It has been shown that nano‐sized particles of secondary explosives are less sensitive to impact and can alter the energetic performance of a propellant or explosive. In this work the Rapid Expansion of a Supercritical Solution into an Aqueous Solution (RESS‐AS) process was used to produce nano‐sized RDX (cyclo‐1,3,5‐trimethylene‐2,4,6‐trinitramine) particles. When a saturated supercritical carbon dioxide/RDX solution was expanded into neat water, RDX particles produced from the RESS‐AS process agglomerated quickly and coarsened through Ostwald ripening. However, if the pH level of the suspension was changed to 7, particles were metastably dispersed with a diameter of 30 nm. When the supercritical solution was expanded into air under the same pre‐expansion conditions using the similar RESS process, RDX particles were agglomerated and had an average size of approximately 100 nm. Another advantage of using a liquid receiving solution is the possibility for coating energetic particles with a thin layer of polymer. Dispersed particles were formed by coating the RDX particles with the water soluble polymers polyvinylpyrrolidone (PVP) or polyethylenimine (PEI) in the RESS‐AS process. Both PVP and PEI were used because they have an affinity to the RDX surface. Small and well‐dispersed particles were created for both cases with both PVP and PEI‐coated RDX particles shown to be stable for a year afterward. Several benefits are expected from these small polymer coated RDX particles such as decreased sensitivity, controlled reactivity, and enhanced compatibility with other binders for fabrication of bulk‐sized propellants and/or explosives.
Color center formation was studied in vacuum sintered Nd3xY3−3xAl5O12 transparent ceramics. The primary color centers were F- and F+-centers as evidenced by optical absorption in the 250–400 nm wavelength range and the presence of an electron spin resonance (ESR) line at g=1.9977. Annealing in air at 1600 °C for 10 h reduced the number of color centers to below the detection limit of ESR. Color center formation is controlled by oxidation and reduction of Fe2+/3+ impurities.
Energetic crystalline nanoparticles have many benefits when incorporated into a propellant or explosive. They have been shown to be less sensitive to impact and can also change the energetic performance of a propellant or explosive. In this study, two processes are investigated and compared for producing nano-scale energetic oxidizer particles. Rapid Expansion of a Supercritical Solution (RESS) was investigated and a similar process called the Rapid Expansion of a Supercritical Solution into an Aqueous Solution (RESS-AS) process was used to produce RDX and bis(2,2,2-trinitroethyl)-3,6diaminotetrazine (BTAT) particles. For similar pre-expansion conditions, the RESS process produced RDX particles with an average size of approximately 100 nm and the RESS-AS process produced RDX particles with an average size of 30 nm. The small RDX particles were able to be coated and stabilized from permanent agglomeration in the RESS-AS process with polyvinylpyrrolidone (PVP) and polyethylenimine (PEI). The energetic material BTAT was produced initially in Germany and reprocessed first by the RESS process and nearly spherical particles of around 100 nm were created that were agglomerated. Later, BTAT particles were produced by the RESS-AS process by expanding into an aqueous solution of SDS and water produced small nano-sized rods (width and height around 100 nm) without agglomeration. The synthesized RDX particles were tested in a TGA/DSC and it was found that RESS synthesized RDX experienced nearly no temperature shift in its melting and decomposition temperature in comparison to larger micron-sized RDX. However, the RESS-AS synthesized RDX particles experience a decomposition exotherm about 25° C below the value for conventional RDX. The lowered melting point suggests that RESS-AS synthesized RDX particles have different thermodynamic properties that should be investigated further. One of these properties associated with the nano-sized particles is the ability of storing extra energy on their surface and/or due the high percentage of surface molecules with lower coordination numbers.
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