Influence of Oxidizing and Reducing Process Gases on Metallic Aerosol Nanoparticles

VINZENT OLSZOK, Philipp Rembe, Alfred P. Weber, Clausthal University of Technology

     Abstract Number: 9
     Working Group: Instrumentation and Methods

Abstract
Metallic nanoparticles consisting of one or more components exhibit unique properties that make them highly suitable for application in catalysis, electronics, and medicine, to name only a few possible fields. With a particular focus on electronic properties such as band gap or electron work function, the affinity for oxidation is a critical aspect when dealing with nanoscaled metal. A simple method to produce metallic nanoparticles is given by spark ablation. Single element or multi-component particles are feasible to synthesize using two metallic electrodes and a continuously flowing process gas. This contribution aims at highlighting the importance of controlling residual oxygen in the chosen process gas. Even a so-called "inert gas" such as nitrogen 7.0 (99.99999%) has been found to enable oxide formation during nanoparticle production. The addition of hydrogen to a process gas seems to be a simple intervention in order to suppress oxide formation. This contribution also shows, on the one hand, that hydrogen is able to adsorb on metallic NP even at room temperature. On the other hand, hydrogen has been found to alter the morphology of openly structured agglomerates made of platinum, which is susceptible to hydrogen adsorption. A self-developed analytical tool (Aerosol Photoemission Spectroscopy, APES) that is able to detect oxidation and adsorption phenomena in an online process will be presented. In addition, a patented gas-cleaning tool will be demonstrated that is able to produce ultra-clean (uc) nitrogen with a corresponding purity of 99.9999999999999999% and exhibit a residual oxygen level equivalent to that in interplanetary space. Using uc N2, metallic and oxide-free aerosol nanoparticles can be produced without the use of hydrogen. By means of electron work function determination by APES, the capability of the gas-cleaning unit will be discussed, as will the interaction of hydrogen and residual oxygen in inert gases with metallic aerosol particles.