| 1. |
- Cui, Daqing, et al.
(författare)
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Surface mediated processes in the interaction of spent fuel α-doped UO2 with H2
- 2008
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Ingår i: Materials Research Society Symposium Proceedings. - 0272-9172. - 9781605110745 ; 1104, s. 87-99
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Konferensbidrag (refereegranskat)abstract
- In most deep disposal concepts, large amounts of hydrogen are expected to be produced by the anoxic corrosion of massive iron containers. At repository temperatures, hydrogen is quite inert and is not expected to contribute to the redox capacity of the deep groundwaters. In several recent works, a large impact of dissolved hydrogen on the dissolution of the LWR or MOX fuel and UO 2(s) doped with 233U or 238Pu has been observed. For hydrogen concentrations above a certain limit, the dissolution rates of these highly radioactive materials drop to very low values. A discussion of the results obtained with spent fuel or ?-doped UO 2 in the presence of a range of hydrogen concentrations is presented. Typical for all measurements under such conditions are the very low long term concentrations of uranium and other redox-sensitive radionuclides, such as Tc and the minor actinides. The concentrations of U are systematically lower than the values measured during UO2(s) solubility measurements carried out in the presence of strong reducing agents. Measurements of the radiolytic oxygen after long leaching periods result in values below detection limit. The investigation of the surface of spent fuel or UO2(s) pellets doped with 233U by XPS after long periods of testing shows absence of oxidation. The kinetics of the release of non-redox sensitive elements such as Sr and Cs, used to estimate fuel matrix dissolution rates, is also discussed. An attempt is made to propose potential mechanisms responsible for the observed behaviour, based mainly on data from studies on the interaction of water adsorbed on the surfaces of metal oxides or actinide oxides with radiation. Another important effect observed in recent studies is the existence of a threshold for the specific alpha activity below which no measurable influence of the alpha radiolysis on the uranium release from UO2 is observed. The importance of such a threshold for the behaviour of spent fuel under repository conditions encompassing very long time scales will be discussed, as well as the necessity to better investigate the mechanisms of recombination reactions in a thin water layer on the surface of actinide oxides affected by ?- radiolysis.
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| 2. |
- Gong, Karin Anne Xia, 1965, et al.
(författare)
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Toughening Effect and Oxidation Behavior of MoSi2-ZrO2 Composites
- 2007
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Ingår i: Materials Research Society Symposium Proceedings. - 0272-9172. ; 980, s. 339-344
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Tidskriftsartikel (refereegranskat)abstract
- Toughening effect of ZrO2-particles on MoSi2-based materials is one of the important toughening mechanisms. In this work, the influence of particle size and volume percentage of unstabilized ZrO2-addition on toughening in MoSi2-matrix composites was studied. The measured data revealed that the fine particle size,
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| 3. |
- Li, Shanghua, et al.
(författare)
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Fabrication of transparent polymer-inorganic hybrid material
- 2005
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Ingår i: Materials Research Society Symposium Proceedings. - : Springer Science and Business Media LLC. - 9781558998308 ; , s. 190-194
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Konferensbidrag (refereegranskat)abstract
- Polymer-inorganic hybrid materials composed of polymethyl methacrylate (PMMA) and zinc compounds were prepared by sol-gel in-situ transition polymerization of zinc complex in PMMA matrix. Zinc acetate dihydrate dissolved in ethanol was used as the inorganic precursor. Monoethanolamine (MEA) acted as a complexing agent to control the hydrolysis of zinc acetate to produce a zinc compound network, and then PMMA, formed in-situ through a radical polymerization, were chemically bonded to the forming zinc compound network to realize a hybrid material. Transparent homogenous hybrid materials with slight colours from pink to yellow were fabricated by varying the composition. TEM, FT-IR were employed to investigate structural and physical properties. The UV-shielding effect was evaluated by UV-VIS. The low content of zinc (around 0.02 wt%) and the fine particle size rendered it visibly transparent and capable of greatly attenuating UV radiation in the full UV range.
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| 4. |
- Marrocchelli, Dario, et al.
(författare)
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Conduction and disorder in Y3NbO7 - Zr2Y2O7
- 2009
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Ingår i: Materials Research Society Symposium Proceedings. - 0272-9172. - 9781605110981 ; 126, s. 71-78
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Konferensbidrag (refereegranskat)abstract
- The construction of interaction potentials for the Y0.5+0.25xNb0.25xZr0.5-0.5xO1.75 system, on a purely ab-initio basis, is described. These potentials accurately reproduce experimental data on both the structure and the dynamics of these systems; the computer simulations also reproduce the experimental trend of the conductivity, which decreases as x increases, and of the level of static disorder within the O2- sublattice, which increases with x. A detailed analysis of these phenomena shows that the static disorder in Y3NbO7 is caused by the high Nb5+ charge and that in this material the conduction is heterogeneous, i.e. some anions are completely immobile while some others are very mobile. The role of the cation sublattice is explained in detail.
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| 5. |
- Odell, Anders, et al.
(författare)
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Ab Initio Study of Switching Properties of Photochromic Dithienylethene Molecules
- 2006
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Ingår i: Materials Research Society Symposium Proceedings. - : Springer Science and Business Media LLC. - 0272-9172 .- 1946-4274. ; 965, s. 296-300
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Tidskriftsartikel (refereegranskat)abstract
- We report an ab initio study of a photochromic dithienylethene derivative. The mechanisms for switching between open and closed conformations are investigated based on total energy calculations for the ground and first excited state. An explanation for the central ring closure based on relaxation of the excited state is presented.
