Résumé
Ultrasound is more and more used in many fields and in particular for the synthesis of nanomaterials.But for the moment only few stbeen conducted to understand the processes involved during thesynthesis of nanomaterials in hydrothermal water under ultrasound, hence the novelty of the subject ofstudy. We are interested in the synthesis of zeolite A and its conversion into sodalite under simultaneousaction of hydrothermal conditions and 20 kHz ultrasound (SHT). To determine the impact of ultrasoundon the kinetics of conversion of zeolite A into sodalite, different experiments were conducted startingfrom dissolved silica and sodium aluminate. First, the syntheses were carried out inconventionalautoclave at temperatures ranging from 80 °C to 150 °C over times varying from 4 h to 48 h. Underthese conditions, the main observed product was zeolite A and sodalite could only be seen in a scarceamount after 4 hours of treatment at 150 °C.Other syntheses were then performed in SHT reactor (Figure 1). Moreover, two methods of precipitationof the amorphous aluminosilicate gel were compared before the treatment within the SHT reactor. Theaim was to determine if, in addition to ultrasound, the precipitation method also influences the formationof zeolite A and its conversion into sodalite. This first step was done by mechanical or ultrasonicprecipitation in a glass reactor with a plunging sonotrode at 20 kHz. After 30 minutes, the compoundswere then transferred to the SHT reactor at 100 °C for a synthesis time ranging from 1 h to 3 h. Sodalitewas formed in every cases. Further experiments were carried out using the mechanical precipitationmethod and then the heat treatment in the SHT reactor by reducing gradually the synthesis time from 1hour 20 minutes. After only 30 min within the SHT reactor at 100 °C, sodalite was detected in XRDagainst more than 24 h at 100 °C under the conventional hydrothermal route (Figure 2). Moreover, thecharacterization of the specimens by scanning and transmission electron microscopy and by X-raydiffractaion shows that in addition to induce a kinetic gain of a factor 48 on the conversion into sodalite,the SHT also has a significant impact on the size reduction of crystallites.