The crystallisation kinetics of nitrate cancrinite Na-7.6[AlSiO4](6)(NO3)(1.6) (H2O2)(2) under low temperature hydrothermal conditions

Investigations on the formation of nitrate enclathrated cancrinite were per formed under low temperature hydrothermal conditions (353 K, autogeneous pr essure). The alkaline transformation of kaolinite in the presence of sodium nitrate was selected as the preferred method of synthesis. All experiments were carried out at high alkalinity, using a 16 molar NaOH solution as wel l as at low NaOH concentrations (2 molar NaOH), Qualitative phase analysis was performed by X ray-powder diffraction and IR-spectroscopy, Besides canc rinite formation no further intermediate phases were formed. Quantitative d ata of the educt conversion into cancrinite was determined by Al MAS NMR sp ectroscopy and integration of the resonance signals of four- and six-coordi nated aluminium. Whereas full conversion could be found already after 24 h of reaction under highly alkaline conditions, only an insufficient progress of the reaction resulted in the case of low alkalinity.