Phase Diagram for the System Na2O−Al2O3−H2O at High Alkali Concentration

The high alkali concentration regions of the phase diagrams for the system Na 2 O−Al 2 O 3 −H 2 O were studied at 95 °C and 110 °C, to provide a chemical database for producing monosodium aluminate hydrate (Na 2 O·Al 2 O 3 ·2.5H 2 O). In the phase diagram at 95 °C, the solid phases of 4Na 2 O·Al 2 O 3 ·12H 2 O and 6Na 2 O·Al 2 O 3 ·12H 2 O, besides Na 2 O·H 2 O, Al 2 O 3 ·3H 2 O, and Na 2 O·Al 2 O 3 ·2.5H 2 O, were discovered. In the phase diagram at 110 °C, 4Na 2 O·Al 2 O 3 ·12H 2 O was found missing. These phase diagrams show that all these sodium aluminate hydrates decompose in the presence of water and that the higher the temperature, the larger the region with Na 2 O·Al 2 O 3 ·2.5H 2 O as the equilibrium solid.