Investigation of shape anisotropy in precipitated silver and silver/palladium particles.

摘要

This study was focused on furthering the understanding of anisometric particle formation during the precipitation of metallic particles, as well as, producing silver and silver/palladium particles as next generation thick-film conductive materials for the electronics industry. Synthesizing anisotropic metal particles through precipitation rather than conventional milling techniques offers the possibility for better control over the final particle properties (size, aspect ratio, composition and surface chemistry) along with the potential for a significant decrease in fabrication cost.;A common precipitation chemistry in which metal nitrates are reduced by ascorbic acid in an acidic, aqueous, environment was investigated. In this system it was found that small amounts of palladium and the presence of oxidizing molecules in the reaction solution had a significant influence on the final particle morphology. Manipulating these variables allowed for the morphology of the particles to be varied from discrete, uniform platelets to particles resembling an ensemble of platelets. By controlling the growth process of the nanosize platelets, the final platelet dimensions (edge-length, thickness and aspect ratio) and silver/palladium composition (alloy and core-shell) could be adjusted.;Investigation of palladium as a dopant, as well as, the role of oxidizers in the reaction solution led to the development of a mechanism which accounted for the two-dimensional shape anisotropy in both the nucleation and growth stages. Specifically, the mechanism identified the catalytic oxidation of ascorbic acid on the newly formed particles as a critical component in morphology determination. In this system the role of ascorbic acid catalysis in particle formation was presented as a three stage mechanism, distinguished by three unique kinetic regimes. This work not only served to develop a novel approach to the formation of industrially relevant anisometric materials but linked several previously unrelated particle formation mechanisms.