纳米HfO_2粉体的制备工艺研究

Preparation and Characterization of Nano-Hafnia Powders

该文以HfOCl2为原料,分别选用分子量为400、1000和6000的3种聚乙二醇(PEG)作分散剂,在70℃和25℃的反应温度条件下,采用反向滴定化学沉淀法制备出HfO2纳米粉体.X射线衍射(XRD)、透射电镜(TEM)的分析结果表明:在70℃的反应温度条件下,加入3种分散剂制备的HfO2粉体的平均晶粒度均小于50nm;用高分子量的分散剂PEG6000所制得的粉体晶粒度更加细小;PEG6000的加入量在0.5%～2.5%质量分数范围内变化对最终的粉体晶粒度影响不大;在25℃的反应温度条件下,加入同样分散剂制备的HfO2粉体的平均晶粒度更加细小,平均晶粒度在30nm左右.用TG/DSC结合XRD对纳米HfO2粉体的研究结果表明:HfO2纳米粉体的晶型转变温度比微米HfO2材料降低了251℃左右(由891℃降低至640℃),并且在焙烧温度大于660℃时,生成了只有在高温高压条件下才能存在的斜方相HfO2.

Nano-HfO_2 powder has been prepared successfully by a reverse-titration precipitation method at 70 ℃ and 25 ℃ with HfOCl_2 as raw material and PEG 400, PEG 1 000 and PEG 6 000 as dispersant agents respectively. The results of X-ray diffraction (XRD) and transmission electron microscope (TEM) show that crystal grain size of all powders prepared at 70 ℃ with the three dispersant agents is less than 50 nm, and the crystal grain size of powders using PEG 6 000 as dispersant agent is less than that of the others. Variation due to addition of PEG 6 000 from 0.5% mass to 2.5% mass does not significantly affect the grain size of HfO_2 powders. Crystal grain size of powders prepared at 25 ℃ with the same dispersant agent is less than those prepared at 70 ℃, and its crystal grain size is about 30 nm. Measured results of TG-DSC and XRD on nano-HfO_2 powders also show that the crystallization temperature of nano-HfO_2 has decreased by approximately 251 ℃ (from 891 ℃ to 640 ℃) as compared with micron crystal grain HfO_2 materials. In addition, the experimental results indicate that, under general pressure and above 660 ℃, the orthorhombic phase, which only exists in high pressure and high temperature, can be obtained.