A Discussion on the Phase Diagram of the System Al2O3-H2O Considering the Transformation Mechanism of the Polymorphs Appearing in It

• Published in: Journal of the Ceramic Association, Japan Vol. 74; no. 847; pp. 94 - 100
• Main Authors: YANAGIDA, Hiroaki, YAMAGUCHI, Goro
• Format: Journal Article
• Language: Japanese
• Published: The Ceramic Society of Japan 01.03.1966
• ISSN: 0009-0255; 1884-2127
• DOI: 10.2109/jcersj1950.74.847_94

The authors have proposed a revised phase diagram for the system Al2O3-H2O. In the system, some transformation mechanisms are very difficult nucleation processes for the more stable phase. The mechanism is as discussed in the previous paper. The authors propose that it must be checked whether seed crystals of the more stable phase is present beforehand or not when an equilibrium curve is measured and illustrated in the diagrams. Addition of seed crystals of the more stable phase often causes very remarkable effects upon the initiation of transformation into the more stable phase. And it must be checked whether the transformation of A into B is a reversible one along the equilibrium curve between A and B illustrated in the diagrams. The transformations of boehmite into corundum and diaspore into corundum have been confirmed to be reversible ones along the curves in the present revised diagram. Other transformations are also discussed. The authors clarify three types of transformation in the phase diagram which are those between two stable forms, between a stable form and a metastable one, and between two metastable forms. Spontaneous transformations are illustrated in the diagram. The present diagram is useful in order to discuss hydrothermal reactions of alumina polymorphs appearing in it.