Adhérence fibre d'acier - matrice cimentaire dans les mortiers fibrés à hautes températures

https://www.polytech.univ-savoie.fr/fileadmin/polytech_autres_sites/sites/augc2012/actes/Contribution1192.pdfNational audienceRÉSUMÉ. Dans cette étude, nous nous sommes intéressés au comportement mécanique des mortiers renforcés de fibres d'acier. Tout d'abord, nous étudions la résistance à la flexion de ces mortiers après traitement thermique. Ensuite, nous nous intéressons à l'évolution de l'adhérence fibre - matrice en fonction de la température. Ces deux études indiquent une dégradation des caractéristiques physico-mécaniques dès 500°C. Des observations au MEB mettent en évidence une corrosion à haute température des fibres d'aciers. Cette corrosion débute à 500°C. A 800°C, près de 85% de la section des fibres est corrodée ce qui explique les pertes de caractéristiques mécaniques observées précédemment. ABSTRACT. In this study, we investigate the mechanical behaviour of steel fibres reinforced mortars. First, we study the flexural strength of mortars after heat treatment. Next, we investigate the evolution of the fibre - matrix adhesion function of temperature. Both studies indicate a deterioration of physical-mechanical characteristics at 500 °C. SEM observations show a high temperature corrosion of steel fibres. The corrosion starts at 500 ° C. At 800 °C, nearly 85% of the fibres section is corroded which explains the loss of the mechanical properties

Electrical and magnetic properties of La0.67Ba0.33Mn1−x (Me) x O3 perovskite manganites: case of manganese substituted by trivalent (Me = Cr) and tetravalent (Me = Ti) elements

International audienceThe effects of non-magnetic Ti4+ substitution on the structural, electrical and magnetic properties of La0.67Ba0.33Mn1−x Ti x O3 (0≤x≤0.1) are investigated and compared to those existing in La0.67Ba0.33Mn1−x Cr x O3 (magnetic Cr3+). The structural refinement by the Rietveld method revealed that Ti-doped samples crystallize in the cubic lattice with space group Pm3¯m , while samples with Cr crystallize in the hexagonal setting of the rhombohedral R3¯C space group for identical contents of dopant. The most relevant structural features are an increase of the lattice parameters, of the cell volume and of the inter-ionic distances with increasing Ti doping level. Both series of samples show a decrease of the paramagnetic-ferromagnetic transition temperature when the amount of chromium or titanium increases. Transport measurements show that when increasing the metal doping, the resistivity increases whereas the metallic behavior of the parent compound La0.67Ba0.33MnO3 is destroyed. For a substitution higher than 5 at.% of Ti and 10 at.% of Cr, the samples exhibit a semiconducting behavior in the whole range of temperature, for which the electronic transport can be explained by variable range hopping and/or small polaron hopping models

Sr1-xBaxSnO3 system applied in the photocatalytic discoloration of an azo-dye

International audienceSemiconductor materials have received substantial attention as photocatalysts for controlling water pollution. Among these materials, perovskite-structured SrSnO3 is a promising candidate for this application, whereas BaSnO3 exhibits very low activity. In the present work, Sr1−xBaxSnO3 (x = 0, 0.25, 0.50, 0.75 and 1) was synthesized by solid-state reaction and was applied in the photocatalytic discoloration of the organic dye Remazol Golden Yellow. The perovskite structure was obtained for all compositions of the solid solutions with both Sr2+ and Ba2+ present in the lattice. A remarkable change in the short-range symmetry was observed as the amount of Ba2+ increased, and this change led to a decrease in the band gap of the material. Although the BaSnO3 was not active toward water photolysis, the discoloration induced by this perovskite was twice that induced by SrSnO3. The two materials appear to feature different mechanisms of photodegradation: the direct mechanism prevails in the case of BaSnO3, whereas the indirect mechanism appears to play a key role in the case of SrSnO3

Do Specialized Cells Play a Major Role in Organic Xenobiotic Detoxification in Higher Plants?

