Study On Rare Earth Doping And Phase Stabilization Of Zirconium Hafnium Oxide Ceramic

With the continuous improvement of the operating temperature of aircraft engines,the traditional yttrium oxide（Y₂O₃）stabilized zirconia（ZrO₂）thermal barrier coating is difficult to meet the service requirements at higher temperatures（above 1200℃）due to its low phase transition temperature.Therefore,hafnia（HfO₂）,which has a higher phase transition temperatures and a structure similar to ZrO₂,has gradually received more attention.However,HfO₂ can only be obtained by separation from zirconium ore,and accounts for only 2 wt%of the zirconium content.Its low production and high price prevented it from being fully used.In order to solve the above problems,in addition to optimizing the existing zirconium and hafnium separation process to increase the output of HfO₂,it is also possible to improve the phase transition temperature of ZrO₂ by forming a ZrO₂-HfO₂ solid solution with high hafnium content,enabling it to be used at higher temperatures.Based on this,this paper studied the process conditions for separating zirconium and hafnium,the phase composition,structure,and properties of Y₂O₃ stabilized ZrO₂-HfO₂ solid solution,and discussed the impact of extracting hafnium on the properties of ZrO₂,as well as the potential of Y₂O₃-ZrO₂-HfO₂ solid solution as a new material for thermal barrier coatings.The main research contents and results are as follows:1.By introducing ammonium sulfate into the raw material solution and washing solution,and utilizing the difference in binding force between zirconium and hafnium and sulfate ions,the separation effect of zirconium and hafnium has been strengthened,and the separation efficiency of the existing MIBK industrial production process has been improved.The optimized process can be well applied to centrifugal extractors,with a single extraction rate of 87.7%for hafnium and a separation coefficient of 4.65.The overall equipment has a small footprint and low energy consumption,which means it has a good application prospect.2.The effect of extracting hafnium on the performance of existing ZrO₂ was studied.Through a comparative study of the phase transition temperature,porosity,hardness,and thermal conductivity of ZrO₂ ceramics without hafnium and existing ZrO₂ ceramics containing hafnium（2 wt%）,it was found that the extraction of hafnium has a relatively small impact on the above-mentioned properties of ZrO₂ ceramics,providing theoretical guidance for the practical application of ZrO₂ without hafnium.3.The phase composition,microstructure,hardness,fracture toughness,and thermal conductivity of Y₂O₃-ZrO₂-HfO₂ solid solution samples with different compositions were studied.The related results indicate that the increase of HfO₂content in this ternary system will seriously weaken the stabilizing effect of Y₂O₃ on the solid solution phase structure.By increasing the content of Y₂O₃,the phase structure of the solid solution can be better stabilized to a cubic phase.In the ZrO₂-HfO₂ system stabilized with 3 mol%Y₂O₃,when the molar ratio of Zr to Hf is equal,the thermal conductivity of the sample reaches a minimum,and the hardness and fracture toughness are both high,which may be related to the formation of an ordered solid solution with a superstructure in the sample.