DEPENDENCE OF CRYSTALLIZATION BEHAVIOR OF SODIUM DIBORATE (NA2O-CENTER-DOT-2B(2)O(3)) ON ITS GLASS STRUCTURE AND THE CHARACTERISTICS OF PHASE-TRANSFORMATION

The crystallization and phase transformation of glassy Na2O.2B(2)O(3) have been studied by X-ray diffraction, infrared spectroscopy, thermal analysis, and density measurement. By employing proper thermal treatment methods, three metastable and two relatively stable polymorphs of Na2O.2B(2)O(3) are obtained, as well as two other compounds, Na2O.B2O3 and 2Na(2)O.5B(2)O(3). The possible structural groups of these phases are deduced, which are found to be similar to that existing in the glass. Current glass models which imply the existence of structural ''granularity'' satisfactorily describe the crystallization behavior. The phase transformation is observed to depend not only on temperature, but also on the density of the phase.