Study On The Thermal Decomposition Dehydrogenation And Ignition Combustion Characteristics Of ?-AlH₃

Aluminum hydride?AlH₃?,as an ideal carrier of hydrogen energy,has became a hot research spot of hydrogen storage materials at home and abroad because of its high hydrogen storage capacity,rapid hydrogen release at low temperature and low toxicity.However,the thermal evolution of hydrogen and ignition combustion characteristics has not been fully revealed.In this paper,the thermogravimetric test system was used to carry out experiments on hydrogen evolution and oxidation of AlH₃,and the effects of particle sizes and different atmospheres on their thermal decomposition and oxidation characteristics were analyzed.The condensed products were analyzed by means of SEM,XRD,XPS and EDS to study the microstructure and composition changes during thermal decomposition and oxidation.The ignition combustion experiment was also carried out,and the influences of particle size and oxygen concentration were studied.Finally,the laser ignition and combustion was carried out by mixing samples with different mass ratios of Al / AlH₃,and the effect of AlH₃ on the ignition characteristics of Al was studied.The main research contents and conclusions of this paper are as follows:?1?In the argon atmosphere,the TG curve shows that the hydrogen evolution stage of AlH₃ is a typical "S" type curve,which is divided into three stages of induction,acceleration and decay;In air atmosphere,the thermal reaction of AlH₃ is divided into three stages: the hydrogen phase,the Al oxidation phase and the Al high temperature oxidation phase.Kinetic analysis shows that the smaller the particle size of the sample,the lower the initial decomposition temperature and the lower the activation energy.The median diameter of 21.88 ?m is the best for hydrogen and oxidation,and the activation energy at each stage in the argon atmosphere is much lower than that in air atmosphere.The inert atmosphere and reduced particle size can increase the performance of thermal decomposition hydrogen.?2?The results of TG-MS showed that the main gas products were m/z 2?H₂?,m/z 18?H₂O?and some small m/z 17?OH?ion peaks in the air atmosphere.It indicated that hydrogen is firstly released and then the hydrogen is oxidized to form water during the heating process.In the nitrogen atmosphere,there was almost only the m/z 2?H₂?ion peak,and the content of H₂ released under a nitrogen atmosphere is much higher than that in the air atmosphere,indicating that the oxidizing atmosphere inhibited the released of hydrogen.The SEM and XRD results of the condensed products showed that the surface of the sample appeared pore structure as the release channel of hydrogen,the remaining aluminum oxidized and agglomerated.The XPS and EDS results showed that the thermal reaction of AlH₃ follows the following process in air atmosphere: The hydrogen release of AlH₃ generation of H₂ and Al,then the oxidation of Al,and the conversion of ?-Al₂O₃ to ?-Al₂O₃.?3?The results of laser ignition experiments showed that: The evolution process of AlH₃ flame is divided into development,stabilization and decay stages.Due to the action of hydrogen gas flow,there is a phenomenon that the flame surface leaves the surface of the samples.The particle size increased from 21.88 ?m to 86.16 ?m,the ignition delay time increases from 12 ms to 130 ms,and the burn time is reduced from 238 ms to 80 ms.Reduces the particle size of AlH₃,which can effectively improve its ignition and combustion performance.As the oxygen content increases?25%,50%,75%,100%?,the brightness and height of the flame increases,and the combustion intensity increases.The maximum temperature increased from 1394.6°C to 1810.3°C,the ignition delay time was reduced from 10 ms to 2 ms,and the burning time was reduced from 1026 ms to 366 ms.The flame adhered to the surface of the sample when pure Al was burned,and the combustion flame of the mixed sample of Al / AlH₃ was burned above the sample due to the hydrogen.The maximum flame height and brightness were greater than pure Al.The ignition delay times of the mixed samples under different mass ratios?1:1,3:2,2:1?were 18 ms,12 ms,and 9 ms,respectively,and the maximum spectral intensities were 1262,1680,and 3140,respectively.The addition of AlH₃ has a significant improvement effect on the combustion of Al.In the experimental range,when the mass ratio of Al / AlH₃ is 2:1,the ignition delay time is the smallest,the maximum spectral intensity and average burning intensity are the largest,and the combustion performance is the best.