Self-irradiated oxides

Wu T, Liu G, Zhao J, Hidaka H, Serpone N. Photoassisted degradation of dye pollutants. V. Self-photosensitized oxidative transformation of rhodamine B under visible light irradiation in aqueous Ti02 dispersions. J Phys Chem B 1998 102 5845-51. 

The actinide with the highest atomic number that has been studied in a solid phase is Es the sesquioxide is its only known oxide phase. The scarcity of this element, and more importantly the intense self-irradiation from the Es-253 isotope which destroys rapidly the oxide matrix, may limit attaining higher oxygen stoichiometries. The structural identification of ES2O3 (Haire and Baybarz 1973) was only accomplished by using very small quantities (10-100 nanograms) and electron diffraction, which provided diffraction patterns in very short times as compared to conventional X-ray techniques. 

The Cm203 (white) displays three crystal modifications, namely the A-, B- and C-type lanthanide structures as shown in table 23 (Eller and Pennemann 1986). A small uptake of oxygen can cause the oxide to acquire a tan to light brown appearance. The C-type (bcc) structure is the low-temperature form, which converts to the B-type (monoclinic) structure above 800°C, which in turn changes to the A-type (hexagonal) structure above 1600°C (Baybarz and Haire 1976). It is the C-type structure that is readily oxidized to higher oxides the monoclinic form is very resistent to oxidation and the monoclinic to cubic transformation via temperature treatment is very diflicult ( irreversible transformation). The B to A and the A to B transformations occur more readily with temperature. Self-irradiation (especially noticeable with the more readily available, shorter-lived Cm-244 isotope) converts the C-form of the sesquioxide to the A-form (Wallmann 1964, Noe et al. 1970). 

The question of the actual O/M ratio in CmOj is an important one. Magnetic data (see later section) yield moments that are too high (1.5 to 3.0 /jB versus zero, as expected for an 5f electron core), which initially was interpreted to mean that the O/M ratio in the oxide was less than two. Several workers have tried different experiments to resolve this problem (Nave et al. 1983, Morss et al. 1989) and a theoretical evaluation of this problem has also been attempted (Goodman 1992). The simplest answer would be that the CmOj is nonstoichiometric (e.g., O/M < 2.00) but this is not a totally satisfactory explanation and is not supported by X-ray analyses of the oxides. Self-irradiation can lead to loss of oxygen in such oxides but the Cm-248 oxides should be relatively free of these effects over modest time periods. 

Self-assembled nanorods of vanadium oxide bundles were synthesized by treating bulk V2O5 with high intensity ultrasound [34]. By prolonging the duration of ultrasound irradiation, uniform, well defined shapes and surface structures and smaller size of nanorod vanadium oxide bundles were obtained. Three steps which occur in sequence have been proposed for the self-assembly of nanorods into bundles (1) Formation of V2O5 nuclei due to the ultrasound induced dissolution and a further oriented attachment causes the formation of nanorods (2) Side-by-side attachment of individual nanorods to assemble into nanorods (3) Instability of the self-assembled V2O5 nanorod bundles lead to the formation of V2O5 primary nanoparticles. It is also believed that such nanorods are more active for n-butane oxidation. 

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