Study On Interface Properties And Application Technology Of HNIW/Bonding System

Hexanitrohexaazaisowurtzitane (HNIW) is the best single explosive synthesized incomprehensive performance so far, of which the high energy density plays a significant rolein the development of advanced weapon system. Owing to its high sensitivity and badprocessability, HNIW needs to be manufactured to polymer bonded explosive (PBX) bycoated by proper polymer binders and desensitizes for the enhancement of safety andcompactibility. As the transitional region between different phases in PBX，the interfacestructure between HNIW and bonding system has a key effect on the overall performanceof PBX. Therefore, in this paper, the properties of interface structures in ε-HNIW-basedPBX were studied using molecular dynamics (MD), on the basis of which thecorresponding formulation molding powders were prepared and characterized, paving abetter way for the application of HNIW in high energy mixed explosive.The structures and properties of the six morphologically important faces of ε-HNIWcrystal (110)(11-1)(001)(200)(011) and (20-1) were investigated using simulation method,including surface atomic distribution, electric property and stability. The results showedthat (110) and (11-1) had more morphological importance than the other faces, and that(11-1) with the most negative charge had the worst stability. On this basis, MD method wasused to investigate the effects of binding energy, N-N interaction energy, cohesive energydensity and mechanical properties of ε-HNIW/binder interface systems on the performanceof PBXs. The results showed that the adding of binders had no influence on the stability ofinterface systems, and that the elasticity of ε-HNIW/binder interface structures wasenhanced compared with that of ε-HNIW crystal face structures, with the order ofε-HNIW/Estane5702>ε-HNIW/F2641>ε-HNIW/PIB>ε-HNIW/F2311. Besides, Theappropriate temperature ranged for the binding of explosive and binders,50~75℃, and theideal temperature for the termination of cooling,25℃, were obtained by comparing thebinding energies of interface systems at different temperatures. Similarly, it was concludedthat the ideal temperature for the processing of PBX should be75℃by comparing themechanical property K/G of interface structures at different temperatures. Accordingly, the molding powders of ε-HNIW/binder were prepared using aqueous suspension method. Theimpact sensitivities of the molding powders of ε-HNIW/binder decreased slightly(0<ΔH50<2cm) compared with that of ε-HNIW, while there was a linear correlationbetween the impact sensitivity and the elasticity of interface structures (1/K+1/G) fromsimulations with R2of0.8723, revealing that polymer binders succeeded in desensitizingε-HNIW through elastic deformation.Meanwhile, MD method was used to investigate the effects of binding energy, N-Ninteraction energy, cohesive energy density and mechanical properties ofε-HNIW/desensitizer interface systems on the performance of PBXs. The results showedthat the strength and compactibility of ε-HNIW/desensitizer interface structures were lowerthan those of ε-HNIW/binder. Then the molding powders of ε-HNIW/desensitizer wereprepared using aqueous suspension method. The mechanical sensitivity test revealed thatPW had a better desensitization effect on ε-HNIW than SA, and confirmed the finedesensitization effect of graphite absorbed on the surface of the molding powders ofε-HNIW/binder as well. Furthermore, the desensitization mechanisms of differentdesensitizers were investigated using both computational and experimental methods. Theresults indicated that PW and SA shared similar endothermic, insulation and lubricationeffects on ε-HNIW, which revealed that the main reason why the desensitization effect ofPW was better than that of SA was that PW was better-distributed on the surface ofε-HNIW than SA with a higher spreading coefficient S (S for PW was12.7mJ·m-2, while Sfor SA was only3.3mJ·m-2). Graphite, in addition, could effectively lubricated ε-HNIWthrough the sliding of its layered structures.The molding powders of different ε-HNIW/binder/desensitizer/graphite formulationswere prepared by choosing F2311and Estane5702as binder, choosing PW and SA asdesensitizer, and using aqueous suspension and dry mixing method, and thus optimizedprocess conditions obtained were as follows: the temperature for adding binders55~60℃,the temperature for adding desensitizers50~55℃, the adding rate for binder1.20mL·min-1, the agitation rate650r·min-1and the range of particle screening12~50mesh.Scanning electron microscope (SEM), Fourier transform infrared spectrometer (FT-IR),differential scanning calorimeter (DSC), mechanical sensitivity and tensile strength test were used to characterize the coated samples, respectively. The results showed that thesystem of binder/desensitizer/graphite could effectively coat ε-HNIW without affecting itscrystal form and thermal stability. By comparison, it was concluded thatε-HNIW/F2311/PW/G (mass ratio94.2/4.3/1.0/0.5) with a reduced impact sensitivity of16%and a reduced friction sensitivity of12%and ε-HNIW/Estane5702/PW/G (mass ratio95.2/3.3/1.0/0.5) with20%and10%, were the formulations that had lower mechanicalsensitivity. The former one had a tensile strength of1.46MPa, while the latter one only0.96MPa. A further analysis of fracture behavior and morphology indicated that the sampleof ε-HNIW/Estane5702/PW/G yielded under the action of tension stress, showing thecharacteristics of ductile fracture.The tensile strength of ε-HNIW/F2311mixed explosive was calculated based on theabove parameter results from the simulations and experiments according to Griffith theory,which turned out to be1.98MPa, evidently higher than that determined by Brazilian test.Afterwards, the strength of ε-HNIW based mixed explosive was enhanced using thesystems of F2311/PW/F2311, PW-polymer and PW-SA. Among them, the two kinds ofcomposite desensitizer systems gained better effects which made the tensile strength closeto the calculated value. When PW-polymer composite system was used, the strength of thesample could be effectively enhanced through the energy consumption caused by the plasticdeformation of polyurethane. It seemed that the samples had lower mechanical when themass ratio of PW/Estane5702or PW/H663equaled to7/5or5/3. The corresponding MDsimulations drew a conclusion that higher ability of polymer to combine with PW resultedin better desensitization effect of composite system on ε-HNIW. When PW-SA compositesystem was used, the tensile strength of ε-HNIW based mixed explosive, with the increaseof SA mass percentage (0%â†'30%â†'70%), shared a similar upward tendency with thecompression strength of the PW-SA composite system used, indicating that the strength ofε-HNIW based mixed explosive was enslaved to that of the desensitizer to a certain extent.The composite system had the comparatively better desensitization effect on ε-HNIW whenusing benzene as solvent with the mass ratio of PW/SA equaling to7/3or3/7. It wasconcluded that more stable and well-distributed PW/SA composite solution might lead tobetter desensitization effect of composite system on ε-HNIW from the corresponding MD simulations.