Characterization of ordering in Fe-6.5%Si alloy using X-ray, TEM, and magnetic TGA methods

Fe-6.5wt%Si steel surpasses the current extensively used Fe-3.2wt%Si steel in lower iron loss, higher permeability, and near zero magnetostriction. As a cost effective soft magnetic material, Fe-6.5wt%Si may find applications in motors, transformers, and electronic components. However, the brittleness of the alloy poses processing challenges. The brittleness in Fe-6.5wt%Si is attributed to the formation of ordered phases. Evaluation of the amount of ordered phases is important for the research and development of Fe-6.5wt%Si. This paper aims to find effective ways to evaluate the ordering degree through a comparison of various characterization techniques. In order to tune the ordering degree, various speeds were used to prepare Fe-6.5wt%Si samples via melt spinning. The varying wheel speed changes the cooling rate, which was confirmed by thermal imaging. In addition to the widely used TEM and normal theta-2theta X-ray diffraction methods, two quantitative methods were adopted for this Fe-6.5wt%Si system to study the ordering degree. One method is based on rotating crystal XRD technique, and the other is magnetic thermal analysis technique. These two methods effectively quantified the varying degree of ordering presented in the samples and were deemed more suitable than the TEM, normal theta-2theta XRD methods for Fe-Si due to their ease of sample preparation and short turn-around time

Long-term responses of riparian plants' composition to water level fluctuation in China's Three Gorges Reservoir.

The water level fluctuation zone (WLFZ) has experienced a novel hydrological regime due to the anti-seasonal operation of China's Three Gorges Reservoir. Overall, hydrological change can significantly influence the riparian environment and shift the riparian vegetation. Although numerous studies have investigated the short-term responses of riparian plants to water level fluctuation in this zone, few have addressed long-term effects. In this study, four permanent plots in the WLFZ of the canyon landform area were chosen to evaluate the long-term responses of riparian plants to water level fluctuation from 2008 to 2015 and to screen candidate plants for ecological restoration. We recorded 146 species in 2008, 110 species in 2009, 68 species in 2012 and 69 species in 2015, indicating a conspicuous loss in riparian plants. Most of the remnant plants were annual and perennial herbs. Of the native species present in 2008, 82, 22 and 8 had disappeared in 2009, 2012 and 2015, respectively. Simultaneously, 45, 15 and 11 non-native species were first found, respectively. Additionally, over half of the native and the non-native species were not found after being subjected to a water level fluctuation. From 2008 to 2015, only 27 native species always presented; however, not all of them were chosen as candidates for ecological restoration because of their decreased importance values. In contrast, the importance value of Cynodon dactylon increased over time, suggesting its high tolerance to long-term winter flooding. We concluded that riparian plants' composition of the canyon landform area dramatically declined after long-term water level fluctuation and their presence was determined by the novel hydrological condition. Our results also suggested that Cynodon dactylon or its combination with other species (i.e. Digitaria chrysoblephara, Setaria glauca, Setaria viridis) is a better candidate for ecological restoration in the WLFZ

From Quasicrystals to Crystals with Interpenetrating Icosahedra in Ca–Au–Al: In Situ Variable-Temperature Transformation

The irreversible transformation from an icosahedral quasicrystal (i-QC) CaAu4.39Al1.61 to its cubic 2/1 crystalline approximant (CA) Ca13Au56.31(3)Al21.69 (CaAu4.33(1)Al1.67, Pa3̅ (No. 205); Pearson symbol: cP728; a = 23.8934(4)), starting at ∼570 °C and complete by ∼650 °C, is discovered from in situ, high-energy, variable-temperature powder X-ray diffraction (PXRD), thereby providing direct experimental evidence for the relationship between QCs and their associated CAs. The new cubic phase crystallizes in a Tsai-type approximant structure under the broader classification of polar intermetallic compounds, in which atoms of different electronegativities, viz., electronegative Au + Al vs electropositive Ca, are arranged in concentric shells. From a structural chemical perspective, the outermost shell of this cubic approximant may be described as interpenetrating and edge-sharing icosahedra, a perspective that is obtained by splitting the traditional structural description of this shell as a 92-atom rhombic triacontahedron into an 80-vertex cage of primarily Au [Au59.86(2)Al17.14□3.00] and an icosahedral shell of only Al [Al10.5□1.5]. Following the proposal that the cubic 2/1 CA approximates the structure of the i-QC and on the basis of the observed transformation, an atomic site analysis of the 2/1 CA, which shows a preference to maximize the number of heteroatomic Au–Al nearest neighbor contacts over homoatomic Al–Al contacts, implies a similar outcome for the i-QC structure. Analysis of the most intense reflections in the diffraction pattern of the cubic 2/1 CA that changed during the phase transformation shows correlations with icosahedral symmetry, and the stability of this cubic phase is assessed using valence electron counts. According to electronic structure calculations, a cubic 1/1 CA, “Ca24Au88Al64” (CaAu3.67Al2.67) is proposed.This document is the Accepted Manuscript version of a Published Work that appeared in final form in Journal of the American Chemical Society, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see DOI: 10.1021/jacs.7b10358. Posted with permission.</p

