Submicron-sized powders of silver azide (AgN 3 ) were prepared by Curtius' reaction between silver nitrate (AgNO 3 ) and sodium azide (NaN 3 ) in aqueous solutions by a new process: the Spray Flash Synthesis (SFS). The SFS process consists in spraying the two precursor solutions in a heated atomization chamber (130-190 °C), maintained under low vacuum (15-30 kPa). The reaction occurs in the droplets which have collided; the final size of particles is limited by the fast evaporation of water and the small amount of matter available in each droplet which can be considered as an individual micro-reactor.The mean particle sizes of silver azide synthesized by the SFS process range from 220 nm to 390 nm, which means that these particles are three times smaller than those obtained by the conventional precipitation method. Submicron-sized AgN 3 powders can be initiated by a photographic flash.

The pyrotechnic compositions made up of potassium perchlorate (KClO 4 ) and titanium hydride (TiH 2 ), known as THKP, have a fast deflagration velocity (~500 m/s), along with low sensitivity and high stability. In this research, a new kind of THKP was formulated from a submicron powder of KClO 4 (50-400 nm) prepared by the Spray Flash-Evaporation (SFE) process. The use of fine KClO 4 not only ensures better oxidation of TiH 2 , but also leads to a transition to detonation in the THKP. This transition is observed in loose powders placed in small diameter tubes (3 mm). The distance of transition is relatively short (17-22 mm) and increases with the KClO 4 content of the THKP mixture. The detonation front propagates steadily, at a velocity of~1250 m/s in THKP powders with 86 % of porosity. The shockwave velocity varies little with the perchlorate content in the domain of composition studied (55-74 wt.% of KClO 4 ). Conversely, in the classical THKP mixtures prepared from micron-sized KClO 4 and tested in the same conditions, no transition to detonation is observed; the combustion slows down and eventually stops. Finally, owing to their high sensitivity thresholds to impact (S Imp. � 44.7 J), friction (S Fr. � 192 N), and electrostatic discharge (S ESD � 34.7 mJ), THKP mixtures prepared from submicron KClO 4 can be classified as low-sensitivity primary explosives.

In this work, tunable caffeine crystals are formulated through a promising aerosol-based technology called spray flash evaporation (SFE). In this process, the vacuum atomization of a superheated and pressurized solution allows for the continuous flow and mass production of organic particles with tunable sizes and morphologies depending on the process parameters. Despite its versatility, the widespread application of SFE technology is still mainly hindered by the lack of systematic experimental works showing the correlation among the aerosol properties, such as the droplet size and solvent evaporation rate, the filtering method, and the final product morphology. Here, we characterize pure solvent aerosols, ethanol and dichloromethane, by in situ phase Doppler particle analysis and apply these solvents to grow caffeine rods with lengths ranging from submicron to 30 μm and different agglomeration states depending on the specific process and collection conditions. The nucleation and growth mechanisms are derived from accurate investigations on scanning electron micrographs. Results show the high potential and versatility of SFE for processing micron and submicron organic particles for many applications in biomaterials and pharmaceutics.

No abstract