The Study On The Reaction Characteristics Of Aluminum/Carbon Dioxide Under Different Combustion States And Aluminum/Water

The content of carbon dioxide?CO₂?on the Mars is 96%.Therefore,the launching mass of rocket and the cost of Mars exploration can be significantly decreased by using the fuel of aluminum powder on Mars.However,there are few researches on Al/CO₂ reaction,and the mechanism of Al/CO₂ reaction is unclear.Thus,the study on nano-scale Al/CO₂ reaction is urgent at present.In this paper,the slow oxidation process of nano-and micro-scale Al/CO₂ at static state and the influences of additives on the Al/CO₂ reaction were studied.Then the experiments on flame propagation in aluminum cloud in CO₂ atmospheres were carried out for comparative study.The effects of aluminum particle size,initial gas temperature,initial gas pressure and mass loading on the flame propagation of aluminum cloud were studied.And the reaction of Al/H₂O was preliminary explored for basic research of the Al/CO₂ reaction with water vapor.In this part,the influences of reaction temperature,additives and additive concentration on Al/H₂O reaction were studied.?1?The slow oxidation processes of nano-and micro-scale Al/CO₂ at static state were studied by thermal analysis.And the thermal reaction products were analyzed by X-ray diffraction?XRD?and scanning electron microscope?SEM?.It's found that the solid-solid diffusion mechanism is the main reaction mechanism of nano-scale Al/CO₂ in static state.And the region of mass gain of nano-scale Al/CO₂ thermal reaction can be divided into three stages.The main oxidation process of nano-scale Al/CO₂ occurrs at stage I?a low temperature of 450 700??with the mass gain of 35.81%,while the main mechanism of micro-scale Al powder is the liquid-gas diffusion mechanism.And the mass gain process of micro-scale Al/CO₂ can be divided into two stages.The thermal reaction of micro-scale Al/CO₂ is mainly concentrated at stage II?a high temperature of 697 1188??with the mass gain of 74.47%.The analyses of thermal reaction products indicate that the crystal change of products of nano-scale Al/CO₂ is amorphous????-Al₂O₃,and particles are shown as sphere.For the thermal reaction of micro-scale Al/CO₂,the crystal change of products is amorphous??????-Al₂O₃.And there are some broken oxide shells in the thermal reaction products of micro-scale Al/CO₂.?2?TG/DTG analyses were used to study the influences of KNO₃ on the thermal reaction processes of nano-and micro-scale Al/CO₂.The ignition phenomena of nano-scale Al/CO₂ reaction and the nano-scale Al/CO₂ reaction with KNO₃ were also stuied.The results show that the initial reaction temperature of nano-scale Al/CO₂ is decreased from 561.0? to 523.1? by adding 5 wt % KNO₃.However,the temperatures of main oxidation region are increased by adding 5 wt % KNO₃.The reaction rate of micro-scale Al/CO₂ at high temperature is obviously increased by adding KNO₃.At meanwhile,the results of visualization tube furnace experiments show that a bright spot is first produced,and then the combustion area diffuses stably with the time of 0.85 s.However,spraye flame is generated after adding 5 wt % KNO₃,and the whole ignition process spends 0.25 s.?3?The suspension combustion device was used to study the single flame propagation in aluminum cloud in CO₂.The combustion products were detected by XRD and SEM.The results show that the flame height change of aluminum cloud can be summarized as the following processes: rises,reaches a stable value,and then decreases,at different atmospheres such as CO₂,air and O₂.However,the aluminum cloud burns more violently in O₂,and the flame height and the flame propagation velocity are the biggest in O₂ than those in other two atmospheres.In addition,the flame propagation height increases with the increasing of initial gas temperature,initial gas pressure and mass loading when the other combustion conditions are the same.And the flame height of 100 nm Al is bigger than that of 50 nm Al at same time.The results of product analysis of nano-scale Al/CO₂ suggest that there are Al,Al₂O₃ and Al₂OC in the product particles which are shown as spherical particles.?4?The suspension combustion device was improved to study the continuous flame propagation in aluminum cloud in CO₂.The results show that at the initial stage of the continuous suspension combustion of nano-scale Al/CO₂,the flame propagation height increases exponentially along with increasing of time.For the flame continuous propagation,the combustion can be divided into three stages,and vapor flame is found above the combustion chamber.Furthermore,at CO₂ atmosphere,when the initial gas pressure is adjusted from 0.05 MPa to 0.06 MPa,the flame height and the flame propagation velocity are the highest at 0.06 MPa.And the flame propagation height in horizontal direction increases linearly with the increasing of time.?5?The hydrogen production process of Al/H₂O reaction was studied by the drainage method,and the products were analyzed by XRD and transmission electron microscopy?TEM?.The results show that the hydrogen yield and hydrogen generation rate of the Al/H₂O reaction can be increased by increasing reaction temperature.And the Al/H₂O reaction is obviously affected by additives.The reaction is promoted by adding Na₂CO₃,but inhibited by adding NaCl.In addition,the hydrogen generation rate is controlled as constant when adding the mixture of Na₂CO₃ and NiCl₂.As for the influence of additive concentration,the results show that the reaction can be further promoted by increasing the concentration of Na₂CO₃,but further inhibited by increasing the concentration of NaCl.The reaction products of Al/H₂O reaction are floc by the analysis of TEM.And the diffraction peaks of Al,Al?OH?₃ and AlO?OH?are found in the products of Al/H₂O without addition of additive and with addition of additives.At meanwhile,NaCl and NaAl₅O₈ are found in the products of Al/H₂O reaction with 5 wt % NaCl and 5 wt % Na₂CO₃ addition,repectively.