Study On Thermophysical Properties And Cmas Corrosion Resistance Of Gd₂(Ce_xZr_1-X)₂O₇ Type Rare Earth Zirconate

Compared with the traditional 6-8wt.%Y₂O₃ partially stabilized ZrO₂?YSZ?ceramic material,the rare earth zirconate ceramic material has lower thermal conductivity,higher high temperature phase stability,stronger anti-corrosion and anti-sintering properties.It is a promising new generation of thermal barrier coating ceramic layer material.However,the rare earth zirconate has a low coefficient of thermal expansion.At the same time,the thermal barrier coating is often corroded by CMAS?CaO-MgO-Al₂O₃-SiO₂?during its service at high temperatures.Therefore,it is of great significance to improve the thermal expansion coefficient and anti-CMAS corrosion performance of rare earth zirconate materials.Studies have shown that rare earth zirconates belong to the A₂B₂O₇ type of compounds,which can increase the thermal expansion coefficient of the material by introducing other elements at the B site.Therefore,in this paper,Gd₂O₃,CeO₂,ZrO₂were used as raw materials,and agglomerated bulk materials of Gd₂(Ce_xZr_1-x)₂O₇?x=0,0.1,0.2,0.3?ceramics were prepared by high temperature solid state reaction.The effects of CeO₂ doping on the thermophysical properties and CMAS corrosion resistance of Gd₂(Ce_xZr_1-x)₂O₇ ceramic materials were investigated.The specific research contents are as follows:?1?Four different compositions of Gd₂(Ce_xZr_1-x)₂O₇?x=0,0.1,0.2,0.3?ceramic materials were designed and prepared.The phase structure of the prepared Gd₂(Ce_xZr_1-x)₂O₇ ceramic material was analyzed by XRD and Raman spectroscopy.The results show that the Gd₂Zr₂O₇ ceramic block with undoped CeO₂ has pyrochlore structure,however,the Gd₂(Ce_0.1Zr_0.9)₂O₇,Gd₂(Ce_0.2Zr_0.8)₂O₇,Gd₂(Ce_0.3Zr_0.7)₂O₇ ceramic blocks have a defective fluorite structure.This indicates that the doping of CeO₂ changes the crystal structure of the Gd₂Zr₂O₇ ceramic block,which transforms it from a pyrochlore structure with a lower degree of disorder to a defect-type fluorite structure with a higher degree of disorder.?2?The mechanical properties of the four ceramic materials prepared were studied.The hardness of the material was measured by a fully automatic microhardness tester,and the fracture toughness of the material was calculated by the indentation method.It was found that when the content of CeO₂ increased from x=0 to x=0.3,the hardness increased from 7.1 GPa to 9.6 GPa.The toughness increased from 1.25 MPa?m^1/2 to 1.81 MPa?m^1/2.The results show that the doping of CeO₂ improves the hardness and fracture toughness of Gd₂Zr₂O₇ ceramic materials,and the hardness and fracture toughness of ceramic materials increase with the increase of CeO₂ content.?3?The thermophysical properties of four ceramic materials were studied.The thermal expansion coefficient of the material was measured by a high temperature thermal dilatometer.The thermal diffusivity and specific heat capacity of the material were tested by laser thermal conductivity meter and differential scanning calorimeter.The actual density of the material was calculated according to the Archimedes principle.The thermal conductivity of the ceramic material is derived.It is found that the thermal expansion coefficient of Gd₂(Ce_xZr_1-x)₂O₇ ceramic material gradually increases from 9.1×10^-6 K^-1 to 11.3×10^-6 K^-1 and the thermal conductivity gradually decreased from 1.55 W/?m?K?to 1.44 W/?m?K?when the content of CeO₂ increases from x=0 to x=0.3 at 800°C.This indicates that the doping of CeO₂ significantly increases the thermal expansion coefficient of ceramic materials and appropriately reduces the thermal conductivity of ceramic materials.?4?A CMAS powder was prepared and the corrosion resistance of Gd₂(Ce_xZr_1-x)₂O₇ ceramic material was studied.It was found that Gd₂(Ce_xZr_1-x)₂O₇ ceramics were corroded for 5 h and 10 h at 1250^oC,and there was no obvious corrosion phenomenon.However,after 20 h of corrosion,obvious cracks appeared on the surface of Gd₂Zr₂O₇ ceramic material,and the ceramic materials of the other three components doped with CeO₂ showed no cracks.This indicates that the CeO₂-doped Gd₂Zr₂O₇ ceramic material has better resistance to CMAS corrosion.