Effects of the Preparative History of Pb-Ti-0 Complex Gels on their Micro-homogenization

Equimolar mixed hydrous gels containing Ti and Pb were prepared via two different routes, i.e., (i) mixing two unitary sols of TiO2 and PbO (MS), and (ii) co-precipitation from a binary aqueous solution of TiCl₄ and Pb (NO₃)2 by NH₃aq (CP). Mechanical pretreatment was also carried out, primarily for the purpose of homogenization. The degree of homogeneity was estimated from the variance of Pb/Ti molar ratio evaluated by the elementary microanalysis under the transmission electron microscopy. CP gel was more homogeneous than MS gel. Ball-milling MS gel for 3 h increased its homogeneity only slightly. However, the homogeneity increased up to that of CP on subsequent heating at the temperature as low as 483 K. This kind of thermal homogenization did not take place for the unground MS gel. Grinding of MS gel brought about the amorphization of small crystallites and the suppression of Pb evaporation. These suggest the ionic migration and the formation of Pb-O-Ti bonds during mechanical activation.