La2Si2O7 (lanthanum disilicate) has emerged as a promising candidate for next-generation thermal barrier coatings (TBCs) due to its exceptional thermal stability and low thermal conductivity. Recent studies have demonstrated that La2Si2O7 exhibits a thermal conductivity of 1.2–1.5 W/m·K at 1200°C, significantly lower than traditional yttria-stabilized zirconia (YSZ) coatings, which range from 2.0–2.5 W/m·K under similar conditions. This reduction is attributed to the complex crystal structure of La2Si2O7, which introduces phonon scattering mechanisms that impede heat transfer. Additionally, La2Si2O7 maintains phase stability up to 1600°C, making it suitable for high-temperature applications in gas turbines and aerospace engines.
The mechanical properties of La2Si2O7 ceramics have been extensively investigated, revealing a fracture toughness of 1.8–2.3 MPa·m^1/2 and a Vickers hardness of 8.5–9.5 GPa, comparable to YSZ but with superior resistance to sintering-induced degradation. Advanced microstructural engineering techniques, such as grain boundary tailoring and doping with rare-earth elements like Gd or Yb, have further enhanced these properties. For instance, Gd-doped La2Si2O7 exhibits a fracture toughness of 2.5 MPa·m^1/2 and a hardness of 10 GPa, achieved through controlled grain refinement and defect engineering.
Thermal cycling performance is critical for TBCs, and La2Si2O7 has shown remarkable durability in this regard. Experimental data indicate that La2Si2O7 coatings withstand over 2000 thermal cycles between room temperature and 1200°C without significant delamination or spallation, outperforming YSZ coatings that typically fail after 1000–1500 cycles under the same conditions. This enhanced performance is attributed to the low coefficient of thermal expansion (CTE) mismatch between La2Si2O7 (9.5 × 10^-6 K^-1) and common substrate materials like Ni-based superalloys (13–15 × 10^-6 K^-1), reducing interfacial stresses during thermal cycling.
The synthesis and processing of La2Si2O7 ceramics have also seen significant advancements. Spark plasma sintering (SPS) has been employed to produce dense La2Si2O7 with a relative density exceeding 98% at sintering temperatures as low as 1400°C, compared to conventional sintering methods requiring temperatures above 1600°C. Furthermore, atmospheric plasma spraying (APS) has been optimized to deposit La2Si2O7 coatings with porosity levels below 5%, ensuring excellent adhesion and mechanical integrity while maintaining low thermal conductivity.
Environmental resistance is another key advantage of La2Si2O7 ceramics. Studies have shown that La2Si2O7 exhibits minimal degradation when exposed to corrosive environments containing molten salts (e.g., NaVO3 + NaSO4), with weight loss rates below 0.05 mg/cm^3 after 100 hours at 900°C—a stark contrast to YSZ coatings, which experience weight loss rates exceeding 0.15 mg/cm^3 under identical conditions. This superior resistance is attributed to the formation of stable lanthanum vanadate phases that inhibit further corrosion.
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