Synthesis of WO3 nanoparticles for superthermites by the template method from silica spheres

Nanosized WO3 tungsten trioxide was prepared by calcination of H3P4W12O40 center dot xH(2)O phosphotungstic acid, previously dissolved in a silica colloidal solution. The influence of the silica spheres/tungsten precursor weight ratio (x) was investigated. The pristine oxide powders were characterized by XRD, nitrogen adsorption, SEM and TEM techniques. A specific surface area and a pore volume of 64.2 m(2) g(-1) and 0.33 cm(3) g(-1), respectively, were obtained for the well-crystallized WO3 powder prepared with x = 2/3 and after the removal of the silica template. The WO3 particles exhibit a sphere-shaped morphology with a particle size of 13 and 320 nm as function of the x ratio. The performance and the sensitivity levels of the thermites prepared from aluminium nanoparticles mixed with (i) the smallest tungsten (VI) oxide material and (ii) the microscale WO3 were compared. The combustion of these energetic composites was investigated by time resolved cinematography (TRC). This unconventional experimental technique consists to ignite the dried compressed composites by using a CO2 laser beam, in order to determine their ignition delay time (IDT) and their combustion rate. The downsizing WO3 particles improves, without ambiguity, the energetic performances of the WO3/Al thermite. For instance, the ignition delay time was greatly shortened from 54 +/- 10 ms to 5.7 +/- 0.2 ms and the combustion velocity was increased by a factor 50 to reach a value of 4.1 +/- 0.3 m/s. In addition, the use of WO3 nanoparticles sensitizes the mixture to mechanical stimuli but decreases the sensitivity to electrostatic discharge. (C) 2011 Elsevier Masson SAS. All rights reserved.