Study On Infrared Emissivity And Thermal Conductivity Of Er₂O₃/MnO₂ Doped Gd₂Zr₂O₇ At High Temperature

The rapid development of aerospace industry has promoted the research and development of aerospace vehicles.The aircraft is moving towards a high thrust weight ratio,the temperature of its turbine engine combustion chamber is rising,and the temperature of turbine blades is higher and higher.The harsh environment of long-term service poses new challenges to thermal barrier coating materials.Thermal conductivity is mainly studied as an important index to characterize the high temperature resistance of thermal barrier coatings.At high temperature,due to the influence of radiation heat transfer,the factor determining the thermal conductivity of thermal barrier coatings is not limited to phonon scattering,in which photons account for a large proportion.At present,the most widely used YSZ thermal barrier coating material has been unable to meet the increasingly harsh service environment.Especially at high temperature,YSZ is almost translucent to thermal radiation.Rare earth zirconate material has the advantages of high phase stability,high melting point,low thermal conductivity and high infrared emissivity（absorption）.It has been widely studied to replace YSZ as a new thermal barrier coating material.Through the doping modification of rare earth zirconate,it is of great significance to explore the relationship between emissivity and photon thermal conductivity.In this thesis,Gd₂Zr₂O₇ was doped with rare earth oxide Er₂O₃ and transition metal oxide MnO₂.The(Gd_1-xEr_x)₂Zr₂O₇ ceramic materials and Gd₂(Mn_xZr_1-x)₂O₇ ceramic materials were prepared by solid-state synthesis and high-temperature sintering.The effects of two different oxides and their contents on the crystal structure,thermal conductivity and emissivity of Gd₂Zr₂O₇ were investigated.The main research contents are as follows:（1）The cell constant of(Gd_1-xEr_x)₂Zr₂O₇ ceramics increases first and then decreases with the increase of Er₂O₃ doping.When a small amount of Er₂O₃ is doped（the doping amount is 0.025mol.%）,Er³⁺does not enter the Gd₂Zr₂O₇ cell,but is dissolved in the gap.At this time,the crystal shows a short-range ordered pyrochlore structure.When the doping amount increases,Er³⁺enters the Gd₂Zr₂O₇ lattice,replaces the position of Gd³⁺and changes into a defective fluorite structure.The thermal conductivity of(Gd_1-xEr_x)₂Zr₂O₇ ceramics decreases with the increase of temperature at first.After 800℃,the thermal conductivity appears an inflection point,suddenly increases with the increase of temperature,and the thermal radiation is strengthened.The infrared emissivity test results at 1100℃3-5μm show that(Gd_1-xEr_x)₂Zr₂O₇ ceramic material.The emissivity in the wavelength range of decreases first and then increases with the doping amount of Er₂O₃,which is opposite to the change of thermal radiation transmittance.The infrared emissivity（absorptivity）affects the photon thermal conductivity,and then changes its high-temperature thermal conductivity.The Raman test results show that the change of emissivity of(Gd_1-xEr_x)₂Zr₂O₇ is mainly due to the change of lattice distortion and bonding vibration caused by Er³⁺ions,which changes the infrared absorption capacity,showing the law of first increasing and then decreasing.（2）In Gd₂(Mn_xZr_1-x)₂O₇ ceramic material,the cell parameters decrease with the increase of MnO₂ doping,Mn⁴⁺ions are completely dissolved into the cell,and the material shows a complete pyrochlore structure.The thermal conductivity of Gd₂(Mn_xZr_1-x)₂O₇ ceramics decreases with the increase of temperature,but the thermal conductivity increases with the increase of temperature after 400℃.Gd₂(Mn_xZr_1-x)₂O₇ ceramic material 1100℃at the 3-5μm wavelength infrared emissivity increases with the increase of doping amount,which corresponds to the change of radiant heat transmittance.The larger the emissivity is,the smaller the thermal transmittance（photon thermal conductivity）is.Compared with Er₂O₃,the influence of Zr（Mn）-O（48F）stretching vibration caused by MnO₂ doping on the emissivity of ceramic materials is more significant.