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Tris-2,2′-bipyridine complexes of Co(II), Ni(II), and Fe(II) and a bis-2,2′,2″-terpyridine complex of Co(II) in aqueous perchlorate media were studied by means of electrode double-layer capacitance measurements at the hanging mercury drop electrode. At potentials where no faradaic process takes place all compounds form two types of compact films with different orientations of species at the interface. The solid-like nature of these films was confirmed from the hysteresis of capacitance vs. potential curves and from the sigmoidal Avrami-type capacitance vs. time dependence. As a new feature of the nucleation/growth process, long-time deviations from the Avrami shapes were found. At potentials where the nucleation rate is very small, the C—t curves exhibit an S-shape, followed by a maximum usually at time s $ 1000 s. An interpretation in terms of a change from 2D- to 3D-type growth is suggested.

The rate of disproportionation of uranium(V) was studied at a hme using single sweep and cyclic voltammetry in sulphate solutions at an almost constant ionic strength (I = 1.2-1.0 mol1−1) as a function of pH and concentration of uranium(VI). The rate constant of disproportionation of uranium(V) in 0.4 M Na2SO4 recalculated for the activity of hydrogen ion equal unity is k0 = 6.3 × 105 mol−212s−1. Also standard rate constants ks were determined. In preliminary dc polarography experiments in other complexing media as citrate, tartarate and oxalate a higher increase of the limiting current than in sulphate was found for the same pH values pointing to the assumption that in these media the disproportionation reaction of uranium(V) might proceed still faster than in sulphate solutions.

Die Geschwindigkeit der Disproportionierung von U(V) in U(VI) und U(IV) in 0.4 M NazSOrLosung wird in Abhangigkeit vom pH bestimmt.