Maxent modeling for predicting impacts of climate change on the potential distribution of Thuja sutchuenensis Franch., an extremely endangered conifer from southwestern China

Objectives: Detailed and reliable information about the spatial distribution of species provides important information for species conservation management, especially in the case of rare species of conservation interest. We aimed to study the consequences of climate change on geographical distributions of the tertiary rare tree species Thuja sutchuenensis Franch. (Cupressaceae) to provide reference for conservation management of this species, including priority area selection for introduction and cultivation of the species. We expect that this approach could be promising in predicting the potential distribution of other rare tree species, and as such can be an effective tool in rare tree species restoration and conservation planning, especially species with narrow distribution or raw presence-only occurrence data. Methods: 107 records covering the whole distribution range of T. sutchuenensis in the Daba Mountains were obtained during a 3-year field survey. The principle of maximum entropy (Maxent) was used to model the species’ potential distribution area under paleoclimate, current and future climate background. Results: The Maxent model was highly accurate with a statistically significant AUC value of 0.998, which is higher than 0.5 of a null model; The location of the potential distribution for the last interglacial period is in southeastern China, with the largest optimal habitat area being only 1666 km2. In other periods, the central location of the potential distribution is accordant with the real present distribution, but the model’s predicted optimal habitat area is outside the current distribution. Conclusions: Our findings can be applied in various ways such as the identification of additional localities where T. sutchuenensis may already exist, but has not yet been detected; the recognition of localities where it is likely to spread to; the priority selection area for introduction and cultivation and the conservation management of such rare tree species

Maxent modeling for predicting impacts of climate change on the potential distribution of Thuja sutchuenensis Franch., an extremely endangered conifer from southwestern China

Objectives Detailed and reliable information about the spatial distribution of species provides important information for species conservation management, especially in the case of rare species of conservation interest. We aimed to study the consequences of climate change on geographical distributions of the tertiary rare tree species Thuja sutchuenensis Franch. (Cupressaceae) to provide reference for conservation management of this species, including priority area selection for introduction and cultivation of the species. We expect that this approach could be promising in predicting the potential distribution of other rare tree species, and as such can be an effective tool in rare tree species restoration and conservation planning, especially species with narrow distribution or raw presence-only occurrence data. Methods 107 records covering the whole distribution range of T. sutchuenensis in the Daba Mountains were obtained during a 3-year field survey. The principle of maximum entropy (Maxent) was used to model the species' potential distribution area under paleoclimate, current and future climate background. Results The Maxent model was highly accurate with a statistically significant AUC value of 0.998, which is higher than 0.5 of a null model; The location of the potential distribution for the last interglacial period is in southeastern China, with the largest optimal habitat area being only 1666 km(2). In other periods, the central location of the potential distribution is accordant with the real present distribution, but the model's predicted optimal habitat area is outside the current distribution. Conclusions Our findings can be applied in various ways such as the identification of additional localities where T. sutchuenensis may already exist, but has not yet been detected; the recognition of localities where it is likely to spread to; the priority selection area for introduction and cultivation and the conservation management of such rare tree species. (C) 2017 The Authors. Published by Elsevier B.V

From Quasicrystals to Crystals with Interpenetrating Icosahedra in Ca–Au–Al: In Situ Variable-Temperature Transformation

