Preparation and properties of improved Al2O3 based MOD coatings as tritium permeation barrier

Highlights: • α-Al₂O₃ and α-Al₂O₃/Cr₂O₃ tritium permeation barriers can be prepared by the metal organic decomposition (MOD) method. • The nanohardness and corrossion resistance of α-Al₂O₃ MOD coatings are improved by a Cr₂O₃ buffer. • An Al₂O₃ MOD single layer tends to perform lower deuterium permeability at higher temperature. -- Abstract: Four kinds of well-crystallized tritium permeation barrier coatings, including γ-Al₂O₃, α-Al₂O₃, γ-Al₂O₃/Cr₂O₃ and α-Al₂O₃/Cr₂O₃, were prepared by the metal organic decomposition (MOD) method using a dipping technique. In this study, we concentrated on the preparation and properties of α-Al₂O₃ and α-Al₂O₃/Cr₂O₃ double-layer coatings. The results showed that the α-Al₂O₃ coating exhibited a pure phase structure, which was entirely and directly transformed from the γ-Al₂O₃ at an annealing temperature of 1000 °C, and no obvious substrate oxides were formed. An unannealed Cr₂O₃ MOD layer with a thickness of 0.8 μm featured higher crystallization and was taken as a buffer layer. However, the template effect of Cr₂O₃ was not obvious because the formation temperature of the α-Al₂O₃ did not decrease. The corrosion resistance (1.068 × 10⁻⁷ A/cm²) and nanohardness (18.49 GPa) of the α-Al₂O₃/Cr₂O₃ double-layer coating improved compared to those of γ-Al₂O₃, α-Al₂O₃, and γ-Al₂O₃/Cr₂O₃ coatings. In contrast, the deuterium permeation test showed that the α-Al₂O₃ MOD coating had the lowest deuterium ion current at temperatures of 400 ˜ 600 °C of the films considered in this study, demonstrating better resistance to deuterium permeation. Relevant mechanisms and explanations are discussed in detail.