The behavior of several materials in molten NaCl–MgCl2 at 600 °C during 168 h was studied. In order to ensure the comparison of their respective corrosion resistance, a dedicated experimental setup and protocol were designed both for the control of the impurity level in the salt and for the corrosion testing. IN625 was used as a reference sample in every test, leading to a qualitative comparison between the different alloys. In these conditions, the SiC showed the best resistance, while TA6V and 316L suffered the most. For Ni-based alloys, Hastelloy G35 seemed to provide the best compromise despite its high chromium content. Thermodynamic calculations unveiled a strong link between the corrosion resistance of the alloy and a high dµCr/dnr leading to consider this as a new criterion for alloy design or selection.

A precise methodology for determining the growth mode of oxide layers on metallic materials at high temperatures is proposed. The approach combines sequential isotopic oxidation tests (using 16O and 18O isotopes) with secondary ion mass spectrometry (SIMS and nanoSIMS) analyses. NanoSIMS provides high-resolution localisation of oxygen diffusion pathways and oxide growth zones. However, its limited accessibility and specialised instrumentation can pose practical constraints. In contrast, dynamic SIMS offers broader accessibility and the ability to directly quantify oxygen isotope ratios across depth profiles. The detection of both conventional atomic (O−) and diatomic (O2−) oxygen signals in dynamic SIMS analysis proved highly effective in offering insights on oxide growth mode, closely replicating nanoSIMS results. The diatomic signal analysis complements the atomic signal data by improving the understanding of oxidant transport within the oxide layer. The methodology was validated through its application to a Co-10Cr alloy oxidised at 900 °C in O2, under sequential exposures to 16O and 18O isotopes. Both SIMS and nanoSIMS revealed the formation of a duplex oxide layer, consisting of an outer layer formed by outward Co cation diffusion and an inner layer growing by inward oxygen penetration, particularly in the grain-boundary regions of the outer oxide layer. The alloy is proposed to oxidise according to the Available Space Model.

Oxidation tests with markers and tracers were carried out to investigate the growth mechanism of chromia scale on a model Ni-30Cr alloy. The location of oriented grains characterized by TEM-ASRAR indicated that the scale grew predominantly outward at 800 and 900 degrees C. Experiments using 18 O and 54 Cr tracers confirmed a cationic transport via grain boundaries at these temperatures, using SIMS and NanoSIMS analyses. In the light of this and previous studies, we propose that the scales grow via diffusion of chromium vacancies at 900 degrees C and oxygen vacancies at 500 degrees C.

Thanks to species identification and growth interface localization experiments, a mechanism of iron corrosion in liquid UF6 at 80 degrees C was suggested. After an UF6 dissociation step, resulting fluorine (HF, F- or F center dot) was adsorbed at the FeF2 external interface and diffused into the iron fluoride layer via fluorine vacancy. FeF2 grew thus at the FeF2/Fe interface. Two FeF2 growth kinetics were observed depending on the presence or absence of NOxF impurities. Both corrosion rates were controlled by the cathodic reaction and presence of NOxF catalysed it.

Sulfation plays a critical role in the biosynthesis of small molecules, regulatory mechanisms such as hormone signaling, and detoxification processes (phase II enzymes). The sulfation reaction is catalyzed by a broad family of enzymes known as sulfotransferases (SULTs), which have been extensively studied in animals due to their medical importance, but also in plant key processes. Despite the identification of some sulfated metabolites in fungi, the mechanisms underlying fungal sulfation remain largely unknown. To address this knowledge gap, we conducted a comprehensive search of available genomes, resulting in the identification of 174 putative SULT genes in the Ascomycota phylum. Phylogenetic analysis and structural modeling revealed that these SULTs belong to the aryl sulfotransferase family, and they are divided into two potential distinct clusters of PAPS-dependent SULTs within the fungal kingdom. SULT genes from two marine fungi isolated from deep-sea hydrothermal vents, Hortaea werneckii UBOCC-A-208029 (HwSULT) and Aspergillus sydowii UBOCC-A-108050 SULT (AsSULT), were selected as representatives of each cluster. Recombinant proteins were expressed in Escherichia coli and biochemically characterized. HwSULT demonstrated high and versatile activity, while AsSULT appeared more substrate-specific. Here, HwSULT was used to sulfate the mycotoxin zearalenone, enhancing its cytotoxicity toward healthy feline intestinal cells.

