粒度对氢氧化铝低温相变动力学的影响

Influence of particle size on kinetics of low temperature phase transformation of aluminum hydroxide

利用综合热分析仪分析技术、激光粒度分析、扫描电镜和X射线衍射研究了粒度对氢氧化铝在低温相变转化成勃姆石过程的影响,并采用Kissinger方程、Ozawa方程和Crane方程进行了不同粒度的氢氧化铝在低温相变过程的动力学参数计算。结果表明:普通砂状氢氧化铝在相变过程有2个较为明显的吸热峰,将砂状氢氧化铝研磨至中位径D50在12μm左右时,相变过程仍然有2个明显的吸热峰;当氢氧化铝中位径D50在1μm左右的氢氧化铝,相变过程则只有1个吸热峰。根据Kissinger方程和Ozawa方程计算结果,随着粒度的降低,其相变活化能也相应的降低,说明降低氢氧化铝粒径,有利于勃姆石的制备。根据XRD图谱显示,低温煅烧后,样品的主要物相为勃姆石,此外还含有少量的三水铝石,粒径越细,煅烧后样品中勃姆石含量越高。

The function of particle size to the transformation of aluminum hydroxide to boehmite under low temperature conditions were investigated by comprehensive thermal analysis technique, laser particle size analyzer(LPSA), scanning electron microscopy(SEM) and X-ray diffraction(XRD). Meanwhile,Kissinger equation, Ozawa equation and Crane equation were applied for analysis of the influence of particle size on phase transformation of aluminum hydroxide. The results showed that two clear endothermic peaks were appeared in the course of phase transformation of normal sandy aluminum hydroxide and grinded sandy aluminum hydroxide, and only one endothermic peak was appeared in the course of phase transformation of micron aluminum hydroxide which medium diameter was about 1μm.According to the results of calculations with Kissinger equation and Ozawa equation, the activation energy of phase transformation of aluminum hydroxide was decreased along with the decrease of particle size,which showed that a lower particle size was benefit for phase transformation from aluminum hydroxide to boehmite. The XRD of aluminum hydroxide after calcinations showed that the primary crystal phase was boehmite and the secondary crystal phase was gibbsite. The content of boehmite was increased with the decrease of particle size.