CRYSTALLIZATION OF LI2O.AL2O3.6SIO2 GLASSES CONTAINING NIOBIUM PENTOXIDE AS NUCLEATING DOPANT

Niobium pentoxide (T form, orthorhombic system) was utilized to promote devitrification in Li2O.Al2O3.6SiO2 glasses. Two or more mole percentage of this nucleating dopant enhanced crystallization in these glasses. Glasses containing 4.0 and 8.0 mol% T-Nb2O5 exhibited a high tendency to form dispersed TT-Nb2O5 (monoclinic system) precipitates during the glass quenching process. The crystallization process in glasses containing 2.0 or 4.0 mol% T-Nb2O5 occurred as microphase separation, followed by the formation of dispersed TT-Nb2O5 crystalline precipitates (760-degrees-C), followed by beta-quartz solid-solution (ss) formation (850-degrees to 900-degrees-C) heterogeneously nucleated from the precipitates. beta-quartz(ss) transformed to beta-spodumene(ss), along with a polymorphic transition from the TT-Nb2O5 to M-Nb2O5 (tetragonal system) crystalline phase.