【作者】 栾伟娜；

【导师】 夏临华；

【作者基本信息】 青岛大学 ， 凝聚态物理， 2007， 硕士

【摘要】 鉴于纳米CeO₂的广泛应用，本文首先利用不同方法制备了单相CeO₂粉体，从粒度、分散性、形貌等方面进行对比研究。结果表明以Ce（NO₃）₃·6H₂O为铈源，采用氨水沉淀法可得到平均粒径9.5nm、分散性好的球形CeO₂颗粒；借助微波的溶胶-凝胶法在成胶和烘干方面大大节省了时间和能源，300℃煅烧后可得到平均粒径为15nm、粒度分布窄的CeO₂粉体；利用NH₄HCO₃沉淀法制备出了平均长度84nm、直径15nm的棒状CeO₂粉体，发现CeO₂与其前驱体Ce₂O（CO₃）₂·H₂O在形貌上具有继承性。通过液相共沉淀法分别制备了Al₂O₃-ZrO₂、Al₂O₃-CeO₂、ZrO₂-CeO₂和ZrO₂-Al₂O₃-CeO₂系粉体，利用X射线衍射、差热-热重分析、透射电子显微术等方法对粉体进行分析表征。认为氨水共沉淀法制备的ZrO₂-30wt％Al₂O₃复合粉体经1200℃煅烧处理后，t-ZrO₂在室温下仍能存在的原因并不是Al₂O₃固溶到ZrO₂晶格中稳定实现的，而是因为热胀系数失配，高弹性模量的Al₂O₃对ZrO₂产生应力作用抑制了t→m相变；Al₂O₃是由非晶态直接转变为高温稳定态α-Al₂O₃。ZrO₂-12mol％CeO₂复合粉体在700℃时即形成结晶良好的立方ZrO₂-CeO₂固溶体；经1200℃煅烧后主要以四方相存在。Al₂O₃-CeO₂复合粉体经700℃煅烧后仅有立方萤石结构的CeO₂，950℃煅烧后有弱结晶的γ-Al₂O₃出现但1200℃后其完全转变为结晶良好的α-Al₂O₃。结合两相复合粉体的分析结果，研究了ZrO₂-Al₂O₃-CeO₂系粉体在煅烧过程中发生的固溶、相变等过程以及在不同温度下的物相组成。结果表明以氨水作沉淀剂制备的ZrO₂-Al₂O₃-CeO₂系复合粉体从室温煅烧至1300℃过程中相转变过程为：非晶态→c-（Zr，Ce）O₂→t-（Zr，Ce）O₂→t-（Zr，Ce）O₂+α-Al₂O₃，不同煅烧温度下均未出现CeAlO₃或其他Ce-Al化合物的衍射峰；CeO₂优先与ZrO₂形成固溶体；Al₂O₃在低温下是以无定形态存在的，直到1300℃才直接转变为结晶度较低的α-Al₂O₃。而碳酸氢铵沉淀法制备的三相复合粉体经1200℃煅烧1h后出现四种物相的衍射峰，分别为立方相（Ce，Zr）O₂固溶体、四方相（Zr，Ce）O₂固溶体、单斜相ZrO₂和α-Al₂O₃，分析认为粉体的不均匀性使其在富铈区域形成c-（Zr，Ce）O₂固溶体，而在富锆区域形成t-（Zr，Ce）O₂固溶体；缺少CeO₂稳定和Al₂O₃抑制作用的t-ZrO₂在1000℃煅烧后就发生t→m相变。更多还原

【Abstract】 Ceria powders were prepared by different ways and compared with the particle size,dipersion and morphology. Results showed that spherical ceria particles with the averagediameter of 9.5 nm and nicer dispersion were obtained using cerium nitrate hexahydrateand ammonia as raw meterials. The sol-gel method assisted with microwave can not onlyreduce the time but save energy on the gel formation and drying, by which ceria powderwith the average diameter of 15nm and narrow distribution was prepared after calcinationonly at 300℃. Rod-like nanocrystallines ceria with 90nm in length and 15nm in diameterwere prepared using NH₄HCO₃ as precipitant and had an inherited relationship onmorphology with precuesor Ce₂O（CO₃）₃·H₂O.The composite powders of Al₂O₃-ZrO₂, Al₂O₃-CeO₂ and ZrO₂-CeO₂ were synthesizedby co-precipitation method and characterized by XRD, DTA, TG and TEM, respectively.The reason why t-ZrO₂ can be stabilized at room temperature after the ZrO₂-Al₂O₃powders were calcined at 1200℃was that Al₂O₃ with high modulus elasticicy producedstress on ZrO₂ during cooling process, which hindered the t→m transformation. As forAl₂O₃, it directly transformed into stable, phaseα-Al₂O₃ at high temperatures fromamorphous structure, but not formed solid solution with ZrO₂. The ZrO₂-CeO₂ powdersprepared by ammonia precipitation method transformed into well crystallized cubic solidsolution after calcined at 700℃and tetragonal after 1200℃, respectively. In Al₂O₃-CeO₂system, only one crystallized phase of CeO₂ with cubic fluorite structure formed aftercalcined at 700℃, and the otherγ-Al₂O₃ phase generated at 950℃but then completelytransformed intoα-Al₂O₃ at 1200℃.The transformations during calcination and the phase composition at differenttemperatures were studied in ZrO₂-Al₂O₃-CeO₂ system synthesized with ammoniaprecipitation method. Results revealed that there wasn’t CeAlO₃ or any chemicalcompounds formed by Al₂O₃ and CeO₂ and CeO₂ was prior to form solid solution withZrO₂. Moreover, amorphous Al₂O₃ also directly transformed into weakly crystallizedα-Al₂O₃ until 1300℃. The transformation during calcination process from roomtemperature to 1300℃proceeded as follows: amorphous→c-（Zr, Ce）O₂→t-（Zr, Ce）O₂→t-（Zr, Ce）O₂+α-Al₂O₃. However, when prepared by NH₄HCO₃ co-precipitation method,c-（Ce,Zr）O₂, t-（Zr, Ce）O₂, m-ZrO₂ andα-Al₂O₃ coexisted after calcination at 1200℃for1h. The inhomogeneity of precursor caused that at the Ce-rich area c-（Ce,Zr）O₂ formedand at the Zr-rich area t-（Zr, Ce）O₂ formed. Furthermore, t→m transformation of ZrO₂happened after 1000℃calcination due to the lack of stabilization by CeO₂ and ihibitingeffect by Al₂O₃.更多还原