Experimental And Theoretical Study On The Crystallization And Morphological Control Of 3,4-Dinitropyrazole

The crystallization and morphological control of energetic materials presents a crucial effect on their application properties.3,4-dinitropyrazole(DNP)is one of new type of cast explosive and its spherical crystals are safer and more needed in the crystallization process.In order to retrieve the perfect single crystals,the solubility parameters of DNP in various solvents were experimentally and theoretically researched.A self-planed software was designed and deployed in the solubility calculation of DNP.Using that,the detailed soluble and thermodynamic data in various solvents were collected and predicted.The single crystals of DNP were finally cultured in optimal solvents according to the above research data and analyzed using molecular dynamics.The morphologies of DNP crystals in other solvents may also be predicted on the calculation.The main content of this paper is as follows.(1)The solubility of DNP in different solvents was firstly determined by the static gravimetric method.The specific data in four p H solution at 288.15-323.15 K were recorded and the thermodynamical data were measured with addition of nitric acid and acetic acid.Then the modified Apelbat,NRTL and Wilson models were calculated to fit the experimental data.The results show that the dissolution process of DNP is spontaneous,and the change of solubility is dependent on the increase of temperature.At the same range of temperature,the crystallization of DNP in organic solvents and water were screened and the solubility of hydrocarbon solvents were found lower than that of alcohols and ethers.In addition,the solubility of DNP showed the highest growth at a p H of around 2.6 and the lower growth rate at a p H of around 7.(2)Related to the incompatibility between current software and operating systems,a more suitable software was designed and developed to calculate the experimental data by the Python computer language.This software will automatically read,calculate,output the predicted solubility,and achieve the fitting of parameters and thermodynamic data.The black-box and white-box testing were conducted to ensure the reliability and stability of the software.(3)DNP crystal-structure files were obtained from the Cambridge Crystal Database.The characteristic crystal-planes of DNP were predicted using BFDH and GM growth method as(10 0),(1 1 0),(0 1 1),(0 2 0)and(1 1-1).The effects of temperature,single solvent,and mixed solvent were predicted and discussed on the crystal formation of DNP.Based on them,crystals of DNP were successfully cultivated using the gas-phase deposition,evaporation,and cooling methods in water,toluene,ethyl acetate,and dimethyl sulfoxide.The crystal morphology of DNP established in the above solvents were compared with the theoretical prediction using molecular dynamics methods and MAE1 model.The results show that DNP crystals are commonly in bulk and rod shapes.The better spherical crystals could be achieved separately in water and ethylene glycol at 318.15 K.The greater impacts on the crystals morphology would occur with the larger proportions in the mixed solvent.