Abstract
Multi-component silicate glasses containing alumina and alkaline earth metal oxides have been used for optical glasses. In these glasses competitive reactions between various kinds of network-forming and network-modifying oxides occur, so that it is effective to differentiate these reactions in terms of an acid-base concept. In this report the reactivities of alkali or alkaline earth oxide with P2O5, Al2O3, B2O3 and SiO2 are discussed based on the result of high-resolution solid state NMR. In alkali aluminoborosilicate glasses the population of four-coordinated boron atom, N4 are expressed well by r/(1-r). However, in the case of alkaline earth aluminoborosilicate glasses, the deviation from the line of r/(1-r) increases in the order of BaO<SrO<CaO<MgO, where r=([M2O] or [MO]-[Al2O3])/([M2O] or [MO]-[Al2O3]+[B2O3]). Alkaline earth oxide reacts with Al2O3 first. Subsequently, residual one reacts with B2O3 or SiO2. Weak base such as MgO reacts mainly with weak acids such as SiO2 rather than B2O3. On the other hand, a strong base such as BaO reacts mainly with B2O3. The equilibrium constant of the reaction, Si (Q3)+B(Q3)=Si(Q4)+B(Q4), can be determined. When K2O and CaO are contained in aluminoborosilicate glasses, it is possible to predict the distribution of the structural units by using the equilibrium constant of individual basic oxide.
