Synthesis And Performance Research Of La₂Ce₂O₇@La₂Zr₂O₇ Core-shell Structure Thermal Barrier Coatings Material

Thermal barrier coatings material is the crucial technique to improve the heat resistance of aeroengine turbine blades.La₂Ce₂O₇and La₂Zr₂O₇are new thermal barrier coatings materials with great potential and highly concerned.But La₂Ce₂O₇has poor sintering resistance,La₂Zr₂O₇has a low thermal expansion coefficient.These performance defects limit their applications in thermal barrier coatings.Whereas it is difficult to fundamentally eliminate their defects through single material modification or simple compounding,and they have shown complementary characteristics.Therefore,in this paper,the core-shell structure was introduced into thermal barrier coatings materials,La₂Ce₂O₇@La₂Zr₂O₇ceramic powders were synthesized with La₂Ce₂O₇as the core.The effects of different synthesis methods,different precipitants,different precipitant concentrations,and different solvents on the structure and morphology of La₂Ce₂O₇nanoparticles were investigated.Meanwhile,one-step,two-step and three-step methods were used to synthesize La₂Ce₂O₇@La₂Zr₂O₇respectively.The most appropriate La₂Ce₂O₇core and La₂Ce₂O₇@La₂Zr₂O₇with the best coating effect were determined by SEM,TEM,XRD,and other characterization techniques.The thermophysical properties of core-shell structure ceramic samples were tested and compared with La₂Zr₂O₇and La₂Ce₂O₇.The results are as follows:(1)La₂Ce₂O₇nanoparticles prepared with high-concentration urea solution(0.3mol/L)or low-concentration trisodium phosphate solution(0.025 mol/L)as precipitating agents under the weak alkaline hydrothermal condition had regular morphology and good dispersion,they were more suitable as core materials.La₂Ce₂O₇@La₂Zr₂O₇powders prepared by the co-precipitation method with the surface modification of La₂Ce₂O₇particles by sodium dodecylbenzenesulfonate had better coating effect than one-step and three-step methods,and the surface coating layer was amorphous La₂Zr₂O₇.(2)Sintering tests indicated that the existence of the core-shell structure contributed to decelerate the process of grain growth and densification.The growth of grain had broken through the constraint of the core-shell structure and was completely controlled by the core at 1500°C.La₂Ce₂O₇@La₂Zr₂O₇showed good sintering resistance when the temperature was lower than 1400°C,and the sintering-resistant temperature was improved by at least 100°C,compared with La₂Ce₂O₇.The thermal diffusivities of La₂Ce₂O₇@La₂Zr₂O₇were higher than that of La₂Zr₂O₇and La₂Ce₂O₇at 300?500°C.The thermal conductivity was only 2 W·m^-1·K^-1at 500°C,which was lower than that of La₂Ce₂O₇,and was comparable to YSZ,represented a good thermal insulation performance.(3)Thermal radiation performance results revealed that,the emissivities of La₂Ce₂O₇@La₂Zr₂O₇at different temperatures were lower than that of La₂Ce₂O₇and La₂Zr₂O₇,the emissivities of La₂Ce₂O₇were the largest at 600°C and 800°C,while the infrared emissivity of La₂Zr₂O₇was the largest at 1000°C,in the ascending band of 2.5?10?m.For the stable band with a wavelength larger than 10?m,the infrared emissivities of La₂Ce₂O₇@La₂Zr₂O₇were stable at 0.86(600°C),0.85(800°C)and0.88(1000°C)respectively.Since the thermal radiation performance in the 2.5?10?m band at high temperature plays a major role,La₂Ce₂O₇@La₂Zr₂O₇with low emissivity is more suitable for thermal barrier coatings material.