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.
Authors:M. Fedoroff, L. Debove, and Ch. Loos-Neskovic
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.
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–Mgalloys.