The results reported here are the first on pure iron corrosion in liquid UF6 at 80 degrees C. Two kinetic behaviours have been observed: one led to micrometric scales (from micron to hundreds of microns after several months) and the other one to hundreds of nanometers for several months. The higher corrosion kinetics resulted in the presence of impurities such as NOxF complexes formed by interaction between the medium and the reactor material. These NOxF catalysed the corrosion reaction leading to a corrosion mechanism controlled by the cathodic reaction rate. Effect of impurities in UF6 coming from experimental conditions or nature of uranium ore should then be systematically and carefully checked. Whatever the corrosion kinetics and the presence of impurities, the nature of the layer was identical: a duplex fluoride scale composed of an iron rich layer, FeF2, and a uranium rich layer evolving over time from U2F9 to UF5.

This study provides a comprehensive investigation of the formation and behavior of a layer enriched in fission products encountered between the (U,Pu)O2 fuel pellet and the cladding, designated as JOG (“Joint Oxyde Gaine” in French). Employing a multifaceted approach that combined thermodynamic calculations, experimental synthesis, and advanced characterization techniques, simulated JOG has been synthetized (without radioactive fission products). Using thermodynamic calculations with the TAF-ID database, the phase compositions in the JOG was assessed for various temperatures, pressures, and oxygen potential conditions, revealing insights into the environmental factors influencing JOG formation. Experimental simulation of the JOG composition, exposed to controlled conditions, confirmed the presence of key compounds such as Cs2MoO4, CsI, and PdTe, as evidenced by SEM, EDS, and XRD analyses. The results of the calculations highlighted notable differences in the nature of the phases constituting the JOG under varying pressure and oxygen potential conditions. At 873 K and oxygen partial pressure of 10–4 bar, Cs2MoO4, Pd–Te, and a gas phase rich in tellurium and CsI were predominant, contrasting with the emergence of liquid phases at 70 bar. This study offered a comprehensive understanding of JOG microstructure, and highlighting the importance of accurate characterization for reactor safety. This information lays the foundations for future studies on the chemical interaction between the JOG and the steel cladding.

A method is developed to exploit data on complex materials behaviors that are impossible to tackle by conventional machine learning tools. A pairwise comparison algorithm is used to assess a particular property among a group of different alloys tested simultaneously in identical conditions. Even though such characteristics can be evaluated differently across teams, if a series of the same alloys are analyzed among two or more studies, it is feasible to infer an overall ranking among materials. The obtained ranking is later fitted with respect to the alloy’s composition by a Gaussian process. The predictive power of the method is demonstrated in the case of the resistance of metallic materials to molten salt corrosion and wear. In this case, the method is applied to the design of wear-resistant hard-facing alloys by also associating it with a combinatorial optimization of their composition by a multi-objective genetic algorithm. New alloys are selected and fabricated, and their experimental behavior is compared to that of concurrent materials. This generic method can therefore be applied to model other complex material properties—such as environmental resistance, contact properties, or processability—and to design alloys with improved performance.

As ammonia does not emit greenhouse gases when burned, it is considered a fuel instead of fossil fuels. However, there are few reports on the corrosion behavior of materials when ammonia is used as fuel. Therefore, this study measured the hydrogen produced by the reaction between ammonia and iron using a hydrogen sensor containing a proton conductor. As a result, the amount of hydrogen produced by the decomposition of ammonia was small at low temperatures but increased at high temperatures. Also, when the ammonia content was low, oxidation of iron occurred preferentially. This way, the relationship between the amount of hydrogen generated and corrosion behavior could be clarified.

Molten salts have been used as heat transfer fluids since the middle of the 20th century. More recently, molten chloride salts have been studied for use in concentrated solar power plants or molten salt reactors. However, none of the materials studied to date has been able to withstand this highly corrosive environment without controlling the salt’s redox potential. The alumina-forming alloy was a promising option, as it has not yet been widely studied. To investigate this possibility, two iron-based alumina-forming alloys were corroded in NaCl-MgCl2 eutectic at 600 °C for 500 h after being pre-oxidised to grow a protective layer of α-alumina on each alloy. A salt purification protocol based on salt electrolysis was implemented to ensure comparable and reproducible results. During immersion, alumina was transformed into MgAl2O4, as shown by FIB-SEM observation. Inter and intragranular corrosion were observed, with the formation of MgAl2O4 in the corroded zones. The nature of the oxides was explained by the predominance diagram. Intragranular corrosion was 2 µm deep, and intergranular corrosion 10 µm deep. Alumina formed at the bottom of the intergranular corrosion zones. The depth of intergranular corrosion is consistent with O diffusion control at the grain boundary.

