纳米CeO_2在热处理过程中的结构和性能变化

Structure and property changes of CeO_2 nanocrystalline in thermal treatment process

采用XRD方法结合粉体相对密度测定研究了热处理条件对沉淀法合成纳米CeO2的结构和性能的影响。结果表明:随焙烧温度升高,CeO2晶粒尺寸显著增大,晶粒发育趋于完整导致晶格畸变度明显降低,结构致密程度增加使得晶格常数减小,粉体烧结程度增大,相应粉体相对密度随之增加;较低温度(如300℃)下,焙烧时间对CeO2晶粒尺寸无明显影响,相应晶格畸变度、晶格常数和粉体相对密度变化不大;较高温度(如700℃)下,CeO2晶粒尺寸随焙烧时间延长而增大,且焙烧初期粒子增长较快,此过程伴随着CeO2晶格畸变度进一步下降,晶格常数却有所增加,粉体相对密度略有下降;认为热处理过程CeO2晶粒生长为扩散生长机制是造成不同焙烧温度下焙烧时间对纳米CeO2结构和性能的影响行为不同的主要原因。

Effects of different heat treatment conditions on the structure and property of CeO_2 nanocrystalline synthesized by precipitation method were studied with XRD method combining with measurement of relative density of CeO_2 nanocrystalline powders. The results indicate that the grain size of CeO_2 nanocrystallites increases sharply with the increase of calcination temperature; the crystal lattice distortion degree reduces obviously because of the crystalline grain growing up to integrity; the increase of compact degree of the structure makes the crystal lattice constant decrease, and the relative density increases remarkably with the rise of calcinations degree of the responding powders. At lower temperature (e.g. 300 ℃) , calcination time makes no obvious influence on the grain size of CeO_2 nanocrystalline , and, the responding crystal lattice distortion degree, crystal lattice constant and relative density changes little. However, at higher temperature (e.g. 700 ℃), the grain of CeO_2 nanocrystalline grows up with the prolonging calcination time, especially at initial stages of calcinations, then tends slower, while this makes the crystal lattice distortion degree reduce more and more, but crystal lattice constant has some increase and relative density decreases a little. It is thought that diffusion growth mechanic plays the main role in the different influence actions on the structure and property by calcination time at different calcination temperatures for CeO_2 nanocrystalline grain growing up in the process of heating treatment.