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| 6. |
- Oertel, CM, et al.
(författare)
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Focused ion beam and electron microscopy analysis of corrosion of lead-tin alloys: Applications to conservation of organ pipes
- 2008
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Ingår i: Materials Research Society Symposium Proceedings. - 0272-9172. - 9781558999886 ; 1047, s. 115-125
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Tidskriftsartikel (refereegranskat)abstract
- Across Europe, lead-tin alloy organ pipes are suffering from atmospheric corrosion. This deterioration can eventually lead to cracks and holes, preventing the pipes from producing sound. Organ pipes are found in compositions ranging from >99% Pb to >99% Sn. For very lead-rich (>99% Pb) pipes, organic acids emitted from the wood of organ cases have previously been identified as significant corrosive agents. In order to study the role of alloy composition in the susceptibility of pipes to organic acid attack, lead-tin alloys containing 1.2-15 at.% Sn were exposed to acetic acid vapors in laboratory exposure studies. Corrosion rates were monitored gravimetrically, and corrosion product phases were identified using grazing incidence angle X-ray diffraction. In a new method, focused-ion beam (FIB) cross sections were cut through corrosion sites, and SEM and WDX were used to obtain detailed information about the morphology and chemical composition of the corrosion layers. The combination of FIB and SEM has made it possible to obtain depth information about these micron-scale layers, providing insight into the influence of acetic acid on alloys in the 1.2-15 at.% Sn range.
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| 7. |
- Samadikhah, Kaveh, 1982, et al.
(författare)
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General elasticity theory for graphene membranes based on molecular dynamics
- 2007
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Ingår i: Materials Research Society Symposium Proceedings. - 0272-9172. - 9781605608266 ; , s. 109-114
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Konferensbidrag (refereegranskat)abstract
- We have studied the mechanical properties of suspended graphene membranes using molecular dynamics (MD) and generalized continuum elasticity theory (GE) in order to develop and assess a continuum description for graphene. The MD simulations are based on a valence force field model which is used to determine the deformation and the elastic energy of the membrane (EMD) as a function of external forces. For the continuum description, we use the expression Econt = Estretching + Ebending for the elastic energy functional. The elastic parameters (tensile rigidity and Poisson ratio) entering Econt are determined by requiring that E cont = EMD for a set of deformations. Comparisons with the MD results show excellent agreement. We find that the elastic energy of a supported graphene sheets is typically dominated by the nonlinear stretching terms whereas a linear description is valid only for very small deflections. This implies that in some applications, i.e. NEMS, a linear description is of limited applicability.
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| 8. |
- Sandén, Björn, 1968
(författare)
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Standing the test of time: Signals and noise from environmental assessments of energy technologies
- 2007
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Ingår i: Materials Research Society Symposium Proceedings. - 0272-9172. - 9781605110158 ; 1041, s. 183-189
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Konferensbidrag (refereegranskat)abstract
- The point of view taken here is that systems analysis is a kind of learning process, not data gathering, not decision making, but the production and effective communication of arguments relevant in a particular context. This idea, that the intended application of the result of an assessment has consequences for methodological choices, is beginning to spread in the LCA research community. One problem is that standard LCA methodology is developed to answer questions about environmental impacts of the current production and use of one unit of a product or minor product or process changes. When this methodology, unchanged, is used to provide answers to questions about strategic technology choice, i.e. not decisions that aim at improving a process within an existing technological environment, but with the long-term goal of changing large-scale technological systems, the result could be of little value or misleading. In many cases, LCAs produce more noise than knowledge. This observation seems to be of particular importance for LCAs of energy technologies and for how energy use is treated in all kinds of LCAs. Here, it is suggested that a better understanding of some critical methodological issues related to time, universality, cause-effect relationships, technical maturity and system innovation, could result in better studies that reveal fundamental environmental issues related to the objects of study and reduce the noise from irrelevant information. Examples are given from the technology fields of solar cells, fuel cells, batteries, renewable transport fuels and carbon nanoparticles.
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| 9. |
- Ödegård Jensen, Arvid, 1968, et al.
(författare)
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Testing of uranium dioxide containing different levels of alpha activity under anaerobic and reducing conditions
- 2008
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Ingår i: Materials Research Society Symposium Proceedings. - 0272-9172. - 9781605110745 ; 1104, s. 115-120
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Konferensbidrag (refereegranskat)abstract
- Samples of UO2 containing 5% 235U and 0, 5, or 10% 233U were tested in a dilute simulated groundwater using N 2 or H2 gas as the atmosphere. Some tests included metallic iron in the solution. Each test condition used samples run in triplicate for at least 21 days and each test condition was run for two consecutive test periods. The results show that the dissolution behavior of the samples is the same in both N2 and H2 atmospheres. The amount of U dissolved under these conditions clearly showed the enhancement of dissolution due to oxidation of the sample surface by radiolysis products for conditions without metallic Fe. When a piece of iron was included in the bottom of the test vessel, the amount of dissolution decreased dramatically indicating that the Fe(II) ions released from the corroding iron were able to react with most of the radiolysis products before they could oxidize the UO2 surface.
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