Le travail presente ici porte sur l'etude du couplage magnetoelastique en tant que methode du controle non destructif. Cette communication rapporte les mesures experimentales hysteretiques et piezomagnetiques effectuees sur un acier dual-phases soumis a differentes conditions de champ magnetique et de contrainte. L'effet du champ magnetique et de la contrainte mecanique, compte tenu des amplitudes statiques ou variables, est discute. Enfin, Une nouvelle modelisation multiechelle de l'hysteresis piezomagnetique est proposee.

This work deals with the study of magnetoelastic coupling in the framework of non-destructive testing. Experimental hysteretic and cyclic piezomagnetic measurements carried out on a dual-phase steel submitted to different magnetic field and stress conditions are reported. The effect of concomitant magnetic field and stress, considering static or variable amplitudes, is discussed. A new multiscale modeling of piezomagnetic hysteresis is finally proposed.

Catalytic methane decomposition was investigated over 40 wt% Fe/Al2O3 catalyst in fluidized bed reactor (FLBR). After optimization of FLBR conditions in terms of catalyst bulk density, particle size, minimum fluidization velocity, and the catalyst bed height, the catalyst activity and stability tests were conducted by comparison with a fixed bed reactor (FBR). Although a similar stable methane conversion was obtained over both reactors, the pressure drop during 35 min operation of FBR was 9 times higher than that of FLBR, which indicated the possibility of continuous operation of methane decomposition process over FLBR. Further, the influence of the space velocity, feed dilution and regeneration on catalysts reactivity was studied in FLBR to conclude that a reaction condition of 12 L/gcat∙h, feed of 20%H2–80%CH4 and CO2-regeneration of deactivated catalysts may be favourable for operating methane decomposition in FLBR continually and effectively to provide stable hydrogen.

In this work, for the first time, iron ores with 91.7%-96.2% Fe2O3, 1.3%-2.3% Al2O3, 1.2%-4.5% SiO2, 1.3%-3.9% Na2O, were studied directly as bulk catalysts for methane decomposition. By hydrogen pre-reduction at 850 degrees C, Fe2O3 species on iron ores were gradually reduced into Fe3O4, FeO and then finally into Fe species. After reduction of 1.6 g of iron ore catalysts of 50 m particle size with 100 mL/min pure H-2 for 3.5 h at 850 degrees C, CMD life testing was conducted at 850 degrees C and GHSV of 3.75 L/g(cat) h and the catalyst showed a stable methane conversion for 5 h. When methane decomposition proceeded on Fe sites, Fe3C species would be formed to deposit graphite around themselves to finally form carbon nano onions. This carbon nano onions material showed excellent application for wastewater purification. All samples were fully characterized with XRF, XRD, H-2-TPR, TEM and Raman. (C) 2018 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

Conducting catalytic methane decomposition over Fe catalysts is a green and economic route to produce H-2 without CO/CO2 contamination. Fused 65 wt% and impregnated 20 wt% Fe catalysts were synthesized with different additives to investigate their activity, whereas showing Fe-Al2O3 combination as the best catalyst. Al2O3 is speculated to expose more Fe for the selective deposition of carbon nano tubes (CNTS). A fused Fe (65 wt%)-Al2O3 sample was further investigated by means of H-2-TPR, in-situ XRD, HRTEM and XAS to conclude 750 degrees C is the optimized temperature for H-2 pre-reduction and reaction to obtain a high activity. Based on density functional theory (DFT) study, a reaction mechanism over Fe catalysts was proposed to explain the formation of graphite from unstable supersaturated iron carbides decomposition. A carbon deposition model was further proposed which explains the formation of different carbon nano materials. (C) 2017 Elsevier B.V. All rights reserved.

Activation of Fe2 O3 -Al2 O3 with CH4 (instead of H2 ) is a meaningful method to achieve catalytic methane decomposition (CMD). This reaction of CMD is more economic and simple against commercial methane steam reforming (MSR) as it produces COx -free H2 . In this study, for the first time, structure changes of the catalyst were screened during CH4 reduction with time on stream. The aim was to optimize the pretreatment conditions through understanding the activation mechanism. Based on results from various characterization techniques, reduction of Fe2 O3 by CH4 proceeds in three steps: Fe2 O3 →Fe3 O4 →FeO→Fe0. Once Fe0 is formed, it decomposes CH4 with formation of Fe3 C, which is the crucial initiation step in the CMD process to initiate formation of multiwall carbon nanotubes.

The presence of a Fe-FeAl2 O4 structure over an Fe-Al2 O3 catalysts is demonstrated to be vital for the catalytic methane decomposition (CMD) activity. After H2 reduction at 750 °C, Fe-Al2 O3 prepared by means of a fusion method, containing 86.5 wt % FeAl2 O4 and 13.5 wt % Fe(0) , showed a stable CMD activity at 750 °C for as long as 10 h.