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International audience; In the present article, metallic nanoparticles (NPs) used as nanogauges and electron backscattered diffraction (EBSD) are combined to investigate deformation mechanisms of the UR45 N duplex steel. The kinematic fields bring precious details in the evolution of the local deformation of austenitic and ferritic phases. The crystallographic information at the initial stage and in the plastic domain is obtained by the EBSD technique. Strain evolutions in each phase are analyzed. The first strain marks appear in austenite just before the elastoplastic transition. Slip and twinning activities in austenite constitute an important part of the work hardening of the material. The slips in ferrite are visible in the plastic domain and present complex geometry. The role of phase boundaries, which act as strain barrier is highlighted. The incompatibilities of deformations between the two phases modify the deformation mechanism of austenite in comparison with a pure austenitic stainless steel as 316 L. Local interactions between phases during the deformation are analyzed. The strong strain heterogeneities in the plastic domain are analyzed in the kinematic fields. Local evolutions of the deformation are also confronted to the macroscopic behavior of the material.

International audience; The fixation of hydrogels to biological tissues is a major challenge conditioning the development of implants and surgical techniques. Here, coatings of procoagulant nanoparticles are devised which use the presence of blood to create adhesion between hydrogels and soft internal organs. Those nanostructured coatings are simply adsorbed at the hydrogel surfaces and can rapidly activate the formation of an interfacial blood clot acting as an adhesive joint. This concept is demonstrated on pig liver capsules with model poly(ethylene-glycol) membranes that are intrinsically poorly adhesive. In the absence of blood, ex vivo peeling tests show that coatings with aggregates of bare silica nanoparticles induce a 2- to 4-fold increase in adhesion energy as compared to the uncoated membrane (3 ± 2 J m–2). This effect is found to scale with the specific surface area of the coating. The highest adhesion energies produced by these nanoparticle-coated membranes (10 ± 5 J m–2) approach the value obtained with cyanoacrylate glue (33 ± 11 J m–2) for which tearing of the tissue is observed. Ex vivo pull-off tests show an adhesion strength of coated membranes around 5 ± 1 kPa, which is significantly reduced when operating in vivo (1.0 ± 0.5 kPa). Nevertheless, when blood is introduced at the interface, the in vivo adhesion strength can be improved remarkably with silica coatings, reaching 4 ± 2 kPa after 40 min contact. In addition, these silica-coated membranes can seal and stop the bleeding produced by liver biopsies very rapidly (

International audience; Scanning Electron Microscopes (SEMs) often generate images with a shaded appearance which gives a natural 3D impression. Ergo, quite a few methods to reconstruct the 3D surface topography from these using shape-from-shading methods are available in the literature. Here, a novel approach is discussed which uses BackScatter Electron (BSE) images from multiple detectors to reconstruct the topography. Classically, algorithms exist which resort to a quad-BSE detector setup. However, other detector configurations are often found in SEMs. A set of images of these non-conforming detectors still contains enough information to allow for reconstruction, but requires a more general algorithm to do so. This article discusses a method based on a modal decomposition of the principal image components. The resulting method is shown to be efficient and independent of the number of detectors or their orientation. In fact, the orientation is identified as part of the algorithm and thus requires very little calibration.

Thermal barrier coatings (TBC) are multilayered systems comprising a metallic oxidation protection layer or so-called bond coat, a ceramic topcoat, and a thermally grown aluminum oxide developing at the interface. The coating systems fail typically by delamination cracking near this interface, which has a complex three-dimensional morphology influencing the crack path. This study combines laser shock adhesion test to introduce an artificial interfacial crack, known in size and location, and focused ion beam coupled with scanning electron microscopy 3D serial sectioning tomography. Methods for proper segmentation of cracks and adjacent materials and quantitative evaluation of the complex crack system are proposed and applied for analyzing the crack tip region. Finally, derived from the three-dimensional segmentation, a finite element model has been achieved and used for thermal analysis highlighting the crucial role of local damage on thermal conductivity of the TBC.

