STUDY OF SOL-GEL TRANSITION DURING HAFNIUM ALKOXIDE HYDROLYSIS

Hydrolysis of hafnium 2-ethyl-hexyloxide, using esterification reaction by adding acetic acid to an ethanol solution, was dependent on alkoxide concentration, hydrolysis ratio and temperature. The formula of the intermediate species was determined by gas chromatograph measurements. Infrared spectra of the xerogel were measured. Hf-0-Hf bonds are present in the network, acetate groups are essentially chelate bidendate ligands and the presence of ethyl hexyloxy groups confirms partial hydrolysis. Gelation was studied using light scattering and viscosity measurements. Particle size and viscosity increase when gelation is 95% complete. Mesopore radii of the gel were measured by thermoporometry. The mean radius was 2.1 nm. These results show that the gel has a dense structure. Monoclinic hafnia was obtained from 500-degrees-C.