Preparation And Characterization Of Magnetic Ferromanganese Transition Metal Oxides And Study On Kinetics Of Thermal Process Of The Precursor

Nano-sized transition metal oxides materials have been received considerable a lot of attention due to their framework and in the diversity and potential application in the fields of magnetics. Focus studied is preparation and correlative properties about transition metal oxides materials. Therefor, in this paper, Cu0.5Zn0.5Fe2O4, Co0.35Mn0.65Fe2O4and LaMnO3were synthesized via solid-state reaction at low heat respectively. Precursor and its calcined products were characterized using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), ultraviolet-visible spectroscopy (UV-vis), thermogravimetry and differential scanning calorimetry (TG/DSC)(or thermogravimetry and differential thermal analyses (TG/DTA)), Fourier transform infrared spectroscopy (FT-IR) and vibrating sample magnetometer (VSM). Besides, Kinetics of thermal process were investigated.X-ray powder diffraction (XRD) results showed:highly crystallization Cu0.5Zn0.5Fe2O4[space group Fd-3m(227)] was obtained when the precursor was calcined at600℃for2h, and its crystallite size is21nm; the precursor of Co0.35Mn0.65Fe2O4dried at80℃was a mixture consisted of CoC2O4·2H2O, MnC2O4·2H2O, and FeC2O4·2H2O. However, when the precursor was calcined at350℃for2h, highly crystallization Co0.35Mn0.65Fe204[space group R-3m (166)] was obtained with a crystallite size of22nm; precursor of LaMnO3was a mixture containing orthorhombic La2(CO3)3·8H2O and rhombohedral MnCO3. When the precursor was calcined at800℃for2h, pure phase LaMnO3with rhombohedral structure was obtained.Magnetic characterization results indicated that Cu0.5Zn0.5Fe2O4obtained at700℃behaved strong magnetic properties, its specific saturation magnetization was52.5Am2·kg-1; the specific saturation magnetization of Co0.35Mn0.65Fe2O4obtained at500℃was66.14Am2·kg-1; rhombohedral LaMnO3only behaved weak magnetic properties.The kinetics of the thermal process of precursor was studied using TG/DTA/DSC techniques. Non-isothermal kinetics of the thermal decomposition of precursor was interpreted by KAS equation, OFW equation, and their iterative equations. The results showed that thermal decomposition of Cu0.5Zn0.5Fe2O4below500℃experienced one step, the value of the activation energy for the thermal decomposition of precursor was determined to be97.13±38.03kJ·mol-1, thermal decomposition of precursor was multi-step reaction mechanisms; The thermal process of Co0.35Mn0.65Fe204precursor experienced two steps, which involves the dehydration of the waters of crystallization at first, and then decomposition of Co0.35Mn0.65Fe2(C204)3and formation of crystalline 5Fe2O4together. The values of the activation energy associated with the thermal processes of Co0.35Mno.65Fe204precursor were determined to be78and146kJ·mol-1for the first and second thermal process steps, respectively. The thermal process of LaMnO3precursor experienced four steps, which involved the dehydration of crystallization water at first, and then decomposition of manganese carbonate into MnO2, and decomposition of La2(CO3)3and MnO2together into La2O2CO3and Mn2O3, and lastly reaction of monoclinic La2O2CO3with Mn2O3and formation of rhombohedral LaMnO3. The value of the activation energy associated with the formation of rhombohedral LaMnO3was determined to be260kJ·mol-1. The value of the Avrami exponent, n, was equal to1.68, which suggested that crystallization process of LaMnO3was the random nucleation and growth of nuclei reaction.