RHEOLOGICAL CHARACTERIZATION OF BATIO3 SOL-GEL TRANSITION

BaTiO3 gels were prepared by hydrolysis and polycondensation reactions between titanium isopropoxide and barium hydroxide in presence of met hoxyethanol, methanol and water. The theology of the sol-gel transitio n was studied with a rheometer allowing low amplitude sinusoidal oscil lations. Experimental data show a continuous increase in the complex v iscosity along with time, showing the progressive character of the tra nsition. The influence of synthesis operating variables was studied. T he gelation time, which definition is based on viscoelastic measuremen ts, increases exponentially when the water content is increased, when the dilution due to the methoxyethanol is reduced or when the temperat ure is lowered. Different growth models were used for the characteriza tion of the particles in the solution. These models suggest that the p olymerisation first produces spherical particles (mass fractals) and t hat these spherical particles then agglomerate to form a linear networ k.