Résumé
Ultrasound is more and more used in many fields and in particular for the synthesis of nanomaterials. But for the moment only few study have been conducted to understand the processes involved during the synthesis of nanomaterials in hydrothermal water under ultrasound, hence the novelty of the subject of study. We are interested in the synthesis of zeolite A and its conversion into sodalite under simultaneous action of hydrothermal conditions and 20 kHz ultrasound (SHT)1. To determine the impact of ultrasound on the conversion kinetics of amorphous gel to LTA and LTA to sodalite, different experiments were conducted starting from dissolved silica and sodium aluminate. First, the syntheses were carried out inconventional autoclave at temperatures ranging from 80 °C to 150 °C over times varying from 4 h to 48 h. Under these conditions, the main observed product was zeolite A and sodalite could only be seen in a scarce amount after 4 hours of treatment at 150 °C. Other syntheses were then performed in SHT reactor (Figure 1a) at 100 °C, varying the synthesis time from 15 minutes to 1 hour. Moreover, two methods of precipitation of the amorphous aluminosilicate gel were compared before the treatment within the SHT reactor. The aim was to determine if, in addition to ultrasound, the precipitation method also influences the formation of zeolite A and its conversion into sodalite. the characterization of the specimens by scanning and transmission electron microscopy and by X-ray diffraction shows that in addition to induce a kinetic gain of a factor over than 96 on the conversion into sodalite, the SHT also has a significant impact on the size reduction of LTA crystallites.