The system kaolin-1.5 Na2CO3 was studied at temperatures 650° to 800°C, and inversion of the high-carnegieite-like phase (L-phase) to nepheline was examined in relation to the starting materials. The L-phase from metakaolin inverts more readily to nepheline than that produced from well-crystallized kaolinite. Excess alkali (>1 mole Na2CO3) stabilizes an alkali-rich carnegieite at around 800°C.
Electron-optical examinations at various stages of the reaction reveal topotactic relationships between the original and product phases. From these observations and kinetic data, the process is interpreted in terms of the random distribution of Na ions in the L-phase which has a similar Si-O framework to that of the starting material.