Publication

Abstract : Nanoengineered composites of metal oxide (oxidizer) and metal(fuel)have shown to exhibit enhanced combustion properties. More specifically, when the sizes of oxidizer and fuel particles are in nanoscale, the heat and the mass transport length scales are drastically reduced, leading to enhanced combustion speeds and reaction rates. Thus, it is quite possible to achieve tunable reaction rates by proper choice and combination of fuel, oxidizer and other chemicals, their dimensions in nanoscale and the mixing ratio. The present work is devoted to the study of reaction rates of conventional and modified nanothermites. We have used a variety of metal oxides, namely, Fe2O3, CuO and MoO3 and Al as the fuel. The conventional nanothermites were also modified by mixing with ammonium nitrate (AN) nanoparticles. The reactivity was determined by monitoring the pressure as a function of time generated during the energetic reaction. The rate of increase in the pressure generated during combustion process is a measure of the reactivity of the material system. Reactivity rate tests were performed in a closed volume using a typical mass of 20 mg in a milli-well with a packing density of 0.33g/cm3. Among the conventional nanothermites studied in this work, CuO-Al system possesses the highest reactivity. The rate of pressure increase is about 3.23MPa/�s and the peak pressure recorded is 40MPa. In comparison, it is 0.01MPa/s for Fe2O3/Al nanocomposite. The reactivity of self-assembled CuO nanorod (NR) - Al nanoparticle composite (3.81 MPa/�s) is higher than that of the one prepared by random mixing of CuO NR and Al nanoparticle (3.23MPa/�s). The CuO NR � Al based conventional nanothermites were modified by mixing with low-grade explosives, such as ammonium nitrate (AN) nanoparticles. These nanoparticles were prepared by employing microemulsion route. The reactivity increases to about 250 MPa/�s and the peak pressure to 600 MPa for the modified thermite composition with 60 % AN nanoparticles. Mixing of micron size AN particles reduced the reactivity drastically. Our studies clearly show that nanoscale mixing of thermites with explosives is necessary to enhance the reactivity of the mixture.