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Synthesis and characterization of nanocrystalline cerium oxide powders by two-stage non-isothermal precipitation

机译：两步非等温沉淀法合成和表征纳米氧化铈粉

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Nanocrystalline CeO2 particles were firstly prepared by two-stage non-isothermal precipitation, i.e. precipitating at 70 degreesC and aging at another temperature. Experimental results showed that the intermediates at the end of precipitation stage were needle-like mixtures of Ce3+- Ce4+ compounds. The subsequent aging temperature played an important role on the shape and size of final products. As the aging temperature suddenly reduced to 0 degreesC, the resultant particles retained their original needle-like structure via the topotactic mechanism, which cannot be obtained by isothermal precipitation. As raising the aging temperature above 50 degreesC, the products were hexagonal and grown up with increasing temperature via the dissolution-recrystallization mechanism. Moreover, all products were cubic-fluorite structured CeO2 with negligible Ce3+ content. As compared to the nanohexagons (aged at 90 degreesC), the nanoneedles (aged at 0 degreesC) exhibited an unordinary red shift in the UV absorption and possessed a smaller bandgap energy. (C) 2004 Elsevier Ltd. All rights reserved.
机译：首先通过两步非等温沉淀，即在70℃下沉淀并在另一温度下老化，来制备纳米晶态的CeO 2颗粒。实验结果表明，沉淀阶段结束时的中间体为针状的Ce3 +-Ce4 +化合物混合物。随后的时效温度对最终产品的形状和尺寸起着重要作用。随着时效温度突然降低至0℃，所得颗粒通过全能机理保持其原始的针状结构，这是不能通过等温沉淀获得的。随着时效温度升高到50℃以上，产品呈六边形，并通过溶解-重结晶机制随着温度的升高而长大。此外，所有产品均为立方萤石结构的CeO2，Ce3 +含量可忽略不计。与纳米六边形（在90摄氏度下老化）相比，纳米针（在0摄氏度下老化）在紫外线吸收方面表现出非同寻常的红移，并且具有较小的带隙能。 （C）2004 Elsevier Ltd.保留所有权利。

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