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Abstract  

The non-isothermal kinetics of precipitation of an Al-12.6 mass% Mg alloy for different heating rates were studied using thermal expansion techniques. The structural changes associated with the precipitation of the and b phases were identified. The conversion degree of each phase was associated with the area under the derivative curve of the thermal expansion with respect to temperature. Using the Kissinger relation and an iso-conversional method we calculated the apparent activation energies associated with formation of the precipitated phases. We report an increasing dependence of the activation energy on the conversion degree, the values obtained being within the range reported in the literature.

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Abstract  

The radioisotope18F with a half-life of 110 min is produced in order to determine fluorine and oxygen by γ photon or charged particles activation. This radioisotope is a β+ emitter and must be separated from other radioisotopes produced from the analysed matrix. The separation was achieved by fixation of fluorine on a plombo-stronsic hydroxyapatite, prepared by synthesis in aqueous medium. Studies of the distribution of radioactive fluorine between the apatite and solutions of variable compositions, showed the optimal conditions, for the separation from the following metals: Al, Mg, Fe, Mo and from the Al−Mg alloy. The separation was applied to the determination of fluorine by γ irradiation and of oxygen by3He irradiation. Due to the great selectivity of this separation, radiochemically clean fluorine is obtained and the limit of detection is lowered.

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. For non-isothermal treatments, the area of the peak of the derivative is related with the transformed phase fraction, as already demonstrated by Luiggi et al. [ 9 ] in the study of β′ and β phases precipitation of Al–Mg alloys. The length

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Al–Mg alloy studied by DSC and TEM . Acta Mater 1998 46 : 3381 – 3397 10.1016/S1359-6454(98)00053-6 . 46. Ozawa , T . Kinetics of non-isothermal crystallization . Polymer . 1971

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