| Gun barrel is one of the most important parts for artillery.With the extensive applications of high energy propellants,barrel erosion has worsened and markedly shortened the useful life of barrel,which becomes a major limitation in developing more powerful artillery.Adding the anti-erosion additives into the propellant charging system is one of the simple and effective ways for reducing the wear and erosion of gun barrel.However,the traditional anti-erosion additives have some disadvantages,such as large dosage,taking up too much propellant charging space and more residues,which cannot meet the requirements for reducing the erosion of advanced artillery.Therefore,it is urgent to design high effective anti-erosion additives for high energy propellants.Nanocomposites have attracted widely interests for their unique physical and chemical properties.In the present study,combining the excellent performances of organic and inorganic materials,various kinds of novel nanocomposites were designed and prepared based on the erosion mechanism of barrel,then their physicochemical properties and the anti-eriosion performances when used in propellants were investigated.The prepared nanocomposite is a potential functional additive for propellant matrix,which can not only reduce the erosion effect of high energy propellant,but also improve its combustion performance as well.The main research contents and results are summarized as follows:(1)TiO2 has been used as ablation-resistant material and coating desensitizer in propellants.In order to improve the applicability of micro/nano-sized TiO2 in propellant matrix,hollow TiO2 spheres with controllable particle sizes were synthesized through a sol-gel process by using mono-dispersed polystyrene(PS)microspheres as templates.Afterwards,a viable processing route for grafting polyimide(PI)brushes on the surface of hollow TiO2 was successfully achieved by "click" chemistry method.The results showed that the prepared TiO2/PI nanocomposites possess some outstanding characteristics such as lightweight,excellent thermostability and flame retardance,which can be used as new functional additives in propellants.(2)Phase change materials(PCMs)such as solid paraffin have the ability to store and release heat during their phase transition process,which can be used as one of the main components of the anti-erosion additives.By virtue of the unique properties of nanomaterials and the outstanding thermal stability,high strength and hardness,excellent thermal shock resistance and wear resistance of inorganic powders(such as Si3N4 and BN),a series of solid paraffin-based composite PCMs were synthesized by using various inorganic nanoparticles as reinforcing materials.The prepared composite PCMs are expect to be used as high-efficiency anti-erosion additives for high energy propellants.Results showed that the obtained composite PCMs appeared spherical shape with a mean diameter of around 10?30?m.They also have a high thermal storage capability and good thermal stability.In addition,the morphology,heat storage performance and thermal stability of the composite microcapsules can be controlled by changing the contents of nanoparticles and paraffin in recipes.(3)Liquid silicone oil is a highly effective inhibitor in the propellant for reducing the erosion of gun barrel.In order to solve the charging and leakage problem of liquid silicone oil,highly stable microencapsulated silicone oil with PS as inner shell and nano-TiO2/Si3N4 as outer shell was prepared by a Pickering emulsion technique.The obtained composite silicone oil microcapsules have an average diameter of 10?20 ?m,and the maximum encapsulation rate can reach 70%.According to the results of thermogravimetric analysis test,the microencapsulated silicone oil showed a considerable increase for initial decomposition temperature and maximum decomposition temperature.Such a notable increment is attributed to the existence of compact hybrid shell on the silicone oil droplets surface,which can give the silicone oil core a protective effect.(4)Zeolitic imidazolate frameworks(ZIFs)are a novel kind of porous organic-inorganic hybrid materials with excellent properties such as large surface areas,outstanding thennal and chemical stabilities as well as adjustable and functionalized skeleton structure.Considering the unique nanostructure and properties of ZIFs,a series of novel paraffin/ZIF composite PCMs was facilely and effectively fabricated.The results showed that the composites possess excellent phase change performance.When adding 10 wt%of ZIF-67 crystals(constructed from Co2+ and imidazolate ligands),the obtained composites present good thermal stability and the corresponding phase change enthalpy is 159.60 J/g.(5)The prepared nanocomposites(including composite silicoine oil microcapsules,inorganic nanoparticles modified composite PCMs and paraffin/ZIF composite PCMs)and a variety of micro/nano particles were employed as anti-erosion additives for high energy propellants.Their anti-erosion effects were studied by an erosion tube test,and the corresponding anti-erosion mechanism was further analyzed.Results showed that the anti-erosion effect of ZIF-67 crystals was the best among the nano-Si3N4,nano-BN,nano-TiO2 and ZIF-67 when added 1%relative to propellant mass.Three kinds of nanocomposites all presented good anti-erosion effects,and their anti-erosion efficiency appeared linear increase with the increase of nanocomposites content.But it is worth mentioning that the paraffin/ZIF composite PCMs presented better anti-erosion effects under a lower loading.The plausible anti-erosion mechanisms for variety kinds of nanocomposites could be:during the combustion of high energy propellants with nanocomposites,the nanocomposites with small size have enormous ability to absorb amounts of heat,and the nanoparticles deriving from composites recipes could be deposited on the surface of barrel and formed a thermal-protective coating.(6)Nanoparticles with good anti-erosion effect were composited with solid paraffin,and a multicomponent nanocomposite was prepared.Then the nanocomposite was used as a functional additive to modify high energy propellants and the modified high energy propellants containing various contents of nanocomposites were manufactured by a semi-solvent extrusion technique through the process of plasticizing,kneading and extruding.The erosion performance of the modified high energy propellants was studied.The results showed that the nanocomposites have some influences on the initial thermal decomposition process of high energy propellants.Importantly,the erosion performance of modified high energy propellants was significantly reduced,and their initial combustion was inhibited at well.The above trend was increased with the increase of nanocomposites content.As the addition of nanocomposites reached the maximum values of 5.1%,the erosivity and powder force of the modified high energy propellant reduced by 37.0%and 5.7%,respectively.In practical application,the adding content of nanocomposites can be adjusted according to the application requirements to achieve the balance of the comprehensive performances. |
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