Surface and bulk crystallization in Nd2O3–Al2O3–SiO2–TiO2 glasses

Neodymium aluminosilicate (Nd2O3–Al2O3–SiO2; NdAS) glasses have been investigated for the effect of concentration of TiO2 on the crystallization mechanism and for the effect of surface condition on crystal growth. NdAS glasses with 0–10 wt.% TiO2 were heat-treated for nucleation and crystal growth and were examined for phase separation and morphology of surface crystals as well as for crystal growth rate. All the glasses exhibit surface crystallization, however, the glass having 8 wt.% TiO2 also exhibits internal crystallization after a two-stage heat treatment. Surface crystallization was dependent on the condition of the glass surface and the amount of TiO2. The crystal growth on the cut surface was faster than on the fractured surface and the growth rate in surface increased with increasing TiO2. The phase separation found in NdAS glasses containing above 8 wt.% TiO2, was confirmed to be an important factor controlling the internal crystallization process in Nd2O3–Al2O3–SiO2–TiO2 glasses.