Key words nucleation kinetics, focused beam reflectance measurement, metastable zone width, RDX.Nucleation kinetics in the cooling crystallization of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) from γbutyrolactone was studied by converting total counts/s measured by in situ focused beam reflectance measurement (FBRM) into number of crystals. The classical nucleation rate model, which is derived exclusively from the thermodynamic state for the nucleation and molecular collision frequency, was found to be inadequate to describe the experimentally measured nucleation rates. However, the nucleation rates predicted by the modified classical nucleation rate model, inclusive of an additional temperature term, were found to be in good agreement with those measured in the present work. Furthermore, the metastable zone widths are also found to be more accurately predicted by the modified classical nucleation rate model than the classical approach, which assumes that the mass-based nucleation rate is an exponential function of supersaturation and is equal to the supersaturation rate.
In
the drowning-out crystallization of hexahydro-1,3,5-trinitro-1,3,5-triazine
(RDX) with a spray, effects of operating parameters such as spray
distance, solute concentration, and antisolvent temperature on crystal
size were investigated. It was found that there exists an optimum
spraying distance of solution for the production of submicrometer-sized
crystals: the crystal size decreases with increasing spray distance
in the distance shorter than the optimum distance due to incomplete
atomization and that increases with the spray distance at the distance
longer than the optimum distance due to coalescence among fluttered
droplets. Higher RDX concentration in starting solution induced larger
product particles. However, too low RDX concentration was also found
to be not preferred for the small-sized product since nucleation occurs
after complete mixing of atomized solution droplets with the antisolvent.
By similar reason, it was found that lower antisolvent temperature,
which causes faster nucleation, is preferred for the small-sized product.
However, too low temperature was shown to be not preferred because
of an increase in coalescence between droplets which leads to agglomeration.
Finally, poly(vinylpyrrolidone) (PVP) was found to act as a nucleation
promoter in the drowning-out crystallization with the acetone/water
system, and RDX particles with an average size of 790 nm were successfully
produced.
Self-assembly of organic molecules is formed spontaneously on surfaces by electrostatic interaction with substrate. This research has shown that the self-assembly improves safety and handling tractability of high-energetic materials (HEMs). According to the recent study, control of the specific crystal size for reducing the internal defects is mightily important, because the internal defects are a factor in unstability of HEMs. In turn, we performed self-assembly of organic molecules and HEMs by using nano-sized HEMs, which were produced by drowing-out or milling/crystallization. Surface modification efficiency was decided by size distribution, zeta-potential, friction sensitivity and electrostatic charge. 입도/표면전하/마찰감도/정전기 전하 등을 측정하여 표면개질 여부를 확인하였다.
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