Surface area changes during the calcination of ammonium uranate

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dc.contributor.authorWoolfrey, JLen_AU
dc.date.accessioned2007-11-22T04:24:14Zen_AU
dc.date.accessioned2010-04-30T04:36:04Zen_AU
dc.date.available2007-11-22T04:24:14Zen_AU
dc.date.available2010-04-30T04:36:04Zen_AU
dc.date.issued1974-09en_AU
dc.description.abstractThe changes in specific surface area observed during the calcination of ammonium uranate in various atmospheres have been studied using constant rate of heating, isothermal and isochronal experiments. X-ray diffraction, thermogravimetric analysis (TGA) and differential thermal analysis (DTA) results have been used to correlate these changes with the stages of reaction which occur during the calcination. During dehydration (20 to 200ºC) AU 'Type II' remains the major phase. Thermal decomposition (200 to 350ºC) produces amorphous U03 and 3-U03 which retain ammonia in their structure. These are subsequently converted to U308 by a self-reduction process (350 to 450ºC). Reduction in a hydrogen atmosphere takes place between 450 and 510ºC to produce U02. In an inert gas or air atmosphere 3-UO and UO persist to much higher temperatures, and the presence of an oxidising atmosphere may completely eliminate the self-reduction reaction. The observed specific surface area increases during dehydration and decomposition and reaches a maximum between 400 and 450ºC. The major increase in the surface area is attributed to the opening up of internal porosity, formed during decomposition, by stress-induced cracking of the particles. The internal stresses are generated by the nucleation and growth of phases which have different specific volumes from that of the parent solid. The maximum surface area was observed if self-reduction occurred. The observed decrease in specific surface area at higher temperatures is due to sintering.en_AU
dc.identifier.citationWoolfrey, J. L. (1974).Surface area changes during the calcination of ammonium uranate (AAEC/E329). Lucas Heights, NSW: Australian Atomic Energy Commission.en_AU
dc.identifier.govdoc542en_AU
dc.identifier.isbn0642996520en_AU
dc.identifier.otherAAEC-E-329en_AU
dc.identifier.placeofpublicationLucas Heights, New South Walesen_AU
dc.identifier.urihttp://apo.ansto.gov.au/dspace/handle/10238/532en_AU
dc.language.isoen_auen_AU
dc.publisherAustralian Atomic Energy Commissionen_AU
dc.subjectAmmonium compoundsen_AU
dc.subjectUranatesen_AU
dc.subjectCalcinationen_AU
dc.subjectX-ray diffractionen_AU
dc.titleSurface area changes during the calcination of ammonium uranateen_AU
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