Papers by Keyword: Sulfidation

Abstract: The high-temperature corrosion behavior of Ni₃Al+2.9 wt% Cr alloy was studied in SO₂-containing environment. Corrosion tests were carried out at 900, 1000, and 1100 °C for 100 h in atmospheric Ar-0.2% SO₂ gas. The alloy corroded relatively slowly due mainly to formation of Al₂O₃ in the scale. Its corrosion kinetics deviated from the parabolic corrosion rate law to a certain extent owing to ensuing scale spallation. This was attributed to (1) stress generated during scaling and the subsequent cooling period, (2) voids that formed due to the Kirkendall effect, and (3) incorporation of sulfur in the scale. The scale that formed after corrosion at 900 °C consisted of the outer NiO scale, middle NiAl₂O₄ scale, and inner Al₂O₃ scale. The increased corrosion rate at 1000 and 1100 °C led to formation of the outer NiO scale, and inner Al₂O₃ scale.

Abstract: Pure Fe₃Al and Fe₃Al+4%Cr alloys were corroded at 1000 °C for up to 200 h in N₂-0.1%H₂S-mixed gas in order to study their corrosion behavior in H₂S-containing atmosphere. The formed scales consisted primarily of α-Al₂O₃, FeAl₂O₄, and Fe₂O₃. In these oxide scales, hydrogen and sulfur dissolved according to the reaction; H₂S→2H+S. Corrosion products of Cr were not identified in the scales from the XRD analysis, indicating that Cr dissolved in the oxide scales. Fe₃Al+4%Cr alloy displayed poorer corrosion resistance than Fe₃Al alloy, indicating that chromium accelerated the corrosion rates of Fe₃Al alloys.

Abstract: The pack-cementation is one of economical, efficient coating processes for Fe-base alloys. It can provide good protection against high-temperature oxidation and corrosion. In this study, the high-temperature corrosion behavior of the aluminized diffusion-coating on low-carbon T20 steel (Fe-2.0Cr-0.5Mo-0.8Mn-0.3S in at.%) was studied at 800 °C in N₂/H₂O/H₂S-mixed gas. The aluminized coating consisted of Fe₃Al. The aluminized T20 steel after corrosion at 800 °C for 10~100h in N₂/H₂O/H₂S-mixed gases, the scale formed on the Fe₃Al coating consisted primarily of α-Al₂O₃, Al₂S₃, FeAl₂O₄ and FeO, with relatively slow scaling rates. The Fe₃Al intermetallics has reasonable corrosion-and oxidation-resistance, because it can form a protective alumina scale. Without the aluminized diffusion-coating, T20 steel corroded fast with serious scale failure. At the surface, coarse FeS grains with cracks formed. Since FeS has a very high concentration of cation vacancies, it grew fast through the outward diffusion of Fe²⁺ ions.

Abstract: The nickel-iron-chromium-based alloy, Incoloy alloy 800, was corroded at 600, 700 and 800 °C for 10-70 h under 1 atm of total pressure in three different atmospheres, viz., 1 atm of N₂, N₂/H₂O, and N₂/H₂O/H₂S-mixed gases. The corrosion rates always increased with addition of H₂O and, much more seriously, with the addition of H₂S gas. In N₂ and N₂/H₂O gases, oxidation prevailed. In N₂/H₂O/H₂S gases, sulfidation dominated. The corrosion resistance increased in the T22 steel displayed better resistance to oxidation and sulfidation than Fe-2Mn-0.5Si steel, owing to the presence of Cr. Strong enrichment of Cr and the presence of Ni and Fe were noticeable in the inner scale. Chromium sulfidized to FeCr₂S₄ in N₂/H₂O/H₂S gases, which was responsible for the enhanced sulfidation resistance of T22 compared with Fe-2.0Mn-0.5Si steel.

Abstract: Sulfidation of undoped and aluminum doped zinc oxide materials has been performed by TGA under a H₂S atmosphere in order to evaluate the impact of the doping element on sulfidation reaction kinetics and mechanism. The presence of aluminum seems to slow-down the reaction kinetics. This phenomenon might be explained by a modification of the solid state diffusion processes involved in ZnO sulfidation reaction and the related ZnS outward growth, assuming the presence of aluminum atoms inside ZnO and ZnS phases. In order to determine solid state diffusion mechanisms controlling the reaction kinetics, molecular dynamics simulations were performed using a Coulomb-Buckingham potential. Firstly, the diffusion of the different elements (Zn, O, S) was simulated for both the oxide and sulfide phases considering a vacancy mechanism. Secondly, simulations of the oxide phase doped by a trivalent cation were also performed. The results obtained in this preliminary work are presented and compared to the literature.

Abstract: SUS316L, TiN and CrN films were corroded at 500 °C for up to 30 h in 1 atm of (N₂/3.1%H₂O/2.42%H₂S)-mixed gas. SUS316L displayed poor corrosion resistance due to the formation of FeS. It corroded to (Fe, Ni)-mixed sulfides and FeS, forming highly fragile, porous, and nonadherent scales. TiN and CrN films suppressed the sulfidation of SUS316L.

Abstract: The thermal barrier coating that consisted of ZrO₂-8Y₂O₃ top-coat and Ni-22Cr-10Al-1Y bond-coat corroded in Ar-1%SO₂ gas at 1000-1200°C for up to 300 h. The top-coat and bond-coat consisted primarily of β-ZrO₂ and (γ-Ni, α-Al₂O₃), respectively. During corrosion, Al oxidized preferentially to α-Al₂O₃ to protect TBC, and sulfidation occurred to a small extent.

Abstract: SUS 310 stainless steels were corroded at 600, 700 and 800°C for up to 30 h in 1 atm of N₂/H₂O/H₂S-mixed gas. The formed scales consisted primarily of (Fe_0.5Ni_0.5)_0.96S, FeNiS₂, and FeCr₂S₄. They were fragile, porous, and susceptible to spallation. During corrosion, Fe, Ni, and Mn diffused outward, while sulfur and a lesser amount of oxygen diffused inward. The diffusion of Cr and Si was not conspicuous. The formation of sulfide scales and the presence of hydrogen and water vapor in the mixed gases made SUS 310 corrode fast.

Abstract: Hot rolled mild steel was corroded in air, Ar/0.2%SO₂ and N₂/0.4%H₂S gases for 20 and 50 h. The corrosion in air at 800 and 1000°C resulted in the formation of Fe₂O₃/Fe₃O₄/FeO layered scales from the surface. The corrosion in Ar/0.2%SO₂ gases resulted in the formation of (FeS, Fe₂O₃, Fe₃O₄, FeO)-mixed scale at 800°C, and (Fe₂O₃, Fe₃O₄, FeO)/FeS layered scale at 1000°C. The corrosion in N₂/0.4%H₂S gases at 650 and 750°C led to the formation of (Fe₂O₃, Fe₃O₄, FeO)/FeS layered scales.

Abstract: The Ni-Cr-Co based superalloy, Inconel 740, was corroded between 700 and 900°C for 20 h in 75% Na₂SO₄-25% NaCl salt. The scale consisted primarily of Cr₂O₃, (Ni,Co)Cr₂O₄, NiO, and Ni₃S₂. During corrosion, oxidation dominated rather than sulfidation. The scale was neither dense nor compact owing to the formation of the (oxides, sulfides)-mixed scale where Na₂SO₄ and NaCl were incoporated.