STUDY OF THE ROLE OF PHASE-TRANSFER CATALYST IN OBTAINING GELS IN HETEROGENEOUS ENVIRONMENTS

Amorphous powders were obtained in the CaO-SiO2, Al2O3-SiO2, and Cr2O3-SiO2 systems, with 1:4(wt%) ratio, from sol-gel processes and by using for this synthesis solvents such as toluene, dichloromethane and acetone. The effects of different phase-transfer catalysts, 18-Crown-6, 15-Crown-5 and tetrabutylammonium-hydrogensulfate when they transport cation from the aqueous phase to the organic phase, were measured by IR spectroscopy, X-ray diffraction, differential thermal analysis, thermogravimetric analysis and scanning electron microscopy techniques. The effects of the precursor salt (chlorides and acetylacetonates) and the solvent were measured by X-ray diffraction, differential thermal analysis, thermogravimetric analysis and scanning electron microscopy techniques. In all cases, gels were obtained. In the fired gels, amorphous powder appears in CaO-SiO2 system prepared from toluene and CaCl2 as precursor using 18-Crown-6 as the phase transfer catalyst (TPC). In the Al2O3-SiO2 system, the samples appear as amorphous powders in all conditions of synthesis. Finally, in the Cr2O3-SiO2 system, amorphous powders are obtained in acetone, toluene and CrCl3 as precursor salt without TPC. By adding 15-Crown-5, amorphous powders were obtained in all cases. It was not possible to obtain gels from chromium acetylacetonate as precursor salt.