The Influence of Powder Surface Chemistry on The Development of Ceramic Microstructures (Sintering, Micro-Agglomerates, Adhesion)

135 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1984.The processing cycle of a ceramic is traditionally divided into two distinct steps: processing before and after firing. In terms of processing conditions and microstructure development, continuity is usually not assumed, and the variability of powder properties is usually thought to not affect the sintering activity of the powder. However, with the development of wet chemical methods of powder preparation, results have been reported in the literature which showed that processing conditions for active powders do indeed affect their subsequent behavior during firing. In particular, the influence of organic solvents on the behavior of fine ceramic powders has been reported for diverse systems such as alumina, zirconia, and PZT. The purpose of this investigation was to determine the role of powder surface chemistry during the development of ceramic microstructures.An oxalate derived barium titanate was studied. Because the formation of agglomerates and their characteristics are inherent to the oxalate method, three different experimental procedures were used for coprecipitation of the salt, and three types of agglomerates were thus obtained. Systematic surface absorption with methanol and acetone were carried out. The resulting microstructures were evaluated by scanning electron microscopy, particularly with respect to the early stages of microstructure development and densification. Powders were characterized by scanning electron microscopy and infrared spectroscopy. A direct correlation between surface treatment and resulting microstructure was established.Several microstructural features were identified, including the formation of microagglomerates (less than a micron), and the occurrence of particle rearrangement. These features were attributed to changes in interparticle adhesive forces which resulted from the modification of surface chemistry. It was found that the changes of surface chemistry were at the origin of the acquisition of hydrophobic character, an acquisition which could occur at a very early stage in the processing cycle.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD