Stabilité thermique de la phase β\betaAl5_5FeSi dans le système ternaire Al-Fe-Si

DTA and isothermal diffusion experiments have been carried out at temperatures up to 727 $^{\circ}$C in the Fe-Al-Si ternary system. in these experiments, we have observed the themal decomposition of the solid ternary compound $\beta$Al$_5$FeSi ($\tau$6) into another ternary compound, $\gamma$Al$_5$Fe$_2$Si$_2$ ($\tau$2), and a liquid. Under the atmospheric pressure, that decomposition of $\beta$Al$_5$FeSi occurs at temperatures ranging hnn $661 \pm 5$ $^{\circ}$C to $667 \pm 5$ $^{\circ}$C. A polythermal projection combining these new results with previously published data is given to describe the crystallisation of ternary Al-Fe-Si liquid alloys upon slow cooling from 727 $^{\circ}$C

A study of surface and structural changes of magnetite cycling material during chemical looping for hydrogen production from bio-ethanol

RX+ECI2D+CTR:FBS:JMIInternational audienc

On the promoting effect of H2S on the catalytic H-2 production over Gd-doped ceria from CH4/H2O mixtures for solid oxide fuel cell applications

ENERGIE:MATERIAUX:SURFACES+GPO:FBS:GBR:NSP:PGEIn order to understand the exceptional tolerance of ceria to high sulfur levels in the fuel for further SOFC applications, the interaction of sulfur with a commercial Ce0.9Gd0.1O2-x (CGO, from Praxair) and its influence on H-2 production from CH4/H2O mixture was studied. The activity tests were performed at 750 C, in the presence of H2S and under gradual internal reforming conditions (large excess of CH4 with respect to water vapor, 10:1). The presence of H2S in the reactant mixture promoted the catalytic activity of CGO. The nature of various species formed by sulfur-ceria interaction is discussed based on CH4-TPR, XRD, XPS, and in situ FTIR results. H2S reacts with ceria fraction in CGO and generates new catalytic sites with improved reactivity toward CH4. The formation and stabilization of oxygen vacancies by S-insertion in ceria lattice are evidenced and directly related to the improved activity. The detrimental effect of Ce2O2S phase, when formed, on the catalytic activity of doped ceria is confirmed. (C) 2014 Elsevier Inc. All rights reserved

Probing Ge Distribution in Zeolite Frameworks by Post-Synthesis Introduction of Fluoride in As-Made Materials

MATERIAUX+URA:FBS:GBR:ATUA new method has been developed to introduce fluoride in the structure of as-made germanium-containing zeolites prepared under pure alkaline media. Incorporation of fluoride species occurs without modification of the framework composition (Si/Ge ratio) and of the crystallinity, as evidenced by Xray diffraction and electron microscopy. After incorporation, F-19 solid-state NMR has been used to probe the location and distribution of Ge atoms in the framework. In the case of ITQ-13 and ITQ-17, which can be prepared from both hydroxide and fluoride routes, incorporated F anions are located in the same structural units as those occupied when zeolites are prepared in the presence of fluoride. In the case of ITQ-22 and ITQ-24, fluoride goes mainly in D4R units, which appear to be in the most energetically favorable positions for these zeolites. All experiments clearly show that zeolites prepared in the absence of fluoride in the synthesis medium are enriched in germanium, compared to the same materials obtained from F-containing gels. Moreover, Ge plays a strong structure-directing role by replacing Si atoms preferentially in D4R, leading to zeolites with mainly [4Si, 4Ge] units in the framework. In the particular case of ITQ-22, a new line observed around -2 ppm in F-19 NMR spectra has been tentatively assigned to [3Si, 5Ge] D4R units, which corroborates the structural data obtained via X-ray diffraction

Au-modified Pd nanoalloy catalyst exhibits improved activity and stability for NO direct decomposition

RX+ING+TEG:FRM:ATU:YSC:FBSInternational audienceNOx direct decomposition over noble metals is thermodynamically favored and does not require reducing agents. However, the challenge is the poisoning of the noble metal surface by oxygen. On the other hand, Au is inactive for NO direct decomposition, but is one of the metals most resistant against oxidation. Our objective is to obtain a durable catalyst for NO direct decomposition by combining inert Au with an active metal such as Pd, which deactivates when used alone. Silica-supported Pd, Au and Pd-Au nanoparticles were prepared using earlier recipes. TEM-EDX analysis of the bimetallic sample showed that most of the particles contained both metals. In situ XRD analyses carried out at various temperatures under H2 evidenced the formation of Pd-Au alloyed phases. Alloyed phases were also present and stable under air at 500 °C, though Pd content decreased. The direct decomposition of NO to N2 and N2O was studied at 450°C. Au/SiO2 is inactive. Interestingly, the Pd-Au was more active than the parent Pd sample. Pd-Au also exhibited a stable activity with time, in contrast to the parent Pd material. Detailed product analyses showed that O release was higher for the Pd-Au catalyst, confirming that Au prevented Pd deactivation by facilitating O desorption

Mechanical testing of titanium/aluminium-silicon interface: Effect of T6 heat treatment

cited By 12International audienceA previous paper reported on the mechanical behaviour of insert-moulded Ti/Al-7Si bimetallic test pieces as studied by a classical push-out test as well as a variant: the circular bending test. When a chemical bond was formed at the Ti/Al-7Si interface, promising results were obtained in terms of joint strength and damage mechanism (Dezellus et al., 2008 [1]). As a continuation, the aim of the present work was to examine the influence on this mechanical behaviour of a T6 heat treatment (re-heating for 10. h at 540 °C, quenching in cold water and ageing for 6. h at 170 °C) applied to the as-moulded Ti/Al-7Si test pieces. For that purpose, push-out and circular bending tests were performed on heat-treated samples, and the results were correlated with a characterization of the morphology, the constitution and composition of both transverse sections through the metal/metal reaction zone and fracture surfaces, as revealed after removal of the Ti insert. As expected, applying the T6 heat treatment to chemically bonded Ti/Al-7Si bimetallic assemblies resulted in an improvement of the mechanical properties of the Al-7Si matrix itself. Moreover, a significant increase of the load level for the onset of joint damage in push-out mode was observed. Concerning the damage mechanism, the presence of angular Si particles in the eutectic region of the Al-7Si matrix near the interface had a weakening effect. After T6 solution heat-treatment, the shape of the Si particles changed from angular to globular. Moreover, due to the formation of Si-rich compounds at the Al-7Si/Ti interface, Si diffuses from the alloy towards the Ti rod and the size and number of Si particles became significantly decreased near the insert/alloy interface. These two features explained the favourable influence of the T6 heat-treatment on the mechanical properties of the Ti/Al-7Si assemblies. © 2010 Elsevier B.V