Electron multipacting and electron cloud have been identified as being the major limiting factors for the beam quality or for the cryogenic system of high-intensity positive particles accelerators. Among conditioning operational techniques and other surface structuration techniques used to decrease the Secondary Electron Yield (SEY) of surfaces, laser surface treatment is a promising method to treat in situ and at atmospheric pressure copper surface of the vacuum chamber. Here, pulsed laser irradiation of copper in parallel lines pattern led to the local ablation and deposition of aggregates of copper particulates on the surface. Tests undertaken at CERN have shown that the modification of the surface morphology by creating roughness at different scales induces a decrease of the SEY by geometrical effects. Nevertheless, the mechanical strength and dust generation of the treated surface have not been addressed yet.In this work, a qualitative analysis of the multi-scale description of the surface morphology was carried out. Scanning Electron Microscopy (SEM), Focused Ion Beam (FIB), Transmission Electron Microscopy (TEM) and Energy Dispersive X-ray Spectroscopy (EDS) were used to investigate morphological characterization such as size and shape of the particulates, chemical composition, metallographic structures and phase transformation on the laser-processed surface.SEM and FIB examinations showed that the surface morphology depends on the local laser energy irradiating the surface and especially, relatively to the ablation threshold. TEM analysis revealed chemical composition and crystalline configuration of the treated material and helped to identify the laser modified and oxidized areas. A variety of superficial structures were observed. Potential vulnerable structures have been identified as oxidized matter redeposited on the ablated near surface. Material continuity and composition play a major role in the mechanical integrity of the generated surface morphology. The adherence of the created structures was assessed analyzing the origin of the dust extracted after mechanical stress.

International audience; The understanding of the mechanical properties at the microstructure scale is a key factor for the material macroscopic behavior comprehension and its appropriate engineering at the scale of the structure. In this study, a new approach which is based on the combination of both nanogauges displacements monitoring and electron backscatter diffraction (EBSD) techniques performed under Scanning Electron Microscope (SEM) during in-situ tensile tests is proposed. Strain evolutions at the microstructure components and the behavior of the material can be compared to the crystallographic data. The approach was applied to austenitic stainless steel 316L specimen in order to bring a proof of concept and put into evidence its potential. Among the information of interest which can be obtained through this technique, one can cite the possibility to highlight the strain initiations in the vicinities of twins and their evolutions during the tensile test or to evidence the strain heterogeneities at the surface of the specimen and its influence over the elongations and rotations of the microstructure components, which tends to be reorganized in order to balance the mechanical stress. Besides, such heterogeneities can be expressed in terms of misorientations and quantified from the EBSD data. The twinning and slip activities can also be correlated to the hardening of the material thanks to this method of characterization. As for its interest for characterizing the plastic domain, the technique can show how some grains may activate more than one slip system. Finally, it has been here demonstrated how complementary and powerful the combination of these two techniques may be considered and how it may give access to a better understanding of the material microstructure properties.

International audience; The present work focuses on the intergranular oxidation of Alloy 600 and its weld material Alloy 82 after exposure in simulated primary water at 340–360 °C during 1000–1400 h. The effects of intergranular chromium carbides, grain boundary character and pre-straining are studied either on industrial heats or model microstructures. Three-dimensional reconstructions of well-chosen grain boundaries are obtained using focused ion beam tomography in a scanning electron microscope. The 3D characterizations show that (1) twin boundaries are less susceptible to oxidation than high-angle grain boundaries; (2) intergranular chromium carbides delay the intergranular oxidation kinetics; (3) the intergranular oxidation depth is quite homogeneous along a given grain boundary except when strain heterogeneity exists in its vicinity, (4) strain heterogeneity tends to accelerate the intergranular oxidation kinetics; and (5) crack initiation in the oxidized grain boundary occurs at the alloy/oxide interface.

International audience; The respective influence of the oxidation and phase transformation on the rumpling of nickel aluminide coatings is reviewed using the thermal treatments in air and Ar atmosphere: β-(Ni,Pt)Al coating deposited on AM1 Ni-base superalloy was subjected to the isothermal and cyclic oxidation at 1100 °C as well as to the thermal cycling in Ar atmosphere. A comparative study of the coating microstructure evolution and surface roughness increase in different conditions suggests that the presence of adherent oxide layer is essential for the rumpling of nickel aluminide coatings on Ni-base superalloys.

