Preparation And Properties Of The Rare Earth Doped Tin Dioxide Ceramics Electrodes

SnO2ceramics are mainly used as electrodes to melt glass, enamel and other materials. It needs not only good conductivity, but better corrosion resistant and higher strength and toughness. Currently in China most of high-grade SnO2electrode has to depend on the imported ones because of the lower quality of SnO2electrode made by domestic factory, which is hard to meet the requirements of production and application.The study on SnO2ceramics currently focused mainly on the sensitive ceramics or transparent films, the requirements of the SnO2ceramics were generally only on the sintering properties or the electrical properties. However, as an electrode, the SnO2ceramics must charactere with both high electrical and good sintering performance.The tin oxide ceramics electrode was prepared by powder metallurgy method in the paper. By controlling strictly the preparation process, it was ensured that the rare earth elements was mixed evenly into the tin oxide powder, and the dense tin dioxide ceramics was sintered in the high temperature. The performances of ceramics were characterized by the various means to discuss the influence of different rare earth dopants on the tin dioxide ceramics.Firstly, the influences of different La2O3concentration on SnO2ceramics were studies. Testing results showed that La2O3could cause the crystal of ceramics more smooth, and crystal boundary denser. When the concentration of La2O3was0.50wt,%, the second phase La2Sn2O7come into being, when the doping amount increased up to1.0wt.%, the crystal of SnO2-based ceramics growed completely. In the certain range of concentration, La2O3could greatly reduce the electrical resistivity of SnO2ceramics at room temperature. The doping amount of La2O3was0.50wt.%in the study, due to oxygen vacancies, free electrons and the second phase, the resistivity of SnO2ceramics was to the minimum value by334Ω·cm, only15%of resistivity of La2O3free sample. When the concentration of La2O3continued to rise, the resistivity of SnO2ceramics at room temperature decreased on the contrary, because crystal defects gradually disappeared.The performances of CeO2doped SnO2ceramics were studied. The influences of CeO2on the crystal growth and microstructure of SnO2ceramics were analyzed by XRD and SEM results. Results showed the doping of CeO2could effectively promote the growth of SnO2crystals, reduced the sintering temperature, and caused the crystal growing well and crystal boundary clear greatly. In the study the doping amount of CeO2was by1.0wt.%, it decreased the sintering temperature and boosted the growth of SnO2-based ceramics crystal, which would reduce gradually or eliminated the gas hole to densify the ceramics and improve the density. CeO2could lead to the formation of more oxygen vacancies, the free electrons and other carriers, so that the room temperature resistivity of SnO2ceramics greatly decreased. However, when the concentration of CeO2was more than1wt.%, the resistivity would be increased again.SnO2Ceramics doped with Pr2O3and Nd2O3were also studied. The doping of Pr2O3would produce more grain boundaries, when the content of Pr2O3was3wt.%, a large number of the second phases rich in Pr2Sn2O7were detected by XRD and EDS, which could significantly promote the conductivity of tin oxide electrodes; When the concentration of Pr2O3was up to5wt.%, over more Pr2O3damaged the SnO2lattice structure, and resulted in the reduction of the sintering properties, the poor density and bad influences on the electrical properties. Because of the high ionization energy and less ionic radius of Nd2O3, it was hard to boost the sintering of tin dioxide. During the preparation process it was easy to produce the second phase, and analysis showed that some second phase could improve the sintering and decrease the resisivity, but extra Nd2O3would lead to high resistivity.According to compare with the properties, the influence on the performance of tin dioxide electrodes doped by different rare earth oxides was analyzed. Results showed that trivalent rare earth ions such as La3+, Pr3+and Nd3+were easily separated out from the SnO2lattice and formed new second phase, while Ce4+ion could easily access to the main lattices and hard to form the second phase, which could promote the sintering. In addition, the sintering mechanism of tin dioxide ceramics doped with rare earth elements was analyzed in detailed. Results showed that the main driving force for the sintering of tin dioxide in the earlier period came from solid-phase sintering, the dense process was realized by the transfer, full and disappearance of the grain boundary. There were lots of wave patterns in the grain boundary surface seen by SEM, so it were inferred at high temperature the liquid phase had come into being transiently. In addition, SEM-EDS indicate a large number of the second phase was formed in the surface of tin ceramics. Analyzed by the phase diagram, during the earlier period of sintering process, it mainly characterized with the solid-phase sintering. With the sintering continued, doping ions would gradually enrich in the grain boundaries, which resulted in the forming of liquid phase. In the later period of sintering, due to the enrichment of dopants in grain boundaries, the enrichment area would start to separate with the SnO2main crystal phase and generate the second phase, and the new phase would separated from the substrate step by step again.Rare earth doped tin dioxide ceramics electrode applied to glass electrical melting furnace was studied. the results showed:rare earth dopants could decrease the room temperature resistivity of SnO2electrode. It would not only reduce the power consumption, but escaped from forming the interior stress. Tin dioxide electrode doped with1wt.%CeO2had still exhibited good sinter properties after using for one year, there was no crack damage and exhibited good corrosion resistant.