International audienceIn the present work, we used a double cell screening approach based on phenanthrene (phe) epifluorescence histochemical localization and oxygen radical detection to generate new data about how some specialized cells are involved in tolerance to organic xenobiotics. Thereby, we bring new insights about phe [a common Polycyclic Aromatic Hydrocarbon (PAH)] cell specific detoxification, in two contrasting plant lineages thriving in different ecosystems. Our data suggest that in higher plants, detoxification may occur in specialized cells such as trichomes and pavement cells inArabidopsis, and in the basal cells of salt glands inSpartinaspecies. Such features were supported by a survey from the literature, and complementary data correlating the size of basal salt gland cells and tolerance abilities to PAHs previously reported betweenSpartinaspecies. Furthermore, we conducted functional validation in two independentArabidopsistrichomeless glabrous T-DNA mutant lines (GLABRA1 mutants). These mutants showed a sensitive phenotype under phe-induced stress in comparison with their background ecotypes without the mutation, indicating that trichomes are key structures involved in the detoxification of organic xenobiotics. Interestingly, trichomes and pavement cells are known to endoreduplicate, and we discussed the putative advantages given by endopolyploidy in xenobiotic detoxification abilities. The same feature concerning basal salt gland cells inSpartinahas been raised. This similarity with detoxification in the endopolyploid liver cells of the animal system is included

Analysis of pulsed laser deposited amorphous chalcogenide film thickness distribution: Plume deflection angle dependence

International audiencePulsed laser deposition exploiting a KrF excimer laser was used to fabricate amorphous As-S thin films from bulk As2S3 glass target. Thickness profile of the film was extracted from variable angle spectroscopic ellipsometry data. The dependence of thickness distribution of prepared thin layer on laser beam plume deflection angle was evaluated and corresponding equations were suggested

Enhancing light trapping of macroporous silicon by alkaline etching: application for the fabrication of black Si nanospike arrays

International audienceThe synthesis of highly absorbing silicon (black Si (BSi)) is a very active research topic with promising applications in the field of sustainable energies, ultrasensitive sensing and antibacterial materials. Here, we show that extended alkaline etching of macroporous Si, fabricated by photoelectrochemical etching drastically influence the surface structures as well as their optical properties. We demonstrate that this treatment can considerably improve the light trapping of the surface and we finally show that it is possible to use it for fabricating very quickly highly-absorbing arrays of sharp and crystalline BSi nanospikes (NSpikes)

Synthesis, Luminescence and Energy Transfer Properties of Ce³⁺/Mn²⁺ Co-Doped Calcium Carbodiimide Phosphors

International audienceCe3+-doped and Ce3+/Mn2+ co-doped calcium carbodiimide (CaCN2) phosphors were synthesized from doped calcium carbonate and carbon nitride by a solid-state reaction at 700 °C under flowing NH3 using a very short reaction time (1 h). The samples were characterized by powder X-ray diffraction, scanning electron microscopy and their diffuse reflectance and luminescence properties were investigated. Single-doped CaCN2:Ce3+ exhibits a blue emission under near-ultraviolet activation (386 nm) corresponding to the 5d1 → 2F5/2 and 5d1 → 2F7/2 transitions of Ce3+. Maximum emission is obtained at temperatures lower than 150 K and then progressively decreases up to 387 K, with an 80% drop in the emission at room temperature. Efficient energy transfers from Ce3+ to Mn2+ via a non-radiative dipole–dipole mechanism are evidenced for the co-doped samples, leading to various colored phosphors under near-ultraviolet activation (386 nm). The emission color of the obtained phosphors can be modulated from blue to red through a shade of white depending on the sensitizer/activator ratio

IR GRIN lenses prepared by ionic exchange in chalcohalide glasses

International audienceIn order to decrease the number of lenses and the weight of thermal imaging devices, specific optical design are required by using gradient refractive index (GRIN) elements transparent in the infrared waveband. While widely used for making visible GRIN lenses with silicate glasses, the ion exchange process is very limited when applied to chalcogenide glasses due to their low T(g) and relatively weak mechanical properties. In this paper, we develop chalco-halide glasses based on alkali halide (NaI) addition in a highly covalent GeSe(2)-Ga(2)Se(3) matrix, efficient for tailoring a significant and permanent change of refractive by ion exchange process between K(+) and Na(+). Optical and structural properties of the glass samples were measured showing a diffusion length reaching more than 2 mm and a Gaussian gradient of refractive index Δn of 4.5.10(-2). The obtained GRIN lenses maintain an excellent transmission in the second (3-5 µm) and third (8-12 µm) atmospheric windows

