Preparation Of Nano-Si@PVDF Composite Energetic Films By Electrospinning And Its Reaction Characteristics

High content of active component,low electrostatic sensitivity and superior long-term storage stability endow nano-silicon powder（Si NPs）powder unique advantages for application in nanoenergetic composites.In this paper,hydrophobic and corrosion-resistant nano-Si@PVDF composite energetic films with different stoichiometric ratios（Φ）were successfully prepared by electrospinning,and their ignition and combustion characteristics,the heat release characteristics and reaction mechanism in the process of thermal analysis have been investigated.The main research contents and results are as follows:（1）The precursor was prepared by adding Si NPs and PVDF powder into the acetone/DMF mixed solution with a volume ratio of 1:1,and nano-Si@PVDF composite energetic films with differentΦwere prepared by electrospinning technique.SEM images show that the diameter of the prepared fiber is 200 nm～1.2μm,and the average diameter increases at first and then decreases with the increase ofΦ.The results of XRD,XPS and FTIR show that no new substances were formed in the preparation process.The tests of contact angle of deionized water and corrosion-resistance of concentrated alkali solution show that Si NPs is effectively protected by PVDF,and the prepared Si@PVDF composite energetic film has excellent corrosion-resistance to deionized water and concentrated alkali solution.（2）Through the electrostatic spark ignition test,it is found that the powder and film composites of Si NPs and PVDF can not be ignited at the energy level of 25 J,showing a very low electrostatic sensitivity.Through the constant volume combustion chamber test and Ni-Cr alloy wire ignition test in open environment,it is proved that the Si@PVDF composite energetic films by electrospinning technique can make non-combustible Si/PVDF physical mixture combustible.TheΦhas a great influence on the combustion performance of Si@PVDF composite energetic thin films.In a constant volume combustor,the sample shows better energy release characteristics at lowΦ（0.5～1.5）.In the open environment,the oxidation of Si NPs is a decisive factor on the optical signal output,in this case,the maximum optical signal intensity detected by Si@PVDF at highΦ（1.5～5）is 4～9 times higher than that of lowΦ（0.5～1）.There is a certain competitive relationship between oxidation reaction and fluorination reaction.（3）Through the TG-DSC characterization of Si@PVDF samples with differentΦ,the results show that there is only one weight loss process and one exothermic peak in the whole thermal reaction process,corresponding to multi-step reaction.With the increase ofΦ,the mass loss of Si@PVDF thin film decrease from 90.1%to 37.3%,the initial reaction temperature decrease from 488.9℃to 452.0℃,the exothermic peak temperature and reaction heat increase at first and then decrease,at the ideal stoichiometric ratio reaches maximum（495.6℃,1339.3J/g）,the thermal reaction of Si NPs and PVDF is carried out most fully.（4）Through TG-DTA-MS analysis,the differences of product composition and signal intensity between pure PVDF fiber film and nano-Si@PVDF composite energetic film at low heating rate were compared,and the thermal reaction mechanism of Si NPs and PVDF was inferred.The Raman,XRD and SEM characterization of the solid residue of DSC show that amorphous carbon and SiC are formed after the reaction is completed,whenΦis greater than1,there is still raw material Si NPs surplus.The thermal reaction mechanism of nano-Si@PVDF composite energetic film is as follows:PVDF is thermally decomposed to form HF gas and amorphous carbon first,then HF reacts with oxide SiO₂ in the outer layer of Si NPs to form H₂O and SiF₄,and then reacts with the exposed Si to form H₂ and SiF₄,Si NPs can also react with amorphous carbon to form SiC.However,this reaction is only a partial reaction and Si NPs can not be completely carbonized.