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- Norberg, Stefan, 1972, et al.
(författare)
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Structural Disorder in Doped Zirconias, Part I: The Zr0.8Sc0.2-xYxO1.9 (0.0 ≤x ≤ 0.2) System
- 2011
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 1520-5002 .- 0897-4756. ; 23:6, s. 1356-1364
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Tidskriftsartikel (refereegranskat)abstract
- The influence of local ordering of the anion vacancies and cation-anion vacancy interactions on the ionic conductivity of the anion-deficient fluorite Zr0.8Sc0.2-xYxO1.9 (0.0 directions. Significantly, an increased proportion of the oxygen vacancies are associated with the Zr4+ cations in Zr0.8Y0.2O1.9, while in Zr0.8Sc0.2O1.9 they show no significant preference for being nearest neighbor to a Sc3+ or a Zr4+ cation. Thus, it is concluded that the lower ionic conductivity at x = 0.2 is predominantly a consequence of the larger size of the Y3+ cation, which induces strain in the lattice and hinders diffusion of the O2-, rather than changes in the local ordering of the anion vacancies.
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- Shafeie, Samrand, 1984-
(författare)
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Properties in New Complex Perovskite-Related Materials, a Matter of Composition and Structure
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This PhD thesis presents investigations of perovskite-related compounds in systems of interest for applications in components in solid oxide fuel cells. The compound compositions derive from substitutions in the parent compounds LaCoO3, LaCrO3 and SrFeO3.Novel phases La2Co1+z(MgxTi1-x)1-zO6 were synthesized and investigated with regard to structure, thermal expansion, electronic and magnetic properties. The study focused on the composition lines La2Co(MgxTi1-x)O6 (z=0), where the oxidation state of Co nominally changes from +2 (x=0.0) to +3 (x=0.5), and La2Co1+z(Mg0.5Ti0.5)1-zO6, with a varying fraction of Co3+ ions. XANES data show that the Co ions in the system have discrete oxidation states of +2 and +3. The TEC increases with increasing x due to an increasing contribution from spin state transitions of the Co3+ ions. Novel compounds La2Cr(M2/3Nb1/3)O6 with M=Mg, Ni, Cu were synthesized and characterized with respect to structure and magnetic properties. XRPD and NPD data indicate Pbnm symmetry; however, SAED patterns and HREM images indicate a P21/n symmetry for M=Mg, and Cu. The magnetic measurements results were rationalized using the Goodenough-Kanamori rules.Oxygen-deficient phases with x≥0.63 in SrxY1-xFeO3-δ and Sr0.75Y0.25Fe1-yMyO3-δ (M=Cr, Mn, Ni and y=0.2, 0.33, 0.5), were synthesized and characterized with respect to structure, oxygen content, thermogravimetry, TEC, conductivity and magnetic properties. Powder patterns of phases agree with cubic perovskite structures. NPD data for x=0.75 reveal anisotropic displacement for the O atom, related to local effects from Fe3+/Fe4+ ions. SAED patterns for x=0.75 reveal the presence of an incommensurate modulation. The compounds start to lose oxygen in air at ~ 400°C. The TEC up to ~400°C for x=0.75 is ~10.5 ppm/K and increase to ~17.5 ppm/K at higher temperatures. The conductivity for x=0.91 is 164 S/cm at 400°C. Partial substitution of Fe by Cr, Mn or Ni does not increase the conductivity or decrease TEC.
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- Tilmes, Simone, et al.
(författare)
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The hydrological impact of geoengineering in the Geoengineering Model Intercomparison Project (GeoMIP)
- 2013
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Ingår i: Journal of Geophysical Research. - : American Geophysical Union (AGU). - 0148-0227 .- 2156-2202 .- 2169-897X. ; 118:19, s. 11036-11058
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Tidskriftsartikel (refereegranskat)abstract
- The hydrological impact of enhancing Earth's albedo by solar radiation management is investigated using simulations from 12 Earth System models contributing to the Geoengineering Model Intercomparison Project (GeoMIP). We contrast an idealized experiment, G1, where the global mean radiative forcing is kept at preindustrial conditions by reducing insolation while the CO2 concentration is quadrupled to a 4×CO2 experiment. The reduction of evapotranspiration over land with instantaneously increasing CO2 concentrations in both experiments largely contributes to an initial reduction in evaporation. A warming surface associated with the transient adjustment in 4×CO2 generates an increase of global precipitation by around 6.9% with large zonal and regional changes in both directions, including a precipitation increase of 10% over Asia and a reduction of 7% for the North American summer monsoon. Reduced global evaporation persists in G1 with temperatures close to preindustrial conditions. Global precipitation is reduced by around 4.5%, and significant reductions occur over monsoonal land regions: East Asia (6%), South Africa (5%), North America (7%), and South America (6%). The general precipitation performance in models is discussed in comparison to observations. In contrast to the 4×CO2 experiment, where the frequency of months with heavy precipitation intensity is increased by over 50% in comparison to the control, a reduction of up to 20% is simulated in G1. These changes in precipitation in both total amount and frequency of extremes point to a considerable weakening of the hydrological cycle in a geoengineered world.
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| 8. |
- Zihms, S, 1980, et al.
(författare)
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Effects of high temperature processes on physical properties of silica sand
- 2013
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Ingår i: Engineering Geology. - : Elsevier BV. - 0013-7952. ; 164, s. 139-145
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Tidskriftsartikel (refereegranskat)abstract
- High temperature processes may alter soil properties, creating potential risks of subsidence, erosion and other hazards. Soils may be exposed to high temperatures during some aggressive contaminant remediation processes as well as natural events such as fires. Characterising the effects of high temperatures on soil properties is essential to understanding the potential hazards that may arise after exposure. Thermal treatment and smouldering remediation were carried out on silica sand used here as a simple soil. Changes observed in physical properties were associated with the treatment type and exposure temperature. Particle, minimum and maximum densities were independent of heat treatment type and temperature. In contrast, particle size distribution, mineralogy, capillary rise, and hydraulic conductivity were linked to treatment type and exposure temperature with the most substantial changes associated with smouldering remediation. Changes in colour and mass loss with increasing temperature suggest changes within the crystal structure of the silica sand beyond loss of moisture content within the pore space and dehydration of iron deposits from goethite to hematite. Based on these observations, exposure to high temperature processes and the complex geo-chemical reactions during smouldering remediation can have significant effects on soil properties. Monitoring after exposure is advisable to determine the severity of exposure and any mitigation measures that may be necessary.
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