A water soluble dye, the Red 33, used in cosmetic industry was immobilized into mesoporous silica by a one-step method which consists in the introduction of the dye molecules in the precursor medium of the mesoporous silica i.e. containing surfactant and silica source. A high loading rate of 25 wt% was achieved. The resulting Red 33-silica pigment is stable in water and oil media. The characterizations carried out on this material have shown that the encapsulation is effective and that the presence of Red 33 has an effect on the structure and texture of the material. The material exhibits an excellent stability in water due to the interactions between the Red 33 molecules, the silicate species and the surfactant molecules. It has been shown that the dye molecules interact with both the silica host matrix through the NH2 and phenyl groups, as well as with the surfactant molecules, via electrostatic interactions between the polar head of the surfactant and the sulfonate group of Red 33 which undergoes no steric hindrance.

Hybrid materials based on amino hydroxyapatite (NH2-HA) and chitosan (CS) were prepared by reticulation in the presence of sodium tripolyphosphate. NH2-HA having different weight percentages (10–75%) was used in the synthesis. The resulting solids were used for the removal of reactive violet 5R—an organic dye—from an aqueous solution. The synergy among the adsorptive properties of the precursors was assessed for the hybrid biomaterials by X-ray diffraction, thermogravimetry, CHN elemental analysis, infrared spectroscopy, and 13C nuclear magnetic resonance spectroscopy. The crosslinking mechanism was also elucidated. The effects of adsorbent dosage, time, pH, and initial dye concentration were investigated. The adsorption capacities of the resulting hybrids were proportional to the CS content in the hybrids and the surfaces were positively charged at pH 1–7. The optimal dye-removal capacity of 350 and 365 mg g-1 was achieved at pH 3 for the solids containing 10 and 25% silylated HA, respectively. Kinetic data were evaluated for the pseudo-first-order, pseudo-second-order, and Elovich models. At equilibrium, various systems were adjusted to the Langmuir models. The amino groups were blocked via the reaction with acetyl chloride, which demonstrated the contribution of different active sites in the prepared hybrids toward dye removal. The Artemia salina tests demonstrated the low toxicity of the prepared hybrids irrespective of their composition. The data indicated that the prepared hybrids were capable of achieving rapid and high dye removal. Additionally, the reuse tests suggested the formation of stable-loaded-dye substrates after adsorption.

International audience; Green earth is a common green pigment based on celadonite and glauconite, used since Antiquity by artists. Two geological minerals, eight commercial green earth pigments and a sample taken from a historical location in Monte Baldo were characterized. A set of different techniques including X-Ray diffraction (XRD), scanning electron microscopy coupled to energy dispersive spectroscopy (SEM-EDS) and numerous spectroscopies: spectrophotocolorimetry, near and mid infrared, Raman, Mössbauer were used to identify the structure and composition of the different earths. The results highlight complex composition with the presence of various phases, which can be due to the pigment sampling at a different location in the same deposit. Mobile and non-invasive analyses were carried out in order to suggest a protocol for the identification of green earth in artworks, and more specifically to distinguish celadonite and glauconite. With the available mobile non-invasive techniques, and the above analyses on the raw pigments, the green area in Nicolas Poussin’s painting, Bacchanales d’enfants (Galleria Nazionale d’Arte Antica (GNAA), Rome) was examined as a case study.

International audience; Two mechanisms are studied to explain the asymmetrical chromium depletions observed ahead of SCC crack tips in nickel-base alloys: diffusion-induced grain boundary migration (DIGM) and plasticity-enhanced diffusion. On the one hand, DIGM is evidenced in a model Alloy 600 by focused ion beam (FIB) coupled with scanning electron microscopy (SEM) cross-section imaging and analytical transmission electron microscopy (TEM) after annealing at 500 °C under vacuum and at 340 °C after exposure to primary water. The occurrence of grain boundary migration depends on the grain boundary character and misorientation. On the other hand, the effect of plasticity on chromium diffusion in nickel single-crystals is investigated by performing diffusion tests during creep tests at 500 and 350 °C. An enhancement of Cr diffusion is observed and a linear relationship between the diffusion coefficient and strain rate is evidenced. At last, in an attempt to discriminate the two mechanisms, an analytical modeling of the Cr-depleted areas observed at propagating SCC crack tips is proposed.