Citronellol is a pleasant-smelling compound produced in rose (Rosa spp.) flowers and in the leaves of many aromatic plants, including pelargoniums (Pelargonium spp.). Although geraniol production has been well studied in several plants, citronellol biosynthesis has been documented only in crab-lipped spider orchid (Caladenia plicata) and its mechanism remains open to question in other species. We therefore profiled 10 pelargonium accessions using RNA sequencing and gas chromatography-MS analysis. Three enzymes from the progesterone 5β-reductase and/or iridoid synthase-like enzymes (PRISE) family were characterized in vitroand subsequently identified as citral reductases (named PhCIRs). Transgenic RNAi lines supported a role for PhCIRs in the biosynthesis of citronellol as well as in the production of mint-scented terpenes. Despite their high amino acid sequence identity, the 3 enzymes showed contrasting stereoselectivity, either producing mainly (S)-citronellal or a racemate of both (R)- and (S)-citronellal. Using site-directed mutagenesis, we identified a single amino acid substitution as being primarily responsible for the enzyme's enantioselectivity. Phylogenetic analysis of pelargonium PRISEs revealed 3 clades and 7 groups of orthologs. PRISEs from different groups exhibited differential affinities toward substrates (citral and progesterone) and cofactors (NADH/NADPH), but most were able to reduce both substrates, prompting hypotheses regarding the evolutionary history of PhCIRs. Our results demonstrate that pelargoniums evolved citronellol biosynthesis independently through a 3-step pathway involving PRISE homologs and both citral and citronellal as intermediates. In addition, these enzymes control the enantiomeric ratio of citronellol thanks to small alterations of the catalytic site.

Molten chloride salts represent a very corrosive medium due to the amount of impurities they contain and that essentially comes from moisture. In this work, an industrial nickel-based alumina-forming alloy was preoxidized and corroded for 500 h in the NaCl–MgCl2 eutectic. Electrochemistry and SEM analyses were used to prepare and analyse the corrosion test. Both the nickel-rich matrix and the alumina scale formed during preoxidation seemed to remain stable during the corrosion test contrary to some of the chromium carbides initially present in the columnar microstructure of the alloy. The use of X-ray tomography coupled with SEM observation revealed a preferential dissolution of the chromium carbides connected to the alloy/salt interface. X-ray tomography reveals a chromium carbides network enabling a deep molten salt infiltration within the alloy due to their preferential dissolution. Molten salt infiltration in the dissolved carbides network then leads to the oxidation of aluminium present in the alloy into a mixed MgAl2O4 spinel. An oxoacido-basic reaction between the alumina scale formed at the alloy surface during preoxidation and MgO dissolved in the salt is also discussed. This work shows that nickel-based alumina-forming alloy present a realistic interest and that the microstructure of the alloy should be optimized in further work to enhance corrosion resistance.

The aim of this paper is to present methods for corrosion mitigation in molten salt environments. The corrosion of structural materials depends directly on the redox potential of the salt. When the redox potential of the salt is higher than the standard potentials of the elements constituting the structural materials, corrosion occurs. If the reverse is true, no corrosion is observed. Herein, a methodology for calculating the theoretical potential of a molten salt is provided and compared with experimental measurements. Three ways to mitigate corrosion by modifying the salt redox potential are proposed: (i) using a soluble/soluble redox system; (ii) using a potentiostatic method; and (iii) using an amphoteric compound such as UCl3, TiCl2, or TiCl3. Immersion tests were conducted under the above conditions to validate the methodology.

Ni-30Cr alloy samples were oxidized at temperatures between 500 and 900 °C to investigate the link between the evolution of the microstructure and the chemical composition in the alloy substrate beneath a growing chromia layer. Before oxidation, a layer of ultrafine grains was observed between the surface and a thick lamellar layer. This structure was replaced by some larger recrystallized grains after oxidation. The growth kinetics of the recrystallized grains was described by a parabolic law with a kinetic constant following an Arrhenius law from 500 to 700 °C. For samples oxidized at 800 and 900 °C, all Cr profiles showed a gradient close to the shape predicted by Wagner models. In the samples oxidized between 500 and 700 °C, many Cr profiles showed a two-step shape, with the smaller Cr fraction in the step closer to the alloy/oxide interface. By considering a fast diffusion accelerated by grain boundaries in the zone of recrystallized grains, the two-step shape can be simulated by numerical resolution of diffusion problem.

