Study of the effect of the nature of the alkali and alkaline earth ions on the structure of a containment glass rich in rare earths

This work presents the progresses of the PhD thesis of Arnaud Quintas in 2006. It is devoted to the study of a rare earth alumino borosilicate glass, which molar composition is 61,81 SiO2 - 3,05 Al2O3 - 8,94 B2O3 - 14,41 Na2O - 6,33 CaO - 1,90 ZrO2 - 3,56 Nd2O3, and envisaged for the immobilization of nuclear wastes originating from the reprocessing of high discharge burn up spent fuel. From a structural viewpoint, has been investigated the role of the modifier cations on the arrangement of the glass network through different modifications of the glass composition: variation of the Na/Ca ratio and modification of the nature of the alkali and alkaline earth cations. The NMR and Raman spectroscopic techniques were useful to determine the distribution of modifier cations among the glass network and also to cast light on the competition phenomena occurring between alkali and alkaline earth cations for charge compensation of [AlO4]- and [BO4]- species. The neodymium local environment could be probed by optical absorption and EXAFS spectroscopies which enabled to better understand the insertion mode of Nd3+ ions among the silicate domains of the glass network. Concerning the crystallization behavior, has been examined how the glass composition may influence the crystallization processes and especially the formation of the apatite phase of composition Ca2Nd8(SiO4)6O2. (author)