title: Synthesis and characterisation of the uranium pyrochlore betafite [(Ca,U)₂(Ti,Nb,Ta)₂O₇].
abstract: Betafite of composition [(Ca,U)2(Ti,Nb,Ta)2O7] was prepared via a solid state synthesis route. The synthesis was shown to be sensitive to initial reactant ratios, the atmosphere used (oxidising, neutral, reducing) and time. The optimum conditions for the synthesis of betafite were found to be heating the reactants required at 1150°C for 48 h under an inert gas atmosphere. XRD characterisation revealed that the synthesised betafite contained minor impurities. EPMA analysis of a sectioned surface showed very small regions of Ca-free betafite on grain boundaries as well as minor rutile impurities. Some heterogeneity between the Nb:Ta ratio was observed by quantitative EPMA but was generally within the nomenclature requirements stated for betafite. SEM analysis revealed the synthesised betafite was comprised mostly of hexaoctohedral crystals of ∼ 3 μm in diameter. XPS analysis of the sample showed that the uranium in the synthesised betafite was predominately present in the U(5+) oxidation state. A minor amount of U(6+) was also detected which was possibly due to surface oxidation.
authors.affiliation: Centre for Advanced Materials and Industrial Chemistry, School of Applied Sciences RMIT University, GPO Box 2476, Melbourne, Vic 3001, Australia.
authors.forename: Scott A
authors.initials: SA
authors.lastname: McMaster
authors.affiliation: Centre for Advanced Materials and Industrial Chemistry, School of Applied Sciences RMIT University, GPO Box 2476, Melbourne, Vic 3001, Australia.
authors.forename: Rahul
authors.initials: R
authors.lastname: Ram
authors.affiliation: Centre for Advanced Materials and Industrial Chemistry, School of Applied Sciences RMIT University, GPO Box 2476, Melbourne, Vic 3001, Australia.
authors.forename: Fiona
authors.initials: F
authors.lastname: Charalambous
authors.affiliation: CSIRO Process Science and Engineering, Bayview Avenue Clayton, Victoria 3168, Australia.
authors.forename: Mark I
authors.initials: MI
authors.lastname: Pownceby
authors.affiliation: Centre for Advanced Materials and Industrial Chemistry, School of Applied Sciences RMIT University, GPO Box 2476, Melbourne, Vic 3001, Australia.
authors.forename: James
authors.initials: J
authors.lastname: Tardio
authors.affiliation: Centre for Advanced Materials and Industrial Chemistry, School of Applied Sciences RMIT University, GPO Box 2476, Melbourne, Vic 3001, Australia. Electronic address: suresh.bhargava@rmit.edu.au.
authors.forename: Suresh K
authors.initials: SK
authors.lastname: Bhargava
mesh_terms: D017610:Calcium Compounds / Q000138:chemical synthesis*; D009556:Niobium / Q000737:chemistry*; D010087:Oxides / Q000138:chemical synthesis*; D056951:Photoelectron Spectroscopy; D011850:Radioactive Waste; D013635:Tantalum / Q000737:chemistry; D014025:Titanium / Q000737:chemistry; D014501:Uranium / Q000737:chemistry*
chemical_list: D017610:Calcium Compounds; D010087:Oxides; D011850:Radioactive Waste; D009556:Niobium; C016709:pyrochlore; D014501:Uranium; D013635:Tantalum; D014025:Titanium
keywords: Betafite, Pyrochlore; SYNROC; Uranium immobilization