Glass structure and crystallization via two distinct thermal histories: Melt crystallization and glass crystallization

This study focuses on the effect of structural inhomogeneity of 44.4CaO-33.2SiO(2)-8.8Na(2)O-6.2Al(2)O(3)-7.4B(2)O(3) glass on its crystallization behavior. The crystallization behavior of the investigated lime-sodium aluminoborosilicate glass system is explored for the two thermal histories of melt crystallization and the heat treatment of quenched glass. The results show that sodium melilite (CaNaAlSi2O7) and larnite (beta-Ca2SiO4) are the dominant crystalline phases during heating (glass crystallization) and cooling (melt crystallization), respectively. In the glass structure from the heat treatment at 610 degrees C, both Si2O7 and AlO4 units (i.e., four-coordinated Al) are dominant. This may induce sodium melilite (CaNaAlSi2O7) crystallization, connecting Si2O7 and AlO4 units with O and linking Ca and Na between interlayers. The melt structure, meanwhile, has more SiO4 and AlO6 units in its silicate and aluminate. Therefore, larnite (beta-Ca2SiO4) crystallizes on cooling by combining SiO4 units and Ca. The crystallization behavior is further discussed considering the inhomogeneity structure of supercooled liquids before nucleation.