Structural transformations and phase stabilization in Na2S04-Na2C03 system

The phase diagram of the system Na2S04-Na2C03 has been determined from room temperature upto liquidus. At low temperature the system shows partial miscibility and the formation of a compound, burkeite. At high temperature, the whole system shows complete miscibility and crystalizes in hexagonal system, with P63/m mc structure. This high temperature phase is quenched from the melt at room temperature, and shows: 1. Shortening of the hexagonal c-axis in the mixed series as a result of substitutions of tetrahedron complex with plane group. 2. Heat treatment of single crystals of intermediate phase of Na2S04 with Cmcm structure shows topotaxial phase change to high phases. 3. Na2CO3 rich region show satellite reflections, which vanish with rise of temperature. 4. Quenched high phase is metastable and reverts to low phases after sometime.