The thermal degradation of zirconia gels prepared from the hydrolysis of modified tetra-n-butoxyzirconium(IV) and subsequent peptization with nitric acid was studied by infrared emission spectroscopy. The colloid precursor was modified by equimolar addition of aliphatic acids to the alkoxide. Structural changes are readily observed by in situ collection of spectroscopic data of gels at elevated temperatures. Spectra were collected at 25 degrees C intervals over the temperature range 100 to 650 degrees C. Structural degradation of the zirconia gel is followed by selection of the appropriate spectral regions. Two bands are observed at 3802.5 and 3834 cm(-1) and are assigned to the zirconia hydrogen-bonded and non-hydrogen-bonded hydroxyl stretching vibrations. Five bands, which are assigned to water hydroxyl groups, are observed at 3506, 3422, 3404, 3284, and 3242 cm(-1). The 3506 cm(-1) band is attributed to "free" water trapped in the zirconia gel. The intensity of this band decreases rapidly and approaches zero by 300 degrees C. The three bands at 3422, 3404, and 3422 cm(-1) are attributed to water in the fixed layer of the zirconia gel. The band at 3242 cm(-1) is assigned to water coordinated to the zirconium in the gel. The spectra of both uni-and bidentate acetates are observed. A model for the decomposition of the zirconia gel is proposed based on the spectrescopic evidence.