Hydrolytic polymerization of zirconium salt solution in a reverse microemulsion: synthesis of zirconia nanoparticles
Date Issued
2004
Date
2004
Author(s)
Hsiao, Bor-Yuan
DOI
zh-TW
Abstract
Abstract
The aim of this work is to synthesize zirconia nanoparticles using hydrolysis of zirconium salt solution in the water/CTAB/hexanol reverse microemulsion. The first part of this study is to prepare zirconia nanoparticles by means of the rapid hydrolysis reaction at room temperature caused by mixing two solutions of reverse microemulsion, one containing Zr4+ aqueous droplets and the other aqueous ammonia droplets with the same water/surfactant ratio. The resulting precipitate was recovered and characterized by using an electron microscopy (TEM and SEM). Thermal decomposition and phase transformation of the samples were characterized using thermogravimetric and differential thermal analysis (TGA/DTA), and X-ray powder diffraction (XRD) techniques. It is concluded that the precursors of zirconia about 5~15nm in size was successfully synthesized and was well dispersed in the surfactant matrix. The calcination temperature was at least 600℃ to burn out impurities and then, the precursor particles crystallized to form tetragonal phase zirconia. The resulting zirconia powder contained a higher fraction of tetragonal zirconia than the direct precipitation product did when calcination was conducted under a temperature range of 500 to 1000℃. The fraction of tetragonal zirconia decreased as the water/surfactant molar ratio (Rw) increased in this experiment.
The yttria-stabilized-zirconia (YSZ) precursors were also prepared by the rapid hydrolysis in a reverse microemulsion. The crystal structure of YSZ powder was pure tetragonal and the tetragonal crystallite sized increased sharply from 16nm to 43nm in the calcination temperatures ranging from 650 to 1050℃. Finally, the YSZ precursors were treated with hexamethyldisilazane (HMDS) so that the siloxyl groups grafted on the surface of YSZ precursors formed Zr-O-Si bonds after calcinations. The EPMA results showed that the amount of doped Si was about 1 mole%. The crystallite sizes of the HMDS-treated YSZ powder were kept smaller and rather uniform by adsorbing the siloxyl groups during calcination and thus the surface area remained high, when calcination was conducted below 1000℃.
In the second part of this study, nanosized spherical zirconia precursors were also successfully produced using slow hydrolysis method conducted by heating the zirconyl nitrate solution in the water/CTAB/hexanol microemulsion. The hydrous-zirconia particles could be synthesized at 60℃ in a few hours, which is lower and shorter than the reaction temperatures and reaction time reported by other hydrolysis processes. In addition, the particles size and shape is greatly influenced by the reaction temperature and compositions of the reverse microemulsion. For reaction temperature at 60℃ nanosized precursor with uniform size and spherical shape were produced at lower water/surfactant ratio or water/oil ratio. The resulting particles are amorphous, and they transformed into tetragonal phase after calcination. In the calcination temperatures between 650 and 850℃，the crystallite sizes greatly increased and the specific surface area reduced quickly from 79m2/g to 1.1m2/g.
Subjects
氧化鋯
水解聚合
奈米粒子
逆微乳膠
hydrolysis and polymerization
reverse microemulsion
nanoparticles
zirconia
Type
thesis