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  • 1.
    Abili Nejad, Maryam
    KTH, Superseded Departments, Chemistry.
    Kinetics for oxidation of CRUD model compounds2004Licentiate thesis, comprehensive summary (Other scientific)
    Abstract [en]

    The formation of CRUD (Chalk River Unidentified Deposit) inwater-cooled nuclear reactors constitute a severe problem. Thestability of CRUD under reactor conditions (high flux ofionizing radition, high temperature and pressure) must be knownin order to minimize the problem. The kinetics for CRUDoxidation by H2O2 and the two more potent oxidants IrCl62-and MnO4- has been studied using aqueous suspensions ofthree metal oxide powders, Fe3O4, Fe2CoO4 and Fe2NiO4. The metal oxides were used as model compounds forCRUD. The latter two oxidants were employed to study therelationship between kinetics and the reduction potential ofthe oxidant. In addition, the activation energies for thereaction between H2O2and the three metal oxides of CRUD model weredetermined. The mechanism of the reaction is discussedindicating that the final solid product in all three cases isFe2O3. Our experimental results show that the reactivityof the metal oxides towards oxidants is in the order Fe2CoO4>Fe3O4>Fe2NiO4. The relative reactivities of Fe2CoO4 and Fe3O4are in contrast with that expected from the studyof the ionization potentials of the divalent metals in theoxides. In addition to the experimental studies, thetheoretical grounds for kinetics of reactions in particlesolutions are discussed. The theoretical discussion is alsoused to explain the somewhat unexpected trends in reactivityobserved experimentally. The same reaction trend is alsoobserved in the reaction of the metal oxides with IrCl62-and MnO4-.

    We found experimentally that the logarithm of second orderrate constants of the reaction of metal oxides with oxidantsagainst the one electron potential of the oxidants follows aparabolic behavior in agreement with the Marcus theory forelectron transfer reactions. This work constitutes a good basisfor the design of further model studies aiming at resolving thestability of CRUD under reactor conditions.

    Keywords:Reactor Chemistry, Radiolysis, Oxidation,Kinetics, CRUD, Metal oxide

  • 2.
    Nejad, Maryam Abili
    et al.
    KTH, Superseded Departments, Chemistry.
    Jonsson, Mats.
    KTH, Superseded Departments, Chemistry.
    Reactivity of hydrogen peroxide towards Fe3O4, Fe2CoO4 and Fe2NiO42004In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 334, no 1, p. 28-34Article in journal (Refereed)
    Abstract [en]

    The kinetics of CRUD oxidation by H2O2 has been studied using aqueous suspensions of metal oxide powder. Fe3O4, Fe2CoO4 and Fe2NiO4 were used as model compounds for CRUD. In addition, the activation energies for the reaction between H,02 and the three CRUD models were determined. The rate constants at room temperature were determined to 6.6 (+/-0.4) x 10(-9), 3.4 (+/-0.4) x 10(-8) and 1.6 x 10(-10) m min(-1) for Fe3O4, FeCoO4 and Fe2NiO4, respectively. The corresponding activation energies are 52 +/- 4, 44 +/- 5 and 57 +/- 7 kJ mol(-1), respectively. The mechanism of the reaction is briefly discussed indicating that the final solid product in all three cases is Fe2O3. In addition to the experimental studies, the theoretical grounds for kinetics of reactions in particle suspensions are discussed. The theoretical discussion is also used to explain the somewhat unexpected trends in reactivity observed experimentally.

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