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Kitatsuji, Yoshihiro
Radioisotopes, 67(10), p.483 - 493, 2018/10
Electrochemical reactions and redox properties of actinides such as uranium and neptunium are outlined. The flow electrolysis enables rapid and high-efficient treatment. It was demonstrated to measure slow processes of actinide redox. Experimental results of electrolysis of actinide ions and the preparation method of oxidation state of the ions based on the fundamental data are described. Mediator reaction and catalysis observed in the process of electrolysis of actinide ions are also explained.
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JAERI-M 7875, 75 Pages, 1978/10
no abstracts in English
Kitatsuji, Yoshihiro; Otobe, Haruyoshi; Kihara, Sorin*
no journal, ,
We have studied electrolytic redox behaviours of U ions under weak acidic conditions. UO
is reduced to UO
reversibly. The UO ion disproportionates to produce U
and UO in an acid solution, and the reaction rate of the disproportionation is lower in weaker acidic solution up to pH ca. 2.1. It was found that reduction current of UO increased abruptly after the induction period of several minutes. Acceleration of UO reduction coincides to adsorption of reduction product on the electrode surface which was observed by the electrochemical quartz crystal microbalance. As a result of electrolytic reduction of UO to U(IV), black fine particles were formed both on the surface of the electrode and in the solution. The size of the U(IV)-containing particles formed in a solution of pH 2.5 was analysed to be ca. 10 nm. The particles in the colloid solution were filtered after aging the colloidal particles, and filtrate was analysed by X-ray diffraction measurement system. Characteristic diffraction peaks of XRD pattern of the U-containing particles can be assigned to be poorly crystallized UO of fluorite structure. These facts suggest that the aggregated U(IV) work as catalyst for the electrolytic reduction and the disproportionation of UO.
Kitatsuji, Yoshihiro; Ouchi, Kazuki; Otobe, Haruyoshi
no journal, ,
Previously we reported the autocatalysis of the U(V) reduction to U(IV) in a weak acid solution where U(IV) forms hydroxide nano particles. Possibility of catalysis of other kinds of metal nano particle such as Zr(IV) hydroxide was investigated to elucidate the reaction mechanism of U(V) reduction. Reduction of U(VI) was observed by measuring the current during bulk electrolysis at the constant potential. In the case of the solution added Zr(IV) hydroxide, the larger reduction current of U(VI) was observed in initial stage of bulk electrolysis. This result indicates that U(VI) was reduced further to U(IV) with catalysis of Zr(IV) hydroxide particle without U(VI) hydroxide particle. It is well known that Zr(IV) is redox inactive. Thus, in the catalytic reduction of U(V) ion, the metal hydroxide particle does not participate directly in electron transfer. The metal hydroxide catalyst seems to provide reaction field to reduction of U(V).
Doshi, Satoru*; Maeda, Kazuki*; Taira, Yoshitaka*; Watanabe, Shinta*; Hirade, Tetsuya
no journal, ,
It has been reported that oxygen vacancies in cerium oxide (CeO) affect catalytic activity. There is a need for highly sensitive in-situ measurements of the state and concentration of oxygen vacancies during catalytic reactions, and we are considering using the positron annihilation method. This time, we measured samples with different particle sizes to clarify the sites where positrons are trapped. From the lifetime spectrum of a particle size of 2 nm, which has a high intensity of the long-lived component, we first determined the lifetime value of the longest-lived component to be 390.8
1.6 ps. Next, in the lifetime spectrum of a particle size of 60 nm, where the longest lifetime component is the smallest, the longest lifetime component was fixed at 390.8 ps, and the lifetime value of the other positron trap site was determined to be 199.47.4 ps. These values are close to the lifetimes of positrons trapped in surface and neutral oxygen defects in first-principles calculations.
Arai, Yoichi; Watanabe, So
no journal, ,
no abstracts in English
by using gamma-ray induced positron annihilation lifetime measurementDoshi, Satoru*; Maeda, Kazuki*; Taira, Yoshitaka*; Watanabe, Shinta*; Hirade, Tetsuya
no journal, ,
Gamma-ray-induced positron annihilation lifetime measurement (GiPALS), which utilizes the generation of positrons inside a sample by pair generation with gamma rays, has a significantly smaller background component than conventional measurement methods. It can perform measurements in harsh environments such as high temperature and high pressure because there is no positron source inside the sample. It has been reported that the positron annihilation lifetime spectrum of CeO can be fitted with two components. However, in reality, it is thought that there are at least three components: a component of annihilation in the bulk, a component of annihilation trapped in lattice defects, a component of annihilation trapped on the surface. Therefore, in this study, we tried to fit three components and assigned each by changing the particle size. In addition, we theoretically investigated the bulk, defect, and surface components in the positron annihilation lifetime of CeO using first-principles calculations.
