6,561 research outputs found
Nonlinear influence of excess Mn on the magnetoelastic transition in (Mn,Cr)<sub>2</sub>Sb
No full textThe influence of excess Mn on the magnetoelastic ferromagnetic-to-antiferromagnetic transition Tt in the magnetocaloric compound (Mn,Cr)2Sb has been studied. With increasing excess Mn the magnetoelastic transition temperature for (Mn,Cr)2Sb initially increases and then decreases. This trend is accompanied by a strong reduction of the (Mn,Cr)Sb secondary phase. With increasing excess Mn a higher Cr content was found in the (Mn,Cr)Sb secondary phase in comparison to the matrix phase. This competition for Cr leads to a nonlinear dependence of Tt with increasing excess Mn at a fixed nominal Cr content. However, we observed that Tt depends linear on the c/a ratio for a wide range of temperatures from 170 to 350 K. A compositional diagram of the c/a ratio was constructed to assist the selection of (Mn,Cr)2Sb alloys with a desired transition temperature.RST/Fundamental Aspects of Materials and Energ
Mobility of toxic elements in carbonate sediments from a mining area in Poland
No full textOspina-Alvarez, N., Głaz, L., Dmowski, K., & Krasnodębska-Ostręga, B. (2014). Mobility of toxic elements in carbonate sediments from a mining area in Poland. Environmental Chemistry Letters, 12, 435–441. doi:10.1007/s10311-014-0468-
Rare earth elements in coastal sediments of the Northern Galician Shelf: influence of geological features
No full textPrego, R., Caetano, M., Bernardez, P., Brito, P., Ospina-Alvarez, N., & Vale, C. (2012). Rare earth elements in coastal sediments of the Northern Galician Shelf: influence of geological features. Continental Shelf Research, 35, 75–85. doi: http://dx.doi.org/10.1016/j.csr.2011.12.01
Surface Oxidation and Wettability of Fe–Mn and Fe–Mn–Si-Alloyed Steel After Annealing
No full textThe surface oxidation and wettability of Mn and Si-alloyed steel after annealing at different conditions are studied with scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and a so-called de-wetting method. After exposure at 950 °C for 1 hour in an Ar + 5 vol pct H2 gas atmosphere with dew points (DP) ranging from – 40 °C to 10 °C, oxides were observed along the grain boundaries or dispersed on the surface for the Fe–1.8 Mn steels while a continuous oxides layer was formed on Fe–1.9 Mn–0.94 Si steels (composition in weight fractions). The oxides formed at different DPs were predicted based on thermodynamic calculations. (Fe,Mn)O was formed on Fe–1.8 Mn steel at the whole range of DPs, while the oxide phase on Fe–1.9 Mn–0.94 Si steel depends on the DP. At low-DP SiO2 were formed and with increasing the DP (Fe,Mn)SiO3 or (Fe,Mn)SiO3 + (Fe,Mn)2SiO4 were formed and finally (Fe,Mn)2SiO4 were formed. An increase of the fraction of Fe in the oxide with increasing DP for both steels was observed with XPS analysis. As a measure for the surface wettability, the contact angle of Pb droplets on the annealed steels surfaces was determined with SEM and image analysis software. Also, the contact angle of Pb on pure Fe and on the Mn and Si alloyed steels free of surface oxides was measured for comparison. The results show that the contact angle of Pb on the steel surfaces after annealing decreases with increasing DP. This improved wettability with increasing dew point is related to the Fe fraction of the oxides formed on the surface.Team Kevin RossiTeam Maria Santofimia NavarroTeam Marcel Herman
Temperature-Dependent Microstructural Evolution of Al-Rich Medium-Mn Steel During Intercritical Annealing
No full textMedium-Mn automotive sheet steels require optimized heat-treatment processes to obtain benefits caused by strain-induced martensitic transformation of retained austenite (RA) during sheet metal forming or crash events. The intercritical annealing (IA) approach at different temperatures in a range of 640 °C to 800 °C is proposed in the study for a 5Mn hot-rolled medium-Mn sheet steel. The experiments were performed in terms of dilatometry. The analysis of the cooling curves allowed development of a new method for calculating the high-temperature phase equilibrium. The calculations were validated by modeling with JMatPro and experimentally verified by X-ray diffraction (XRD). The microstructure evolution was characterized using light optical microscopy and scanning electron microscopy (SEM), including electron backscatter diffraction (EBSD). The quantitative determination of the fraction, morphology, chemical composition, and stability of the RA was done. Mechanical properties were determined by hardness measurements. The research showed a substantial influence of the IA temperature on the RA fraction and chemical stability and properties of medium-Mn Al-alloyed steel. At temperatures of 680 °C and 700 °C, the largest fraction of over 35 pct of stable RA was obtained, which does not transform to martensite during cooling.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Team Kevin Ross
Mn/Ca ratios of Ammonia tepida as a proxy for seasonal coastal hypoxia
No full text Climate variability has major implications for marine geochemical cycles and biogenic carbonate production. Therefore, past climate-driven changes in marine environments are often inferred from geochemical data of the marine carbonate archive. Proxy calibration studies are essential for the reconstruction of such past environmental changes. Here, we use the geochemical composition of living specimens of the benthic foraminifer Ammonia tepida at three sites in a seasonally hypoxic (oxygen concentration < 63 μmol/L) marine coastal system (Lake Grevelingen, the Netherlands) to explore the use of Mn/Ca as a proxy for coastal hypoxia. The study is based on samples from three stations along a depth transect, that show contrasts in the seasonal cycle of Mn 2+ concentrations in the pore water of the surface sediment. In general, the sediment and pore water geochemistry of the three stations in Lake Grevelingen show increased Mn 2+ concentrations in late winter/spring, combined with increased Mn refluxing in summer, which are due to cable bacteria activity and bottom water hypoxia/anoxia, respectively. Laser Ablation-ICP-MS (LA-ICP-MS) allowed a comparison of Mn/Ca ratios of different parts of the benthic foraminiferal test. Our results show that higher Mn/Ca ratios are registered at the deepest station, which experiences the longest and most severe seasonal periods of hypoxia/anoxia. Additionally, the signal preserved in the central part of the benthic foraminiferal tests, which is thought to reflect the entire calcification history of the analysed specimen, appears to be driven by high pore water Mn 2+ concentrations due to cable bacteria activity in late winter/spring. Conversely, high Mn/Ca ratios in the last chambers reflect increased Mn refluxing in the surface sediment due to summer hypoxia/anoxia. Thus, Mn/Ca ratios of A. tepida give insight into the complex spatial and temporal variability of pore water manganese. Accepted Author ManuscriptBT/Environmental Biotechnolog
