Fabrication And Study On Hafnium Oxide Composed By Rare Earth Oxide High Temperature Infrared Radiation Coating

Infrared radiation materials with high emissivity at high temperature are widely used in energy-saving heating and drying in industrial fields,medical health and thermal protection in the aerospace field due to their excellent infrared radiation performance and chemical stability in high temperature environments.With the rapid development of China's aerospace industry,the traditional infrared radiation coatings can no longer be applied in areas with high service temperatures.Therefore,it is urgent to develop a novel high-emissivity infrared radiation material with higher service temperatures.In this work,ultra-high temperature material hafnium oxide(Hf O₂)and four different rare earth oxides(Pr₆O₁₁,Tb₄O₇,Sm₂O₃ and Gd₂O₃)were used as raw materials.The spherical agglomerated mixed powder was prepared by spray granulation,and then calcined at 1600°C for 4 hours to obtain Hf O₂-based high-temperature infrared radiation powder.The roasted powder in the range of 40-65?m was sieved out for spraying.The Hf O₂-based high-temperature infrared radiation coating was prepared on the high-temperature nickel-based alloy substrate by using atmospheric plasma spraying method(APS).Finally,the phase composition,microstructure and element distribution of the powder and the coating were characterized in detail,and the infrared radiation performance and thermal stability of the coating were tested and analyzed.The test results showed that the addition of rare earth oxides can significantly improve the infrared radiation performance of Hf O₂materials.Among them,when the addition of rare earth oxide was 10 wt.%,the infrared emissivity of the composite coating was the highest(0.852-0.863),which was more than 37%higher than that of pure Hf O₂ coating(0.618).The infrared emissivity relationship between the four kinds of coatings with different rare earth oxides under the same addition amount was:?_TH>?_PH>?_SH>?_GH.The main reason that the rare earth oxide composite Hf O₂ coating has a higher infrared emissivity than the pure Hf O₂ coating is that a small amount of rare earth ions(Re³⁺)can replace Hf⁴⁺during the high temperature reaction process.On the one hand,oxygen vacancies can be generated,which can attract electrons to form a color center.The color center can generate local energy levels in the band gap of Hf O₂ to increase electron absorption.On the other hand,it can reduce the symmetry of the lattice structure of Hf O₂,thereby enhancing the lattice absorption.At the same time,the rare earth oxide can react with Hf O₂ to form the rare earth hafnate with a higher intrinsic emissivity than Hf O₂,so it is also conducive to the improvement of the infrared emissivity.Among the four rare earth oxides,Tb₄O₇ showed the best addition effect.This is mainly because a small amount of Tb³⁺was converted to Tb⁴⁺existed in the Tb₄O₇ composite Hf O₂ coating,which can increase the electron density in the crystal lattice,thereby enhancing electron absorption.At the same time,there is a small amount of Hf O₂ with monoclinic phase converted into cubic phase Hf O₂ in the coating,which can increase the asymmetry of the lattice,so the lattice vibration absorption of the material is enhanced.The thermal stability test results revealed that Hf O₂-based high-temperature infrared radiation coating exhibited good thermal shock resistance and thermal resistance,which can withstand 60 hours of heat preservation at 1600?or more than39 thermal shock cycles from room temperature to 1200?in the atmospheric environment.During the thermal stability test,the phase composition and microstructure of the coating did not change significantly.At the same time,the infrared radiation performance of the coating at room temperature and high temperature decreased little,and remained at a relatively high level.