The insertion of magnesium into α-U 3O 8

Abstract

The chemical and electrochemical insertion of magnesium into α-U 3O 8 was achieved at ambient and elevated temperatures with the topochemical formation of a product Mg x U 3O 8 (0< x<0.65). Galvanometric discharges in both non-aqueous and aqueous cells show the existence of two single phase regions at 0.20≤ x≤0.27 and x≥0.40. These regions shifted to higher x-values when the discharge was performed at 100°C with DMF as the electrolyte solvent. A fcc phase ( a ≈ 5.42 Å) was identified in the cathodic products when cells were discharged beyond x ≈ 0.65. This could be related to the known high temperature fluorite phase Mg x U 1− x O 2± y . Equilibrium potential measurements were made to determine the integral free energy of magnesium insertion. Kinetic measurements showed magnesium diffusivity in Mg x U 3O 8 to be three to four orders of magnitude less than that for lithium in the compound Li x U 3O 8.