Fe-Mn/ZrO2 catalysts: Sulfate-based-advanced oxidation process for the degradation of olive oil industry model pollutants
No full textFe, Mn and a bimetallic Fe[sbnd]Mn catalysts supported on ZrO2 were synthesized and tested for the activation of persulfate (PS) and peroxymonosulfate (PMS) in the degradation reaction of three different organic compounds: cinnamic acid (CA), benzoic acid (BA), and catechol (C). The catalysts were prepared and tested in order to evaluate the effect of the metal and the metal combination on the generation of reactive oxygen species (ROS). The characterization of the catalysts was carried out by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and atomic absorption spectroscopy (AAS). The best degradation results were obtained when PMS was activated with the bimetallic Fe-Mn/ZrO2 catalyst in the CA degradation. Moreover, the Fe-Mn/ZrO2 catalyst reusability was tested for up to three consecutive cycles of reaction, with mineralization levels >90%. A synergistic effect between the Fe and Mn metal species, which increases the catalyst activity if compared to the monometallic catalysts, is postulated. Both sulfate and hydroxyl radicals were generated in the PMS activation process. The activation mechanisms of the oxidants were proposed.Fil: Loffredo, Camila Macarena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; ArgentinaFil: Dennehy, Mariana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; ArgentinaFil: Alvarez, Mariana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentin
The Influence of Mn(II) and Aging Time in the Ferrihydrite to Goethite Transformation
No full textThe ferrihydrite-goethite transformation in samples of pure- and Mn-ferrihydrite was investigated in order to elucidate the effect of Mn(II) in the aging process. Samples of pure- and Mn-ferrihydrites were aged for different times, and their structural changes were described on the basis of Rietveld structure refinements. A comparison of two series of samples with (A-series) and without Mn (F-series) shows b- enlargement and a- and c- shortening due to the presence of Mn during the complete aging process. However, with aging different trends are observed in both the series. In the samples synthesized without Mn(II) the variations in all the unit-cell constants are virtually negligible, whereas in the series with Mn(II) more significant changes are reflected by the enlargement of a- and c- and the shortening of the b. These results confirm that the dimensions of the lattice parameters depend not only on the substitution ratio but also on the aging history of the sample.Fil: Alvarez, Mariana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca; Argentina. Universidad Nacional del Sur. Departamento de Química; ArgentinaFil: Rueda, Elsa Haydee. Universidad Nacional del Sur. Departamento de Química; ArgentinaFil: Paiva Santos, Carlos O.. Universidade Estadual Paulista Julio de Mesquita Filho; BrasilFil: Sileo, Elsa Ester. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentin
Kinetics of internal oxidation of Fe-Mn-Cr steel alloys
No full textSelective oxidation behaviour of Fe-Mn-Cr steel alloys annealed at 950°C in Ar plus 5 vol.% H2 atmosphere under different annealing time and dew points was studied. The Fe-Mn-Cr steel alloys are externally oxidized when annealing at dew point of -45 °C, while internally oxidized at dew points of -10 and 10 °C. The internal oxides formed in the Fe-Mn-Cr steel alloys are (Mn, Fe)O and (Cr, Mn, Fe)3O4. The kinetics of internal oxidation of Fe-Mn-Cr alloys at 950 °C is diffusion controlled and follows parabolic growth rate law. The measured kinetics of internal oxidation of Fe-Mn-Cr alloys and the concentration depth profiles of internal oxides are in good agreement with simulation results. Adding Cr to the Fe-Mn steel alloys decreases the kinetics of internal oxidation. The growth rate of internal oxidation zone can be predicted by a modified Wagner’s internal oxidation model. The external oxides formed during annealing of Fe-Mn-Cr steel alloys cannot be reduced by H2. However, an oxide-free steel surface can be obtained by first forming and then reducing a Wüstite scale.Materials Science and Engineerin
Efficient and Practical Transfer Hydrogenation of Ketones Catalyzed by a Simple Bidentate Mn−NHC Complex
No full textCatalytic reductions of carbonyl-containing compounds are highly important for the safe, sustainable, and economical production of alcohols. Herein, we report on the efficient transfer hydrogenation of ketones catalyzed by a highly potent Mn(I)−NHC complex. Mn−NHC 1 is practical at metal concentrations as low as 75 ppm, thus approaching loadings more conventionally reserved for noble metal based systems. With these low Mn concentrations, catalyst deactivation is found to be highly temperature dependent and becomes especially prominent at increased reaction temperature. Ultimately, understanding of deactivation pathways could help close the activity/stability-gap with Ru and Ir catalysts towards the practical implementation of sustainable earth-abundant Mn-complexes.Accepted Author ManuscriptChemE/Inorganic Systems EngineeringChemE/Algemee
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