High Temperature Phase Stability And Molten Salt Corrosion Behavior Of Sc2O₃ Based Multiple Rare Earth Oxides Codoped Stabilized ZrO₂ Ceramics

At present,the first generation of thermal barrier coatings ceramics is 6-8wt.%Y₂O₃ stabilized ZrO₂（YSZ）,which is prone to phase transformation,sintering and grain growth when the temperature is higher than 1200℃,resulting in the increase of thermal conductivity,Young’s modulus and the decrease of high temperature corrosion resistance,thus accelerating the spalling failure of thermal barrier coatings.Therefore,the research and development of a new generation of thermal barrier coatings which can withstand 1500℃ ultra high temperature,sintering resistance and corrosion resistance is a hot spot in the field of high temperature protective coatings.In this paper,chemical co-precipitation and calcination method were adopted to prepare Sc₂O₃ based co-doped with mutiple rare earth oxide.The properties of SGYSZ ceramics,the phase stability at 1500℃ and the corrosion behavior of Na2SO₄+V2O5 molten salt were studied.The results show that:1.The shrinkage rates were over 28%when SGYSZ and 4.5YSZ were sintered at 1500 ℃for 200h.The shrinkage of 6.5S2.5G2.5YSZ is relatively small and the amount of rare-earth oxide solid solution is larger.The density of SGYSZ ceramics sintered at 1500℃ for 5h exceeded 90%,and increased with the increase of rare earth doping content.2.SGYSZ doped with more than 4.5mol%Sc₂O₃ has excellent phase stability at high temperature.SGYSZ didn’t undergo phase transformation and was still keep all non-equilibrium tetragonal phase（t’）.3.5S2G1.5YSZ has poor phase stability at high temperature due to less Sc₂O₃ doping,and 14%c phase was formed after heat treatment for 100h.Sc₂O₃ is beneficial to phase stability at high temperature,and rare earth doping has an important effect on phase stability of zirconia ceramics at 1500 ℃.3.The corrosion products of SGYSZ at 1000℃ Na2SO₄+V2O5 after molten salt corrosion are YVO₄,GdVO₄ and m-ZrO₂.The content of Sc₂O₃ has an important effect on the corrosion resistance to high temperature molten salt,and the higher the content of Sc₂O₃,the better the corrosion resistance.6.5S2G1.5YSZ has the best resistance to molten salt corrosion of Na2SO₄+V2O5.4.There weren’t formed corrosion layer on the cross section of SGYSZ,Sc₂O₃ was dissolved because of mineralization,pores and cracks were formed in the ceramics.The molten salt could penetrate into the samples along these pores and cracks to destroy the structure of the samples.Doping of Gd₂O₃ and Y₂O₃ can protect Sc₂O₃.5.Corrosion reaction follows Lewis acid-base theory and Gibbs free energy and the order of reaction is Y₂O₃>Gd₂O₃>Sc₂O₃.