The thermal behavior of a woolly erionite-K sample (Lander County, NV, USA), chemical formula (Ca2.03Na0.73K2.52Mg0.26)[Al8.22Si27.78O71.80]·35.94H2O, was investigated in the 303â1173 K thermal range by in situ X-ray powder diffraction. Present data suggest a general thermally-induced volume contraction whose magnitude increases as(formula presented) ratio becomes smaller. An inverse correlation between(formula presented) ratio and Tdehydris observed because higher(formula presented) ratio values are associated to lower dehydration temperatures. A positive dependence exists between(formula presented) ratio and Tbreak. A higher Si content results in a greater thermal stability, in agreement with the general trend observed in zeolites. On the contrary, no correlation has been found between Tbreakand weighted ionic potential (Z/r)wtas suggested by reference data. Heating produces a general depletion of the Ca1, Ca2, Ca3, and K1 sites, which is counterbalanced by an increase of the K2 site scattering, even though the latter is not populated at RT. No âinternal ion exchangeâ mechanism was apparently acting in the present sample differently from other erionite samples analysed in the past. At 303 K approximately 20 eâallocated at the OW H2O sites might be assigned to (extra-framework) EF cations. Such fraction increases due to their migration from the extra-framework cation sites following the same mechanism reported in reference data.
Thermal stability of woolly erionite-K and considerations about the heat-induced behaviour of the erionite group
Bloise, Andrea;
2018-01-01
Abstract
The thermal behavior of a woolly erionite-K sample (Lander County, NV, USA), chemical formula (Ca2.03Na0.73K2.52Mg0.26)[Al8.22Si27.78O71.80]·35.94H2O, was investigated in the 303â1173 K thermal range by in situ X-ray powder diffraction. Present data suggest a general thermally-induced volume contraction whose magnitude increases as(formula presented) ratio becomes smaller. An inverse correlation between(formula presented) ratio and Tdehydris observed because higher(formula presented) ratio values are associated to lower dehydration temperatures. A positive dependence exists between(formula presented) ratio and Tbreak. A higher Si content results in a greater thermal stability, in agreement with the general trend observed in zeolites. On the contrary, no correlation has been found between Tbreakand weighted ionic potential (Z/r)wtas suggested by reference data. Heating produces a general depletion of the Ca1, Ca2, Ca3, and K1 sites, which is counterbalanced by an increase of the K2 site scattering, even though the latter is not populated at RT. No âinternal ion exchangeâ mechanism was apparently acting in the present sample differently from other erionite samples analysed in the past. At 303 K approximately 20 eâallocated at the OW H2O sites might be assigned to (extra-framework) EF cations. Such fraction increases due to their migration from the extra-framework cation sites following the same mechanism reported in reference data.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.