Hydration process of rare-earth sesquioxides having different crystal structures
Hydration process of rare-earth sesquioxides having different crystal structures
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DOI：
10.1021/la020954y
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发表时间：
2003-10-28
期刊：
影响因子：
3.9
通讯作者：
Kuroda, Y
中科院分区：
文献类型：
--
作者：
Nagao, M;Hamano, H;Kuroda, Y
通过测定稀土倍半氧化物（主要是氧化钕）在水蒸气中的吸附量、红外光谱和含水量，研究了稀土倍半氧化物在水蒸气中的反应性及其水化过程。水蒸气吸附在氧化钕a型和c型Nd2O3上，形成氢氧化钕Nd(OH)(3)。吸附量（重量）随水汽暴露时间的变化表明，水化过程因倍半氧化物钕的晶体结构而异。结合红外光谱和含水量数据，发现a型Nd2O3经过约30 min的诱导期后，水化过程为一步[转化为Nd(OH)(3)]，而c型Nd2O3的水化过程为两步[通过NdOOH转化为Nd(OH)(3)]。考察了水蒸气在其他稀土倍半氧化物上的吸附性能；a型氧化镧（La2O3）的水化过程与a型Nd2O3相似，而c型倍半氧化物Nd2O3、氧化钐（Sm2O3）和氧化钇（Y2O3）的水化过程不同。这些氧化物水化速率的差异可以与氧化物的基本性质相联系。因此，水化速率最终取决于稀土金属离子的离子半径，因为氧化物的碱度取决于金属离子的离子半径。为了使Nd2O3表面耐水，还尝试了通过吸附金属醇氧化合物蒸汽进行表面改性或涂层。结果表明，表面包覆氧化钕（即钛包覆Nd2O3）具有防水性能。
The reactivity of rare-earth sesquioxides, mainly neodymium oxide, in water vapor and their hydration process have been investigated by measuring the adsorbed amounts, infrared spectra, and water contents. The adsorption of water vapor on neodymium oxides, A-type and C-type Nd2O3, led to the formation of a neodymium hydroxide, Nd(OH)(3). The variation of adsorbed amounts (in weight) with exposure time to water vapor suggested that the hydration process is different depending upon the crystal structure of neodymium sesquioxides. Combining with the data of IR spectra and water contents, it has been revealed that the hydration of A-type Nd2O3 takes place in one step [into Nd(OH)(3)] after an induction period of about 30 min, while that of C-type Nd2O3 proceeds in two steps [into Nd(OH)(3) via NdOOH]. The adsorption of water vapor on other rare-earth sesquioxides was also examined; the hydration process of A-type lanthanum oxide (La2O3) was similar to that of A-type Nd2O3, while those of C-type sesquioxides, Nd2O3, samarium oxide (Sm2O3), and yttrium oxide (Y2O3), were different from each other. The difference in the rates of hydration for these oxides can be correlated with a basic nature of oxide. Therefore, the rate of hydration is eventually governed by the ionic radius of rare-earth metal ion because the basicity of oxide depends on the ionic radius of metal ion. To make the Nd2O3 surface resistant to water, the surface modification or coating was also tried by adsorbing a metal-alkoxide vapor. As a result, it was revealed that the surface-coated neodymium oxide (i.e., titania-coated Nd2O3) has a water-resistant property.