Enthalpies of formation of Ce-pyrochlore, Ca0.93Ce1.00Ti2.035O7.00, U-pyrochlore, Ca1.46U4+0.23U6+0.46Ti1.85O7.00 and Gd-pyrochlore, Gd2Ti2O7: three materials relevant to the proposed waste form for excess weapons plutonium

Helean, Katheryn B.; Navrotsky, Alexandra; Vance, E. R.; Carter, M.L.; Ebbinghaus, B B; Krikorian, O.H.; Lian, Jie; Wang, L.M.; Catalano, Jeffrey G.

doi:10.1016/s0022-3115(02)00795-x

Cited by 84 publications

(52 citation statements)

References 30 publications

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“…The experimental values of ΔdsH for SrCO3 and CaCO3 are in quite good agreement with the literature data [49][50][51]. On the other hand, our results and the published [52] values of ΔdsH(Nb2O5) are quite different.…”

Section: Evaluation Of Enthalpy Of Formationsupporting

confidence: 89%

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Calorimetric Determination of Heat Capacity, Entropy and Enthalpy of Mixed Oxides in the System CaO–SrO–Bi2O3–Nb2O5–Ta2O5

Leitner¹,

Sedmidubský²,

Svoboda³

2013

Applications of Calorimetry in a Wide Context - Differential Scanning Calorimetry, Isothermal Titration Calorimetry and Microca

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Section: Evaluation Of Enthalpy Of Formationsupporting

confidence: 89%

“…These data are necessary for the evaluation of the ΔoxH values for the mixed oxides, and furthermore, these data could be compared with the literature data [49][50][51][52]. For the AECO3 carbonates, the measured heat effect consists of three contributions:…”

Section: Evaluation Of Enthalpy Of Formationmentioning

confidence: 99%

Calorimetric Determination of Heat Capacity, Entropy and Enthalpy of Mixed Oxides in the System CaO–SrO–Bi2O3–Nb2O5–Ta2O5

Leitner¹,

Sedmidubský²,

Svoboda³

2013

Applications of Calorimetry in a Wide Context - Differential Scanning Calorimetry, Isothermal Titration Calorimetry and Microca

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“…Given that calcium is divalent, this seems to imply that it cannot only be stabilizing excess charge due to Mn(III). The other well-known cause for excess structural charge is the presence of Mn(IV) vacancies (31)(32)(33). Thus, these highly disordered materials may contain both Mn(III) "defects" and Mn(IV) vacancies.…”

Section: Resultsmentioning

confidence: 99%

Energetic basis of catalytic activity of layered nanophase calcium manganese oxides for water oxidation

Birkner

Nayeri²,

Pashaei³

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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Previous measurements show that calcium manganese oxide nanoparticles are better water oxidation catalysts than binary manganese oxides (Mn 3 O 4 , Mn 2 O 3 , and MnO 2 ). The probable reasons for such enhancement involve a combination of factors: The calcium manganese oxide materials have a layered structure with considerable thermodynamic stability and a high surface area, their low surface energy suggests relatively loose binding of H 2 O on the internal and external surfaces, and they possess mixed-valent manganese with internal oxidation enthalpy independent of the Mn 3+ / Mn 4+ ratio and much smaller in magnitude than the Mn 2 O 3 -MnO 2 couple. These factors enhance catalytic ability by providing easy access for solutes and water to active sites and facile electron transfer between manganese in different oxidation states.nanomaterials | thermochemistry R esearch on calcium manganese oxides (CaMnOs) has been inspired by the water-oxidation centers in photosystem II (1-5), which is a manganese-calcium cluster Mn 4 CaO 5 (H 2 O) 4 supported by a protein environment. Because the capability for efficient water oxidation is unique to photosystem II among all biological photosystems (6, 7), these CaMnO materials that mimic the elemental composition, manganese oxidation state, and particle size of the photosynthetic water oxidation center are of special interest (8)(9)(10)(11)(12). Although a number of other metal compounds function as water-oxidizing catalysts (13), many contain rare and expensive metals like iridium and ruthenium; the advantage of manganese oxides (Mn-oxides) is that they are earth-abundant, inexpensive, and environmentally friendly (1)(2)(3)(4)(5)14).CaMnO phases have short-range order structure and lamellar morphology (12), which are hallmarks of phyllomanganates (classically known as hydrous Mn-oxides), and they possess a layered structure (15)(16)(17)(18)(19)(20). In this family of structures, manganese octahedra (and vacancies) form the layers, and charge-balancing cations (i.e., alkali and alkaline earth ions, protons) and water occupy the interlayer space.Our previous calorimetric studies of various oxide nanoparticles, including those of manganese, iron, and cobalt (21), show that different polymorphs and phases with different oxidation states have significantly different surface energies. For particle sizes below 100 nm, these differences affect the free energies of phase transitions and of oxidation-reduction reactions, shifting the latter by as much as several log(fO 2 ) units at a given temperature. This thermodynamic effect on redox equilibria is significant when one considers electrochemical potentials for water splitting or other catalytic reactions involving nanoparticles (14). In a chargecompensated layered structure, the Mn(III)/Mn(IV) equilibrium will be different from that of binary Mn-oxide phase assemblages, namely, Mn 3 O 4 (hausmannite), Mn 2 O 3 (bixbyite), and MnO 2 (pyrolusite). Thus, particle size, morphology, crystal structure, and mixed valence in the more complex ...

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“…These data are necessary for the evaluation of the ox H values for the mixed oxides, and furthermore, these data could be compared with the literature data [23][24][25][26]. For the AECO 3 carbonates, the measured heat effect consists of three contributions:…”

Section: Resultsmentioning

confidence: 99%

Enthalpy of formation of selected mixed oxides in a CaO–SrO–Bi2O3–Nb2O5 system

Leitner¹,

Nevřiva²,

Sedmidubský³

et al. 2011

Journal of Alloys and Compounds

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Enthalpies of formation of Ce-pyrochlore, Ca0.93Ce1.00Ti2.035O7.00, U-pyrochlore, Ca1.46U4+0.23U6+0.46Ti1.85O7.00 and Gd-pyrochlore, Gd2Ti2O7: three materials relevant to the proposed waste form for excess weapons plutonium

Cited by 84 publications

References 30 publications

Calorimetric Determination of Heat Capacity, Entropy and Enthalpy of Mixed Oxides in the System CaO–SrO–Bi2O3–Nb2O5–Ta2O5

Calorimetric Determination of Heat Capacity, Entropy and Enthalpy of Mixed Oxides in the System CaO–SrO–Bi2O3–Nb2O5–Ta2O5

Energetic basis of catalytic activity of layered nanophase calcium manganese oxides for water oxidation

Enthalpy of formation of selected mixed oxides in a CaO–SrO–Bi2O3–Nb2O5 system

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