| Elemental Al powder,as the most common metal fuel in the field of solid propellants,has some shortcomings that are difficult to overcome,such as incomplete combustion,high ignition temperature and easy condensation of products due to its dense oxide film.In this paper,active element Li was added to prepare Al-Li alloy fuels to improve its combustion efficiency,and the effect of Li content on the performance of alloy powders was studied.Li increased the activity of alloy powders,but they were easy to be oxidized at the same time.In order to protect the activity of the Al-based alloy powders,the surface of powders was coated by a layer of polystyrene and a layer of styrene-acrylic acid copolymer separately by in-situ polymerization.A series of Al-Li alloy powders were prepared by the gas atomization method.XRD,SEM and TG/DTA were used to characterize and analyze the phase,morphology and thermal properties.The results show that the Al-Li alloy powder prepared by the gas atomization method has good sphericity.With the increase of Li content,the oxidation heat release and the weight gain of Al-Li alloy powders continue to increase.When Li content reaches 10 wt.%,the oxidation heat release is 9263.5 J/g,and the weight gain is 90.3%,which is close to the theoretical weight gain(91.4%).However,after aging in air at a relative humidity of more than 60% at room temperature for two weeks,the oxidation weight gain of Al-10(wt.%)Li alloy powders decreased to 53.2%.The attenuation rate was 41.1%,and the activity loss was serious.According to the orthogonal test and the simple comparison method,the optimum conditions for coating Al-10 Li alloy powders by in-situ polymerization of styrene were as follows: m(St)/m(Al-10Li)was 1:1;m(AIBN)/m(St)was 5%;the reaction temperature was80 °C;the reaction time was 4 h.The structure,surface morphology,thermal properties and aging stability were characterized by XPS,FTIR,SEM and TG/DTA.The results show that the attenuation rate of the weight increase of the active metal of Al-10 Li alloy powders coated by polystyrene decreases to 6.5% after two weeks of aging under the same conditions,which demonstrates that the polystyrene coating effectively protects its activity.A layer of styrene-acrylic acid copolymer was coated on the surface of Al-10 Li alloy powders by in-situ copolymerization.The optimal monomer dosage ratio is m(AA)/m(St)=0.2 through the corrosion inhibition efficiency.The surface composition,morphology,thermal properties and aging stability of the coated powder were characterized by the same test method.The results show that the attenuation rate of the weight increase of the active metal of Al-10 Li alloy powders coated by styrene-acrylic acid copolymer is 6.1% after two weeks of aging under the same conditions,indicating that the styrene-acrylic acid copolymer coating can also effectively protect its activity.In summary,the Al-10 Li alloy powders coated by two methods not only have excellent thermal reactivity,but also have good storage stability,so they have broad application prospects in the field of solid propellants. |
