Mass spectrometric analysis of clusters and nanoparticles during the gas-phase synthesis of tungsten oxide

The combustion synthesis of nanoscale tungsten-oxide particles from tungsten hexafluoride is investigated in a low-pressure hydrogen/oxygen flat flame. The reactor is equipped with molecular-beam sampling of post-flame gases at variable height above burner (HAB). Main species of the flame, intermediate tungsten species, and tungsten-oxide clusters are studied with time-of-flight mass spectrometry (TOF-MS) as a function of HAB. Various WOx (OH)(y) are identified within the flame front. With increasing HAB, (WO3)(n) clusters with increasing cluster size appear in the burnt gases at the expense of the concentration of W-1 species. Clusters with n = 3-7 arise at 70 mm HAB, followed by larger clusters at even larger heights. Clusters up to (WO3)(38) were identified. The subsequent formation of nanoparticles is detected with particle mass spec-trometry (PMS) and a quartz crystal microbalance (QCM) from 120 mm HAB and the increasing particle size and mass flux have been determined. (C) 2016 by The Combustion Institute. Published by Elsevier Inc.