Sintering of SiO2-Al2O3-TiO2 and SiO2-Al2O3-ZrO2 obtained by the sol-gel process

An experimental strategy was developed to obtain Si-Al-Ti and Si-Al-Zr transparent sots via the sol-gel process. Acetylacetone (2, 4 pentanedione, acacH) and Itaconic anhydride (2-methylenesuccinic anhydride, anhH) were employed separately as chelating agents to stabilize At, Ti and Zr precursors, in order to slow down the chemical reactivity, avoiding precipitation. The molar ratio chelating agent/M (M: At, Ti, and Zr) was 2.0. The starting materials were Si(OEt)(4) (TEOS), Ti(OEt)(4) (OEt: OCH2CH3), Al(OBus)(3) (OBus: C2H5CH(CH3)O) and Zr(OPrn)(4) (OPrn: OCH,CH, CH3). The molar ratio Si:AI:Ti or Zr was 80:7:13, respectively. The sots were clear and homogeneous at macroscopic scale during gelation. The gets were dried at 423 K for 24 h in air. Xerogels were calcined at 673, 773, 873 and 1123 K for 24 h in air. The samples were analyzed by X-ray diffraction and found to be amorphous up to 873 K. The solids calcined have small pore size (micro and mesopores). The solids were also studied by scanning electron microscopy (SEM), and X-ray diffraction (XRD) to compare the influence of size and structure of the chelating agent in the particle size and the cristallite size distribution.