Basic Research On Application Of Dihydroxylammonium 5,5’-bistetrazole-1,1’-diolate

Dihydroxylammonium 5,5’-bistetrazole-1,1’-diolate（TKX-50）was first synthesized in2012,which possesses favorable application prospect in the energetic materials field considering its excellent comprehensive properties:high detonation performance,low impact sensitivity and low toxicity.In this paper,the purity analysis method,crystal morphology,crystal spheroidization and cocrystal structures of TKX-50 were studied systematically.5,5’-bistetrazole-1,1’-diolate dihydrate（1,1-BTO）was the synthetic precursor of TKX-50,the purity analysis conditions of 1,1-BTO using high performance liquid chromatography（HPLC）were established as follows:UV detection wavelength was set at 213nm,and the sample was separated by reversed phase column（Sino Chrom ODS-BP,4.6mm×200mm,5μm）using binary mobile phase acetonitrile and water（volume ratio of 30/70）with flow rate of 1.0 m L/min at column temperature of25℃.External standard method was chosen to analyze the purity of 1,1-BTO by comparison,and the linear equation obtained is H=573.78C-1.18 with the linear correlation coefficient of 0.9998.The relative standard deviation is in the range of0.48%～1.00%and the average recovery is in the range of 98.10%～100.64%,indicating that the method is accurate and sensitive.Purity analysis conditions of TKX-50 using HPLC were established as follows:UV detection wavelength was set at 200nm,and the sample was separated by reversed phase column（Sino Chrom ODS-BP,4.6mm×200mm,5μm）using binary mobile phase acetonitrile and water（volume ratio of 50/50）with flow rate of 1.0 m L/min at column temperature of 25℃.The external standard method was suggested to analyze the purity of TKX-50 by comparing different methods.The linear equation of external standard method is H=2286.33C+205.91 with the linear correlation coefficient of 0.9998.The predicted result by Growth Morphology model was selected as the crystalmorphology of TKX-50 by comparison.The aspect ratio of TKX-50 crystal is 1.97,and there are six important growth facets.Among them,（100）,（011）and（020）facets occupy relatively large area percentage,which are the slow-growing crystal facets and they possess larger morphological importance.The（110）,（11-1）and（12-1）facets occupy relatively small area percentages,which are the rapid-growing crystal facets.The（020）and（011）facets are electrically neutral,the（100）facet is positively charged,and the（110）,（11-1）and（12-1）facets are negatively charged.From the molecular dynamics（MD）simulations results of TKX-50 supercell structure at different temperatures,it can be seen that the simulated lattice parameters are consistent with the experimental results,and the PCFF force field chosen can be applied to the simulation system of TKX-50.The cohesive energy density（CED）value of TKX-50 is large,which indicates that its sensitivity is very low.The rigidity,hardness and fracture strength of TKX-50 are large,indicating that its mechanical properties are needed to be improved.Thus,TKX-50 can not be directly used for mechanical processing and appropriate modified methods are needed for its property modification.PCFF force field was used in MD simulations to predict the influences of dozens of different kinds of additives on each crystal facet of TKX-50.The calculated results indicate that ethanol,ethylene glycol and acetic acid additives can effectively reduce the aspect ratio of TKX-50 crystal and they are more favorable to the crystal spheroidization,the spherical effects of other additives on TKX-50 crystal are not obvious and some additives are even detrimental to the spheroidization of TKX-50.The calculated results can provide theoretical supports for the additive selection of the spheroidization system of TKX-50.Ethanol,ethylene glycol and acetic acid additives were added in the recrystallization experiments of TKX-50,respectively.The results indicate that the aspect ratio of recrystallization products with adding additives decreases obviously and their crystal morphology tends to be spherical shape,meanwhile,their particle size decreases obviously and the particle size is uniform with the narrow granularity distribution,their purity possesses the same specification with the common recrystallization product and their structures do not change with the addition of additives,their stability and apparent density are also improved compared with the crude sample.TKX-50/CL-20,TKX-50/HMX and TKX-50/RDX cocrystal models wereconstructed,respectively.Then energy,radial distribution function（RDF）,X-ray powder diffraction（XRD）,the maximum trigger bond（N-NO₂）length(L_max),CED and mechanical properties were calculated based on the equilibrium structures of these models by MD simulations to deduce the formation mechanism and features of cocrystal structures.The calculated results indicate that the cocrystal models are stable due to the large energy values,and the cocrystal models of TKX-50 substituted by CL-20 or HMX on its（011）,（100）and（020）facets are more stable.There are many kinds of hydrogen bonds and van der Waals force in each cocrystal model,which are the main conditions for the formation of cocrystal.The XRD diffraction peaks of each cocrystal model quite differ from the monocomponent’s and there are new peaks appear,thus each cocrystal model forms as a new stucture.The cocrystal structures can greatly improve the high sensitivity defect of CL-20,HMX and RDX.The rigidity,hardness and fracture strength of cocrystal models decrease and the ductility increase simultaneously,indicating that the cocrystal materials show better mechanical properties and they are more favorable for mechanical processing.