Results 1 - 10 of 1920
Results 1 - 10 of 1920. Search took: 0.026 seconds
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[en] Highlights: • We show a discrete Fe2TiO5-incorporation in hematite to improve the performance. • It can be well coupled with surface P-modification with a synergetic effect. • It shows a high photocurrent of 2.90 mA/cm2 at 1.23 VRHE with Co-Pi catalysts. • It provides a good insight to understand other Ti-based treatments of hematite. Hematite is a promising photocatalyst for solar water splitting while its performance has been severely limited by various factors. Recently surface Fe2TiO5 layer was widely reported to enhance the performance of hematite with a favorable band position to facilitate hole transport. Here we further show that the Fe2TiO5-incorporation in bulk hematite can also improve the performance with faster charge separation. Moreover, it can be well coupled with surface P-modification to simultaneously improve charge separation and hole transfer with a synergetic effect. The Ti and P co-modified hematite shows a significantly enhanced photocurrent of 2.37 mA/cm2 at 1.23 V vs. RHE when compared to the pristine value of 0.85 mA/cm2. After coupling with Co-Pi catalysts, the hematite sample can even achieve a stable, high photocurrent of 2.90 mA/cm2 at 1.23 V vs. RHE. The design of Ti and P co-modified hematite hollow nanostructures can be used as a promising candidate for solar water splitting applications. The discrete Fe2TiO5-incorporation also provides a good insight on the mechanism to understand other Ti-based treatments of hematite.
[en] The objectives of the confirmatory surveys were to provide independent contractor field data reviews and to generate independent radiological data for use by the NRC in evaluating the adequacy and accuracy of the licensee's procedures and survey results.
[en] Complete text of publication follows. The crystal symmetry of hematite in the basal plane predicts three easy magnetization axes for the antiferromagnetic spins. Spin canting then leads to three preferred magnetization axes perpendicular to these easy axes. We measured magnetic hysteresis loops and remanence curves on single hematite crystals as a function of rotation angle in order to verify this prediction and to better understand the interplay between spin canting, remanence and magnetic susceptibility. While our results qualitatively coincide nicely with theoretical predictions, a quantitative evaluation requires more complex modeling.
[en] Complete text of publication follows. One of the best preserved terrestrial records of past climate are in loess-palaeosol sequences around the world. Except classical Chinese loess, European sequences are widely used for palaeoenvironmental reconstructions. Low Danube loess deposits are part of the south-eastern loess cover, linking loess belt in Asia with Central European loess. Its magnetic properties have been extensively studied, putting emphasis on present continental conditions. In the present work, role of Black sea as climatic factor playing role in setting up rock magnetic properties of samples from Durankulak loess outcrop have been studied. Combined use of magnetic and DRS data show that magnetic enhancement of palaeosols is accompanied by an increase of hematite content, suggesting that pedogenic maghemite (magnetite) and hematite are simultaneously formed during warm interglacial periods. Comparison with data from a loess-palaeosol section in the countryside (away from maritime climates) suggests that more humid and warmer conditions favour faster growth of pedogenic Fe oxides towards stable SD magnetic grain sizes. Possible role of diagenetic effects will be discussed.
[en] Complete text of publication follows. Studies of modern tropical soils have demonstrated that the relative abundance of pedogenic goethite and hematite is controlled by moisture availability. To evaluate the utility of a G/H ratio as a paleo-precipitation proxy, we conducted a rock-magnetic study of paleosol samples from a known paleo-environmental context. Goethite and hematite content of the studied samples has been estimated based on saturation IRM values of the corresponding magnetization components as identified by a statistical analysis of IRM acquisition curves. Independently, goethite contribution to the high coercivity fraction has been determined by the low-temperature cycling of the IRM. Both methods give identical estimates for the goethite content. The Neogene Siwalik strata of Pakistan are composed of several thousand meters of stacked fluvial floodplain and channel deposits representing deposition by ancient river systems that drained the Himalaya Mountains and foothills. The Middle Miocene Chinji Formation, which is dominantly fine-grained, provides particularly good exposures of successive floodplain paleosols. G/H ratios of samples collected over 100's of meters along a lateral transect in a single Chinji Fm. paleosol show a good correlation (R2 =0.88) with δ18O of soil carbonate, indicating that the ratio can be effectively used as an indicator of moisture availability during pedogenesis. Based on lateral fluvial architecture and varying thickness of this paleosol, we can test the prediction that G/H ratios are lower on topographic highs compared with G/H ratios from topographic lows. Siwalik paleosols affected by fire show a significant change in the high coercivity fraction. In contrast to unbaked samples, burned paleosols lack the goethite component, while the hematite component shows a ∼ 350 mT increase in the mean coercivity value. Evidence for paleo-fires as well as the G/H ratios and their correlation with soil carbonate δ18O provide new insights on varying environmental conditions that characterized the Miocene sub-Himalayan alluvial plains.
[en] During the oxidation of iron, poorly crystallized phases are firstly formed: 2- and 6-line ferrihydrite, which presents for the last phase, a similarity with wustite FeO but also with hematite α-Fe2O3. Crystallization increases with time and the solid phase obtained is dependent on temperature and pH. Obviously, high temperature favours the formation of the oxide hematite α-Fe2O3. As for the pH factor, it is more complicated. Low and high values of pH (2-5 and 10-14) favour the formation of goethite α-FeOOH, while obtaining hematite is favoured at neutral pH (values around 7). Goethite or hematite are obtained either through a dissolution-crystallization process or in the solid state, through a topotactic transformation. Given the structural relationships observed between ferrihydrite and wustite and hematite, it is allowed to think that a structural continuity could exist between wustite Fe(1-x)O and hematite via ferrihydrite
[en] The feasibility studies of magnetic concentration of the Campo Alegre de Lourdes ore were carried out, trying to obtain a maximum recovery of vanadium. As a consequence of the complex nature of the ore, mainly due to the presence of ilmenite as a exolutions in the interior of hematite/martite particles, it was not possible to separate the hematite-ilmenite eficiently, wich would be necessary for obtaining a high grade vanadium concentrate with low titanium content. (author)
[pt]Foram avaliadas as possibilidades de concentracao magnetica do minerio de Campo Alegre de Lourdes, visando principalmente a maxima recuperacao do vanadio. Verificou-se que devido a natureza complexa do minerio, principalmente em funcao da presenca de ilmenita na forma de exolucoes no interior dos graos de hematita/martita, nao foi possivel realizar-se uma eficiente separacao hematita-ilmenita, o que seria fundamental para obter-se um concentrado com alto teor de vanadio e baixo teor de titanio. (autor)
[en] In the present work, hematite iron oxide nano-particles are synthesized through a facile wet chemical precipitation route. The phase formation behavior and microstructure evolution of the synthesized nano-particles are studied using infrared spectroscopy in conjunction with x-ray diffraction analyses and electron microscopy. Chemi-resistive type hydrogen sensing characteristics (e.g. response %, response time, recovery time) of hematite iron oxide nano-particulate sensing element are evaluated using an automated, dynamic flow gas sensing measurement set-up. The sensing characteristics are measured by varying the operating temperature (275–350 °C) of the sensor and concentration of hydrogen (250–1660 ppm). From the operating temperature dependence of response and recovery times, we have estimated the respective activation energies for response and recovery processes. (paper)