Effect of anatase–brookite mixed phase titanium dioxide nanoparticles on the high temperature decomposition kinetics of ammonium perchlorate

Abstract

In the present study, titanium dioxide (TiO2) nanocatalyst was synthesized using a titanium alkoxide precursor. The nanocatalyst was found to consist of anatase and brookite phases, with an average particle size of ∼10 nm. Formation of the nanostructured anatase–brookite mixed phase TiO2 was confirmed by powder XRD and SAED studies. The nanocatalyst was further characterized by TEM, FTIR and thermogravimetry. Catalytic effect of the TiO2 nanocatalyst on the solid state thermal decomposition reaction of ammonium perchlorate (AP), a solid rocket propellant oxidizer, was evaluated. To evaluate the effectiveness of this nano TiO2 catalyst, the activation energy of the catalyzed decomposition reactions of AP was computed by a non-linear integral isoconversional method. The calculated activation energy value was then compared with that of non-catalyzed AP decomposition reactions. The catalyzed AP decomposition showed an unaffected low temperature decomposition (LTD) at the extent of conversion (α) between 0 and 0.30. Further, a characteristic slowdown and a nanocatalyst influenced high temperature decomposition (HTD) at α between 0.35 and 1 was observed. The possible reasons for the catalytic effect of TiO2 nanoparticles on the HTD of AP are discussed based on the fact that the exposed cations and anions on the transition metal oxide nanoparticle surface act as acid–base site pairs and adsorb gaseous reactive molecules formed during the LTD of AP.