Abstract View
Vapor-phase Chemical Speciation and Condensation of Cerium Oxide
KATE RODRIGUEZ, Batikan Koroglu, Zurong Dai, Kim Knight, LLNL
Abstract Number: 628
Working Group: Aerosol Chemistry
Abstract
We track the vapor-phase synthesis of cerium oxide nanoparticles created in a plasma flow reactor, starting with early-stage oxidation of the gaseous metal atoms and subsequent homogeneous nucleation and continuing to later-stage particulate condensation and eventual agglomeration. Incipient chemical speciation and consequent product formation are investigated as a function of both temperature and oxygen fugacity. In situ optical emission spectroscopy is used to detect the presence of atomic, ionic, and molecular species and measure their relative variations with temperature and oxygen content. Condensed cerium oxide nanoparticles are also collected and analyzed ex situ via transmission electron microscopy and X-ray scattering techniques to determine their elemental composition, crystal structure, and size distribution. We find that the relative rate of gas-phase oxidation of cerium is highly dependent on both the temperature and local redox conditions within the flow reactor, while the size and morphology of the condensed nanoparticles depends predominantly on temperature, forming the same crystal type with the same size distribution regardless of oxygen availability. In this way, we show that the processes that underpin the vapor-phase chemical speciation and subsequent gas-phase evolution of cerium oxide are highly dependent on the local environment.