International audience; Aluminum (Al) powders with spherical and irregular particle shapes were mixed with two alumina (Al2O3) powders with either a spherical or an angular particle shape to achieve high-performance cold-sprayed coatings onto steel. Two effects of the aluminum particle shape were observed. First, coating microstructure observation showed impinging heterogeneity depending on particle shape. Second, particle jet differences depending on particle morphology were shown by velocity maps. From the latter, SEM and XRD, three effects of the alumina particle shape were also shown, i.e., higher in-flight velocity of angular particles, fragmentation of spherical hollow particles and embedding of alumina particles with aluminum. Numerical simulation of particle impacts was developed to study the densification of Al coating due to Al2O3 addition through elucidation of Al-Al2O3 interaction behavior at the scale of the coating. Al/Al and Al/Al2O3 interfaces were investigated using TEM to understand coating strengthening effects due to alumina addition at the scale of the particle. As a whole, Al and Al2O3 particle shape effects were claimed to explain coating mechanical properties, e.g., microhardness and coating–substrate bond strength. This study resulted in specifying criteria to help cold spray users in selecting powders for their applications, to meet economic and technical requirements.

International audience; Alloy 600 is used in pressurized water reactors (PWRs) but is susceptible to primary water stress corrosion cracking (PWSCC). Intergranular chromium carbides have been found beneficial to reduce PWSCC. Focussed ion beam coupled with scanning electron microscopy (FIB/SEM) 3D tomography has been used to reconstruct the morphology of grain boundary oxide penetrations and their interaction with intergranular Cr carbides in Alloy 600 subjected to a PWR environment. In presence of intergranular Cr carbides, the intergranular oxide penetrations are less deep but larger than without carbide. However, the intergranular oxide volumes normalized by the grain boundary length for both samples are similar, which suggest that intergranular oxidation growth rate is not affected by carbides. Analytical transmission electron microscopy (TEM) shows that the intergranular oxide consists mainly in a spinel-type oxide containing nickel and chromium, except in the vicinity of Cr carbides where Cr 2 O 3 was evidenced. The formation of chromium oxide may explain the lower intergranular oxide depth observed in grain boundaries containing Cr carbides.

International audience; Phase transformation of Pt-modified nickel aluminide coating β-(Ni,Pt)Al into γ′ phase was studied during isothermal and cyclic oxidation at 1100 °C. The transformation occurred with homogeneous β and γ′ phases with chemical compositions depending on oxidation conditions. Cyclic oxidation led to a higher volume fraction of topologically close-packed (TCP) phases formed in the interdiffusion zone and the chemical composition of TCP phases was found to vary with oxidation conditions. This difference in TCP precipitation in the interdiffusion zone for isothermal and cyclic oxidation was suggested to be responsible for different β and γ′ compositions. The experimental observations were discussed using thermodynamic calculations by Thermo-Calc software, and some explanations were given.

The potential use of l-3, 4-dihydroxyphenylalanine (l-DOPA) amino acid in the treatment of Parkinson’s disease is hindered by an oxidative polymerization under air that might be at least partially circumvented by the immobilization on an inorganic matrix. This study reports on the preparation of dihydroxyphenylalanine (DOPA)–zeolite beta composites. The materials obtained from the oxidative reactions of DOPA in aqueous solution in the presence of the zeolitic matrix are characterized by a combination of different spectroscopic techniques including Raman, infrared, ultraviolet–visible, and NMR, and by periodic density functional theory calculations in order to understand the mode of interaction between the biomolecules and the inorganic matrix. The set of experimental data unambiguously proves that the oxidation of DOPA is slowed in acidic medium and that a dimerization occurs in the pores of the inorganic lattice. The states of DOPA and its cyclized forms (dopachrome and leucodopachrome) are determined. The results of the study can be used to control the immobilization of amino acids on porous matrices.

