Project 7 Chemical and electronic properties of Actinide compounds and their applications (R2P7)

概要

INTRODUCTION:
Actinide compounds shows a unique chemical and elec- tronic nature due to the partial and insufficient shield of 5f orbital electrons as inner transition elements. We have a deep interest in the aspect of the electronic properties of the actinide compounds and formed the group consisting of three major fields: (1) inorganic and coordination chem- istry, (2) electronic properties and (3) theoretical chemistry and its users. These studies will be also useful for applica- tion research area such as the handling of the 1F debris and developments of nuclear medicines.
Such research environments to handle actinides elements are extremely difficult to build in ordinary university insti- tutes. The hot laboratory of the KURNS offers unique op- portunities for the above-mentioned characteristic re- search activities.

EXPERIMENTS:
The second fiscal year of the project has been devoted to the setting up the experimental environment and initial test experiments. Each of research fields has made their pro- gress as followings:
(1) T. Suzuki et al. has the investigated adsorption behav- iors of actinides on polyvinylpolypyrrolidone (PVPP) in nitric acid and hydrochloric acid solutions. The adsorption behaviors were evaluated through measurements of the distribution coefficient.
(2) Y. Haga et al. has synthesized the novel uranium inter- metallic compound U2Pt6Ga15. The single-crystalline sam- ples of this compound have been investigated by the meas- urements of crystallographic, thermodynamic, and transport properties.
(3) M. Nakase et al. has studied properties of Phthalocya- nine (Pc) as a ligand for an effective extraction of U. First, they built an electrical furnace for purifications of complex materials. A test operation of the furnace was performed by using a Pc-Zn complex they synthesized.
(4) T. Yamamura et al. has studied the hydrothermal syn- thesis of actinide compounds for the U-Zr, U-Fe, and U-Si systems as the simulating-debris compounds. The condi- tions were (2) 150ºC for 8 h, and (1) 450ºC for 30 min, and an addition of acetaldehyde as organic additive. The char- acterization was carried out by using XRD.

RESULTS:
(1) From the distribution coefficients measured for uranyl ions on PVPP, T. Suzuki et al. confirmed that only acti- nides adsorb on PVPP and can separate the actinides form other elements such as alkaline earth elements. They con- cluded that the hexavalent actinide is adsorbed on PVPP both in the nitric acid solution and in the hydrochloric acid solution. They also revealed that the tetravalent actinide is not adsorbed on PVPP in the hydrochloric acid solution but adsorbed in the nitric acid solution.

(2) A newly synthesized compound U2Pt6Al15 crystallizes in a layered structure of honeycomb planes with an inter- layer disorder. The average crystal structure belongs to the hexagonal space group. This compound was revealed to show a magnetic phase transition at approximately 25 K. The relatively sharp transition implicated by the magnetic susceptibility measurement the magnetic ordering is con- sidered to be dominated by the in-plane correlations.

(3) The electric furnace for sublimation purifications (Fig. 1) has been built in the Hot Laboratory of KURNS. The test heating of the ZnPc yielded some impurities out of the crude product, indicating a sign for the purification. Cur- rently the equipment is still being adjusted, and this setup will be fixed and systematic test is planned.

(4) Not only the very moderate hydrothermal condition (1), but also relatively severe condition (2), produced the dif- fractograms based on the UO2, independent from the met- als coexisted. The result agrees well with our previous re- sult without coexisting other metal ions [1]. The atmos- phere is indicative of being reductive enough to transfer U(VI) to U(IV). An coexistence of other anions could re- sult in the formation of new salt compounds such as sili- cates and phospites [2-3]. The conditions are to be im- proved in future studies.

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