Study On The Surface Properties And Hydrogen Release Mechanism Of AlH₃

Aluminum hydride?AlH₃?is a metastable crystal at normal temperature.With high hydrogen concentration and fast hydrogen releasing rate,it is used as an explosive,a reducing agent,a solid rocket propellant and a hydrogen source.Compared with traditional rocket solid propellant,AlH₃ can decrease the temperature of combustion chamber and enhance energy performance of solid propellant.However,the safety of peopeellant is poor because of high sensitivity.The objective of research in this thesis including:characterize,hydrogen release kinetics and surface features of AlH₃ their effects on propellant safety,which will lay solid theoretical foundation for industrial application of AlH3 as propellant.To be detailed,element analysis,ICP,SEM,IR,XPS have been applied to characterize contamination within AlH₃ and surface features.The results show that?1?AlH₃ samples consist of a lot of small crystal grains,while the large particles are formed by the accumulation of small particles.There are compact Al2O3 thin films wrapping on the surface of all samples.There are three granules?acicular granule,cubic granule and floccular granule?in these samples.The oxide layer of acicular granule is thicker compared with those on the other two type of granules.Roughness of surface is proportional to the thickness of Al₂O₃ oxide layer.?2?The surface of small particles is glossy and the content of mixed crystal is lower.On the contrary,the surface of large particles is rough and there are more defects and higher content.?3?The concentration of acerbic site on AlH₃ sample surface is low and the magnitude is around 10^-22 mmol/g.The concentration of acerbic site on samples is higher if the samples were prepared by a wet process.However,it can T be reduced by coating treatment process.?4?In addition to Al₂O₃,there are Li,Cl and C residues within AlH₃ samples.The content of Cl on the surface of the samples is higher than samples inner part and Li mainly comes from unreacted reactant?LiAlH₄?.Crystal structure of the different samples has been characterized by X-ray powder diffraction.Besides of?-AlH₃,there is a small amount of?-AlH₃,??-AlH₃ in the sample.A method for quantitative analysis of the content of?crystal in aluminum hydride powder was established by X-ray powder diffraction based on the internal standard method.The silicon powder was determined as internal standard substance and the relative standard deviation of multiple testing results is less than 2%.TG-DSC was used to investigate the thermal decomposition of AlH3 and the kinetic equation of isothermal decomposition was established.The results show that?1?The kinetic model of AlH₃ pollows with Avrami-Erofeev theory and n?Avrami-parameter?of acceleratory and decay period is 3 and 2,respectively.It indicates that the decomposition of AlH₃ is controlled by Al nuclear three-dimensional growth mechanism in acceleratory period and two dimensional growth mechanism in decay period.?2?The kinetic equations of AlH₃ powders decomposition were calculated.The activation energy of isothermal decomposition is 95.27-107.0kJ/mol.The reliability of the kinetic equation was verified by testing against decomposition curves at 135?.This paper has discussed the effect of different AlH₃ surface topology on the safety of propellant.The results show that:as the size of granules,roughness of samples or content of?-crystal decreases,the safety of propellant increases.It's because there are more active sites and hot spot on AlH₃ with rougher surface,higher content of mixed crystal or surface defects.