Preparation Cr₂O₃ and CrN diffusion barriers for stainless steel supported palladium membrane

Abstract

In this research, chromium oxide (Cr₂O₃ ) and chromium nitride (CrN) thin films were fabricated as the intermetallic diffusion barriers between the palladium (Pd) membrane and stainless steel (SS) support. Three different methods for preparation of Cr₂O₃ were investigated, i.e., thermal oxidation, oxidized Cr-electroplating, and oxidized Cr-sputtering. The thickness of chromium thin films was controlled by chromium deposition time and measured by gravimetric method and SEM. They were found to be 2 to 6 µm as determined by SEM. The optimum condition for the oxidation of chromium to Cr₂O₃ was at 600°C for 6 hours. The CrN thin film was formed by Cr-sputtering in nitrogen atmosphere. The composition and phase structures of Cr-based thin films were studied by EDS and XRD. The Pd membranes were then developed on top of Cr-based thin films by electroless plating. The efficacies in preventing intermetallic diffusion were assessed employing SEM-EDS to analyze the elemental content of the palladium layer after hydrogen exposure for 24 hours at 400, 500 or 600°C. After the hydrogen exposure, all Cr-based thin films acted as the good intermetallic diffusion barriers, with no detectable presence of elementals from the SS disk on Pd layer. Among the four types of thin films, Cr₂O₃ created by sputtering and oxidation showed the highest permeation flux which was measured at 350-500°C in pressure differences of 1-3 atm.