THE DECOMPOSITION OF ZIRCONIA GELS - AN INFRARED-EMISSION SPECTROSCOPIC STUDY

The thermal degradation of zirconia gels prepared from the hydrolysis of modified tetra-n-butoxyzirconium(IV) and subsequent peptization wit h nitric acid was studied by infrared emission spectroscopy. The collo id precursor was modified by equimolar addition of aliphatic acids to the alkoxide. Structural changes are readily observed by in situ colle ction of spectroscopic data of gels at elevated temperatures. Spectra were collected at 25 degrees C intervals over the temperature range 10 0 to 650 degrees C. Structural degradation of the zirconia gel is foll owed by selection of the appropriate spectral regions. Two bands are o bserved at 3802.5 and 3834 cm(-1) and are assigned to the zirconia hyd rogen-bonded and non-hydrogen-bonded hydroxyl stretching vibrations. F ive bands, which are assigned to water hydroxyl groups, are observed a t 3506, 3422, 3404, 3284, and 3242 cm(-1). The 3506 cm(-1) band is att ributed to ''free'' water trapped in the zirconia gel. The intensity o f this band decreases rapidly and approaches zero by 300 degrees C. Th e three bands at 3422, 3404, and 3422 cm(-1) are attributed to water i n the fixed layer of the zirconia gel. The band at 3242 cm(-1) is assi gned to water coordinated to the zirconium in the gel. The spectra of both uni-and bidentate acetates are observed. A model for the decompos ition of the zirconia gel is proposed based on the spectrescopic evide nce. (C) 1998 Academic Press.