ORIENTATIONAL DISORDER AND HETEROGENEOUS REACTION BEHAVIOR OF NO-2(-) AND NO-3(-) ANIONS INSIDE A SODALITE MATRIX

The crystallization of nitrite/nitrate enclathrated sodalite solid solutions has been investigated under hydrothermal conditions in the system Na2O-SiO2-Al2O3-NaNO2-H2O. The oxidation potential within the silver-lined autoclaves at elevated temperatures (T greater-than-or-equal-to 773 K) and pressures (p greater-than-or-equal-to 0. 15 GPa) gives rise to the formation of a temperature dependent nitrite/nitrate ratio within the crystals. Structural investigations on nitrite/nitrate sodalite have been carried out using IR spectroscopy, MAS NMR as well as single crystal structure refinement. Considering both of the imbibed anions have a ''rigid body'' their real positions within the sodalite cages could be found. Besides synthesis and the structural characterization the heterogeneous reaction behavior of nitrite/nitrate sodalite in a CO2 atmosphere has also been investigated. At elevated temperatures (1073 K) a total anion exchange could be established, yielding to the formation of carbonate sodalite. (C) 1994 Academic Press, Inc.