| Abstract
| - The adsorption of water on Nd2O3 has been investigated by measuring the adsorption isotherm of water,water content, temperature-programmed desorption (TPD), and near-infrared (NIR) spectra and also bydielectric measurement. The water content of Nd2O3 was found to be appreciably larger than that of typicalmetal oxides. Two distinct desorption peaks were observed in the TPD spectrum of Nd2O3, as in the caseof Nd(OH)3. The most characteristic feature of the adsorption of water on Nd2O3 was the appearance ofa break in the adsorption isotherm at a relative pressure of approximately 0.028. The NIR spectra of thissample gave a broad band at around 7050 cm-1 and a sharp band at 7140 cm-1 due to the overtone of thestretching vibration of the OH group, though the combination mode was not observed. These facts areinterpreted in terms of the occurrence of bulk hydration at room temperature. The following hydrationprocess is proposed; first Nd2O3 changes to NdOOH and then to Nd(OH)3. Dielectric relaxation of physisorbedwater at a coverage of 2.5 was observed at 50 kHz and at 169 K, indicating the restricted motion of waterowing to a strong interaction with the surface layer. On the basis of the O1s binding energy observed at528.9 eV for Nd2O3, these phenomena are explained by the concept of basicity due to the large ionic radiusof the rare-earth metal ion. To protect the surface of Nd2O3 from hydration, surface fluoridation was tried.As a result, it was clearly shown that surface fluoridation is very effective for protecting against hydrationof Nd2O3. The depression of surface conduction observed in the dielectric behavior of the fluoridated samplealso supports the depression of bulk hydration.
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