Search

Abstract: Nanosized WO3 tungsten trioxide was prepared by calcination of H3P4W12O40·xH2O 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 m2 g−1 and 0.33 cm3 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. [Copyright &y& Elsevier]

Metal sulfates (Ba, Bi, Ca, Cu, Mg, Mn, Na, Zn, Zr) were used as oxidizers in reactive compositions with Al nanopowder. These new kinds of nanothermites have outstandingly high reaction heats (4-6 kJ g(-1) ) compared to conventional Al/metal oxides (1.5-4.8 kJ g(-1) ) and also have good combustion velocities (200-840 m s(-1) vs 100-2500 m s(-1) ). These compositions are extremely insensitive to friction making their preparation and handling easy and safe. The sulfate hydration water increases the reaction heats and has a significant effect on the sensitivity to impact and to electrostatic discharge. The reaction of Al with water is easier to initiate than the one with sulfate which leads to two possible decomposition modes for samples exposed to an open flame. The pyrotechnical properties observed with sulfates have also been found for other sulfur oxygenates (SO3 (2-) , S2 O3 (2-) , S2 O8 (2-) ) which opens up new horizons in the domain of metastable interstitial composites., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)