Fabrication And Properties Of Bi₂O₃-Y₂O₃-ZrO₂ Oxygen Sensitive Ceramic

The YSZ solid electrolyte has been the preferred material of oxygen sensors and fuel battery because of its virtues,such as excellent oxygen ion conduction, mechanical property,oxidation-resistance,corrosion-resistance,no reacting with electrode materials and so on.So,more and more researches focus on the study on molding and dopant research of this material.We focused on the electrical properties and the microstructure composition of YSZ with different amount of Bi₂O₃,so through the sdudy on the fabrication and the dopant research of Bi-Y-Zr materials,we can support valuable data for application of oxygen sensed ceramic material.In this work,Bi₂O₃ as additives was added into 3mol%YSZ,made the slurry and the green-body through the Gel-casting technique.Disscussed the impact of Zeta-potential,pH,the amount of dispersant,and solid loading of the slurry on preparing the ceramic slurry with low viscosity and high solid loading.During the experiment,we found some results as following:the introduce of the dispersant and the changing of pH not only have much affect on the zeta-potential which is the main factor of static stabilization,but also make the polymer adsorbed on the surface of the ceramic particals,therefore operate the steric effect.We fixed the suitable amount of dispersant as 1.6wt%and the pH as 10,made out the solid content as 53vol%slurries suitable for Gel-Casting.Because of the low amount of organic compounds,the degreasing and sintering process can proceed at the same time.However,consider the phase transition and volatilization of Bi₂O₃,the heating rate should be controlled strictly,and the sintering temperature should be under 1000℃.Bi₂O₃ as a sintering assistant,can decrease the sintering temperature of YSZ because of its low melting point;meanwhile,Bi₂O₃ exhibits high oxygen ion conductivity at low temperature,which improves the oxygen ion conductivity of YSZ largely.This experiment adopts different doping of Bi₂O₃ and studies conductivity, composed phases and microstructure of the materials.We found:the solution between Bi₂O₃ and ZrO₂ produces oxygen vacancy,resulting in a higher conductivity;the doping of excessive Bi₂O₃ forms 5-Bi₂O₃,which exhibit high conductivity,can also improves the conductivity of YSZ;the doping of Bi₂O₃ causes the precipitation of m-ZrO₂,mainly because of the Y₂O₃ doping into the Bi₂O₃,so theδ-Bi₂O₃ appeared,and also that's why the precipitation of m-ZrO₂,but the certain mechanism is still in studying.While,the precipitation of m-ZrO₂ also deteriorated the mechanical properties and the thermal resistance performances.The choice of sintering schedule also affected electrical performances,composed phases and microstructure of Bi₂O₃-3YSZ.The experiment exhibits that when the doping of Bi₂O₃ is 3mol%,we have no Bi₂O₃ by furnace cooling;only adopt cooling in air,can we find a little amount of Bi₂O₃;when the doping of Bi₂O₃ is 5mol%,we can find Bi₂O₃ phase by any cooling modes.This means the solubility limit of Bi₂O₃ in 3YSZ is between 3mol%and 5mol%;the grain size grows apparently with the increasing of sintering time.