Résumé
For over 10 years, SHT has enabled the synthesis of numerous materials with remarkable properties(1,2). The aim of the present work was to investigate, for the first time, the simultaneous coupling of ultrasound and hydrothermal conditions (HT) for the synthesis of zeolites and their mechanism of formation. The zeolite LTA was selected for this purpose. Its conversion to sodalite was also examined under these coupling conditions. Zeolite synthesis was carried out under sonohydrothermal (SHT)1 conditions using a specially designed reactor to coupling low frequency ultrasonic irradiation and hydrothermale conditions. Ultrasound irradiation is achieved using 2 cm diameter sonotrode supplied by a 20 kHz generator (130VCX Vibracell-Sonics) with an acoustic power of 10 W and a capacity of 80 mL heated to 100°C under autogenous pressure (1. 6 bar) for a solution volume of 50 mL (figure 1a). The action of ultrasound during the gel precipitation stage, as well as during the material crystallization process, was studied. Syntheses were carried out in the SHT reactor, varying time from 15 minutes to hours. We were able to demonstrate the importance of absorbed acoustic power on LTA crystallization by varying the reactor filling ratio and also we studied the effect of gel density. Similar syntheses were carried out under hydrothermal conditions, and the results obtained were compared with those of SHT.Characterization by scanning electron microscopy and XRD revealed the impact of SHT treatment on the size of the products obtained, as well as a kinetic gain on conversion of LTA to sodalite of a factor greater than 96 compared with hydrothermal synthesis. Changes in the morphological aspects of our solids were also observed on compounds obtained under hydrothermal conditions (figure 2). In SHT, the cubic morphology of the LTA particles was obtained in all cases, regardless of the experimental conditions.