Effect of the TiO₂ nanoparticle size on the decomposition behaviors in aluminum matrix composites

The decomposition behaviors and the effect of particle size on the kinetic rate are studied for Al-3 vol.% titanium dioxide (TiO₂) composites by using three different types of TiO₂ particles (15, 50, and 300 nm). Thermal analysis shows that the reaction is stepwise with the first reaction starting before the melting temperature of Al. Since the high chemical potential of nanoparticles enhances reactivity, the TiO, Al₃Ti, and α-Al₂O₃ phases are found to be formed during the first reaction regardless of particle size. Based on observations of microstructure, the formation mechanism of Al₃Ti and α-Al ₂O₃ is understood to be solution precipitation. Non-isothermal kinetic analysis reveals that the reaction mechanism is closely related to the three-dimensional continuous nucleation and the growth limited by diffusion. Particle size is found to be having considerable effect on the kinetic rate. As the particle size decreases, the rate constant increases, while the pre-exponential factor and the activation energy decreases. A non-linear relationship between the rate constant and the reciprocal of the size is found and evaluated.