CHARACTERIZATION AND STRUCTURAL DEVELOPMENTS OF GEL-DERIVED BOROSILICATE GLASSES - A MULTINUCLEAR MAS-NMR STUDY

Twelve different homogeneous sodium borosilicate glasses were prepared by the alkoxide-gel method. To study the development from the dried g el to the glass and the structure of the final product, after annealin g at various temperatures B-11, Si-29, H-1 and Na-23 MAS-NMR methods h ave been applied in a magnetic field of 7 T. Chemical shifts and quadr upole parameters have been measured and related to the structure. Cond ensation, copolymerization and removal of hydrogen-containing groups h ave been observed. With one exception where phase separation occurred, all the glasses appeared to be homogeneous. In contrast to molten gla sses, they have been modeled by a uniform distribution of copolymerize d SiO4, BO3 and BO4 polyhedra. Relationships between the isotropic che mical shifts and the composition of the materials have been obtained.