Thermal Decomposition Mechanism And Kinetics Of Rare Earth Oxalate

Rare earth oxalate often is conducted as RE2O3 precursor because of its high crystallinity and good crystal type.In order to better control the morphology and grain size of RE2O3,the study of the thermal decomposition process and kinetic data of rare earth oxalate provides some theoretical basis for RE2O3 with good morphology and grain size.Thermal decomposition behavior of rare earth oxalate was studied by the simultaneous thermal analysis technique TG-DTA in an air atmosphere.The thermal decomposition kinetics parameters of six rare earth oxalates were determined by using Ozawa-Flynm-Wall method、Kissinger method、Crane method、Simultaneous thermal analysis method and Coats-Redfem method.Curve of TG-DTA shows:(1)The thermal decomposition of La2(C2O4)3·1OH2O passes 4 stages,the first two stages are the dehydration process,the after two stages are the thermal decomposition of La2(C2O4)3.E of the four stages are 83.92、76.04、136.26、162.61 KJ·mol-1 respectively,A are about 4.92×1010、6.1×107、2.1×109、8.46×106s-1,n is about 1,the decomposition mechanism of the third step is controlled by F1,g(a)=1-α。(2)The thermal decomposition of Pr2(C2O4)3·8H2O passes 2 stages.E of the two stages are 38.93、155.76KJ·mol-1,n are 0.5、1.5.the decomposition mechanism of the first step is controlled by chemical reaction,g(α)=(1-α)1/3,A=1.2×1011s-1.(3)The decomposition process of Sm2(C2O4)3·8H2O passes 4 stages,the first two stages are the dehydration process,the after two stages are the thermal decomposition of Sm2(C2O4)3.E of the four stages are 40.77、85.15、56.13、69.86KJ·mol-1,n are 0.5、0.84、1/3、0.45.The thermal decomposition process of third step is controlled by chemical reaction.g(α)=[-ln(1-α])2/3.(4)The thermal decomposition of Dy2(C2O4)3·CH2O passes 2 stages,E of the two stages are 36.69、83.58 KJ·mol-1,n are 0.55、2/3,The thermal decomposition process of first step is controlled by A-E equation,g(a)=[1Ln(1-α)]2/3.(5)The thermal decomposition of Ho2(C2O4)3·4H2O passes 3 stages,the first stage is the dehydration process,the after two stages are the thermal decomposition of Ho2(C2O4)3.E of the three stages are 68.13、75.56、158.77KJ·mol-1,n are about 1,A are 7.2×108、8.27×108、2.3×107s-1,the thermal decomposition process of second step is controlled by F1,with random nucleation,g(α)=-ln(1-α).(6)The thermal decomposition of Y2(C2O4)3·9H2O passes 2 stages.E of the two stages are 47.83、69.44 KJ·mol-1,n are 0.75、2/3,the thermal decomposition process of second step is controlled A-E equation,g(α)=[-ln(1-a)]2/3,A=3.6×105s-1.