Thermal decomposition of Np(IV) and Pu(III, IV) oxalates

Reaction mechanisms of the thermal conversion of Pu(IV) oxalate into plutonium oxide

“…Under air, the transitory reduction of Pu(IV) into Pu(III) is for the first time established directly by structural analysis of the solid intermediates: the Pu(III) intermediates are mixed oxalate-carbonate structures, confirming previous hypotheses of Rao et al [3], and not anhydrous Pu(III) oxalate as sometimes described [2,[6][7][8]. The UV-vis spectra of the first solid intermediates after dehydration of the Pu(IV) oxalate highlight indeed a total and quite durable reduction of the Pu(IV) to Pu(III).…”

“…However, the structure of the intermediates during the oxalic conversion of Pu(IV) into oxide is often speculative and the reaction mechanisms are quite misunderstood and divergent from one study to another [2][3][4][5][6][7][8]. This work deals with a detailed structural investigation on the main solid intermediates formed when calcining Pu(IV) oxalate into oxide under air or argon.…”

Quantitative Microstructural Characterization of Plutonium Oxalate Auto‐Degradation and Evidence for PuO2 Nanocrystal Formation

“…Plutonium oxalates have been observed to change color over the course of months [5a] and lose weight, depending on the aging environment, in some cases. [5a,6a] There is some evidence that both plutonium (III) and (IV) oxalates age to form the same decomposition product(s), [6a,7] and it has been hypothesized these oxalates transform into carbonates, [8] oxycarbonates, [6b,d,9] oxides or a mixture of carbonates and oxyoxalates, [6a] though the aging process may take years to reach a persistent chemical phase. [6a,b,7,9] Inconsistencies become more apparent when reviewing studies of the oxidation state of Pu throughout the aging process.…”

“…[6a,b,7,9] Inconsistencies become more apparent when reviewing studies of the oxidation state of Pu throughout the aging process. Reports can be found claiming the Pu oxidation state in decomposing plutonium (IV) oxalate either does not change [6b] or changes to Pu(III), [8] at least temporarily, before eventually returning to Pu(IV). [6a,c,9] A summary of previously reported optical spectra for relevant Pu-containing species is provided in Table 1.…”

Technical Basis for Doe Standard 3013 Equivalency Supporting Reduced Temperature Stabilization of Oxalate-Derived Plutonium Oxide Produced by the Hb-Line Facility at Savannah River Site

“…Early work is summarized in Cleveland (1979). Subsequent studies have added information on the decomposition steps by using techniques such as infrared spectroscopy to identify reaction intermediates Karelin et al, 1990;Vigier et al, 2007).…”