Studies of the effect of paramagnetic impurity in the structure of sodium disilicate glass

Magic angle spinning nuclear magnetic resonance (MAS NMR) is used to measur e the Si-29 chemical shift and full width at half maximum in Na2O . 2SiO(2) . xMnO for 0.0 less than or equal to x less than or equal to 0.8 glasses. T he large space varying magnetic field of the paramagnetic centers increases the line width and moves the chemical shift to a lower frequency, i.e. mor e shielded, with the increase of Mn++. The T-1 relaxation time falls rapidl y and the relaxation rate is shown to be proportional with the concentratio n of MnO. The differential thermal analysis (DTA) results show that the gla ss transition temperature, T-g, crystallization temperature, T-x, and liqui dus temperature T-L do not change due to addition of MnO. This suggests tha t Mn++ does not form chemical bond with the network. However, the Mn++ acts as nucleating agent and enhances the crystallization and the rate of cryst allization can be tailored by judicious choice of the amount of MnO. (C) 20 00 Kluwer Academic Publishers.