Flow Phase Reaction Preparation Of Nano Lamo <sub> 3 </ Sub> And The Kinetics Of Thermal Decomposition

In this thesis,a rheological phase reaction method was introduced to synthesize LaMO₃(M=Mn,Co)complex oxide nanometer powder of which the structure and function were studied.As a new reaction method,the rheological phase reaction method is the process of preparing compounds or materials from a solid-liquid rheological mixture.That is,the solid reactants are fully mixed in a proper molar ratio, and made up by a proper amount of solvents to a solid-liquid rheological state(neither solid nor liquid).The product can be obtained under a suitable experimental condition from the solid-liquid rheololgical state.In the rheological phase system there are many advantages:the surface area of solid particles can be efficiently utilized,the contact between solid paricles and liquid is close and uniform,heat change is very efficient,local overheating can be avoided,and the reaction temperature can be easily controlled.In addition,many substances have greatly increased solubility and taken new reaction behavior.The La₂O₃,MnO₂ and Co₂O oxides nanometer powder were synthesized by rheological phase reaction method of normal metal oxides and H₂C₂O₄·2H₂O;with it, La_0.98MnO_3.05and LaCoO₃ complex oxides nanometer powder were obtained in the similar materials and process.The influences of heat time,heat temperature, decomposing temperature and decomposing time on particle size were investigated by means of orthogonal experimental design.The results showed that product diameter was mostly influenced by decomposing temperature,followed by heat temperature, decomposing time and heat time.To LaMnO₃,the optimal preparation condition were heat temperature=60℃,heat time =3h,decomposing temperature =900℃, decomposing time =3h.Under these conditions La_0.98MnO_3.05nano-particles with average diameter of 23.8nm and crystal form of orthorhombic and space group of R3c were obtained.To LaCoO₃,the optimum condition were heat temperature=70℃, heat time=3.0h,decomposing temperature=880℃,decomposing time =3.5h.Under these conditions La_0.98MnO_3.05nano-particles with average diameter of 23.4nm and crystal form of orthorhombic and space group of R3c were obtained. Moreover,TG-DTA and DSC chemical reaction kinetic theory was employed here,and the Ozawa integral method and Coats-Redfern integral method were used. After the calculation and comparison,activation energy and reaction order in heat decomposition process of precursor of La_0.98MnO_3.05:E≈139.2KJ/mol,n≈0.67(stageâ… );E≈223.5KJ/mol,n≈0.67(stageâ…¡).The heat decomposition mechanism of both precursors is the stochastic coring and afterward growing.The kinetic index of grain growth was calculated while precursors were calcined.The average kinetic values of La_0.98MnO_3.05are acquired:E≈58.6KJ/mol,n≈2.82.