Vitrification and crystallization of barium aluminosilicate glass ceramics from zeolite precursors

Barium ion exchanged zeolite powders were used as precursors for the formation of a barium aluminosilicate glass which were then crystallized to form celsian (BaAl2Si2O8) glass ceramics. Three powder formulations were examined: a barium exchanged zeolite; a barium plus lithium exchanged zeolite; and a barium plus lithium exchanged zeolite seeded with monoclinic celsian crystals. Heat treatment of the zeolite powders between 610 and 630 degrees C resulted in the collapse of the open framework structure to form a glass which then crystallized between 1000 and 1100 degrees C to the hexagonal polymorph of celsian, hexacelsian. The vitrification and crystallization kinetics were studied by using various heating rates with the differential thermal analyzer (DTA). The activation energy for the vitrification transformation was found to be 183 +/- 6 kJ/mol with a frequency factor of 6.4 +/- 3.8 x 10(8) s(-1). For crystallization, the activation energy and frequency factor were found to be 490 +/- 15 kJ/mol and 1.6 +/- 0.5 x 10(18) s(-1), respectively. The activation energies are similar to those reported for melt quenched glasses. The addition of lithium or seeds did not affect any of the kinetic data.