Abstract: Doping two single transition-metal (TM) atoms on a substrate host opens numerous possibilities for catalyst design. However, what if the substrate contains more than one vacancy site? Then, the combination of two TMs along with their distribution patterns becomes a design parameter potentially complementary to the substrate itself and the bimetal composition. In this study, we investigate ammonia synthesis under mild electrocatalytic conditions on a transition-metal-doped porous C24N24 catalyst using density functional theory (DFT). The TMs studied include Ti, Mn, and Cu in a 2:4 dopant ratio (Ti2Mn4@C24N24 and Ti2Cu4@N-24(24)). Our computations show that a single Ti atom in both catalysts exhibits the highest selectivity for N-2 fixation at ambient conditions. This work is a good theoretical model to establish the structure-activity relationship, and the knowledge earned from the metal-N-4 moieties may help studies of related nanomaterials, especially those with curved structures.

Abstract: Unlike the profound knowledge of the reaction mechanisms occurring in water phase photocatalysis, still fairly little is known on the reaction mechanisms occurring on the catalyst surface when dealing with gaseous pollutants. Unfortunately, there are some differences between both reactions. For one, there are no abundant hydroxyl radicals present in the gas phase, so that possibly other species prove to be important in abating the pollutant. In order to unravel the mysteries of gas phase photocatalytic reaction pathways, in situ techniques must be used to allow the detection and identification of reaction intermediates on a working catalyst. Several techniques were already used in the past, of which Fourier transform infrared spectroscopy seems to be the most versatile. This review will therefore give a selective overview of different spectroscopic reaction cells constructed for the in situ study of photocatalytic gas phase reactions.

Abstract: ZnO is a wide band-gap (ca. 3.4 eV) semiconductor, piezoelectric, pyroelectric, biocompatible, transparent in the visible spectrum and UV light emitting material. The fabrication in 2001 of the first nanobelts of semiconductor oxide materials lead to a rapid expansion of researches concerning one dimensional nanostructures (nanotubes, nanowires, nanobelts), given their possible application in optics, optoelectronics, piezoelectricity, catalysis. Researches carried on up to date evidenced the possibility to obtain an extraordinary variety of ZnO nanostructures, in function of the experimental parameters and the used growth methods. In this work we present morphostructural results on nanostructured ZnO layers obtained by electrochemical deposition. The films have been grown on gold covered glass plates and Si wafers, in various experimental conditions such as: nature of the wetting agents, electrical polarization of the substrate (continuous, pulsed). The influence of the growth conditions on the crystalline structure and morphology of the films is revealed by scanning and transmission electron microscopy studies. The films show a variety of growth morphologies, from entangled-wires-like to honeycomb-like layers. These large-specific-surface layers will be tested as nanostructured substrates for photovoltaic cells with improved efficiency.

Abstract: This work addresses the dissolution corrosion behaviour of 316L austenitic stainless steels. For this purpose, solution-annealed and cold-deformed 316L steels were simultaneously exposed to oxygen-poor (<10-8 mass%) static liquid lead-bismuth eutectic (LBE) for 253e3282 h at 500 °C. Corrosion was consistently more severe for the cold-drawn steels than the solution-annealed steel, indicating the importance of the steel thermomechanical state. The thickness of the dissolution-affected zone was nonuniform, and sites of locally-enhanced dissolution were occasionally observed. The progress of LBE dissolution attack was promoted by the interplay of certain steel microstructural features (grain boundaries, deformation twin laths, precipitates) with the dissolution corrosion process. The identified dissolution mechanisms were selective leaching leading to steel ferritization, and non-selective leaching; the latter was mainly observed in the solution-annealed steel. The maximum corrosion rate decreased with exposure time and was found to be inversely proportional to the depth of dissolution attack.

