八面体形细粒度高品质RDX晶体的制备及生长机理

Preparation and Growth Mechanism of Octahedral Fine⁃grained High⁃quality RDX Crystal

采用溶剂-反溶剂法,在二甲基亚砜(DMSO)-乙二醇(EG)体系中,以1-乙基-3-甲基咪唑醋酸盐(EmimOAc)离子液体为添加剂,制备了平均粒径为9.35μm的八面体环三亚甲基三硝胺晶体(O-RDX)。系统研究了溶剂体系、溶液浓度、结晶温度、添加剂、搅拌速率等结晶参数对RDX晶体生长行为的影响规律,发现过饱和度是决定RDX晶体生长方式的主要因素,随着过饱和度的逐渐减小,RDX晶体经历了粗糙生长-二维生长-螺旋生长的变化过程,RDX晶体形态由树枝状逐渐演化为八面体形状。与原料RDX相比,O-RDX的晶型未发生改变,为常用的α晶型;O-RDX晶体密度增加,内部缺陷减少;分解温度提高5℃;撞击感度和摩擦感度分别降低60%和50%。为揭示O-RDX的形成原因,采用附着能AE模型,分子动力学(MD)方法,预测了RDX在真空下和EmimOAc作用下的晶体模型。预测结果表明,真空条件下RDX具有6个重要的生长面:(1 1 1)、(2 0 0)、(1 0 2)、(0 2 0)、(2 1 0)、(0 2 1),EmimOAc则使RDX主要晶面的生长速率趋于一致,导致八面体RDX晶体的形成,理论模拟与实验结果基本一致。

The octahedral cyclotrimethylenetrinitramine crystal(O-RDX)with an average particle size of 9.35μm was prepared through the solvent-antisolvent method in the dimethylsulfoxide(DMSO)-ethylene glycol(EG)system using 1-ethyl-3-methy-lethimidazole acetate(EmimOAc)as an additive.The effects of crystallization parameters such as solvent system,solution con-centration,crystallization temperature,additive and stirring speed on the growth behavior of RDX(cyclotrimethylenetrinitra-mine)crystals were systematically studied.It was observed that the main factor influencing the growth of RDX crystals was the su-persaturation.With the gradual decrease of supersaturation,RDX crystals experienced the changes of rough growth,2D growth and spiral growth,and the morphology of RDX crystals gradually evolved from dendritic to octahedral crystals.The results of ana-lytical tests revealed that O-RDX crystals were in theα-form which was consistent with the raw RDX,showing high crystal densi-ty with few crystal internal defects and an increase of 5℃in decomposition temperature.Moreover,compared to the raw RDX,the impact sensitivity and the friction sensitivity of O-RDX decreased by 60%and 50%,respectively.To further explore the for-mation mechanism of O-RDX,adhesion energy model and the molecular dynamics method were applied to simulate the crystal morphology of RDX in the presence of EmimOAc.The simulated results demonstrated that there were six main crystal faces of RDX:(111),(200),(102),(020),(210),and(021).The formation of the double-cone octahedral morphology origi-nated from the uniform growth rates of the main crystal faces of RDX under the action of EmimOAc.The theoretical simulations generally agreed well with the experimental phenomena.