Study On Thermal Properties Of Al-Li And Al-Eu Alloy Fuels And Their Effects On Ammonium Perchlorate Decomposition

As the most widely used metal fuel in solid propellant,Al powder has inherent disadvantages such as incomplete combustion and easy aggregation of products.In this paper,aluminum-based alloy fuels were prepared by adding Li and Eu elements respectively to improve the combustion efficiency,and the basic thermal properties of the metal fuels were evaluated.Their effects on the thermal decomposition of ammonium perchlorate?AP?were systematically investigated,the effect mechanism was discussed.A series of Al-Li and Al-Eu binary alloy fuels were prepared by gas atomization method,and their phase composition,microstructure and thermal properties were characterized by XRD,SEM/EDS and TG/DTA respectively.The results show that both alloy fuels have good sphericity,the surface of Al-Li alloy particles is obviously oxidated,and the surface of the Al-Eu alloy particles exhibits a staggered"scaly shape".The preferential oxidation effect of intermetallic compounds formed by alloying elements and aluminum imparts excellent thermal properties to Al-3Eu and Al-10Li.Compared with elemental Al,the oxidation heat release of Al-3Eu increases from 1655.1 J/g to 7811.5 J/g,and the actual/theoretical weight gain ratio increases from 0.33 to 0.85.The oxidation heat release of Al-10Li alloy is higher,reaching 9263.5.J/g,weight gain ratio is 0.99.The effects of Al-Li and Al-Eu alloy fuels on the thermal decomposition of AP were studied by non-isothermal kinetic method,and the influence mechanism was analyzed.The results show that Al-Li inhibits the low temperature decomposition of AP and accelerates its high temperature decomposition,so that the decomposition peaks are concentrated into a single exothermic peak.These effects enhance with the increase of Li content,when the Li content reaches 10 wt.%,the high temperature decomposition peak of AP is advanced by79.9°C,the apparent decomposition heat increases from 422.5 J/g to 1046.2 J/g,and the activation energy decreases by 62.9 kJ/mol.The Li salt on the surface of the alloy particles consumes the dissociation product of AP and inhibits its low temperature decomposition,while the oxidizing gas generated by the high temperature decomposition of AP undergoes a redox reaction with the active Li of the surface layer of the alloy particles,accelerating the decomposition process.With the increase of Eu content,the effect of alloy fuel on the low temperature decomposition of AP is gradually weakened,and the effect on the high temperature decomposition is continuously enhanced.When the content of Eu is higher than3 wt.%,the low temperature decomposition is inhibited.This is mainly due to the special surface of Al-Eu which limits the dissociation and sublimation of AP at low temperatures,allowing more molecules to enter the high temperature decomposition.In addition,the nano-sized Eu₂O₃ dispersed on the surface of the particles has a strong catalytic effect on the high temperature decomposition of AP.The thermal decomposition of ternary composites containing hydroxyl-terminated polybutadiene?HTPB?were also explored.The results show that the introduction of HTPB limits the mutual contact between AP and metal particles,which weakens the effect of metal fuel on AP thermal decomposition.In summary,Al-10Li and Al-3Eu alloy fuels have excellent and comprehensive practical application performance,and have broad application prospects in the field of propellants.