The Raman spectra of Na
2O–Al
2O
3–SiO
2 system with different Al
2O
3contents (up to 25 mol%) and with Na
2O/SiO
2ratio from 1 to
2have been measured at 1 673 K.
In the disilicate systems, the Raman spectra do not change significantly with increasing of Al
2O
3 content except the development of the 500 cm
-1 band which is assigned to the three-dimensional network structural unit consisted of Si
4+ and Al
3+ ions. Also it is found that Al
3+ 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 Al
2O
3 content. According to the following equilibrium reaction in the metasilicate composition,
-O–Si–O
- (chain-like unit)↔Si–O
2-(monomer) +
-O–Si–O
0 (sheet-like unit)
it is confirmed that Al
3 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 SiO
44− and construct three-dimensional network units involving Al
3+ and Si
4+ ions randomly. So it is ob-viousthat the role of Al
3+ ions for constructing the network structure is found to be quite different from that of Fe
3+.
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