Preparation And Properties Studing Of Nanometer Zirconia Materials Of The Planar Oxygen Sensor

As the increasing of automobile number and more and more strict requirement of environment, the demand of oxygen sensors grows fast, the accuracy of oxygen measurement increases, and the range of oxygen measurement expands. The materials of an oxygen sensor plays a decisive role to its integrated performance. Ceramics are the main materials of oxygen sensors, including solid electrolyte, porous protective layer, diffusion barrier and support layer. The improvement of preparing method of the ceramics and the optimization of their microstructure are the improment routes to improve the integrated performance of oxygen sensors.In this paper, the 8 mol% Y₂O₃-ZrO₂（8YSZ） powders prepared by ammonia co-precipitation method, hydrothermal method and sol-gel method were researched. The microstructure of the powders was characterized by transmission electron microscopy（TEM）, finding that ultrafine powders with particle sizes between 8 and 10 nm were synthesized, regardless of which method was used. However, it was found that the phenomenon of spontaneous agglomeration existed for the particles, which would result in the formation of large pores in the region of ceramic and low density. A novel method of direct sintering zirconyl oxalate（ ZrOC₂O₄） sol to prepare dense ceramic was proposed. The optimal molar ratio of ZrO²⁺ and C₂O₄^2-to synthes stable ZrOC₂O₄ sol was determined by the state of sols, particle size and zeta potential. The results showed that when the molar ratios of ZrO²⁺ and C₂O₄^2-was fixed at 4:2, the average particle sizes was 238 nm, zeta potentials was 5.48 m V, and the sol was stable.The thermal decomposition process of the green body prepared by Zr OC 2O4 sol, the changes of crystalline form and crystallite size with the increasing heat treatment temperature and the microstructure of the ceramics sintered at different temperatures were analyzed by thermogravimetry and differential thermal analysis（TG-DTA）, X-ray diffraction（XRD） and field emission scanning electron microscope（FESEM）, respectively. And this method was compared with the method of sintering nano meter 8YSZ powder. The results showed that, ZrOC₂O₄ and organic auxiliary agents had decomposed before 550 ℃, turning to cublic 8YSZ. The crystallite size of 8YSZ increased with the increasing of sintering temperature in the range between 550 and 1200 ℃. However, the crystallite size remained stable over the sintering temperature of 1200 ℃. The dense ceramic sintered at 1300 ℃ by sintering ZrOC₂O₄ sol exhibited a high densification with homogeneous microstru cture, and the grains were fine with a narrow size distribution. After sintered at 130 0 ℃, the relative density of the ceramic prepared by the former method reached a value of 98.5%, while the value of the ceramic prepared by the latter method was just 92. 3%. When the tested temperature was 900 ℃, the conductivity reached a value of 127 m S ·cm^-1 for the former dense ceramic, but only 63 m S·cm^-1 for the latter ceramic.Several methods of preparing porous ceramic were compared, including the method of adding pore-forming agent, the method of adding foaming agent and partial sintering method. The microstructures showed that the most appropriate method was partial sintering method. That is to say, adding a-Al₂O₃ to ZrOC₂O₄ sol and then heated treatment at lower temperature than the sinter point. The effects of addition amount and particle size of aluminium oxide on the porous ceramic were researched. The results showed that the porosity of the ceramic increased with the increasing of addition amount in the condition of the particle size remained unchanged. While, the porosity of the ceramic increased or decreased with the increasing of particle size in the condition of the addition amount remained unchanged. When 50 nm Al ₂O₃ with a an amount of 30 wt% was added, the porosity reached a value of 37%. For the porous ceramics prepared by this method, open porosity was much larger than closed porosity, and the gas was able to pass through the porous ceramic film.In this paper, the effects of sintering aid（self-manufactured glass powder） and nanometer aluminum oxide with different amount on the mechanical property of zirconia matrix ceramic were investigated. The results showed that glass powder added in TZ-3Y2 OA powder was able to reduce the sintering temperature, however, excess glass powder would weaken the flexural strength and thermal shock resistance of the ceramic. Nanometer Al₂O₃ added in TZ-3Y2 OA powder was able to enhance the flexural strength of the ceramic, however, excess nanometer Al ₂O₃ would elevate the sintering point, and then weaken the flexural strength and thermal shock resistance of the ceramic. 3 wt% glass powder and 5 wt% nanometer Al ₂O₃ were added into TZ-3Y2 OA powder simultaneous, the ceramic sintered at 1300 ℃ possessed a better mechanical property. The flexural strength reached a value of 591 MPa, and the retention rate of flexural strength after quenching at 8 00 ℃ was 0.58.