Key Takeaways & Executive Findings
- •• Sub-micron La2Zr2O7 ceramic with pyrochlore structure was successfully synthesized via sol-gel and high-temperature sintering, achieving an average grain size of 895 nm. • At 1673 K, CFAS melt rapidly infiltrates the LZO ceramic, but the formation of rod-shaped Ca2La8(SiO4)6O2 apatite and m-ZrO2 phases effectively hinders further diffusion, limiting corrosion depth. • After 30 h of CFAS corrosion, the corrosion depth was only 160.3 μm, demonstrating excellent high-temperature resistance of sub-micron LZO ceramic. • The findings highlight LZO ceramic as a promising candidate for thermal/environmental barrier coatings (T/EBCs) in aerospace and nuclear applications, outperforming YSZ at temperatures above 1473 K.
Abstract
Herein, a sub-micron lanthanum zirconate ceramic (La2Zr2O7, LZO) with a pyrochlore structure was prepared by the sol-gel and high temperature sintering methods. The corrosion behavior and mechanism of calcium-ferrum-alumina-silicate (CFAS) powder (33CaO: 10FeO1.5: 13AlO1.5: 44SiO2) on the sub-micron LZO ceramic at 1673 K was investigated. The results indicate that the average grain size of sub-micron LZO ceramic was 895 nm. The CFAS melt rapidly diffused into the interior of the LZO ceramic wafer and reacted with it to generate high melting point rod-shaped Ca2La8(SiO4)6O2 apatite and m-ZrO2 phases, which can effectively hinder further diffusion of CFAS melt, resulting in a slow increase in corrosion depth with corrosion time. After 30 h of CFAS corrosion at 1673 K, the corrosion depth of the LZO ceramic wafer was only 160.3 μm, demonstrating its excellent high-temperature resistance to CFAS corrosion.
1. Introduction
Carbon fiber reinforced SiC ceramic matrix composites (Cf/SiC) have been widely used as a thermal structural material in aerospace and nuclear industry owing to their high specific strength (150−250 kN·m/kg), low density (1.9−2.6 g/cm3), high temperature resistance, good creep resistance (10−7−10−6 s−1, 1473 K), etc [1−7]. Therein, silicon carbide ceramic (SiC) exhibits extremely high hardness and strength, with a melting point of 2973 K [4, 5]. However, the surface of SiC ceramic oxidizes to form a layer of SiO2 film in the high-temperature and high-speed engine airflow containing water vapor [6, 7]. The volatilization of SiO2 film leads to a decrease in the mechanical properties of (Cf/SiC) structural materials and shortens the service life [8, 9]. To address this, researchers have developed thermal environment barrier coatings (T/EBCs) to efficiently protect CMC structural materials in environments with high-temperature and high-speed airflow erosion and corrosion [10−16].
Up to now, 6 wt%−8 wt% Y2O3 stabilized ZrO2 ceramic (YSZ) is widely used as T/EBCs due to its excellent thermophysical properties [17−19]. Nevertheless, the YSZ ceramic coating cannot be applied at temperatures exceeding 1473 K due to the phase transition from monoclinic (m-ZrO2) to tetragonal (t-ZrO2), and its corrosion resistance to CMAS (CaO-MgO-Al2O3-SiO2) is poor at such high temperatures [20, 21]. Furthermore, the surface service temperature of aero-engine thermal structure components has reached 1673 K or even above due to the continuous increase of the thrust-to-weight ratio [22, 23]. Thus, there is an urgent need for T/EBCs materials with superior thermal physical properties and corrosion resistance to elevate the service temperature of thermal structural components.
The new developed generation of T/EBCs materials primarily includes rare-earth silicates (RE2Si2O7) [24−26], rare-earth zirconates (RE2Zr2O7) [27−29], rare-earth tantalates (RETa3O9) [30, 31], and rare-earth hafnates (RE2Hf2O7) [32−34], etc. Among these, rare-earth zirconates (RE2Zr2O7), particularly lanthanum zirconate (La2Zr2O7, LZO), have garnered significant research attention owing to the high melting point (2573 K), low thermal conductivity, extremely low oxygen-ion diffusion rate, and no phase transition during high-temperature heating process (<1673 K) [35, 36]. The calculation results indicate that LZO ceramic exhibits the lowest thermal conductivity among rare-earth zirconates, and the measured thermal conductivity of LZO ceramic is about 45% lower than that of YSZ ceramic [37, 38]. Meanwhile, both calculation and experimental results indicate that LZO ceramic has a lower elastic modulus than YSZ ceramic, which helps reduce thermal stress during high-temperature service [39, 40].
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CHEN Peng-ju, HE Ling, PAN Ling, TIAN Tian, ZHANG Hao, XIAO Peng, LI Yang (2025). Interaction and mechanism of sub-micron La2Zr2O7 ceramic with calcium-ferrum-alumina-silicate (CFAS) melt at 1673 K. Journal of Central South University. https://doi.org/10.1007/s11771-025-6104-2
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Frequently Asked Questions
What is the significance of the sub-micron La2Zr2O7 ceramic in this study?
The sub-micron La2Zr2O7 ceramic, with an average grain size of 895 nm, exhibits excellent resistance to CFAS corrosion at 1673 K, making it a promising candidate for thermal/environmental barrier coatings in high-temperature aerospace applications.
How does the CFAS melt interact with the LZO ceramic?
The CFAS melt rapidly diffuses into the LZO ceramic and reacts to form high-melting-point rod-shaped Ca2La8(SiO4)6O2 apatite and m-ZrO2 phases, which effectively hinder further diffusion and limit corrosion depth.
What was the corrosion depth after 30 hours of CFAS exposure?
After 30 hours of CFAS corrosion at 1673 K, the corrosion depth of the LZO ceramic wafer was only 160.3 μm, demonstrating its excellent high-temperature resistance.
Why is La2Zr2O7 considered superior to YSZ for high-temperature applications?
La2Zr2O7 has a higher melting point (2573 K), lower thermal conductivity (about 45% lower than YSZ), no phase transition up to 1673 K, and better corrosion resistance to CMAS/CFAS, making it more suitable for next-generation T/EBCs.
What methods were used to prepare the sub-micron LZO ceramic?
The sub-micron LZO ceramic was prepared using sol-gel and high-temperature sintering methods, resulting in a pyrochlore structure with an average grain size of 895 nm.
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