Photoelectrochemical Sensing of Hydrogen Peroxide on Hematite

International audienceDue to its abundance and chemical stability, hematite (α-Fe 2 O 3) is a promising n-type semiconductor photoelectrode. This is particularly true in the frame of the rapidly developing area of photoelectrochemical (PEC) sensing, where the short excited-state lifetime and the small carrier diffusion length of hematite can be beneficially employed. On the other hand, H 2 O 2 is an essential molecule for biological, environmental and industrial applications. In this article, we report a simple method to prepare photoelectroactive hematite layers on fluorine-doped SnO 2 (FTO) and we use these surfaces for H 2 O 2 PEC sensing. The so-created sensors allow to reliably detect H 2 O 2 down to a sub-µM concentration with a large linear range and a good reusability. H 2 O 2 is a crucial molecule. First, it is a marker for oxidative stress and a major factor of pathophysiological complications in serious diseases. [1,2] H 2 O 2 is also present in the natural environment [3] and commonly employed as a reagent in paper, textile or food industry. Hence, fast and accurate monitoring of H 2 O 2 is of great interest to medicine, environmental and industrial processing. Analytical protocols based on chromatography, [4] titration, [5] spectrophotometry, [6] fluorescence, [7] chemiluminescence, [8] and electrochemistry [9,10] have been used to detect this molecule and the development of H 2 O 2 sensors attracts considerable attention. [9,11] Photoelectrochemical (PEC) sensing is based on the photoinduced charge transfer at a semiconductor/liquid interface. It is a rather new and rapidly-developing research area which sensing combines aspects of electrochemical and optical sensing. [12,13] PEC sensing decouples excitation (light) and detection (electrochemical) signals, which is expected to significantly increase the signal-to-noise ratio with respect to electrochemical sensing. [13] Besides, it is also promising because it enables 2D reaction confinement on the transducer surface (i.e. on the photoelectrode) [14,15] which can be useful for electrode reuse [16,17] or for the design of multiplexed arrays. [18,19] So far, PEC sensing has been mainly employed for the detection of biological macromolecules, [20] in immuno-[21] or apta-[22] assays and has also been explored for the detection of small organic molecules such as antioxidants [23] or glucose. [24,25] While H 2 O 2 is a widely-employed hole scavenger in the field of energy-related photoelectrochemical research (typically used to probe the upper performance of water-splitting photoanodes), [26,27] the PEC sensing of H 2 O 2 has been only reported on TiO 2 , [28-30] WO 3 , [31] ZnO, [32,33] BiVO 4 , [34,35] and Si [36]-based photoanodes and on Cu 2 O, [37] CuO, [38] CdS, [39] and CuInS 2 [40]-based photocathodes. Hematite (α-Fe 2 O 3) is a promising photoanode material due to its great abundance, low-cost, chemical stability and its high theoretical photoconversion efficiency. [41,42] Nevertheless, it also has a short excited-state lifetime and a small hole diffusion length. This is a severe drawback for energy-related applications [41,42] but can be a great advantage for the design of PEC sensor arrays activated by micrometer-sized spots of light. [15,17] Hematite photoanodes have been previously employed for the PEC sensing of biological macromolecules, [43,44] neurotransmitters, [17] endocrine disruptors, [45,46] glucose, [25,44] inorganic pollutants, [47] and metal cations. [48] In this paper, we report the preparation of hematite photoanodes by a convenient spin-coating/annealing method and the use of these surfaces for H 2 O 2 PEC sensing. Figure 1. a) Scheme showing the method used to deposit hematite on FTO. b) Colored SEM image showing a cross-section of the hematite deposited on FTO. c) SEM image showing a top view of the hematite coating on FTO. d) XRD pattern of the deposited layer (black line), the red lines indicate the peaks position and relative intensity for hematite (ICSD #15840). e) High-resolution TEM image of the prepared hematite layer, the distance between the (210) planes is indicated. f) [12 1] zone axis SAED patterns recorded on hematite. Our hematite precursor is poly(vinylferrocene) (pvf), a Fe-containing polymer, dissolved in tetrahydrofuran (THF), which was spin-coated onto FTO slides and subsequently annealed, as shown in Figure 1a. A similar approach was previously employed by our group, however, with a low annealing temperature (300 °C) in order to deposit amorphous catalytic FeO x layers. [49] In the present work, we wanted to assess the feasibility of growing semiconductor films, we thus employed a higher annealin