The structural studies of aluminosilicate gels and thin films synthesized by the sol-gel method using different Al2O3 and SiO2 precursors

Aluminosilicate materials were obtained by sol-gel method, using different Al2O3 and SiO2 precursors in order to prepare sols based on water and organic solvents. As SiO2 precursors, Aerosil 200 (TM) and tetraethoxysilane TEOS: Si(OC2H5) 4were applied, while Disperal TM and aluminium secondary butoxide ATSB: Al(OC4H9)3were used for Al2O3 ones. Bulk samples were obtained by heating gels at 500 degrees C, 850 degrees C and at 1150 degrees C in air, while thin films were synthesized on carbon, steel and alundum (representing porous ceramics) substrates by the dip coating method. Thin films were annealed in air (steel and alundum) and in argon (carbon) at different temperatures, depending on the substrate type. The samples were synthesized as gels and coatings of the composition corresponding the that of 3Al2O3center dot 2SiO2mullite because of the specific valuable properties of this material. The structure of the annealed bulk samples and coatings was studied by FT-IR spectroscopy and XRD method (in standard and GID configurations). Additionally, the electron microscopy (SEM) together with EDS microanalysis were applied to describe the morphology and the chemical composition of thin films. The analysis of FT-IR spectra and X-ray diffraction patterns of bulk samples revealed the presence of gamma-Al2O3 and delta-Al2O3 phases, together with the small amount of SiO2 in the particulate samples. This observation was confirmed by the bands due to vibrations of Al-O bonds occurring in gamma-Al2O3 and delta-Al2O3 structures, in the range of 400 to 900 cm(-1). The same phases (gamma-Al2O3 and delta-Al2O) were observed in the deposited coatings, but the presence of particulate ones strongly depended on the type of Al2O3 and SiO2 precursor and on the heat treatment temperature. All thin films contained considerable amounts of amorphous phase.