Thermal decomposition of tetravalent and trivalent plutonium oxalates

Abstract

Using a Kurnakov registering pyrometer, we investigated the thermal decomposition of tetra- and trivalent plutonium oxalates. The composition of the intermediate products was determined with a Berg gas burette, by potentiometric titration and by Penfild's method. It was established that freshly precipitated Pu (IV) oxalate lost three molecules of water at 110 ° C. After standing for 3–4 days at 110 ° C the oxalate also gave 1.5–2.7% of CO+CO₂ due to decomposition induced by the α-radiation of the plutonium. At the same time partial reduction to trivalent plutonium occurred. In the temperature range 170–200 ° C two more molecules of water and 13% CO+CO₂ were liberated and the plutonium was reduced to the trivalent state to form mainly Pu₂(C₂O₄)₃H₂O; at 380 ° the oxalate was converted to plutonium dioxide. At 140 ° Pu (III) oxalate was completely dehydrated and at 270 ° C in air it was converted to plutonium dioxide. In an inert medium at 330 ° C the oxalate decomposed to give oxalate-carbonate. At 460 ° C the oxalate-carbonate decomposed and the trivalent plutonium was oxidized to the tetravalent state with the formation of the dioxide.