International audience; Acidic magadiite (HMag) was directly reacted with ethylene sulfide (ES) under various controlled conditions producing an intercalated hybrid silicate (MagS). The sodium, acidic and modified magadiites were characterized using elemental analysis, thermogravimetric analysis (TGA/DTG), infrared spectroscopy, 13C and 29Si NMR spectroscopies, scanning electronic microscopy and energy dispersive spectrometer. The modified solids were used to retain lead found in aqueous solutions. The results showed that ethylene sulfide was grafted as a dimer in the interlayer space of HMag, which was concluded from the XRD experiments due to an increase in the basal spacing from 1.34 to 1.81 nm. This was in agreement with the high sulfur content obtained by elemental analysis. A higher amount of ethylene sulfide was immobilized in the layered material without the use of a solvent. The adsorption of lead revealed the formation of interlayer complexes involving the cation and the mercapto chelating groups. The method described herein provides a simple route for the synthesis of inorganic-organic magadiite.

International audience; Nickel-base alloys are widely used in nuclear Pressurized Water Reactors (PWRs). Most of them have been found susceptible to Stress Corrosion Cracking (SCC) in nominal PWR primary water. The time to initiation depends on the material and is longer for weld metals than for Alloy 600. This study will focus on Alloy 82, which is used in Dissimilar Metal Welds (DMWs). In service, DMWs are either in the as-welded state or have undergone a stress relief treatment. Previous SCC studies showed that the heat treatment reduces significantly the SCC susceptibility of the weld. In this context, this study focuses on the microstructure characterization of the weld in the as-welded state and in the heat-treated state. As chromium content is also a key factor for the SCC susceptibility, welds with low chromium content and medium chromium content were studied. The lower SCC susceptibility of the heat-treated welds was attributed to intergranular Cr23C6 resulting from a combined effect of heat treatment and chromium and carbon contents. These intergranular carbides could explain the better behavior of Alloy 82, compared to other nickel-base alloys.

International audience; This work deals with the study of the irradiation assisted stress corrosion cracking. The purpose is to improve the understanding of irradiation effects on the mechanical behaviour of internal stainless steel structures in PWR environment. The aim is to identify the physical mechanisms responsible for plasticity and damage in relation with the microstructure heterogeneities and to separate the effects induced by the chemical environment to those due to mechanical loading and irradiation. Proton-irradiations are performed in the Michigan Ion Beam Laboratory. Slow Strain Rate Tensile tests are performed both in PWR primary water and under inert atmosphere to study the deformation mechanisms of irradiated samples and their coupling with the environment. To correlate cracking to microstructure, full field analysis are performed, at a microscale, by SEM digital imaging correlation technique coupled with EBSD cartography of the grain orientations after irradiation. Moreover, cracking features are characterized using SEM and TEM.

Zeolite Beta particles with size of 0.1, 0.5 and 1 μm were employed as molds for the synthesis of microporous carbon. After infiltration and pyrolysis of propylene at 800 °C for 2 h, zeolite/carbon composites were obtained and further subjected to acid extraction of the zeolite precursor. The initial zeolite samples, zeolite/carbon composites and carbon replicas were studied by XRD, TG analysis, SEM/TEM, DLS, N2 adsorption measurements and chemical analysis. The experimental data revealed that the carbon replicas faithfully replicate the zeolite morphology and possess higher micropore volume than that of the parent zeolite molds. The use of zeolite molds of different sizes resulted in carbons with fairly different pore structure. Thus, larger (0.5 and 1 μm) zeolite crystals provided replicas with a pore structure possessing mainly micropores, whereas the carbon replication of 0.1 μm zeolite aggregates built of much smaller crystallites resulted in a material with lower micropore volume and substantial contribution of mesopores to the total pore volume. The different pore structure of the latter carbon was found to be a result of the larger external surface area of the nanosized mold, loss of crystallinity during the preparation procedure and the presence of interparticles porosity.

