| The preparation of high-energy insensitive explosives is the common goal in the field ofenergetic materials. Hexanitrohexaazaisowurtzitane （HNIW） is considered as a typicalexample of high energy density materials and the best substitution of HMX. However, theapplication of HNIW is restricted due to its high mechanical sensitivity. Preparing ultrafineexplosive is one of the effective methods to reduce the mechanical sensitivity of explosive.Recrystallization and atomizing kinetic crystallization are used to prepare fine HNIW. Theinfluences of different factors on the effect of ultrafine and the polymorphs transformation ofHNIW in mixed solvent are researched.It turns out that during the progress of recrystallization of HNIW, part of β-HNIW isobtained with the speed of dropping of heptane added to15ml/min. The anti-solvent heptanewhich volume is eight times as much as the solvent is bubbled into the saturated solution ofHNIW at the speed of5ml/s, and the ε-HNIW which particle size is about3μm～5μm isobtained after the solution is stirred for one hour. HNIW particle size will be bigger with thestirring time is increased.With ethyl acetate as solvent, n-heptane as solvent, the spray was used to recrystallizatethe HNIW solution under different concentrations and different temperatures, the resultsshows that the β-HNIW was prepared with a saturated solution at60℃after refining andfreeze drying. Its D50was449.8nm, and the granularity of span was0.091. With theincreasing of concentration of explosive solution and temperature difference between solutionand anti-solvent, particle size of HNIW is decreasing, and the distribution of particle sizeranged narrowly.Adding small amount of β-HNIW prepared by atomizing kinetic crystallization to themixed solution of ethyl acetate and n-heptane （V ethyl acetate: V n-heptane=1:10）, and itwas stirred for6.5h, so the ε-HNIW of2.5μm can be got. As the amount of HNIW added to50g, and the velocity of the solution and anti-solvent in the process of refining to make thevolume of ethyl acetate and n-heptane is1:50,1:40,1:30,1:20, farther it is found that even if the percentage of ethyl acetate was increases to1:20, the conversion of β-HNIW to ε-HNIWnever occurs after stirring for7h. When the time extends to8h, though almost all the β-HNIWtransformed to ε-HNIW, the particle size has grown up to15μm.The impact sensitivity of HNIW samples which refined by atomizing kineticcrystallization is tested, the H50of β-HNIW is32.82cm which D50is449.8nm. Comparedwith raw HNIW, its H50has increased for78%. The impact sensitivity decreased obviously. |
