Study On The Isothermal Decomposition Behavior And Mechanism Of AlH₃/Hydrogen Getters

By virtue of high energy density,the ability to reduce ignition temperature,releasing H₂ and heat during combustion,AlH₃potentially might be an ideal fuel for solid propellant instead of aluminum powder.However,its storage is difficult due to poor thermal stability even at room temperature,resulting in lower energy,cracks,and shortened storage life of propellant grin.Moreover,the temperature is very important for AlH₃.Hydrogen getter is an effective strategy to reduce the amount of H₂ released from AlH₃-containing solid propellant.In this area,research workers focus on the hydrogen absorption effect,the interaction between hydrogen getter and AlH₃,and the influence laws of temperature.Herein,their thermal decomposition behaviors of AlH₃and AlH₃/hydrogen getter were studied by an isothermal decomposition method.The abilities of absorbing hydrogen were evaluated in depth.The relevant works provide data and technical support for the application of AlH₃in solid propellant.The main research work is as follows:（1）The isothermal thermal decomposition behavior of AlH₃ was studied.The isothermal thermal decomposition process of AlH₃ was studied by isothermal thermal decomposition gas measuring device,and the thermal decomposition pressure-time curves at six temperatures of 333 K,343 K,353 K,363 K,373 K and 393 K were obtained.The kinetic parameters of AlH₃before and after the inflection point were calculated by Arrhenius equation and mode matching method,indicating that the calculation results of the two methods were similar.The calculation results of the model fitting method show that the thermal decomposition curve of AlH₃ before the inflection point satisfies the Mampel Power law,and the corresponding E_ais 120.4 kJ·mol^-1,ln(A/s^-1)=21.65.The thermal decomposition curve of AlH₃ after the inflection point satisfies the law of shrinking sphere（volume）,the corresponding E_ais 102.1 kJ·mol^-1,ln(A/s^-1)=20.12.The gas and solid residues after AlH₃decomposition were characterized by XRD,GC and TEM.The possible thermal decomposition mechanism of AlH₃ was proposed,indicating that the thermal decomposition of AlH₃ can be divided into three steps:induction period,acceleration period and deceleration period.（2）Functional fullerene derivatives as hydrogen getters were prepared and studied by isothermal thermal decomposition.C₆₀p-methoxy arylamine pyrrolidine derivatives were synthesized by Prato reaction using C₆₀,N-aryl glycine derivatives（p-methoxyaniline）and p-methoxybenzaldehyde as raw materials.C₆₀p-methylaniline derivatives were synthesized by nucleophilic substitution reaction using C₆₀Cl₆ and p-methylaniline derivatives as raw materials.AlH₃/hydrogen getter mixtures were prepared by solvent evaporation method with AlH₃ and hydrogen getters including DEB,C₆₀,fullerene p-methoxy arylamine pyrrolidine derivatives,fullerene-ethoxy arylamine cyclopropane derivatives,fullerene p-toluidine derivatives and C₇₀,respectively.The effects of absorbing hydrogen were assessed by measuring the amount of gas released by the isothermal decomposition dynamics research instrument.The isothermal decomposition processes of mixtures were monitored and measured in real time by isothermal decomposition dynamics research instrument.Relevant gaseous pressure-time curve were record and obtained.The thermal decomposition kinetics and mechanism function of the mixed material were obtained by Arrhenius method and model-fitting method.The thermal decomposition products were analyzed by XRD,HPLC and TEM.The results showed that the releasing gaseous of the above systems were 2.85mL·g^-1,2.02 mL·g^-1,2.41 mL·g^-1,2.35 mL·g^-1,2.43 mL·g^-1,2.54 mL·g^-1and 1.92 mL·g^-1.Fullerene and its derivatives as hydrogen getters are effective and outstanding,among them C₇₀is excellent.After the addition of hydrogen getter,the activation energy of mixture is similar to that of pure AlH₃,indicating that the original composition of AlH₃ is unchange before and after hydrogen absorption.The isothermal decomposition dynamics research instrument is expected to be applied to the performance evaluation of hydrogen getter in AlH₃ solid propellant and the screening of hydrogen getter.