2005 Fiscal Year Final Research Report Summary
Determination of thermodynamic quantities of the complex formation of actinoids by microcalorimetry
| Project/Area Number |
14208058
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| Research Category |
Grant-in-Aid for Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Nuclear engineering
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| Research Institution | Tohoku University |
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Principal Investigator |
TOCHIYAMA Osamu Tohoku University, Institute of Multidisciplinary Research for Advanced Materials, Professor, 多元物質科学研究所, 教授 (70005479)
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| Co-Investigator(Kenkyū-buntansha) |
NIIBORI Yuichi Tohoku University, Graduate School of Engineering, Associate Professor, 大学院・工学研究科, 助教授 (90180562)
TANAKA Koichi Tohoku University, Graduate School of Engineering, Assistant, 大学院・工学研究科, 助手 (10005928)
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| Project Period (FY) |
2002 – 2005
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| Keywords | microcalorimetry / calorimetric titration / enthalpy of complexation / actinoid / temperature dependence of equilibrium constant / high level radioactive waste / entropy of complexation / carboxylic acid |
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| Research Abstract |
Potentiometric and microcalorimetric titration techniques were applied to determine the Gibbs free energies and enthalpies of the protonation and Eu(III), U(VI) complexation of formic, acetic, glycolic, oxalic, malonic and malic acids in 1.0 M NaClO_4 solution at 25℃, where Eu(III) was used as a chemical analog of radiologically important Am(III). By using the values of ΔG determined by potentiometric titrations, the results of calorimetric titrations were analyzed to give the values of ΔH and ΔS. To support the discussion on the obtained thermodynamic quantities, the hydration numbers of Eu(III) in the complexes were obtained by TRLFS measurement, where the luminescence lifetime of Eu(III) excited by 394nm laser was measured.
In the reaction with these carboxylates, proton, Eu^<3+> and UO_2^<2+> showed the typical hard Lewis acid character, and the enthalpies of the reactions were very small or slightly positive, indicating that the protonation or the complexation of these carboxylates were entropy-driven, that is, |-TΔS|>>|ΔH| in ΔG=ΔH-TΔS. The result of TRLFS measurement revealed that the dehydration occurred not only in the cation but also in the ligand anion. The numbers of hydrated water liberated in complexation were found to be controlled by the geometrical conditions such as denticity (mono- or bidentate coordination of the ligand), bulkiness or hydrophilicity/hydrophobicity of the ligand, dioxo-structure of UO_2^<2+>, and congestion of the ligands around the cation (stepwise complex formation).
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