Abstract: The present work reports on the microstructural evolution of a new heat of 24% cold worked austenitic DIN 1.4970 (15-15Ti) nuclear cladding steel subjected to ageing heat treatments of varying duration between 500 and 800 degrees C (by steps of 100 degrees C). The primary aim was studying the finely dispersed Ti-C nanoprecipitate population, which are thought to be beneficial for creep and swelling resistance during service. Their size distribution and number density were estimated through dark field imaging and bright field Moire imaging techniques in the transmission electron microscope. Nanoprecipitates formed at and above 600 degrees C, which is a lower temperature than previously reported. The observed nucleation, growth and coarsening behavior of the nanoprecipitates were consistent with simple diffusion arguments. The formation of nanoprecipitates coincided with significant dissociation of dislocations as evidenced by weak beam dark field imaging. Possible mechanisms, including Silcock's stacking fault growth model and Suzuki segregation, are discussed. Recrystallization observed after extended ageing at 800 degrees C caused the redissolution of nanoprecipitates. Large primary Ti(C,N) and (Ti,Mo)C precipitates that occur in the as-received material, and M23C6 precipitates that nucleate on grain boundaries at low temperatures were also characterized by a selective dissolution procedure involving filtration, X-ray diffraction and quantitative Rietveld refinement. The partitioning of key elements between the different phases was derived by combining these findings and was consistent with thermodynamic considerations and the processing history of the steel. (C) 2018 Elsevier B.V. All rights reserved.

Abstract: The microstructural features of intergranular irradiation-assisted stress corrosion crack tips from a redeemed neutron-irradiated flux thimble tube (60 dpa) have been investigated using focused-ion beam analysis and (scanning) transmission electron microscopy. The current work presents a close examination of the deformation field and oxide assembly associated with intergranular cracking, in addition to the analysis of radiation-induced segregation at leading grain boundaries. Evidence of stress induced martensitic transformation extending from the crack tips is presented. Intergranular crack arrest is demonstrated on the account of the external tensile stress orientation, and as a consequence of MnS inclusion particles segregating close to the fractured grain boundary. Exclusive observations of grain boundary oxidation prior to the cracking are presented, which is in full-agreement with the internal oxidation model.(c) 2022 Elsevier B.V. All rights reserved.

Abstract: We introduce a differential geometry description of the path lines, stream lines and particles contours in hydrodynamics. We present a generalized form of a Korteweg-de Vries type of equation for the exterior of a circle. Nonlinearities from the boundary conditions, surface tension and the Euler equations are taken into account, but the flow is considered inviscid and irrotational. For the circular case we describe the traveling waves shapes, solitons and the particles trajectories.

Abstract: Hollow silica spheres were quickly synthesized by an octylamine (OA) templating method using tetraethyl orthosilicate (TEOS) as the silica source. N2-sorption results indicate that the hollow spheres have high surface areas and pore volumes. XRD and TEM measurements reveal that the structure of the hollow spheres depends on the amount of TEOS used in the synthesis. When low amount of TEOS is added, the template-containing precursor spheres depict an XRD pattern with two peaks, which can be indexed to a lamellar phase. After the removal of the template, the obtained hollow spheres show no diffraction peaks in the XRD pattern, suggesting that the nanopores in the silica shells are disordered. If increasing the amount of TEOS, either the uncalcined or the calcined sample gives an XRD pattern with a single diffraction peak. The mesostructure of these hollow silica spheres is typically as HMS materials. TGA analyses suggest that the interaction between the silica species and surfactant is stronger in the latter case.

Abstract: Nanocrystalline ZnO:Al nanoparticles are suitable building blocks for transparent conductive layers. As the concentration of substitutional tetrahedral Al is an important factor for improving conductivity, here we aim to increase the fraction of substitutional Al. To this end, synthesis parameters of a solvothermal reaction yielding ZnO:Al nanorods were varied. A unique set of complementary techniques was combined to reveal the exact position of the aluminium ions in the ZnO lattice and demonstrated its importance in order to evaluate the potential of ZnO:Al nanocrystals as optimal building blocks for solution deposited transparent conductive oxide layers. Both an extension of the solvothermal reaction time and stirring during solvothermal treatment result in a higher total tetrahedral aluminium content in the ZnO lattice. However, only the longer solvothermal treatment effectively results in an increase of the substitutional positions aimed for.