging any pre-existing graphene platelets. The powders are consolidated to 99 % by SPS, producing samples where a FLG film is located along the grain boundaries of the submicron α-Al2O3. Compared to the pure α-Al2O3, the composites are moderately stronger and similarly tough and hard due to crack-deflection and crack-bridging and they are electrically conducting with a percolation threshold below 0.74 vol.% of carbon. The high conductivity values reflect the high quality of the thin FLG film and its continuous nature over very long distances. The samples are characterized by Raman spectroscopy, X-ray photoelectron spectroscopy, scanning and transmission electron microscopy.
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•Native oxides on the inner surface of 690 steam generator tubes were characterized.•Their composition, structure and morphology were studied by XPS and TEM techniques.•Duplex native ...films were revealed with an inner layer enriched in Cr(III) oxides.•Ni, Cr, Fe and O were detected by STEM-EDS in both layer of the films.•The two techniques used provided complementary results for the nanoscale films.
Ni based alloys steam generator (SG) tubes in pressurized water reactors may suffer generalized corrosion and Ni release in primary water. The processes of corrosion and oxidation are strongly dependent on the surface properties. In particular, the chemical composition and structure of the native oxide films present at the surface of the SG tubes are crucial and improving the passive properties of the surface could contribute to reduce the corrosion damage and Ni release. The native oxides on the inner surface of two as-received Ni base alloy SG tubes were investigated using two main techniques, namely X-ray photoemission spectroscopy and transmission electron microscopy. The chemical elements present in the native film for the two tubes were identified and the structure and composition of the native film at the nanoscale was determined. A duplex oxide structure was identified for both samples, but with differences in the chemical composition of the inner and outer oxide layer. Chemical heterogeneities such as alumina, Ti oxides and Cr oxides were also detected; they are considered to play a role in the evolution of the surface exposed to primary water. The two techniques used allowed a multi-scale description of the surface and led to complementary results.
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