Theoretical and experimental investigation of Xenotime-type rare earth phosphate REPO4, (RE = Lu, Yb, Er, Y and Sc) for potential environmental barrier coating applications

Abstract

& fan Wan the mechanical and thermophysical properties of Xenotime-type Repo 4 (Re = Lu, Yb, er, Y and Sc) have been theoretically and experimentally investigated for a potential environmental barrier coating (eBc) topcoat application. the results show that the current studied Repo 4 exhibits a quasiductile property, suggesting a potential long life expectancy of its made coatings. further, from the study of underlying parameters governing thermophysical properties of a ceramic, low thermal expansion coefficients (TECs) and low thermal conductivities cannot be achieved simultaneously, due to mutual exclusive nature of above two parameters. Repo 4 has been unveiled to have rather small tecs, attributing partly to its weak lattice anharmonicity, and is thus well-matched with silicon carbide based ceramic matrix composites. Last, the current investigated Repo 4 exhibits very good high-temperature water vapor corrosion resistance, excellent calcium-magnesium aluminosilicates (cMAS) resistance as well as excellent chemical compatibility with silicon bond coats at elevated temperatures. therefore, the Xenotime-type rare earth phosphates are a promising eBc topcoat material. In order to achieve a higher thermal efficiency, according to Carnot Cycle, there is endless driving force to increase the inlet temperature of advanced gas turbines 1-3. With the increase of operation temperatures, it of course imposes more thermal loads to hot-section components, and hence makes the thermal environment more deteriorate and thus severely challenges corresponding materials. Unfortunately, the conventional nickel based superalloys cannot survive these demanding environments, and silicon carbide based ceramic matrix composites (CMCs) are a promising candidate to replace those superalloys due to a combination of superior properties such as: superior high-temperature mechanical properties, excellent oxidation/thermal shock resistances, high reliability and damage tolerance, low densities, as well as their excellent high temperature stability, which is capable of surviving temperatures higher than 1,400 °C, a temperature well above superalloy's upper limit 4. However, one fatal drawback of silicon carbide based CMCs as a gas turbine hot-section component is that they tend to react with high-temperature water vapor, a byproduct of fuel combustion, which results in a rapid recession of CMCs and thus cannot satisfy the reliability and durability criteria for aero-engine application. In this sense, the prevention and protection of silicon carbide based CMCs in high-temperature combustion gases that are both oxidative and rich in water vapor is the core and bottleneck technology 5-7. In order to address above problems, there are mainly two strategies. One is to develop a more oxidation and water-vapor resistant CMCs, such as to employ an oxidation and water vapor-resistant compounds to modify both interphase 8,9 and matrix 10,11 of CMCs. This work is still under way. The other strategy is more direct and

Synthesis of NiFe2O4@AC/UiO‐66(Zr) for Enhancement of the Photocatalytic Performance of Alizarin Yellow R Under Visible‐light

“…It is also observed that the addition of NiFe 2 O 4 @AC composite to UiO‐66(Zr) MOF does not destroy the diffraction pattern compared with bare UiO‐66(Zr). According to Bragger's law, The deviation of peaks of NiFe 2 O 4 @AC/UiO‐66(Zr)‐ 2 than the pristine NiFe 2 O 4 @AC and UiO‐66(Zr) to lower angle is attributed to the incorporation of NiFe 2 O 4 @AC with UiO‐66(Zr) MOF with increasing size of the prepared material [30] . Also, the MOFs can adsorb the moisture from the atmosphere.…”

Evaluation of environmental barrier coatings: A review

“…The use of alumina tubes at temperatures higher than 1500 • C produces Al(OH) 3 and causes alumina pollution, which makes it difficult to quantitatively formulate the corrosion process. Han et al 96 found that the alumina tube reacted with water vapor to form Al(OH) 3 , and then it reacted with REPO 4 (RE = Lu, Yb, Y, and Sc) ceramics to form Al 5 RE 3 O 12 . Similarly, Opila 97 found that the oxidation rate of SiC in water vapor was an order of magnitude higher than that in the molten quartz tube furnace.…”

The excellent protection effects of silicon/ytterbium silicate bilayer environmental barrier coatings on SiCf/SiC composites

“…Without any protection, SiC f /SiC composites cannot be applied in gas turbines. Environmental barrier coatings (EBCs) are conventionally employed to physically isolate SiC f /SiC composites from direct contact with corrosive combustion steam 10–12 . Normally, they are composed of at least two layers, namely, the bond coat and topcoat, respectively.…”