Preparation Of Nano-CuM₂O₄ (M=Co, Cr) With Different Morphologies And Their Catalytic Performance For Thermal Decomposition Of AP

Nano burning-rate catalysts(BRCs)are a type of nano materials those can effectively catalyze the thermal decomposition of ammonium perchlorate(AP).The main factors affecting catalytic performance of nano BRCs are their morphologies and specific surface areas.In this thesis,nano CuCr₂O₄ was prepared by both microwave and reflow methods,and nano CuCo₂O₄ was prepared by hydrothermal method.Their morphologies and structures were characterized by XRD,SEM,TEM,BET,XPS.DSC and TG techniques were employed to study catalytic activity of CuCr₂O₄ and CuCo₂O₄ for thermal decomposition of AP.The main research contents are as follows:(1)Nano CuCr₂O₄ was prepared by microwave method with ammonium fluoride(NH4F)as morphology modifier and hexamethylenetetramine(HMT)as precipitant.It was found that reaction time,addition amount of NH4F and calcination temperature exhibit great influences on the morphology and purity of the nano CuCr₂O₄.After a series of experiment condition screening,it was found that when the molar ratio of the raw materials is Cu²⁺:Cr³⁺:NH₄F:HMT=1:2:5:5,reaction time is 40 min,and calcination temperature is 400?,the morphology of the prepared CuCr₂O₄ sample is 15-40 nm thick nano-flaky cubic phase CuCr₂O₄(sample M2),with good dispersion and large specific surface area(95.41 m²·g^-1).The sample M2 shows the most catalytic effect on AP thermal decomposition.The thermal decomposition temperature peak of AP shifted from 403.4? to 330.3?,and the apparent decomposition heat of AP increased from-746.53 J·g^-1 to-1237.06 J·g^-1.(2)Nano CuCr₂O₄ was additionally prepared by static reflux method with trisodium citrate(TSC)as morphology regulator and HMT as precipitant.The studies found that calcination temperature has the greatest effect on the nano CuCr₂O₄ morphology.Ultra-thin CuCr₂O₄ sheet(sample R1)with ca.5 nm thickness was collected at 350?;agglomerated nano-sheet CuCr₂O₄(sample R2)was collected at 380?,its surface being doted by nano-particles,and the sample contains a small amount of CuCrO4;nano-particle cubic phase CuCr₂O₄(sample R3)was obtained at 400? and nano-particle tetragonal CuCr₂O₄(sample R4)was gathered at 500?.The BET test results indicated that the specific surface area of CuCr₂O₄ decreases from 88.34 m²·g^-1 to 13.37 m²·g^-1 with the increase of the calcination temperature.DSC and TG tests showed that the specific surface area of sample R4 was the smallest,but the catalytic effect on the AP therma degradation was the best,due probably to CuCrO4 impurity particlesin both samples R1 and R2.(3)Nano CuCo₂O₄ was prepared by hydrothermal method.Nano-particle CuCo₂O₄ with particle size of 20-50 nm was prepared by using urea as precipitator without adding morphology regulator;nanorods CuCo₂O₄ with a diameter of 50-120 nm and a length of 100-800 nm was prepared by using urea as precipitant and NH4F as morphology regulator;taking HMT as precipitant and NH4F as morphology modifier,CuCo₂O₄ was prepared as 20-40 nm thick nano-sheets,which were stacked as three-dimensional structure.Using HMT as precipitant and TSC as morphology modifier,CuCo₂O₄ was prepared as ultrathin nanosheet,its thickness being less than 10 nm.The BET,DSC and TG tests results indicated that the specific surface area of the ultrathin nano-sheet CuCo₂O₄ was the largest(100.22m·g^-1),and it exhibited the best catalytic effect on the thermal decomposition of AP,the high-temperature decomposition peak of AP being advanced from 403.4? to 289.4?.(4)The thermal decomposition kinetics of nano-sheets CuCr₂O₄(sample M2)and ultrathin nano-sheets CuCo₂O₄(sample A)mixed with AP in 1:4 ratio,respectively,were studied by DSC.The Kissinger equation,Ozawa equation and integral method were used to evaluate the kinetic process of catalytic thermal decomposition of AP with both samplesA and M2 as additives.The kinetic parameters of related thermal decomposition and the most feasible mechanism functions for catalytic thermal decomposition of AP were given.The results showed that the low temperature decomposition peak and high temperature decomposition peak of AP combined into one peak with addition of sample A or M2,which may be due to the addition of M2 and A changing the thermal decomposition mechanism and process of AP from the original two-step reaction to the one-step reaction.By calculation,it was found that the addition of M2 and A to AP can reduce the total activation energy of AP thermal decomposition,indicating that both samples have good catalytic effects on the thermal decomposition of AP.