The structural behavior of Al3+ in peralkaline melts and glasses in the system Na2O-Al2O3-SiO2

The structural behavior of Al3+ in peralkaline glasses and melts along the Na2Si3O7-Na-2(NaAl)(3)O-7 join has been examined to 1200degreesC at ambient pressure with Si-29 MAS NMR and Raman spectroscopy. The distribution of Al3+ among coexisting Q(4), Q(3), and Q(2) structural units in the glasses and melts was determined as a function of bulk Al/(Al+Si) and temperature. The Al3+ resides principally in Q(4) structural units, which contain more than 70% of the total amount of Al3+. The Q(2) units contain the smallest amount of Al3+ among the Q(4), Q(3), and Q(2) structural units. There is no evidence for temperature-dependent distribution of Al3+ among the coexisting structural units at least to 1100-1200degreesC.