The corrosion characteristics of type 316 stainless steel, component metals of the steel (Fe, Cr, Ni, and Mo), and Al in the downstream effluent of a CF4/O2 plasma have been examined as a function of temperature (25-300°C) and feed gas composition (0-30 vol % O2). Type 316, Fe, and Ni showed weight gains due to the formation of surface reaction films, which consist predominantly of involatile metal fluorides and grow parabolically with exposure time. Pure Cr and Mo exhibited weight losses due to the formation of volatile metal fluorides or oxyfluorides. The corrosion rate of these metals increased with increasing temperature, while that of Al was less than the limit of detection at all temperatures examined. The corrosion rates of Cr and Mo increased with increasing O2 content of the reactant gas and reached maxima at ∼20 vol % O2, whereas those of type 316, Fe, and Ni were nearly independent of the O2 content. At 300°C, Cr2O3 films underwent etching in a similar manner as Cr metal, while Fe2O3, NiO, and Al2O3 films transformed into involatile fluorides or oxyfluorides. Mass spectrometric analyses suggested that F atoms and O2 molecules are dominant species responsible for corrosion in the downstream effluent. The phase stability diagrams estimated metal fluorides to be the thermodynamically favored reaction products on the metals exposed to the effluent.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Renewable Energy, Sustainability and the Environment
- Surfaces, Coatings and Films
- Materials Chemistry