Speaker
Prof.
Karin Popa
("Al.I. Cuza" University, Department of Chemistry)
Description
Data on structure and properties of actinide phosphates are needed for the development of phosphate ceramics envisaged as possible hosts for long-term sequestration of actinides generated by the nuclear fuel cycle. In that aim an extensive study on the crystal structures, thermal stability, and thermodynamic properties on a number of crystalline trivalent and tetravalent actinide phosphates was undertaken.
PuPO4 with monazite structure was obtained and characterized in terms of thermal stability and thermal expansion. The decomposition of PuPO4 to Pu2O3 was observed at 1573 K. Its high-temperature heat capacity is to be measured up to 1500 K by drop calorimetry.
MIINp(PO4)2 (MII= Ca, Sr, Ba) were obtained by solid state reaction. The influence of ionic radius of MII (MII= Ca, Sr, Ba) on the crystal structure is further discussed. Pure phase of CaNp(PO4)2 with monazite structure (P2/n) was obtained by solid state reaction after several thermal treatments and readjustments in stoichiometry. The lattice parameters are a= 6.65085(3) Å, b= 6.83893(5) Å, c= 6.35378(3) Å, and β= 104.117(9) o. SrNp(PO4)2 seems to adopts an inedited double-monazite structure with a= 6.895 Å, b= 13.272 Å, c= 6.892 Å, and β= 99.22 o, probably due to the Sr/Np ordering responsible for the non-negligible reflections with k = 2n +1; in this case, the two cations seem too different in size to allow disorder, contrarily with CaNp(PO4)2. Pure BaNp(PO4) with monoclinic C2/c was also obtained. Its structure was inferred with the one reported for RbEu(SO4)2, the lattice parameters being a= 12.69095(13) Å, b= 5.36179(6) Å, c= 9.40949(11) Å, and β= 102.516(68) o. The pattern looks similar with the one previously found for the Th-counterpart.
Primary author
Prof.
Karin Popa
("Al.I. Cuza" University, Department of Chemistry)
Co-authors
Prof.
Damien Bregiroux
(UPMC Univ. Paris 06, CNRS-UMR 7574, ENSCP- ParisTech, Laboratoire de Chimie de la Matiere Condensee de Paris, 11 rue Pierre et Marie Curie, 75231 - Paris Cedex 05, France)
Prof.
Gilles Wallez
(UPMC Univ. Paris 06, CNRS-UMR 7574, ENSCP- ParisTech, Laboratoire de Chimie de la Matiere Condensee de Paris, 11 rue Pierre et Marie Curie, 75231 - Paris Cedex 05, France)
Dr
Philippe E. Raison
(European Commission, Joint Research Centre, Institute for Transuranium Elements, P.O. Box2340, 76125 - Karlsruhe, Germany)
Dr
Rudy J.M. Konings
(European Commission, Joint Research Centre, Institute for Transuranium Elements, P.O. Box2340, 76125 - Karlsruhe, Germany)
