In-situ Process Monitoring for Plasma Synthesis of Alumina Nanoparticles J-W Shin 1 , H Miyazoe 1 , M Leparoux 1 , S Siegmann 1 , J-L Dorier 2 , and C Hollenstein 2 1 Swiss Federal Institute for Materials Science and Technology EMPA Feuerwerkerstrasse 39, CH-3602 Thun, Switzerland 2 Centre de Recherches en Physique des Plasmas, Ecole Polytechnique Fédérale de Lausanne EPFL PPB Station 13, CH-1015 Lausanne, Switzerland ABSTRACT The process parameters of an inductively coupled thermal plasma used for nanopowder synthesis are experimentally investigated using various plasma diagnostics and in-situ powder monitoring methods. An enthalpy probe technique is applied to characterize the plasma properties under particle-free conditions. The evaporation of microscale alumina precursors is monitored in-situ by optical emission spectroscopy and laser light extinction measurements. Hereby, the influence of two significant process parameters, flow rates of plasma central gas and feed rates of precursor powder are extensively investigated. The emission line intensity of aluminum metal vapor is used as an indicator for alumina precursor evaporation. The number fraction of plasma-treated precursors is calculated from the precursor number density obtained from laser light extinction. The synthesized powders are collected in a sampling unit and characterized ex-situ by particle size analysis, X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) measurement, and scanning electron microscopy (SEM). At low flow rates (LCG) of the torch central gas, higher plasma enthalpy, a more laminar powder flow, a faster cooling, a higher quenching efficiency, and a smaller particle size of the synthesized nanoparticles have been observed in comparison to high amounts of the central gas (HCG). KEYWORDS: Alumina Nanoparticle, Thermal Plasma, Process Monitoring