Mechanochemical Synthesis of ZrTiO 4 Precursor from Inhomogeneous Mixed Gels
- PDF / 289,940 Bytes
- 5 Pages / 414.72 x 648 pts Page_size
- 11 Downloads / 249 Views
Effects of vibration ball-milling of a powdered mixture of two gels, prepared from mixing ZrO2, and Ti0 2 sols, on crystallization processes during heating are studied in order to elucidate enhanced mechanochemical reactions with the aid of hydroxyl groups. TiO 2 (anatase) and ZrO 2 (tetragonal) crystallized at 698 K and 712 K, respectively, when heating non-milled gel mixture at 10 K min-1 in air. Few reactions between the two phases were detected below 1023 K. After vibro-milling a powdered gel mixture at room temperature for 3 to 30 h, ZrTiO 4 (orthorhombic) crystallized directly from non-crystalline precursors on heating to 1023 K. The fraction of crystallized ZrTiO 4 , determined by Raman spectroscopy, increased linearly with increasing the index of micro-homogeneity for non-heated gels. We suggest that short-range ordering of ZrTiO 4 rather than crystallization of individual oxides occurs through the non-thermal atomic movement between different metallic species under mechanical stress. INTRODUCTION
Efforts to enhance the mechanochemical reactivity, using hydrous gels as precursors, have recently been attempted. 1,2 Since bridging hydrogen bonds in hydrous gels have wide variations of polarization and are able to be temporally broken by gentle mechanical stress, networks containing different metal ions are cross-linked during the relaxation of broken bonds. This initiation of ion exchange between dissimilar species causes the enormous increase in solid-state
reaction rates during mechanical treatments as well as post-heat treatments. In the present study, we report the effects of mechanical stress on the crystallization of mixture of ZrO2 and TiO2 gels, as compared with those of unitary and co-precipitated gels, in order to elucidate the difference between mechanochemical and thermal processes.
EXPERIMENTAL Preparation of Materials ZrO2 and TiO2 sols were prepared by mixing 500cm 3 of 0.1 M ZrOCI2 and 0.1 M TiCI4 aqueous solutions with 500cm 3 of 0.5 M NH3 aqueous solution, respectively, as reported elsewhere 3 . The mixture of ZrO2 and TiO2 sols, cooled in ice water, was stirred at 2500 rpm at 10 min. The filtered precipitate was dried at 323 K for 24 h. The massive gel was ground in an agate mortar and then dried at 373 K for 5 h under a reduced pressure of 1.3 kPa. This powdered gel is denoted as ZT-MS. The co-precipitate sol was prepared by admixing 500 cm 3 binary aqueous solution, containing 0.025 mol ZrOC12 and 0.025 mol TiC14, into 500 cm 3 of 0.5 M NH3 aqueous solution. The filtered co-precipitate was dried under the same condition as the sample of ZT-MS to obtain a powdered gel, denoted as ZT-CP.
273 Mat. Res. Soc. Symp. Proc. Vol. 346. 01994 Materials Research Society
Mechanical Treatment Mechanical treatment was carried out at room temperature in air using a vibration ball-mill (Glen Creston, England) with 12 Hz and 50 mm amplitude. A 1.3 g mixed gel powder, ZT-MS, was put into a 25 cm 3 agate vessel with eight 10 mm agate balls. A sample ground for t hours is denoted with an extension tag,
Data Loading...
