Study On The Preparation Of Multi-doped Zirconia Solid Electrolyte And Its Properties

The oxygen probe for iron and steel refining has been used extensively, but traditional MgO-single stabled zirconia solid electrolyte, due to the effect of electronic conductivity in low oxygen (10ppm) refining conditions, has some measurement precision problem. And acknowledge in the effect of monoclinic transformation on high-temperature conductivity and thermal shock resistance is lack, the prior authors had more focus on the thermal shock resistance, but they despised the influence of phase-change degree on high-temperature conductivity. Therefore, this paper tries to prepare partially stabled zirconia (PSZ) with high ion conductivity and then thermal shock resistance by adding multi-doping with reasonable heat treatment.Firstly, we have adopted the mechanically mixed method and dry pressing to prepare multi-doped zirconia body, then have investigative test to study the pressure less sintering procedure and get the multi-doped zirconia solid electrolyte with higher density and homogeneous elements distribution. By studying the heat treated samples with different doping ratio after sintering, we found that doped Y2O3content in composite materials plays a leading role in m phase content. The heat treatment after sintering can change the grain size of multi-doping material by different temperature, which particles obviously grown up after heat treatment is at1150℃. Spinel formed by doping of Al2O3can effectively inhibit the particles to grow up in multi-doping material.The results of thermal expansion and thermal shock resistance test show that the higher the relative doped proportion of Y2O3and MgO under certain total amount, the narrower the transition temperature range of monoclinic phase, also the higher initial transition temperature, that lead to the larger strength loss rate of multi-doping material after thermal shock. The higher degree of the volume contraction between800-1000℃is, the bigger loss rate of strength is. After fitting the AC impedance spectrum of PSZ solid electrolyte at different temperature, we found that the trend of total electrical conductivity activation energy was consistent with the grain boundary activation energy, this indicated that the grain boundary conductivity was major influencing factor on the conductivity of PSZ electrolyte. And the grain boundaries conductivity was higher than grain conductivity at mid-high temperature. On the basis of fitting equivalent circuit analysis, the microstructure evolution model with temperature changing was obtained.Based on the thermal expansion properties, thermal shock resistance, electric performance mentioned above, a linear relationship model between average thermal expansion coefficient under different preparation condition and m phase content was developed by aggregate analysis, which be considered as a reference for choosing raw material and the sintering process selection; it can theoretically get solid electrolyte materials with good thermal shock resistance by the quantization of m phase content and controlled the relationship between t phase thermal expansion coefficients and m phase content. At the same time, the numerical evolution model between the t phase content and electric conductivity was established; we found that the mutation point of thermal expansion coefficient during high temperature can be as an important index for predicting the solid electrolyte electric property. On the basis of classification of each affect factor in two models, the phase proportion in solid electrolyte could be designed to ensure the material properties.