Reinvestigation of pure Na-nepheline like compounds obtained from the thermal conversion of zeolite LTA

In this contribution a nepheline like sample synthesized from the thermal transformation of zeolite Na LTA was investigated. In a previous work the product of the thermal treatment has been described to be a standard nepheline. Our TEM investigations conducted on the synthesized polycrystalline material proved the presence of a structure with a tripled c unit cell parameter compared to that observed in classical nepheline. Consequently we compared the theoretical X ray powder diagrams of all known trinepheline compounds with the experimental powder pattern and concluded that the material is actually a mixture of two phases. Rietveld refinement against XRPD data using structural models of (a) classical Na nepheline (S. G. P63 a = 9.971(3) c =8.349(2) ) and (b) monoclinic trinepheline (S. G. P1121 a = 9.995(4) b = 9.963(4) c = 24.988(7) ? = 119.75(3)) resulted in a satisfying agreement between calculated and observed step intensities (?2 = 1.96 Rwp = 11.3 Rp = 8.77). The additional quantitative analyses of the samples obtained in a temperature range of stability of nepheline (900 – 1100 ?C) showed the presence of both structures and also a gradual increase of the weight fraction of the monoclinic trinepheline phase with increasing temperature.