The Al₂O₃-Sio₂ System: Logical Analysis of Phenomenological Experimental Data

Abstract

Presence or absence of (αAl₂O₃ as a source of Al₂O₃ molecules in the starting materials used for determining the phase equilibria in the SiO₂/Al₂O₃ system is shown to be responsible for reported differences in phase diagrams. Equilibrium amounts of Al₂O₃ molecules dissolved in alumino-silicate liquids from αAl₂O₃ as a source are determined by the bond strength of the source. Under a balance, or saturation of the liquid with (αAl₂O₃, the liquid molecular structure does not become saturated with clusters of Al₂O₃ molecules. Monophasic starting materials, however, can provide sufficient less strongly held Al₂O₃ molecules to possibly saturate the alumino-silicate liquid molecular structure. The significance of this condition is that a cooling alumino-silicate liquid precipitates (αAl₂O₃ spontaneously only when its atomic structure becomes saturated with clusters of Al₂O₃ molecules. However, when the free energy of the liquid relative to Al₂O₃ becomes equal to the free energy necessary to dissolve αAl₂O₃, precipitation of αAl₂O₃ can not occur spontaneously but precipitation can occur on introduction of “seeds” or nucleating agents of αAl₂O₃. Discussions of these phenomena relative to thermodynamic stability are presented in the text.