International audience; Numerous mercaptopropyl-functionalized silica spheres have been prepared by either post-synthesis grafting of MCM-41 and MCM-48 or self-assembly co-condensation of mercaptopropyltrimethoxysilane (MPTMS) or mercaptopropyltriethoxysilane (MPTES) and tetraethoxysilane (TEOS) precursors in hydroalcoholic medium in the presence of a cationic surfactant as templating agent and ammonia as catalyst. These materials of approximately the same particle size and morphology featured different functionalization levels, various degrees of structural order, and variable distribution of thiol groups in the mesopores. Their reactivity in solution has been studied using Hg(II) as model analyte. Total accessibility (on a 1:1 S:Hg stoichiometry basis) was demonstrated and quantified for well-ordered materials whereas less open and less organized structures with high degrees of functionalization were subject to less-than-complete loadings. Capacities measured at pH 2 were lower than at pH 4 because of distinct mercury-binding mechanisms. Kinetics associated to the uptake process were studied by in situ electrochemical monitoring of Hg(II) consumption from aqueous suspensions containing the various adsorbents. They indicate only little difference between materials of the MCM-41 and MCM-48 series at similar functionalization levels, fast mass transport in well-ordered mesostructures in comparison to the poorly or non-ordered ones (except at pH 2 where charge formation induced some restriction in materials characterized by long-range structural order), and even faster processes in the wormlike frameworks (characterized by shorter range structural order). Hg(II) binding to thiol-functionalized materials obtained by post-synthesis grafting was found to occur more rapidly in the early beginning of the uptake process as a result of a higher concentration of binding sites at the pore entrance in comparison to the more homogeneous distribution of these groups in the mesochannels of materials obtained by co-condensation.

International audience; A wide range of mercaptopropyl-functionalized silica spherical particles of MCM-41 and MCM-48 (M41S family) have been prepared by co-condensation of mercaptopropyl trimethoxysilane (MPTMS) or mercaptopropyl triethoxysilane (MPTES) and tetraethoxysilane (TEOS) precursors in hydroalcoholic medium in the presence of a cationic surfactant as templating agent and ammonia as catalyst. It was possible to control the mesostructure type (hexagonal or cubic) by monitoring the water-to-ethanol ratio and the type of organoalkoxysilane precursor employed. Materials displaying various functionalization levels were obtained by varying the MPTMS or MPTES contents from 3 to 50% in the co-condensation synthesis medium. This gave rise to a wide range of porous solids with approximately the same particle size and morphology but featuring different functionalization levels and various degrees of structural order. They were characterized by X-ray diffraction (XRD), N2 adsorption-desorption isotherms and BET analysis, scanning and transmission electron microscopy, 29Si and 13C solid state nuclear magnetic resonance (NMR), particle size distribution measurements, and elemental chemical analysis. Mercaptopropyl groups were readily incorporated with high yields (>90%) by the co-condensation route. All samples exhibited spherical morphology with similar particle size but both the level of ordering and porosity of solids obtained by co-condensation were found to decrease when increasing the amount of organo-functional groups.

International audience; The classical approach to prepare dithiocarbamate-functionalized silica involves a two-step procedure based on the reaction of carbon disulfide with a pre-formed amine modified silica sample. A novel approach is proposed here, involving the direct grafting of silica surfaces with the aid of a siloxydithiocarbamate precursor. Functionalization has been applied to three silica samples (a non-ordered silica gel and two ordered mesoporous solids with distinct pore size) to evidence possible effects of mesostructural order and/or pore size of the materials. The performance of the one-step method has been compared to the two-step one and qualitatively discussed in terms of derivatization efficiency regarding the integrity of dithiocarbamate organo-functional groups. Thanks to complementary physico-chemical techniques (N2 adsorption/desorption, solid-state NMR, XPS, XRD), the interest of direct grafting has been clearly demonstrated as it allows to access in one step dithiocarbamate-functionalized silicas free of residual amine groups. Moreover, the use of a base in the two-step procedure is likely to induce some degradation of the silica materials. The advantageous features of the direct grafting process were also discussed with respect to Hg(II) adsorption to these materials.

International audience

The present study demonstrates that for the nanocasting process with zeolites, a careful choice of the zeolite structure type (EMT) allows the formation of faithful carbon replica exhibiting up to three well resolved XRD peaks.