THE INFLUENCE OF THE STRUCTURAL COMPACTNESS AT A SUB-NANOMETRIC SCALE ON SOME GLASS PROPERTIES OF THE Na2O-Al2O3-B2O3 SYSTEM

In the Na2O-Al2O3-B2O3 system, six glasses were synthesized having the (35-x) Na2O center dot xAl(2)O(3)center dot 65B(2)O(3) molar composition, where x = 0; 5; 10; 12.5; 15; 17.5. For these synthesized glasses the following physical properties were measured: density; refractive index; linear thermal expansion coefficient; glass transition temperature. The structural compactness, the molar volume and the volume of oxygen ion, considered as structural characteristics for the first level of analysis (atomic), at a sub-nanometric scale, were also calculated. The correlation analysis of the properties indicated that these structural characteristics, even at this atomic level, sub-nanometric, influence the physical properties considered at a macroscopic scale. Moreover, the dependency graphs show a series of particular points (return points) that suggest structural transformation areas generated by the [BO3] -> [BO4] and [AlO6] -> [AlO4] transformations, according to the chemical composition of the glasses.