Jump to main content
Jump to site search

Issue 14, 2015
Previous Article Next Article

Energetics and structural evolution of Na–Ca exchanged zeolite A during heating

Author affiliations

Abstract

The properties of zeolite A change significantly upon sodium–calcium exchange. The impact of cation composition on the temperature-induced phase transformations and energetics of Na–Ca exchanged zeolite A was studied systematically using powder X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and high-temperature oxide melt solution calorimetry. As the temperature increases, the structural evolution of each Na–Ca exchanged zeolite A sample undergoes three distinct stages – dehydration, amorphization, and densification/recrystallization. Initially complete dehydration does not result in framework degradation, but further heating leads to zeolite phase degradation into other aluminosilicate phases. Both amorphization and recrystallization shift to higher temperatures as the calcium content increases. On the other hand, the enthalpies of formation for the high temperature aluminosilicate phases, the amorphous phase (AP) and the dense phase (DP), appear to be a linear function of calcium content (average ionic potential) with diminishing of energetic stability upon increasing the Ca content. 100% Na-A heated at 1200 °C has the most exothermic enthalpy of formation from oxides (−65.87 ± 0.87 kJ mol−1 – TO2), while 97.9% CaNa-A heated at 945 °C has the least exothermic value (−5.26 ± 0.62 kJ mol−1 – TO2). For different aluminosilicates with the same chemical composition, the dense phase (DP) assemblage is more stable than the amorphous phase (AP).

Graphical abstract: Energetics and structural evolution of Na–Ca exchanged zeolite A during heating

Back to tab navigation

Article information


Submitted
03 Jan 2015
Accepted
21 Feb 2015
First published
26 Feb 2015

Phys. Chem. Chem. Phys., 2015,17, 9241-9247
Article type
Paper
Author version available

Energetics and structural evolution of Na–Ca exchanged zeolite A during heating

H. Sun, D. Wu, X. Guo and A. Navrotsky, Phys. Chem. Chem. Phys., 2015, 17, 9241
DOI: 10.1039/C5CP00016E

Social activity

Search articles by author

Spotlight

Advertisements