Impact of Friction Stir Welding on the microstructure of ODS steel

We have assessed the impact of the welding parameters on the nano-sized oxide dispersion and the grain size in the matrix of an ODS steel after friction stir welding. Our results, based on combined small angle neutron scattering and electron microscopy, reveal a decrease in the volume fraction of the particles smaller than 80 nm in the welds, mainly due to particle agglomeration. The increase in tool rotation speed or decrease in transverse speed leads to a higher reduction in nano-sized particle fraction, and additionally to the occurrence of particle melting. The dependence of the average grain size in the matrix on the particle volume fraction follows a Zener pinning-type relationship. This result points to the principal role that the particles have in pinning grain boundary movement, and consequently in controlling the grain size during welding.</p

Microscopic origin of the scattering pre-peak in aqueous propylamine mixtures: X-ray and neutron experiments versus simulations

International audienceThe structure of aqueous propylamine mixtures is investigated through X-ray and neutron scattering experiments, and the scattered intensities compared with computer simulation data. Both sets of data show a prominent scattering pre-peak, which first appears at propylamine mole fraction x ≥ 0.1 around scattering vector k ≈ 0.2 Å−1, and evolves towards k ≈ 0.8 Å−1 for neat propylamine x = 1. The existence of a scattering pre-peak in this mixture is unexpected, specifically in view of its absence in aqueous 1-propanol or aqueous DMSO mixtures. The detailed analysis of the various atom–atom structure factors and snapshots indicates that significant micro-structures exist, which produces correlation pre-peaks in the atom–atom structure factors, positive for like species atom correlations and negative for cross species correlations. The scattering pre-peak depends on how these two contributions cancel out or not. The way the amine group bonds with water produces a pre-peak through an imbalance of the positive and negative scattering contributions, unlike 1-propanol and DMSO, where these 2 contributions compensate exactly. Hence molecular simulations demonstrate how chemical details influence the microscopic segregation in different types of molecular emulsions and can be detected or not by scattering experiments

Interfacial Water and Micro-heterogeneity in Aqueous Solutions of Ionic Liquids

In this work, aqueous solutions of two prototypical ionic liquids (ILs), [BMIM][BF4] and [BMIM][TfO], were investigated by UV Raman spectroscopy and small-angle neutron scattering (SANS) in the water-rich domain, where strong heterogeneities at mesoscopic length scales (microheterogeneity) were expected. Analyzing Raman data by a differential method, the solute-correlated (SC) spectrum was extracted from the OH stretching profiles, emphasizing specific hydration features of the anions. SC-UV Raman spectra pointed out the molecular structuring of the interfacial water in these microheterogeneous IL/water mixtures, in which IL aggregates coexist with bulk water domains. The organization of the interfacial water differs for the [BMIM][BF4] and [BMIM][TfO] solutions, being affected by specific anion−water interactions. In particular, in the case of [BMIM][BF4], which forms weaker H-bonds with water, the aggregation properties clearly depend on concentration, as reflected by local changes in the interfacial water. On the other hand, stronger water−anion hydrogen bonds and more persistent hydration layers were observed for [BMIM][TfO], which likely prevent changes in IL aggregates. The modeling of SANS profiles, extended to [BPy][BF4] and [BPy][TfO], evidences the occurrence of significant concentration fluctuations for all of the systems: this appears as a rather general phenomenon that can be ascribed to the presence of IL aggregation, mainly induced by (cation-driven) hydrophobic interactions. Nevertheless, larger concentration fluctuations were observed for [BMIM][BF4], suggesting that anion−water interactions are relevant in modulating the microheterogeneity of the mixture

Structural probing of clusters and gels of self-aggregated magnetic nanoparticles

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Influence of the polymer molecular weight on the microstructure of hybrid materials prepared by gamma-irradiation

Hybrid materials have been the object of intense research due to their potential for biomedical applications as well as in other fields. They are usually prepared by sol-gol but the method of gamma irradiation of the precursors is an alternative avoiding the addition of any other chemicals. The study of the hybrids prepared by this method has been progressing to understand the impact of different variables on the microstructure. In this work, the influence of the polymer's molecular weight on the microstructure of the materials is investigated. Hybrids were obtained from a mixture of polydimethylsiloxane (PDMS) silanol terminated, tetraethylorthosilicate (TEOS) and zirconium propoxide (PrZr) in the wt% composition 20PDMS-73TEOS-7PrZr varying only the PDMS molecular weight. The obtained materials are homogeneous, transparent and flexible and their microstructure was analysed by Scanning Electron Microscopy (SEM) and Small-Angle Neutron Scattering (SANS). It was found that different microstructures were obtained, depending on the polymer molecular weight. (C) 2014 Elsevier Ltd. All rights reserved

Y Nanostructure of PDMS-TEOS-PrZr hybrids prepared by direct deposition of gamma radiation energy

Organic-inorganic materials have been the object of intense research due to their wide range of properties and therefore innumerous applications. We prepared organic-inorganic hybrid materials by direct energy deposition on a mixture of polydimethylsiloxane silanol terminated (33 wt% fixed content), tetraethylorthosilicate and a minor content of zirconium propoxide that varied from 1 to 5 wt% using gamma radiation from a Co-60 source. The samples, dried in air at room temperature, are bulk, flexible and transparent. Their nanostructure was investigated by small angle neutron scattering. It was found that the inorganic oxide network has fractal structure, which becomes denser as the zirconium propoxide content decreases. The results suggest that oxide nanosized regions grow from the OH terminal group of PDMS which are the condensation seeds. Their number and position remains unaltered with the variation of zirconium propoxide content that only affects their microstructure. A model is proposed for the nanostructure of the oxide network that develops in the irradiation processed hybrid materials. (C) 2015 Elsevier B.V. All rights reserved