Kinetics of nano titanium dioxide catalyzed thermal decomposition of ammonium nitrate and ammonium nitrate-based composite solid propellant

Abstract

This study deals with the influence of nanosized titanium dioxide (TiO2) catalysts on the decomposition kinetics of ammonium nitrate (AN) and ammonium nitrate-based composite solid propellant. TiO2 nanocatalyst with an average particle size of 10 nm was synthesized by sol-gel method using titanium alkoxide as precursor. Formation of nanostructured TiO2 and presence of its anatase and brookite phases was confirmed by powder X-ray diffraction (PXRD) and selected area diffraction (SAED) studies. Nano TiO2 was further characterized by transmission electron microscopy (TEM), infrared (IR) spectroscopy, and thermogravimetry. The catalytic effect of TiO2 nanocatalysts on the solid state thermal decomposition reaction of AN and nonaluminized HTPB/AN propellant was evaluated. To ascertain the effectiveness of the TiO2 nanocatalyst, the thermal kinetic constants for the catalytic and non-catalytic decomposition of AN and AN propellant samples were computed by using a nonlinear integral isoconversional method. Catalytic influence was evident from the lowering of activation energy for the catalyzed decomposition reactions. Apparently, the nanocatalysts provide Lewis acid and/or active metal sites, facilitating the removal of AN dissociation products NH3 and HNO3 and thereby enhance the rate of decomposition. The changes in the critical temperature of thermal explosion of AN and AN propellant samples due to the addition of TiO2 nanocatalyst were also computed and the possible reasons for the changes are discussed.