Browsing by Author "A. Boumaza"

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    Estimation of the intrinsic stresses in a-alumina in relation with its elaboration mode
    (2010-06-06) A. Boumaza
    The specific signatures of a-Al2O3 by Fourier transform infrared (FTIR) spectroscopy were investigated to estimate the intrinsic stress in this compound according to its elaboration mode. Thus, a-alumina was prepared either by calcination of boehmite or gibbsite and also generated by oxidation of a metallic FeCrAl alloy. FTIR results were mainly supported by X-ray diffraction (XRD) patterns that allowed to determine the crystallite size and the strain in the various alpha aluminas. Moreover, the infrared peak at 378.7 cmÿ1 was used as a reference for stress free a-alumina and the shift of this peak allowed to estimate intrinsic stresses, which were related to the morphology and to the specific surface area of aluminas according to their elaboration mode. These interpretations were confirmed by results obtained by cathodoluminescence experiments.
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    Specific signatures of α-alumina powders prepared by calcination of boehmite or gibbsite
    (2010-04-09) A. Boumaza
    The specific signatures of α-Al2O3 powders by a combination of X-ray diffraction (Rietveld analysis), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, thermal analysis (TG–DTA) and cathodoluminescence (CL) were investigated. Thus, α-alumina was prepared by calcination of boehmite or gibbsite at 1573 K for 24 h. The size of α-alumina crystallites obtained using boehmite precursor was smaller than that obtained using gibbsite precursor. The difference in oxygen vacancies (F+-centers) amount between α-Al2O3 powder obtained by calcination of gibbsite and boehmite was confirmed by CL spectra. Furthermore, the Ti3+ emission at 1.71 eV is absent in α-Al2O3 powder obtained by calcination of gibbsite. CL has been demonstrated as a possible method for differentiation between the various α-alumina powders.