Investigation Of The Crystallization Kinetics And Crystal Defects Of HMX

HMX is extensively used in initiating explosive material and solid-fuel rocket propellant due to its advantages such as stable performance, excellent detonation performance, and high energy. β-HMX is the thermodynamically stable form at atmospheric pressure and temperature. More recent advanced studies on HMX suggest that the quality of HMX is intensively affected by the shape of crystal, distribution of crystal size, and especially the crystal defects (external and internal defects). The fewer defects are included, the lower sensitivity and the better crystal quality are obtained. Various defects and heterogeneities are included in the original HMX crystal resulting in formation of hot spots that often cause explosion easily. The high quality crystal has the potential to reduce the hazards of HMX storage and transport capabilities. In addition, the crystal defects of HMX have greatly impact on the energy output. Recrystallization is an important separation and purification unit operation in chemical and pharmaceutical industries for the preparation of valuable materials such as drugs, catalysts, photographic, and energetic materias.High quality crystal with removing of the impurities and decreasing the amountof crystal defects can be obtained by recrystallization techniques. To obtain thequality of HMX crystals optimization, solution recrystallization can be usedfor reduction of the number of crystal defect, its quality is improved greatly. This study not only provides a dependable theoretical basis for technology optimization of the high-quality HMX, but also provides technical reference for the study of other high-quality explosives. Consequently, this study has an important significance for developing high-quality explosives. The main contents of this thesis are as follows:(1) The investigation on the metastable zone of HMX:The solubility data of HMX in γ-butyrolactone solvent are accurately measured by using of the laser-monitoring observation technique. The relationships between solubility data and temperature are correlated by using an Apelblat empirical equation. The parameters are derived by the multiple linear least squares method. Combined with the classical nucleation theory to cooling speed, stirring speed, we studied the relation to the interface stability zone width, and calculated the nuclear series corresponding temperature. The results show that the interface stability zone width broadens significantly along with the increase of temperature and cooling rate, and narrows gradually with the increase of stirring rate.(2) The nucleation process of HMX in γ-butyrolactone solvent:We Studied the nucleation process at different degrees of supersaturation, and different initial saturation temperatures. The nucleation induction time was measured under different conditions. The result shows that:when the supersaturation of HMX solution S> 1.35, primary homogeneous nucleation mechanism dominates the process of nucleation; When S<1.35, primary heterogeneous nucleation dominates. In addition, according to the classical nucleation theory, in this paper, we calculated the HMX nucleation parameters under different conditions, such as solid-liquid surface tension, surface entropy factor, and the nucleation rate constant.(3) The crystal growth of HMX in γ-butyrolactone solvent:By determining the induction period data, the growth mechanism is studied based on the method of induction period. Through the analysis of the fitting results, it indicates that the growth mechanism of HMX in y-butyrolactone is the two-dimensional nucleation mechanism.(4) The influences of nucleation mechanism on crystal defects:The nucleation mechanism affects the crystal defect:the matching refractive optical microscope (OMS) and the field emission scanning electron microscope (SEM) are used to Characterize the defects of HMX samples obtained in different conditions. Combining the nucleation mechanism with internal defects, it is obvious that the nucleation mechanism has srong infullences on crystal defect.