Study On Tape Casting Process And Properties Of Zirconia Substrates

With the more and more serious air pollution, emission regulations have become increasingly stringent. Planar-type oxygen sensor, which gives the advantages in fast light off capability and small element size, is one of the major trend in the development of automobile exhaust sensor. The ceramic substrate technique is the basic and key step for the planar-type oxygen sensor research. In this dissertation, tape-casting technique of zirconia substrate has been exhaustively studied. Detailed work is as following: Research on ceramic powder has been carried out based on processing of ultra-fine powder from industry market. Through calcining and milling, particle morphology, particle size distribution and packing density of the powder have been improved and the requirement of tape-casting has been met. The suitable calcining temperature and milling time have been given. The influences of three different dispersants(Triethanolamine, Phosphate ester and Terpineol), pH value of the slurry, binder, plasticizer, ball milling time on the properties of the slurry have been studied systemically through the measurements and analytical methods to rheological properties, sediment experiment and capabilities of green tape and sintered tape. Results show that triethanolamine is an effective dispersant for zirconia powder with the advantages of less dispersant content(1.5wt%), high stability of slurry and high tape density between pH 9 and 11.5. High intensity and ductibility of green tape have been gotten when the binder content is 5wt%. The optimum content of the additives and the other technical parameters have been determined and the optimum formulation of the tape casting slurries has been given. In the tape-casting process, the fluid flow model of zirconia slurry has been analyzed, and the factors, especially the drying process, which influence the properties of green tape greatly, have been discussed. The disfigurement of tape casting has been analyzed. The technical parameters in the aqueous and non-aqueous tape-casting process have been studied respectively. The results show that green tape with high density, good intensity and ductibility properties can be gained by limiting the tape velocity at 12cm/min and the temperature at 25℃when drying in the air for the aqueous tape-casting and in the solvent atmosphere for the non-aqueous tape-casting. The sintering process has been studied. The results show that high sintering temperature is of advantage to improve the density of ceramic substrate. But it is difficult to get stable tetragonal polycrystals zirconia under so high sintering temperature that the grain size has increased over the critical size. It has been determined that the proper sintering temperature is 1500℃. The analysis results show that the sintered substrates formed by tape-casting process, exhibit good properties with homogeneous microstructure, high body relative density of 97.8%, the ionic conductivities of 1.187×10-2S·cm-1 at 1073K. From the microstructure of the zirconia substrates, the main phase is tetragonal polycrystal. Therefore the zirconia substrates can be used as the substrate of the solid electrolyte. Research on co-sintering technique of zirconia substrates has been carried out. The interface microstructure analysis shows that the substrates have been tightly combined under proper pressure.