La_2O_3、Nd_2O_3、Y_2O_3对高岭石高温相变动力学的影响

Effect of La_2O_3,Nd_2O_3 and Y_2O_3 on Kinetics of High Temperature Phase Transformation of Kaolinite

利用综合热分析技术、X射线衍射(XRD)、傅里叶变换红外光谱(FT-IR)和扫描电镜(SEM)研究了La_2O_3、Nd_2O_3、Y_2O_3对高岭石高温条件下转变成莫来石过程的作用,并采用Kissinger方程、Ozawa方程以及JMA修正方程(Ⅰ)和(Ⅱ)分析了La_2O_3、Nd_2O_3、Y_2O_3对高岭石高温相变动力学的影响。结果表明:3种稀土氧化物的掺入对高岭石的相变动力学参数产生了影响,相变活化能和频率因子与未掺入稀土氧化物的高岭石相比有所降低,析晶方式则未发生变化,均属于体积晶化。对比掺入3种稀土氧化物的高岭石相变活化能和频率因子可以看出,Y_2O_3对于高岭石高温条件下相变的促进作用最为明显,相变活化能最低。稀土氧化物对于高岭石高温相变产物影响不大,主晶相为莫来石相,次晶相为方石英相,但稀土氧化物的掺入使得方石英相的结晶度明显提高。

The functions of La2O3,Nd2O3 and Y2O3to the transformation of kaolinite to mullite under high temperature conditions were investigated by comprehensive thermal analysis technology,X-ray diffraction（XRD）,Fourier transform infrared spectroscopy（FT-IR）and scanning electron microscopy（SEM）.Meanwhile,Kissinger equation,Ozawa equation and JMA modified equation（Ⅰ）and（Ⅱ）were applied for analysis of the effects of La2O3,Nd2O3 and Y2O3on the kinetics of kaolinite in phase transformation at high temperatures.The results showed that the addition of 3kinds of rare earth oxides influenced the crystallization kinetic parameters of kaolinite.Crystallization activation energies and frequency factors of the kaolinite mixed with La2O3,Nd2O3 and Y2O3 respectively were decreased compared with the kaolinite without any mixture,while crystallization behaviors were not changed,and belonged to volume crystallization.Comparing each crystallization kinetic parameter and frequency factor of the kaolinite mixed with La2O3,Nd2O3 and Y2O3,the promotion of Y2O3 to the phase transition of kaolinite under high temperature conditions was the most significant,which meant the crystallization activation energy was the lowest.The influences of rare earth oxides on the phase transition product of kaolinite at high temperatures were not great.The primary crystal phase of calcined kaolinite was mullite and secondary crystal phase was cristobalite,while the crystallinity of cristobalite phase was significantly enhanced after the addition of rare earth oxides.