Comparative Roles of Al³⁺ and Fe³⁺ Ions for Network Construction in Sodium Silicate Melts

抄録

The Raman spectra of Na₂O–Al₂O₃–SiO₂ system with different Al₂O₃contents (up to 25 mol%) and with Na₂O/SiO₂ratio from 1 to₂have been measured at 1 673 K.
In the disilicate systems, the Raman spectra do not change significantly with increasing of Al₂O₃ content except the development of the 500 cm^-1 band which is assigned to the three-dimensional network structural unit consisted of Si⁴⁺ and Al³⁺ ions. Also it is found that Al³⁺ ions possibly interact with monomers and form three-dimensional structures.
In the metasilicate systems, intensities of 950 and 850 cm^-1 bands gradually decrease while that of 1 100 cm^-1 band increases with the increase of Al₂O₃ content. According to the following equilibrium reaction in the metasilicate composition,

^-O–Si–O^- (chain-like unit)↔Si–O ^2-(monomer) + ^-O–Si–O⁰ (sheet-like unit)

it is confirmed that Al³ ions in the metasilicate systems do not interact with the polymerized silicate anions, such as chain-like or sheet-like structural units. On the other hand, it has a high tendency to interact with SiO₄⁴⁻ and construct three-dimensional network units involving Al³⁺ and Si⁴⁺ ions randomly. So it is ob-viousthat the role of Al³⁺ ions for constructing the network structure is found to be quite different from that of Fe³⁺.