One of the key factors for the environmental degradation of high-temperature metal structural materials is oxidation, and whether or not it is resistant to oxidation can form an oxide film that is dense, has a low thermal growth rate, and has high thermal stability. Thermal growth of Al2O3 is a typical protective oxide. A great deal of research has been conducted on the high-temperature oxidation behavior of Al2O3 grown alloys and coatings, and it has been found that the addition of small amounts of rare earths (RE) or their oxides (RExOy) can further reduce The growth rate of Al2O3 films formed by alloys and coatings produces the so-called active element effect (REE). There are many models of REE interpretation. There are currently two more popular interpretation models for REEs that affect oxidation kinetics. One is the “Interfacial Poisonization Model (PIM)†proposed by the famous metal material scientist RA Rapp et al., in which the rare earth element (RE) atoms in the metal substrate are segregated at the oxide film/metal matrix interface during the oxidation process and pinned. Misfits of dislocations on the interface climb to inhibit the growth of oxide film. The other is the "grain boundary segregation model," in which the RE ions segregate at the grain boundary of the oxide film, preventing the "short-circuit" diffusion of positive (or negative) ions for film growth. RE grain boundary segregation was confirmed by TEM EDS work. Based on this model, BAPint at the Oak Ridge National Laboratory in the United States proposed the "dynamical segregation model (PIM)". It is believed that the RE ions are dynamically segregated at the Al2O3 grain boundary and that it is driven to the surface by the oxygen potential between the surface and the interface. migrate. Thermodynamically, RExOy is more stable than Al2O3. How does the RExOy produce RE ions that trap toward the interface? The PIM model is not specifically described, but the PIM model is also believed to be due to the oxygen partial pressure difference between the interface and the metal matrix. For this explanation, the Peng Xiao group of the Institute of Metal Research of the Chinese Academy of Sciences has raised doubts that although the partial pressure of oxygen in the metal matrix will be slightly lower than the equilibrium oxygen partial pressure of the interface Al2O3/Al, the reduction value is not sufficient to cause decomposition of RExOy. It is suggested that the RE ions trapped at the grain boundary of the Al2O3 film come from the trace dissolution of RExOy in the film, while the RExOy doping into the film is related to the growth of a-Al2O3, and is verified by studying the oxidation of the CeO2 dispersed aluminized coating. (Corros. Sci., 53 (2011) 1954), but this explanation lacks strong evidence. Recently, the researchers further used TEM and HREM to characterize the microstructure of thermally grown Al2O3 films on the aluminized coating and traced Ce from the coating to the film. The distribution, presence, and evolution of CeO2 morphology and structure were analyzed. The following results were obtained: : 1) There is no elemental Ce in the coating; 2) The Al2O3 film consists of an externally grown g phase and an in-grown a phase (Figure 1); 3) In-growth of a-Al2O3 causes CeO2 dispersion particles to enter the film and dissolve slightly Ce4+ is produced, which tends to segregate at the grain boundaries (Fig. 2); 4) Ce4+ diffuses outward along the a-Al2O3 grain boundary (in which the absorbed electrons are converted to Ce3+) and the g-Al2O3 twin boundaries (Fig. 1). Ce2O3 precipitated in the surface along the twin boundaries (Fig. 3). Based on this, a REE model for effecting oxidation of CeO2 is proposed (Fig. 4), which explains the reason why RExOy generates RE ions that are trapped in grain boundaries of Al2O3 films. In the case of single element REs added to the alloy or coating, REs will precipitate out of RE-rich particles due to their low solid solubility, and the latter tend to oxidize (due to the high affinity of RE and O) to form RExOy particles. Therefore, the model is expected to be explained. RE produces the essential reason for the related REE. Related work has been published online in the Science Report (Sci. Rep. 6, 29593, 2016; doi: 10.1038/srep29593). S32205 Ap Tube,S32205 Duplex,Round Steel Tubing Sizes,Seamless Stainless Steel Tubing Zhejiang Ruimai Stainless steel Tube Co.,Ltd. , https://www.ruimaitube.com