酸化物ガラス及び融液の化学反応と塩基度概念による評価の研究 : 多成分ケイ酸塩ガラスの NMR

抄録

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.