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 usin g for this synthesis solvents such as toluene, dichloromethane and ace tone. The effects of different phase-transfer catalysts, 18-Crown-6, 1 5-Crown-5 and tetrabutylammonium-hydrogensulfate when they transport c ation from the aqueous phase to the organic phase, were measured by IR spectroscopy, X-ray diffraction, differential thermal analysis, therm ogravimetric analysis and scanning electron microscopy techniques. The effects of the precursor salt (chlorides and acetylacetonates) and th e solvent were measured by X-ray diffraction, differential thermal ana lysis, thermogravimetric analysis and scanning electron microscopy tec hniques. In all cases, gels were obtained. In the fired gels, amorphou s powder appears in CaO-SiO2 system prepared from toluene and CaCl2 as precursor using 18-Crown-6 as the phase transfer catalyst (TPC). In t he Al2O3-SiO2 system, the samples appear as amorphous powders in all c onditions of synthesis. Finally, in the Cr2O3-SiO2 system, amorphous p owders are obtained in acetone, toluene and CrCl3 as precursor salt wi thout TPC. By adding 15-Crown-5, amorphous powders were obtained in al l cases. It was not possible to obtain gels from chromium acetylaceton ate as precursor salt.