【作者】 胡永刚；

【导师】 肖建中；

【作者基本信息】 华中科技大学 ， 材料学， 2012， 博士

【摘要】 氧化锆固体电解质定氧探头在钢铁精炼中已经获得了广泛应用,但是在低氧(10ppm)条件下,传统氧化镁单一稳定的部分稳定氧化锆由于固体电解质电子电导的影响使其测量精度受到影响。另外,对固体电解质室温下单斜相(m)在升温过程中的相转变程度对高温电导及抗热震性的影响规律的认识不足,前人对于定氧探头的研究思路较倾向于优先保证足够的抗热震性,却轻视了室温相向高温相转变程度对高温电导的影响。因此,本文试图通过多元复合掺杂,并结合热处理,在保证氧化锆高温离子电导的条件下,获得足够的抗热震性能。论文首先采用机械复合法制备多元掺杂氧化锆固体电解质,探讨了多元复合掺杂氧化锆陶瓷的无压烧结工艺,通过调整烧结工艺参数获得了相对密度较高,掺杂元素分布较均匀的复合掺杂固体电解质陶瓷材料。同时,通过对不同掺杂比例的试样进行烧结后热处理实验研究,发现复合掺杂材料中Y203含量对m相含量起主导作用。烧结后的不同温度热处理可以改变复合掺杂材料的晶粒尺寸,经1150℃热处理后复合掺杂材料中颗粒长大最明显。A1203的加入形成尖晶石可以有效抑制复合掺杂材料颗粒的长大。热膨胀及抗热震性试验结果表明,在掺杂总量一定时Y203与MgO的相对比例越高,单斜相转变温度范围越窄,且起始转变温度越高,导致复合掺杂材料热震后的强度损失率越大。800-1000℃之间的收缩程度越大,强度损失率也越大。通过研究不同掺杂含量的烧结试样的电阻抗性能,发现复合稳定的氧化锆固体电解质的电性能并不是随着某一掺杂剂含量的升高而线性变化的。此结果与传统的单一稳定剂在全稳定范围内电性能随稳定剂含量线性增长的规律有所差异。但对比Mg-PSZ在900℃时的总电导率,可以看出,复合稳定的PSZ电解质的总电导率要高一个数量级。对PSZ固体电解质不同温度交流阻抗谱拟合后发现,晶界电导活化能与总电导活化能的走势一致,说明晶界电导率对PSZ电解质电导率的影响占主要地位。并且中高温下的晶界电导高于晶粒电导。在对等效拟合电路进行分析的基础上,得到材料内部组织结构随温度变化的演变趋势模型。通过对热膨胀性质及抗热震性、电性能的研究,并结合现有理论分析,建立了不同制备条件下得到的平均热膨胀系数与m相含量之间的线性关系模型,将其作为原料选择及制定烧结工艺的参考依据；对m相含量进行量化、控制t相热膨胀系数与m相含量之间的关系,理论上可以得到抗热震性优良的固体电解质材料。同时,建立了t相含量与电导率之间的数值演化模型；发现材料体系高温下出现的热膨胀系数突变点,可以作为预测固体电解质电性能的一个重要指标。对两类模型各影响因素的分类分析,能够为固体电解质制备过程中的相比例的控制提供依据。更多还原

【Abstract】 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.更多还原