Plutonium Chemistry. From: Chemistry of actinides Nuclear properties and isotope production Pu in nature Separation and Purification Atomic properties Metallic state Compounds Solution chemistry. Pu nuclear properties. Isotopes from 228≤A≤247 Important isotopes 238 Pu
Fig. 7.117 Oxidation state distribution diagram showing the predominant oxidation state of
plutonium in 1 M (H,Na)ClO4 solution as a function of pH and (a) average oxidation state
Pu(IV), and (b) average oxidation state Pu(V)
Fig. 7.118 Kinetics for disproportionation of plutonium in 1 M (H,Na)ClO4 solution at
(a) pH 1 and average oxidation state Pu(IV), and (b) pH 3 and average oxidation state
Pu(V) (calculations courtesy of T. W. Newton of Los Alamos).
Plutonium exhibits six different crystallographic phases at ambient pressure (it has a seventh phase under pressure). In addition, unlike most metals, plutonium contracts on melting. Transformations to different crystal structures occur readily and are accompanied by very large volume changes. Aluminum expands monotonically on heating in the solid phase, and it also expands on melting. The dashed lines show that thermal contraction on cooling the liquid (L) phase of plutonium extrapolates to that of the β-phase; the thermal contraction on cooling the ε-phase extrapolates to that of the γ-phase.
Plutonium is notoriously unstable under almost any external disturbance. Over a span of only 600°, it exhibits six different allotropic phases with large accompanying volume changes before it melts. Pressures on the order of kilobar (100 megapascals) are sufficient to squeeze out the high-volume allotropes (Morgan 1970). Small chemical
additions can stabilize these high-volume phases.