Study On The Preparation Technology And Performance Of Yttrium-stabilized Zirconia Solid Electrolyt

Yttrium stabilized zirconia（YSZ）is widely used as structural and functional ceramics due to its excellent mechanical,electrical,and thermal stability.Among them,3mol%yttrium stabilized zirconia（3YSZ）usually exists in the form of a tetragonal phase and has excellent mechanical properties.8mol%yttrium stabilized zirconia（8YSZ）usually exists in a cubic phase and has good ion conductivity,mainly used in solid fuel cells and oxygen sensors.This article uses 3YSZ as the structural ceramic material,5mol%yttrium stabilized zirconia（5YSZ）and 8YSZ as functional ceramic materials,and 8mol%yttrium stabilized hafnium free zirconia（8YSZ₀）as supplementary solid electrolyte material.The ceramics are prepared by dry pressing and pressureless sintering,and two-step sintering and optimization of powder process are used as the path for grain refinement.Laser particle size analyzer,SEM,XRD,EBSD,Raman,universal testing machine,microhardness tester,nanoindentation tester The characterization and testing of powder particle size,ceramic sample morphology,grain size,phase,mechanical and electrical properties were carried out using equipment such as AC impedance analyzer.The main conclusions are as follows:（1）The forming and sintering processes of four types of 3YSZ were studied,and the effects of different sintering temperatures on the structure and mechanical properties of the samples were studied.The optimal molding process for the sample is to maintain a pressure of 1 minute,a molding pressure of 4 MPa,a heating rate of 3℃/min,and a holding time of2 hours.Vickers hardness and bulk density have a strong dependence,and the relationship between bending strength and sintering temperature is related.The 3YSZ ceramics studied are a mixture of intergranular and transgranular fractures;（2）The 5YSZ and 8YSZ grinding processes adopt a manual granulation process of grinding before firing for 5 minutes and secondary grinding after firing for 20 minutes.The optimal formula for the manual granulation process is 15 wt%liquid phase 3 wt%PVA,with a glue discharge system of 0.5℃/min to 700℃,and insulation for 2 hours.The temperatures for complete densification of 5YSZ and 8YSZ ceramics are 1450℃and1400℃,respectively,and the optimal calcination temperature for 8YSZ is 1050℃.The flexural strength and fracture toughness of the two ceramics increased first and then decreased with sintering temperature,and the total conductivity increased first and then decreased with sintering temperature at 450℃and 550℃;（3）Two step sintering is an effective way to refine grains,and the degree of densification of the sample depends on T₁and T₂.The average grain size is mainly affected by T₂.The main sintering mechanism of two-step sintering is grain boundary diffusion and volume diffusion,and the total conductivity of the sample is mainly affected by the grain size and grain boundary area of the electrolyte.Compared to conventional sintering,the maximum total conductivity of the 5YSZ and 8YSZ samples at 680℃test temperature ranges from3.39×10^-3S/cm、6.09×10^-3S/cm increased to 4.52×10^-3S/cm、7.87×10^-3S/cm,respectively;（4）Both 8YSZ and 8YSZ₀ceramics form dense bodies at 1400°C.Under the same sintering conditions,the average grain size of 8YSZ₀is slightly smaller,and 8YSZ ceramics have better crystallinity.However,the cubic phase cell parameters and tetragonal phase c/a values of 8YSZ₀ceramics increase,resulting in a higher cubic phase content.The bending strength,fracture toughness and Vickers hardness of 8YSZ₀ceramics are lower than those of 8YSZ ceramics,which may be attributed to the differences in phase contrast,grain orientation and CSL grain boundary structure.The oxygen ion migration activation energy of 8YSZ₀ceramics decreases,and the conductivity is slightly better than that of8YSZ ceramics.Through this paper,we can study the influence of conventional preparation process of YSZ on its structure,mechanics,electricity and thermal properties from multiple dimensions,which is conducive to comprehensive evaluation.On the other hand,we can study the structure and properties of Hf free 8YSZ ceramics,and point out the application prospects of Hf free zirconia ceramics.