Author: Michiaki Yamasaki, An Pang Tsai
Institute: National Institute of Materials Science, 1-2-1, Sengen, Tsukuba 305-0047, Japan
Oxidation of quasicrystalline Al63Cu25Fe12 alloys with additional elements is a complex and multifaceted process that is important for both theoretical understanding and practical applications. Quasicrystals, having a unique structure, demonstrate anomalous chemical and physical properties, which makes them especially interesting when studying their reaction to oxidizing environments.
When such alloys are oxidized, oxide phases are formed that affect mechanical properties and corrosion resistance. The introduction of additional elements such as Mg, Ti and Zr can significantly change the behavior of the alloy during oxidation, improving the protective properties of the oxide film and reducing the corrosion rate. Oxidation conditions, including temperature, pressure and atmosphere, also play an important role, affecting microstructural changes and thermodynamic parameters.
Research aimed at analyzing oxidation processes in quasicrystalline alloys allows for a deeper understanding of the mechanisms of interaction between materials and the environment and contributes to the development of new high-quality alloys with improved performance properties.
High-temperature oxidation of (AlCu25Fe12)100−xCex (x=1, 2, 3, 4) and Al62Cu24Fe12Zn2 alloys was studied. The Al62Cu24Fe12Zn2 alloy, having a quasicrystalline structure, demonstrates a high degree of oxidation stability at 773 K compared to zinc-free Al63Cu25Fe12. In contrast, the (Al63Cu25Fe12)100−xCex alloys include both quasicrystalline and crystalline phases. When oxidized in air at 773 and 1073 K, an increase in mass change is observed depending on the cerium content. The results show that zinc suppresses oxidation, while cerium, on the contrary, promotes it. Powders containing cerium and zinc are oxidized to FeAl2O4. The surfaces of zinc-containing powders oxidized at 773 and 1073 K are smaller compared to the powders of the three-component alloy. At the same time, the surface area of cerium-containing powders oxidized at 1073 K increases with increasing cerium content.
In the context of the study of the application of quasicrystals, the reaction of steam reforming of methanol was carried out on the catalyst of Al63Cu25Fe12 obtained by the leaching method. Control of the surface area and topology of alloy powders is the key to improving the catalytic activity. For this purpose, oxidation in air has proven itself as a simple way to increase the surface of some alloys. Despite this, aluminum-based quasicrystals have high stability due to the formation of a protective oxide layer. However, such a protective layer prevents the production of powders with a large surface area, which is critical for their use as catalyst precursors. The study of the behavior of quasicrystalline Al63Cu25Fe12 powders during oxidation showed that the icosahedral phase is more resistant to oxidation compared to crystalline phases. Surface oxide layers on bulk Al63Cu25Fe12 samples at high temperatures were also evaluated. The results showed that the oxidation behavior of quasicrystals differs from that of powders, and copper content affects this. Copper particles on the surface are believed to activate methanol steam reforming reactions.
There are studies showing that metal catalysts from amorphous alloys of Group VIII and transition metals are obtained by oxidation-reduction treatment. In addition, the addition of rare earth elements to nickel amorphous alloys increases the amount of nickel on the surface and accelerates oxidation processes, forming a fine-grained oxide structure.
Thus, the addition of rare earth elements to alloys including group VIII metals promotes oxidation and the formation of nanoscale oxides. It is expected that the introduction of rare earth elements into Al63Cu25Fe12 quasicrystals will accelerate the oxidation processes and form nanoscale oxides on the surface. In this work, the oxidation behavior of (Al63Cu25Fe12)100−xCex and Al62Cu24Fe12Zn2 powders was studied to clarify the role of added elements in the Al–Cu–Fe quasicrystal.