Dehydration mechanism of AlPO4-5: A high-resolution synchrotron X-ray powder diffraction study

Abstract

We present the results of a study on the thermal stability and dehydration dynamics of the porous aluminophosphate AlPO4-5, from room temperature to 850 °C, carried out by in situ synchrotron X-ray powder diffraction experiments. No phase transitions were observed in the investigated T range. Due to the very low interactions among framework and water molecules, dehydration is already complete at 152 °C. It occurs in two main T ranges, one between 60 and 80 °C and the second one between 90 and 120 °C. During these two stages, the cell volume tends to increase to facilitate the water release. Overall, across the full explored T range, the cell volume increase is only 0.84%, indicating that AlPO4-5 is one of the most rigid zeolite frameworks studied to date. Specifically, after complete dehydration at 200 °C, AlPO4-5 undergoes a negative thermal expansion as a consequence of the decrease in both a and c cell parameters. The expansion coefficients for V, a and c cell parameters, in the 152-850 °C range, are αV =-7.12 (10-6/K), αa=-2.5 (10-6/K), αc=-2.2 (10-6/K), respectively.

Mechanical Characterization of Anhydrous Microporous Aluminophosphate Materials: Tridimensional Incompressibility, Ductility, Isotropy and Negative Linear Compressibility

“…However, the orthorhombic structure is increasingly more stable as the pres creases. The enthalpy difference becomes 12.1 kJ per formula unit (AlPO 4 ) at P = The hexagonal-orthorhombic polymorphism in the anhydrous and hydrated f ALPO-5 is a long-standing problem [8,9,[346][347][348][349][350][351][352][353][354][355][356]. The presence of one or anoth morph is not only dependent on the temperature but also on the method used synthesis of this compound [356].…”

Combining a nine-crystal multi-analyser stage with a two-dimensional detector for high-resolution powder X-ray diffraction

“…1(b)]. ID22 can be exploited for a wide range of powder diffraction measurements, with various applications in materials science, including the characterization of unknown crystallographic structures (Veselovsky et al, 2018), of disordered materials (Coduri et al, 2017) and of advanced materials (Polishchuk et al, 2017), dynamic and in situ studies of materials versus temperature (Polisi et al, 2018) or gas absorption (Giacobbe et al, 2017), and residual strain mapping of bulky samples (Amjad et al, 2017). A 41 Â 41 cm medical-imaging detector (PerkinElmer XRD 1611) allows complementary measurements as needed, for example for texture characterization or fast pair-distribution-function (PDF) analysis (Checchia et al, 2016;Zhang, et al, 2017;Ortatatli et al, 2018).…”