Behaviour of rare earth sesquioxides exposed to atmospheric carbon dioxide and water

The behaviour of the rare earth sesquioxides, when exposed to atmospheric water and carbon dioxide under ordinary conditions of temperature and pressure, is reviewed. Data corresponding to eleven samples from seven different oxides systematically investigated by X-ray diffraction (XRD), IR spectroscopy, thermogravimetry (TG)and temperature-programmed decomposition (TPD), are reported. The BET surface areas of all these samples are also given. In accordance with the results summarized, upon exposure to air, the lanthanide sesquioxides all become hydrated and carbonated in bulk. However, the rate and intensity of these processes, as well as the nature of the resulting phases, are not the same for the whole group of oxides. Furthermore, the characterization carried out on the oxides aged in air suggests that throughout the lanthanide series at least three types of behaviour can be distinguished. In some cases, the behaviour has been found to depend on the origin of the samples, which prevents the generalization of definite sequences of reactivity for the whole series of oxides. Also, the use of a single technique, particularly XRD, does not allow one to establish the nature of the aged phases, or even to determine whether or not alterations in the bulk of the starting oxides have occurred. © 1987.