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Thermal and X-ray diffraction analysis studies during the decomposition of ammonium uranyl nitrate

“…Halldal and Sorensen [14] observed that the decomposition of AUC thermally under a hydrogen atmosphere up to 400 °C, resulted in the production of UO 3 (H 2 O) 0.15 , which is amorphous hydrated urania. Govindan [16] reported that an amorphous UO 3 (H 2 O) x was produced due to the loss of ammonia and thermal disassembly of carbonate oxy-anion during the thermal decomposition of AUC. It was found in this study, through an X-ray diffraction analysis, that the amorphous UO 3 was crystallized into α-UO 3 , β-UO 3 and γ-UO 3 at 480 °C under the nitrogen and air atmospheres, and at 430 °C under a hydrogen atmosphere, respectively, yet no weight loss took place as shown by the TG curve.…”

Uranyl ammonium carbonate precipitation and conversion into triuranium octaoxide

“…Several studies have reported similar evidence for the formation of intermediate compounds during the decomposition of UO 3 to U 3 O 8 . Previous studies [ 24 , 40 , 41 ], investigated the transformation of UO 3 into U 3 O 8 in a nitrogen environment and found that the amorphous phase of UO 3 crystallizes into α-UO 3 before it decomposes into U 3 O 8 . The crystallization of amorphous UO 3 into α-UO 3 occurs in the temperature range of 400–480 °C, while the reduction of UO 3 into U 3 O 8 occurs at 490–600 °C.…”

“…To the best of our knowledge, there is only one study on AUC precipitation from a UO 2 F 2 solution [ 22 ], whereas several studies have reported the precipitation of AUC from uranyl solutions [ [23] , [24] , [25] , [26] ]. Therefore, the objective of this study was to optimize AUC precipitation from the UO 2 F 2 +HF precursor solution to obtain a highly pure AUC precipitate of free ammonium uranyl fluoride (AUF).…”