【作者】 高冬云；

【导师】 郭瑞松；

【作者基本信息】 天津大学 ， 材料学， 2010， 博士

【摘要】 Y掺杂锆酸钡陶瓷是理论上最好的高温质子导体,它既有良好的化学稳定性,又有较高的晶粒电导率,是固体氧化物燃料电池电解质的重要候选材料。然而,这种材料难以烧结,总电导率偏低,难以用于需要高功率密度的场合。本论文研究了降低BaZrO₃基陶瓷的烧结温度和提高其电导率的方法。研究了使用烧结助剂降低BaZr_0.9Y_0.1O_3-δ陶瓷烧结温度。通过对各种物质进行筛选,找出可以促进BaZr_0.9Y_0.1O_3-δ陶瓷烧结的P₂O₅、CuO和NiO三种氧化物并进行详细研究。P₂O₅促进锆酸钡致密化是依靠液相烧结机理,4 mol%的P₂O₅可使BaZr_0.9Y_0.1O_3-δ在1600°C保温4 h的条件下达到94.2%的理论密度。CuO和NiO通过固溶作用促进BaZr_0.9Y_0.1O_3-δ陶瓷的致密化。2 mol%的CuO可使1600?C烧结的BaZr_0.9Y_0.1O_3-δ试样的相对密度达到95.4%,远远高于不含CuO试样的67.9%的理论密度。由电动势法测得的含1² mol% CuO的BaZr_0.9Y_0.1O_3-δ在600⁸00°C的质子迁移率为_0.95⁰.85,基本可以满足燃料电池的要求。NiO对BaZr_0.9Y_0.1O_3-δ烧结的促进作用更加明显,1² mol%的NiO可使BaZr_0.9Y_0.1O_3-δ在1500°C的烧结温度达到>95%的相对密度。烧结助剂能将BaZr_0.9Y_0.1O_3-δ的高于1700°C的致密化温度大大降低,为研制燃料电池共烧工艺提供了基础。研究了gel-casting工艺制备掺杂BaZrO₃粉体。因为凝胶中各组分是在分子水平混合,因此粉体具有很好的化学均匀性。Gel-casting可以降低合成粉体的温度。对gel-casting法来说,1200°C保温4 h就可以合成纯的钙钛矿,而对固相法来说,却需要在1400°C保温10 h。Gel-casting法大大改善了合成粉体的烧结性,用gel-casting法粉体制备的陶瓷在1600°C保温4 h可达到理论密度的92.8%,而固相法粉体制备的陶瓷在相同的烧成制度下只达到了67.9%的理论密度。采用gel-casting法制备了不同稀土元素掺杂的BaZr_0.9M_0.1O_2.95（M= Yb, Dy, La）粉体,并研究了不同掺杂元素对粉体烧结性以及粉体所制备的陶瓷材料的电性能的影响。实验证明gel-casting是制备掺杂BaZrO₃粉体的一种简单快捷的工艺。使用二次烧成工艺将BaZrO₃基陶瓷与硫酸盐或碳酸盐复合制成复相质子导体,尽可能地保留了盐类的原始相组成,同时使BaZrO₃基陶瓷与盐类之间的反应减少到最小,将BaZr_0.9Y_0.1O_3-δ陶瓷的质子电导率提高了一到两个数量级,在600⁸00°C达到了10-2 S/cm的数量级,远远高于单相BaZr_0.9Y_0.1O_2.95陶瓷。添加硫酸盐（Na2SO4、K2SO4和Li2SO4:K2SO4=1:1）和碳酸盐（Na₂CO₃、K₂CO₃和2Li₂CO₃+Na₂CO₃）的BaZr_0.9Y_0.1O_3-δ复相材料还观察到了明显的超质子电导现象。更多还原

【Abstract】 Y-doped BaZrO₃ ceramics is the best one among several high temperature proton conductors in theory. With the combining merits of good chemical stability and high bulk conductivity, it is a promising candidate for electrolytes in solid oxide fuel cells. However, the material is difficult to densify. Its total conductivity is low due to the large area and high resistance of the grain boundary. This inhibits its high-drain applications. Methods of lowering the sintering temperature and improving the conductivity of BaZrO₃-based ceramics are investigated in this work.Several sintering aids, such as P₂O₅, CuO and NiO, which can densify BaZr_0.9Y_0.1O_3-δ at a lower temperature, were chosen and researched thoroughly. BaZrO₃-based ceramics were densified by P₂O₅ through liquid sintering mechanism. 94.2% of theoretical density was reached for BaZr_0.9Y_0.1O_3-δ sintered at 1600°C for 4 h by adding 4 mol% P₂O₅. CuO and NiO promoted the densification of BaZr_0.9Y_0.1O_3-δ by solid solution mechanism. 95.4% of theoretical density was reached for the sample sintered at 1600 ?C by adding 2 mol% of CuO, much higher than the 67.9% of theoretical density for the sample without CuO. The proton transport number of BaZr_0.9Y_0.1O_3-δ with 1² mol% of CuO ranged from _0.95 to 0.85 between 600⁸00°C, which could basically fulfill the request for the fuel cells. NiO could promote the densification of BaZr_0.9Y_0.1O_3-δ much more effectively. 1² mol% NiO could make the BaZr_0.9Y_0.1O_3-δ sample to reach >95% of theoretical density when sintered at 1500°C. Therefore, the sintering temperature of BaZr_0.9Y_0.1O_3-δ at >1700°C as previously reported in literature could markedly be lowered by sintering aids. This provides a guarantee for the co-firing process in the preparation of solid oxide fuel cells.Gel-casting process was studied to prepare BaZrO₃-based powders. As the mixing of the constituents at a molecular level during the gel formation is achieved, the powders have a very high degree of chemical homogeneity. Lower calcining temperature and shorter holding time were required to synthesize the uniform BaZr_0.9Y_0.1O_2.95 powders compared with the traditional solid-state reaction method. Pure perovskite phase was obtained at 1200°C for 4 h by gel-casting process, whereas 1400°C for 4 h was required by solid state reaction. Sinterability of the powders was obviously improved by gel-casting method. 92.8% of theoretical density was reached for the ceramics prepared by gel-casting method, much higher than the 67.9% of theoretical density for the samples made by the solid state reaction. Different rare earth elements doped BaZr_0.9M_0.1O_2.95 （M= Yb, Dy, La） powders were prepared by gel-casting methods. The results demonstrated that the gel-casting process is a simple, fast and convenient method for preparing a high-temperature proton conductor BaZr_0.9M_0.1O_2.95 powders.Two times sintering process was applied to prepare the composites of Y-doped BaZrO₃/sulphates and BaZrO₃/carbonates. The original phases of the salts were preserved as high as possible by this process; meanwhile the reaction between BaZrO₃-based ceramics and the salts were reduced to the lowest level. The conductivities of BaZrO₃-based ceramics were increased by one or two orders of magnitude, reaching the order of 10-2 S/cm for BaZr_0.9Y_0.1O_3-δ/salt composites at 600⁸00°C, much higher than that of the monolithic BaZr_0.9Y_0.1O_3-δ. Superprotonic conductivity phenomena were observed in the composites with sulphate （Na2SO4, K2SO4 and Li2SO4:K2SO4=1:1） and carbonate （Na₂CO₃, K₂CO₃ and 2Li₂CO₃+Na₂CO₃）.更多还原