Improvements for imaging ceramics sintering in situ in ESEM

International audienceSintering of green samples of alumina produced by ice-templating was followed in situ in an environmental scanning electron microscope (ESEM) up to temperatures as high as 1375 degrees C. These alumina samples with well-defined architectures are of great interest in the field of materials science due to their high specific strength (especially in compression), low density and adaptable porosity. For the present study, they also have the advantage to exhibit an important topography, inducing interesting contrast when imaged in an ESEM. Improvements of the imaging conditions in the ESEM were essential to really follow the sintering process involving formation of necks between grains or shift of the centre of grains. This paper describes the improvements made and the results observed on the sintering process of alumina green samples processed by ice-templating

Evidence for the formation of distorted nanodomains involved in the phase transformation of stabilized zirconia by coupling convergent beam electron diffraction and in situ TEM nanoindentation

International audienceThe transformation of zirconia from its tetragonal to its monoclinic phase is an important feature of the zirconia system. First found to be an advantage due to its important toughening effect, it can also be very detrimental when it occurs in the framework of low-temperature degradation, particularly in the case of biomaterial applications. One way to avoid or to control this phase transformation is to understand how it initiates and more particularly the stress states that can trigger it. A new technique available inside a transmission electron microscope seems to be particularly well suited for that type of study: convergent beam electron diffraction, a well-known technique to reveal stresses, was coupled to in situ transmission electron microscopy mechanical nanoindentation. The experiments reveal the presence of sheared nanoregions at grain boundaries. These could act as embryos for tetragonal-to-monoclinic phase transformations. This is an important first step in the understanding of the earliest stage of zirconia phase transformation

Internalization pathways into cancer cells of gadolinium-based radiosensitizing nanoparticles

International audienceOver the last few decades, nanoparticles have been studied in theranostic field with the objective of exhibiting a long circulation time through the body coupled to major accumulation in tumor tissues, rapid elimination, therapeutic potential and contrast properties. In this context, we developed sub-5 nm gadolinium-based nanoparticles that possess in vitro efficient radiosensitizing effects at moderate concentration when incubated with head and neck squamous cell carcinoma cells (SQ20B). Two main cellular internalization mechanisms were evidenced and quantified: passive diffusion and macropinocytosis. Whereas the amount of particles internalized by passive diffusion is not sufficient to inducein vitro a significant radiosensitizing effect, the cellular uptake by macropinocytosis leads to a successful radiotherapy in a limited range of particles incubation concentration. Macropinocytosis processes in two steps: formation of agglomerates at vicinity of the cell followed by their collect via the lamellipodia (i.e. the "arms") of the cell. The first step is strongly dependent on the physicochemical characteristics of the particles, especially their zeta potential that determines the size of the agglomerates and their distance from the cell. These results should permit to control the quantity of particles internalized in the cell cytoplasm, promising ambitious opportunities towards a particle-assisted radiotherapy using lower radiation doses

Microstructure and mechanical properties of TiC-TiN based cermets for tools application

International audienceThe objective of this work is to develop materials with both a good hardness and a good toughness. Titanium carbonitride has a significant hardness (2000Hv), but its toughness (6 MPa√m) is insufficient for tools applications. Toughness can be improved by addition of a metallic binder. Cermets based on TiC and TiN with Ni as binder are the most developed materials. In the present work, the effect of TiN addition and binder content on the microstructure and the properties of the TiC based cermets elaborated by pressureless sintering have been investigated. Results show that dense cermets with specific core/rim structure have been obtained. The rupture strength and the toughness increase with the addition of Ni. The optimum values of mechanical properties were found for the cermet with 15 wt% Ni and 10 wt% TiN addition, respectively, which exhibits a Vickers hardness over 1400 Hv0.3 and a fracture toughness around 13.6 MPa√m

Direct Synthesis of Periodic Mesoporous SilicoBoron CarboNitride Frameworks via the Nanocasting from Ordered Mesoporous Silica with Boron-Modified Polycarbosilazane

International audienc

Characterization of organo-mineral cement materials

International audienceConclusion: A multi-scale characterization of building material is essential to optimize their properties and was sucefully performed by coupling different electron microscopy techniques. Hydrates morphologies, effect of the addition of latex on the cement microstructure were characterized. Full scale analysis is still under completion CONTEXT-MATERIAL Whatever the applications biomedial, tranportation, energy or construction; there is a lack of knowledge on the true organization at the nano scale of mineral and organic phase (qualitative image, together with quantitative analysis). This study was focused on the characterization of cementitious materials, and mainly on organo-mineral composite. Many innovative applications in the field of high-performance construction materials and building insulation systems are under developpement The addition of an organic phase in the form of a latex suspension may improve mortar functional properties (rheology, substrate adhesion hygro-thermal). The mechanical properties are also upgraded, and in particular the crack resistance. The latex addition effect should be characterized at different scales and therefore require the use of different electron microscope techniques

Sintering behavior of lanthanide-containing glass-ceramic sealants for solid oxide fuel cells

cited By 27International audienceThis article reports on the influence of different lanthanides (La, Nd, Gd and Yb) on sintering behavior of alkaline-earth aluminosilicate glass-ceramic sealants for their application in solid oxide fuel cells (SOFCs). All the glasses have been prepared by the melt-quench technique. The in situ follow up of sintering behavior of glass powders has been done by a high temperature-environmental scanning electron microscope (HT-ESEM) and a hot-stage microscope (HSM) while the crystalline phase evolution and assemblage have been analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). All the glass compositions exhibit a glass-in-glass phase separation followed by two stage sintering resulting in well sintered glass powder compacts after heat treatment at 850 °C for 1 h. Diopside (CaMgSi 2O 6) based phases constituted the major crystalline part in glass-ceramics followed by some minor phases. The increase in lanthanide content in glasses suppressed their tendency towards devitrification, thus resulting in glass-ceramics with a high amount of residual glassy phase (50-96 wt%) which is expected to facilitate their self-healing behavior during SOFC operation. The electrical conductivity of the investigated glass-ceramics varied between (1.19 and 7.33) × 10 -7 S cm -1 (750-800 °C) while the coefficient of thermal expansion (CTE) varied between (9.4 and 11.2) × 10 -6 K -1 (200-700 °C). Further experimentation with respect to the long term thermal and chemical stability of residual glassy phase under SOFC operation conditions along with high temperature viscosity measurements will be required in order to elucidate the potential of these glass-ceramics as self-healing sealants. © 2012 The Royal Society of Chemistry

Characterization of xenon behaviour in titanium nitride at high temperature by combination of XAS and TEM

International audienc