Chemical processing of lead metatitanate by co-precipitation and sol-gel methods: The role of powder and gel characteristics on crystallization behavior

This thesis reports on preparation of PbTiO$\sb3$ by two chemical methods: (i) aqueous co-precipitation and (ii) organo-metallic sol-gel processing. The effects of chemical processing conditions on material properties were determined. Particular attention was paid to the evolution of structure on heat treatment, and crystallization. Materials prepared by the two methods were amorphous in the as-prepared state, but transformed to the stable perovskite structure on heat treatment. Crystallization kinetics for the chemically prepared materials were compared with another type of amorphous PbTiO$\sb3$ prepared by rapid solidification. This comparison led to the identification of material parameters which aided in crystallization.Co-precipitation was carried out by spray-atomizing a solution containing inorganic salts of lead and titanium into a continuous flow constant volume reactor. Temperature, pH, and other reactor parameters were controlled. The precipitated powders, which were dried by spray-drying, had a uniform spherical morphology with particle sizes in the micron range, and surface areas $>$100 m$\sp2$/g. Crystallization into the perovskite structure occurred at 375$\sp\circ$C.The second chemical method was sol-gel processing of PbTiO$\sb3$ from metal alkoxide solutions. Effects of hydrolysis, additive (i.e., acid or base), and drying conditions on the physical, structural, and chemical nature of the material were characterized, as was the evolution of material properties with thermal processing. Results indicated that manipulation of preparation conditions gave a significant degree of control over material properties. Correlations of material properties with preparation conditions were explained by a model which related differences in gel network structure (and structural rearrangements on heat treatment) with the level of polymeric crosslinking. Differences induced in wet gels through control of preparation conditions persisted in the amorphous and crystalline states. TEM observations indicated that densification and crystallization occurred at relatively low temperatures (400-450$\sp\circ$C).Lead titanate was also prepared by a third physical method, rapid solidification. Compared with the rapidly solidified material, the co-precipitated and sol-gel derived materials exhibited enhanced crystallization kinetics and lower crystallization temperatures. The chemically prepared materials were also characterized by greater surface areas and free volumes than the rapidly solidified material. The enhanced crystallization behavior was therefore believed to be at least partially due to the internal surfaces present in the chemically prepared materials.U of I OnlyETDs are only available to UIUC Users without author permissio