Effects of water vapor on protectiveness of Cr₂O₃ scale at 1073 K

Abstract

Abstract. Fe-Cr alloy is commonly being used as boiler tube's material. It is subjected to prolonged exposure to water vapor oxidation. The ability to withstand high temperature corrosion can normally be attributed to the formation of a dense and slow growing Cr-richoxide scale known as chromia, Cr 2 O 3 scale. However, oxidation may limit the alloy's service lifetime due to decreasing of its protectiveness capability. This paper is to presents an experimental study of thermo gravimetric and Fourier transform infrared analysis of Cr 2 O 3 at 1073 K in dry and humid environment. Samples were used from commercially available Cr 2 O 3 powder. It was cold-pressed into pellet shape of 12 mm diameter and 3 mm thick with hydraulic press for 40 min at 48 MPa. It then sintered at 1173 K in inert gas environment for 8 h. The samples are cooled and placed in 5 mm diameter platinum pan. It is subjected to reaction in dry and wet environment at 1073 K by applying 100%-Ar and Ar-5%H 2 gas. Each reaction period is 48 h utilizing Thermo Gravimetric Analyzer, TGA to quantify the mass changes. After the reaction, the samples then characterized with Fourier Transform Infrared Spectroscopy, FT-IR and Field Emission Electron Scanning Microscopy, FE-SEM. The TGA result shows mass decreasing ratio of Cr 2 O 3 in wet (P H 2 O =9.5x10 5 Pa) and dry environment is at a factor of 1.2 while parabolic rate at 1.4. FT-IR results confirmed that water vapor significantly broaden the peaks, thus promotes the volatilization of Cr 2 O 3 in wet sample. FESEM shows mostly packed and intact in dry while in wet sample, slightly porous particle arrangement compare to dry. It is concluded that water vapor species decreased Cr 2 O 3 protectiveness capability.

Oxidation behavior of Cr-coated zirconium alloy cladding in high-temperature steam above 1200 °C

“…The voids are just on the surface of Cr 2 O 3 . Since the Cr 2 O 3 could continue to react with H 2 O to form CrO 2 (OH) 2 (Reaction 3), the formation of voids may be attributed to the evaporation of gaseous CrO 2 (OH) 2 37 . As abovementioned, there are two reasons for the disappearance of green particles.…”

Corrosion Degradation Mechanism of Cr-Coated Zr-4 Alloy under Simulated Nuclear Conditions for Accident-Tolerant Fuel

“…Oxides are likely to dissolve under high-pressure water vapor, or fall off in a loose state. Based on the analysis, potential reactions for the formation of Cr oxide and volatilization under pure steam conditions are summarized below [ 40 ]. Cr(s) + 3H 2 O(g) = Cr 2 O 3 (s) + 3H 2 (g) 1/2Cr 2 O 3 (s) + H 2 O(g) + 3/4O 2 (g) = CrO 2 (OH) 2 (g) 2Cr 2 O 3 (s) + H 2 O(g) = 2CrO 2 (OH)2(g) + 1/2O 2 (g) …”

“…Oxides are likely to dissolve under high-pressure water vapor, or fall off in a loose state. Based on the analysis, potential reactions for the formation of Cr oxide and volatilization under pure steam conditions are summarized below [40].…”

Effect of Water Vapor on the Oxidation Behavior of the Eutectic High‐Temperature Alloy Mo‐20Si‐52.8Ti

“…[11,12] It is well-known that some oxides which exhibit excellent oxidation resistance in dry air, e.g., Cr 2 O 3 , lose their protectiveness when H 2 O is present in the oxidizing atmosphere. [13,14] Studies on the oxidation resistance of Mo-Si-based alloys in moist air are rather limited. Hansson et al found that the oxidation rate of MoSi 2 increases if an atmosphere with p(H 2 O) ¼ 0.1 atm is used.…”

“…The products of combustion contain ≈10% of water vapor independent of fuel‐to‐air ratio . It is well‐known that some oxides which exhibit excellent oxidation resistance in dry air, e.g., Cr 2 O 3 , lose their protectiveness when H 2 O is present in the oxidizing atmosphere . Studies on the oxidation resistance of Mo–Si‐based alloys in moist air are rather limited.…”