Study by Means of the Mass Spectrometry of Volatile Species in the Oxidation of Cr, Cr2O3, Al, Al2O3, Si, SiO2, Fe and Ferritic/Martensitic Steel Samples at 923 K in Ar+(10 to 80%)H2O Vapor Atmosphere for New-Materials Design

Mass spectrometry was used to study in-situ the role of volatile species in the oxidation of reference materials Cr, Cr₂O₃, Al, Al₂O₃, Si, SiO₂, Fe and ferritic/martensitic steels (P91 and P92) at high temperatures. All samples were heated to 650°C at 1 atm in a mixture of Ar with 10–80% range H₂O vapor. Oxidation times varied between 100 and 200 h. Cr(g), CrH(g), CrO(g), CrOH(g), CrO₂(g), CrOOH(g) and Cr(OH)₂(g) chromium-oxy-hydroxides species were identified during the corrosion of Cr oxidized in a steam atmosphere of Ar+80%H₂O for 100 h. CrO(g), CrO₃(g) and Cr(OH)₆(g) species were present in mass loss of a Cr₂O₃ sample in similar conditions for 200 h of oxidation. However a mass gain was observed when Cr₂O₂(g) and CrO(OH)₄(g) species were present. Simultaneously, thermogravimetric studies of the oxidation kinetics of the samples were made with one in-situ thermobalance. The P91 and P92 steels were studied with afore-mentioned techniques at the beginning of breakaway oxidation. During 100 h of oxidation at 650°C in Ar+10%H₂O atmosphere: Cr(OH)₆(g), CrOOH(g) and CrO₂(OH)₂(g) chromium oxy-hydroxides volatile species were detected in the P91 steel, and Cr(OH)₂(g), Cr(OH)₃(g), Cr(OH)₄(g), CrO(OH)₂(g) and CrO(OH)₄(g), species in the P92 steel. The morphology/composition and structure of the oxidized steel samples were also characterized using SEM/EDAX and XRD techniques, respectively.