A global transition towards more sustainable, affordable and reliable energy systems is being stimulated by the Paris Agreement and the United Nation's 2030 Agenda for Sustainable Development. This poses a challenge for the corrosion industry, as building climate‐resilient energy systems and infrastructures brings with it a long‐term direction, so as a result the long‐term behaviour of structural materials (mainly metals and alloys) becomes a major prospect. With this in mind “Corrosion Challenges Towards a Sustainable Society” presents a series of cases showing the importance of corrosion protection of metals and alloys in the development of energy production to further understand the science of corrosion, and bring the need for research and the consequences of corrosion into public and political focus. This includes emphasis on the limitation of greenhouse gas emissions, on the lifetime of infrastructures, implants, cultural heritage artefacts, and a variety of other topics.

Cr2O3 is not only a promising functional material, but also an essential barrier to protect chromia-forming alloys against high temperature corrosion. The Cr2O3 protecting layer grows slowly via defect-mediated diffusion. Several types of point defects could be responsible for the diffusion process depending on the oxidation environment, resulting in different semiconductor characters of chromia. According to the literature, the defect chemistry of Cr2O3 in the antiferromagnetic (AFM) state has been well studied using density functional theory (DFT) calculations but not in the paramagnetic (PM) state, which is the fundamental state of Cr2O3 above 318 K. PM Cr2O3 is simulated in this study using special quasi-random structures (SQS). The formation energies of intrinsic point defects in AFM and PM Cr2O3 are calculated to study the defect chemistry and the semiconductor properties in different oxidation environments (temperature and oxygen partial pressure PO2) using a thermodynamic model. It is found that O vacancies and insulating-type Cr2O3, in which commensurate electrons and holes are dominant before atomic defects are more favorable at high temperatures and at low PO2, while Cr vacancies and p-type Cr2O3 are more favorable at low temperatures and at high PO2, according to the calculations both in AFM and PM Cr2O3. However, the limits of dominant zones for defects and for semiconductor characters shift to higher temperatures or lower PO2 in PM state calculations.

Thermodynamic and kinetic calculations are commonly used for forecasting phase transformations in multicomponent alloys as a function of composition, temperature, and time. They also turn to be very useful for new alloy design. Thus, in the framework of the qualification of existing industrial alloys and the development of new ones (chromium [Cr]-coated zirconium [Zr] alloys, for instance), a new generation of thermodynamic databases has been developed thanks to the systematic use of ab initio calculations. Indeed, density functional theory calculations are significant for the determination of formation enthalpies of stable and metastable phases. Moreover, the special quasirandom structure method is used for the prediction of face-centered cubic, body-centered cubic, and hexagonal closest packed mixing enthalpies in binary solid solutions. The resulting thermodynamic database is a very powerful tool for correctly predicting second-phase precipitate occurrence in industrial alloys and precisely calculate their volume fraction, chemical composition, and existence domain as a function of temperature. The second part of the paper deals with the development of the Ekinox-Zr numerical tool that has been linked to the Zr thermodynamic database using the OpenCalphad Application Software Interface (OCASI) interface of the OpenCalphad software (a free software for multicomponent equilibrium calculations). This tool has been developed to accurately simulate oxide growth and oxygen diffusion into the alloy during high-temperature isothermal oxidation of Zr alloys. The recent developments have been dedicated to the simulation of high-temperature transients showing a good agreement with experimental data.

Samples of Ni-30Cr alloy were oxidized at different temperatures from 500 to 900 °C in a nominal oxygen partial pressure of 5 × 10−6 atm. The parabolic rate constants for growth of the oxide scales, which were confirmed to be chromia, were in agreement with the literature following an Arrhenius law. The semiconductor character of the chromia scale was investigated in order to reveal the nature of the dominant point defects responsible for the diffusion process during oxidation. An n-type semiconductor was found at low temperature (500 °C), and p-type semiconductor at high temperature (900 °C). Our results suggest that oxygen vacancies and chromium vacancies are dominant in grown chromia of n- and p-type, respectively.