The steps of thermal treatment of Na-magadiite: a computational study using ab initio DFT calculations

Abstract

We investigated each of the successive transformations of this material using ab initio calculations based on DFT. Possible structures produced from three reaction steps of the thermal treatment were simulated. Thermodynamic analysis was performed to assess the energy stability of each reaction. The dehydration of the interlamellar region confirmed the selective loss of water molecules, with axial H₂O being responsible for the first part of the mass loss experimentally observed in TG-DTA while the loss of equatorial H₂O molecules is observed above 150 °C. The reactions of the proposed intermediates after dehydration indicated that the formation of a zeolite Si₁₄O₂₈ is thermodynamically unfavorable in relation to zeolite sodium silicate. Kinetic effects and new heat treatment protocols should be studied to improve the understanding of these materials. The final steps indicated that after the condensation of the layers, sodium silicate was formed together with quartz.