Characterization of Liquid Inclusion of RDX Crystals with a Cooling Crystallization

Abstract

Liquid inclusion phenomenon of cyclotrimethylene trinitramine (RDX) crystals commercially produced (Hanwha-RDX as a conventional RDX and I-RDX as a reduced sensitivity RDX (RS-RDX)) and recrystallized by a cooling method was quantitatively analyzed by using matching refractive index/digital image analysis, scanning electron microscopy, X-ray diffraction, and gas chromatography. Quantitative estimation of inclusion of RDX crystals by area distribution was made using image analysis and average values of Hanwha-RDX and I-RDX were 9.3% and 5%, respectively, and that of RDX recrystallized from γ-butyrolactone with a controlled cooling policy was 3.5−3.8% with initial crystallization temperatures smaller than 90 °C. It was found that the solvent content of RDX crystals from γ-butyrolactone by a linear cooling from 90 to 20 °C was about 1686−3140 ppm (cooling rates: 0.5, 1, 1.5, and 2 °C/min) and was reduced to 970.7 ppm by controlled cooling. Liquid inclusions in RDX crystals produced from γ-butyrolactone were found to increase rapidly at the initial stage of crystallization. These results suggest that reduction of the amount of liquid inclusion in RDX is possible by a careful controlled cooling strategy at nucleation and the initial step of crystal growth.