Jean Mahenc

Formation of corrosion-resistant layers by electrodeposition of refractory metals or by alloy electrowinning in molten fluorides

The electrolytic treatment of less resistant metals such as iron, copper and nickel with tantalum or niobium has been carried out in K2TaF7-LiF-NaF or K2NbF7-LiF-NaF solutions in the 550 to 1050°C temperature range. Two kinds of experiments have been used.(i)At lower temperatures, electroplating with pure tantalum and niobium on inert cathodes was performed. The electrodeposition mechanism of each metal was studied and coherent electroplates were prepared which were tested in electrocatalytic applications.(ii)At higher temperatures (850–1050°C), using nickel cathodes, intermetallic compounds were obtained at more positive potentials than that for pure electrodeposition (Ta2Ni, TaNi, TaNi2, TaNi3, NbNi, NbNi3). The electrowinning of stable TaNi3 and NbNi3 layers was carried out by the metalliding process which makes these materials resistant to corrosion in various media. Further, a study of the kinetics of growth of the diffusion layer allowed a diffusion parameter to be determined which was in agreement with other results obtained by conventional methods.

Mise en régime des colonnes de thermodiffusion gravitationnelle—I Méthode de calcul numérique

Resume On reprend une idee de Grew et Ibbs pour decrire le fonctionnement des colonnes de thermodiffusion gravitationnelle, et on propose une methode de calcul de la mise en regime. Cette methode fait intervenirachaque niveau de la colonne lesechanges de matiere par convection, par effet Soret et par diffusion. Les calculs peuventeˆtre effectuesapartir desequations theoriques du transfert, ou mieux,apartir de donnees experimentales.