文摘

Stoichiometric α-hexacelsian_LTA and non-stoichiometric α-hexacelsian_FAU phases were synthesized by the method of high-temperature induced transformation of Ba-exchanged LTA and FAU zeolites. The unit cell thermal expansion properties were followed using synchrotron X-ray Powder Diffraction (XRPD) data in the temperature range between 25°C and 700°C. Both samples exhibit normal thermal behavior with all unit cell axes expanding upon heating. The expansion properties of the unit cell volumes are similar in the temperature range between 25°C and 325°C. At 325°C the unit cell volume of the α-hexacelsian_LTA phase increases. This is caused by structural inversion to the β-hexacelsian_LTA phase. The thermal expansion of the unit cell of the α-hexacelsian_FAU phase does not show any discontinuities. The distinct unit cell volume properties observed upon heating at 325/dgC, are consistent with results of DSC measurements of α-hexacelsian_LTA and α-hexacelsian_FAU samples. The crystal structures of the α- (at 25°C) and β-forms (at 362°C) of Si, Al ordered hexacelsian_LTA and disordered hexacelsian_FAU phases, were refined in the trigonal space group P-3 (147), from synchrotron XRPD data by the Rietveld method. These structures were refined with agreement factors: R_wp = 6.19, R_p = 4.29, R_Bragg = 6.68 for α-hexacelsian_LTA; R_wp = 5.11, R_p = 3.53, R_Bragg = 5.42 for α-hexacelsian_FAU; R_twp = 7.002, R_p