Preparation of Cr2O3 nanoparticles for superthermites by the detonation of an explosive nanocomposite material

This article reports on the preparation of chromium(III) oxide nanoparticles by detonation. For this purpose, a high explosive—hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX)—has been solidified from a solution infiltrated into the macro- and mesoporosity of Cr2O3 powder obtained by the combustion of ammonium dichromate. The resulting Cr2O3/RDX nanocomposite material was embedded in a cylindrical charge of pure explosive and detonated in order to fragment the metallic oxide into nanoparticles. The resulting soot contains Cr2O3 nanoparticles, nanodiamonds, amorphous carbon species and inorganic particles resulting from the erosion by the blast of the detonation tank wall. The purification process consists in (i) removing the carbonaceous species by an oxidative treatment at 500 °C and (ii) dissolving the mineral particles by a chemical treatment with hydrofluoric acid. Contrary to what could be expected, the Cr2O3 particles formed during the detonation are twice larger than those of initial Cr2O3. The detonation causes the fragmentation of the porous oxide and the melting of resulting particles. Nanometric droplets of molten Cr2O3 are ejected and quenched by the water in which the charge is fired. Despite their larger size, the Cr2O3 nanoparticles prepared by detonation were found to be less aggregated than those of the initial oxide used as precursor. Finally, the Cr2O3 synthesized by detonation was used to prepare a superthermite with aluminium nanoparticles. This material possesses a lower sensitivity and a more regular combustion compared to the one made of initial Cr2O3.