Crystallization of lanthanum and yttrium aluminosilicate glasses

The crystallization behaviour of aluminosilicate glasses of lanthanum (LAS) and yttrium (YAS) containing 2–8 mol% of Ln₂O₃ (Ln = La or Y), 12–30 mol% of Al₂O₃, and 64–80 mol% of SiO₂ has been studied by DTA, XRD and SEM-EDX analysis. X-ray diffraction results indicate the presence of the mullite phase and La₂Si₂O₇ in the monoclinic high-temperature G form (group space P2₁/c) for the LAS glasses, and mullite y-Y₂Si₂O₇ in the monoclinic structure (group space C2/m) and a small amount of β-Y₂Si₂O₇ in the orthorhombic structure (space group Pna2) for the YAS. For both cases, very little tridymite phase is observed. The results also show that the values of T_g for YAS are higher than those for LAS glasses. The crystallization of LAS glasses is more difficult than that of YAS. For all samples, we observed only one kind of mullite (Al/Si = 3.14).