Structures of Molten Silicate and Aluminosilicate Slags
Yasushi SASAKI, Kuniyoshi ISHII
Molten silicate and aluminosilicate slag structures have been reviewed based on the recent experimental results measured by such as Raman spectroscopy, high temperature NMR, high temperature X ray analysis. The structures of these melts discussed in this review may be summarized as follows:
The anionic structure of alkali and alkaline earth oxide-silica binary melts can be considered a mixture of a small number of coexisting anionic units. In terms of stoichiometric expression, these units are described as SiO4-4, Si2O6-7, SiO2-3, Si2O2-5 and SiO2 units. High temperature NMR studies have made it clear that the structures of anionic units are not lasting, but exchange their structures each other very rapidly at high temperature.
The structure of aluminosilicate melts is consistent with tetrahedrally coordinated Al3+ provided that there is a sufficient supply of metal cations for electrical charge-balance. Electrical charge-balanced alkali aluminosilicate melts consist of three-dimentionally interconnected 6-membered rings of Si and Al tetrahedral units that mix randomly. Electrical charge-balanced alkaline earth aluminosilicate melts probably consist of mixtures of three-dimentionally interconnected rings with no Al3+ (six-membered SiO2-ring), rings with Al/Si = 1(four-membered Al2Si2O2-8 rings) and rings with no Si4+ (six-membered AlO2- ring).
In most Fe bearing silicate melts, ferrous iron is a network modifier (octahedral coordination) while ferric iron works both as a network former (tetrahedral coordination) and as a modifier depended on the slag compositions. Melts along the Na2SiO3-NaFeSi2O3 (acmite) joins become progressively more polymerized as Fe3+ content of the system increases and the end component of acmite melts has a three dimensional network structure.
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