Study On The Catalytic Effect Of Transition Metal Oxides On The Thermal Decomposition Of Ammonium Perchlorate

The solid propellant of combustion properties composes the core part in the technology of powders and explosives.According to the thermal decomposition of the predominant components in composite propellants,the behavior of the catalysts can be derived.This dissertation contains two aspects of works.Firstly,a series of nano-sized compound transition metal oxides are prepared and characterized,and their catalytic effects on the thermal decomposition of ammonium perchlorate(AP) are studied.This work affords the experimental and theoretical basis for developing catalysts which have good catalytic performance.Secondly,the catalytic effects of micron-sized transition metal oxalates and acetates on the thermal decomposition of AP via the in situ catalytic mechanism are studied,to afford a new way of preparing the catalysts for the thermal decomposition of AP.Main research contents are shown as follows.Orthorhombic structural perovskite NdCrO₃ nanocrystals and cubic structural perovskite NdCoO₃ were prepared by microemulsion method,and characterized by XRD, TEM,HRTEM,SEM,EDS and BET.The catalytic effects of NdCrO₃ and NdCoO₃ for thermal decomposition of AP were investigated by differential scanning calorimetry(DSC) and thermogravimetry-mass spectrometry(TG-MS).The results revealed that the NdCrO₃ nanoparticles had effective catalysis on the thermal decomposition of AP.Adding 2%of NdCrO₃ nanoparticles to AP decreased the temperature of thermal decomposition by 87℃and increased the heat of decomposition from 655 J g^-1 to 1073 J g^-1;adding 2%of NdCoO₃ nanoparticles to AP decreased the temperature of thermal decomposition by 100℃and increased the heat of decomposition from 655 J g^-1 to 1363 J g^-1.Gaseous products during thermal decomposition of AP were NH₃(m/z=17), H₂O(m/z=18),O₂(m/z=16,32),HCl(m/z=35,36,37,38),N₂O(m/z=30),NO(m/z=44),NO₂ (m/z=46)and Cl₂(m/z=70,72,74).With the catalysis of NdCrO₃,the gaseous products were produced at around 336℃.The ion current intensities increased greatly and the curves exhibited shaper shape.The decomposition process was finished in shorter times;with the catalysis of NdCoO₃.the gaseous products were produced at around 318℃and the curves had broader shape comparing to the curves under the catalysis of NdCrO₃ on the thermal decomposition of AP.The oxidation reaction is occurred colliding with ammonia and oxygen adsorbed by NdCrO₃.Besides,the catalytic activity is dependent on the specific surface area of NdCrO₃. Due to the large area and more reaction active centers of NdCrO₃ nanoparticles,it is beneficial for the adsorption of NH₃ and O₂ on the surface of NdCrO₃.The nanocrystalline can produce large numbers of the reaction active center.Nanosized NdCrO₃ should be considered to be the catalyst accelerating both the decomposition of perchloric acid and oxidation of ammonia.The mechanism of catalytic action is based on the presence of superoxide ion(O₂) and oxygenic ion(O^-,O^2-) on the surface of NdCrO₃.The O₂^-,O^- and O^2-.ions formed during decomposition of perchlorates and the surface of the oxides itself are proton traps.Thus they simplify thermal decomposition of AP.When the partial pressure of oxygen is increased,the formation of O₂^- covered sites on NdCrO₃ is increased, and then the presence of oxygen accelerates the thermal decomposition process of AP as well as the oxidation of NH₃.The self-propagating combustion synthesis method was used to synthesis YCrO₃, SmCrO₃ and ErCrO₃ nanocrystals.The products were characterized by XRD,TEM, HERTEM,SEM,EDS and BET.The catalytic effect of YCrO₃,SmCrO₃ and ErCrO₃ for thermal decomposition of AP was investigated by DSC and TG-MS.The results revealed that the ReCrO₃(Re=Y,Sm,Er) nanoparticles had effective catalysis on the thermal decomposition of AP.Adding 2%of YCrO₃ nanoparticles to AP decreased the temperature of thermal decomposition by 68℃and increased the heat of decomposition by 595 J g^-1; adding SmCrO₃ nanoparticles to AP decreased the temperature of thermal decomposition by 82℃and increased the heat of decomposition by 551 J g^-1;adding ErCrO₃ nanoparticles to AP decreased the temperature of thermal decomposition by 79℃and increased the heat of decomposition by 758 J g^-1.With the catalysis of ReCrO₃(Re=Y,Sm, Er),the ion current intensities increased greatly,the curves exhibited shaper shape at around the decomposition temperatures and the decomposition process was finished in shorter times.Nano-CuCo₂O₄ and nano-CuCr₂O₄ were prepared by salt-assisted solution combustion synthesis.The prepared nano-CuCo₂O₄ and nano-CuCr₂O₄ were characterized by XRD,TEM,FT-IR,Laser Raman Spectroscopy(LRS) and SEM.The results showed that the nanocrystalline of CuCo₂O₄ and CuCr₂O₄ were almost cubic-like,and the sizes were about 50nm and 150nm,respectively,with good dispersion.The catalysis performance of the thermal decomposition of AP by nano-CuCo₂O₄ and nano-CuCr₂O₄ was studied by differential thermal analysis(DTA).It was found that their catalytic performance on thermal decomposition of AP were superior to a single-component nano-metal oxides,such as CuO,Co₃O₄ and Cr₂O₃,etc.This was probably related to the specific spinel structure of metal oxides.Transition metal and rare earth oxalates were prepared by co-precipitation.The prepared oxalates were characterized by XRD,FT-IR,Raman and SEM.In situ catalytic thermal decomposition of AP was investigated over COC₂O₄.The catalytic activity measurements were carried out by DSC and TG-MS.The results show that the new ecological nano-cobalt oxides exhibit better catalytic performance in thermal decomposition of AP.Adding 2%of COC₂O₄ to AP decreases the decomposition temperature by 104℃and increases the heat of decomposition from 655 J/g to1469 J/g. Products of thermal decomposition of AP are H₂O,NH₃,O₂,HCl,Cl₂,NO,N₂O,and NO₂.The oxidation of adsorbed ammonia by cobalt oxides via the superoxide active centers takes place on the surface of cobalt oxide.The presence of oxygen can accelerate the oxidation of thermal decomposition process of AP,with a clear increase in DSC heat release.Adding 2%of CUC₂O₄ to AP decreases the decomposition temperature by 119℃and increases the heat of decomposition from 655 J/g to 1560 J/g.The influence of metal acetates on the thermal decomposition of AP was studied. Results showed that cobalt acetate decrease the thermal decomposition temperature greatly. The decomposition temperature was decreased by 119℃and the heat was increased by 985J/g;copper acetate has little influence at lower decomposition temperatures during the thermal decomposition of AP.After adding copper acetate,the decomposition temperature was decreased by 69℃and the heat was increased by 919J/g.Cobalt acetate and copper acetate have in-situ catalytic performance on the thermal decomposition of AP.During the decomposition process,the nano-sized cobalt oxides and copper oxides were formed directly among the catalytic mediums media.The new-ecology catalysts had better catalytic effects as well as greater surface area,and took part in the catalytic reaction directly,which full play the catalytic effects of nano-sized catalysts.