  An aluminoborosilicate glass, containing high amount of rare earth (RE)
accordingly to the following composition 50.68 SiO2 - 4.25 Al2O3 - 8.50 B2O3 -
12.19 Na2O - 4.84 CaO - 3.19 ZrO2 - 16.35 RE2O3 (wt.%), is currently under
study for the immobilization of nuclear waste solutions. In this work, we
wanted to investigate the effect of changing the RE cation type on the glass
structure and on its crystallization behavior. For this purpose, a glass series
was elaborated in which the nature of the RE is varying from lanthanum to
lutetium. In this glass series, only little effect was observed on the glass
structure. On the contrary, a strong impact was put in evidence on the
crystallization behavior through different heat treatments. A slow cooling of
the melt at 1^/circC/min, revealed significant crystallization of apatite
Ca2RE8(SiO4)6O2 in sample containing rare earths with ionic radii close to that
of calcium. Another heat treatment consisting of successive nucleation and
growth stages, performed to force the crystallization in the bulk and reduce
any surface crystallization effect, put in evidence the existence of a strongly
heterogeneous second rare earth rich silicate phase for samples containing RE
with low ionic radius (from Y to Lu).