The irreversible transformation from an icosahedral quasicrystal (i-QC) CaAu_4.39Al_1.61 to its cubic 2/1 crystalline approximant (CA) Ca₁₃Au_56.31(3)Al_21.69 (CaAu_4.33(1)Al_1.67, <i>Pa</i>3̅ (No. 205); Pearson symbol: <i>cP</i>728; <i>a</i> = 23.8934(4)), starting at ∼570 °C and complete by ∼650 °C, is discovered from in situ, high-energy, variable-temperature powder X-ray diffraction (PXRD), thereby providing direct experimental evidence for the relationship between QCs and their associated CAs. The new cubic phase crystallizes in a Tsai-type approximant structure under the broader classification of polar intermetallic compounds, in which atoms of different electronegativities, viz., electronegative Au + Al vs electropositive Ca, are arranged in concentric shells. From a structural chemical perspective, the outermost shell of this cubic approximant may be described as interpenetrating and edge-sharing icosahedra, a perspective that is obtained by splitting the traditional structural description of this shell as a 92-atom rhombic triacontahedron into an 80-vertex cage of primarily Au [Au_59.86(2)Al_17.14□_3.00] and an icosahedral shell of only Al [Al_10.5□_1.5]. Following the proposal that the cubic 2/1 CA approximates the structure of the i-QC and on the basis of the observed transformation, an atomic site analysis of the 2/1 CA, which shows a preference to maximize the number of heteroatomic Au–Al nearest neighbor contacts over homoatomic Al–Al contacts, implies a similar outcome for the i-QC structure. Analysis of the most intense reflections in the diffraction pattern of the cubic 2/1 CA that changed during the phase transformation shows correlations with icosahedral symmetry, and the stability of this cubic phase is assessed using valence electron counts. According to electronic structure calculations, a cubic 1/1 CA, “Ca₂₄Au₈₈Al₆₄” (CaAu_3.67Al_2.67) is proposed

From Quasicrystals to Crystals with Interpenetrating Icosahedra in Ca–Au–Al: In Situ Variable-Temperature Transformation

The irreversible transformation from an icosahedral quasicrystal (i-QC) CaAu4.39Al1.61 to its cubic 2/1 crystalline approximant (CA) Ca13Au56.31(3)Al21.69 (CaAu4.33(1)Al1.67, Pa3̅ (No. 205); Pearson symbol: cP728; a = 23.8934(4)), starting at ∼570 °C and complete by ∼650 °C, is discovered from in situ, high-energy, variable-temperature powder X-ray diffraction (PXRD), thereby providing direct experimental evidence for the relationship between QCs and their associated CAs. The new cubic phase crystallizes in a Tsai-type approximant structure under the broader classification of polar intermetallic compounds, in which atoms of different electronegativities, viz., electronegative Au + Al vs electropositive Ca, are arranged in concentric shells. From a structural chemical perspective, the outermost shell of this cubic approximant may be described as interpenetrating and edge-sharing icosahedra, a perspective that is obtained by splitting the traditional structural description of this shell as a 92-atom rhombic triacontahedron into an 80-vertex cage of primarily Au [Au59.86(2)Al17.14□3.00] and an icosahedral shell of only Al [Al10.5□1.5]. Following the proposal that the cubic 2/1 CA approximates the structure of the i-QC and on the basis of the observed transformation, an atomic site analysis of the 2/1 CA, which shows a preference to maximize the number of heteroatomic Au–Al nearest neighbor contacts over homoatomic Al–Al contacts, implies a similar outcome for the i-QC structure. Analysis of the most intense reflections in the diffraction pattern of the cubic 2/1 CA that changed during the phase transformation shows correlations with icosahedral symmetry, and the stability of this cubic phase is assessed using valence electron counts. According to electronic structure calculations, a cubic 1/1 CA, “Ca24Au88Al64” (CaAu3.67Al2.67) is proposed.</p

Characterization of ordering in Fe-6.5%Si alloy using X-ray, TEM, and magnetic TGA methods

Fe-6.5wt%Si steel surpasses the current extensively used Fe-3.2wt%Si steel in lower iron loss, higher permeability, and near zero magnetostriction. As a cost effective soft magnetic material, Fe-6.5wt%Si may find applications in motors, transformers, and electronic components. However, the brittleness of the alloy poses processing challenges. The brittleness in Fe-6.5wt%Si is attributed to the formation of ordered phases. Evaluation of the amount of ordered phases is important for the research and development of Fe-6.5wt%Si. This paper aims to find effective ways to evaluate the ordering degree through a comparison of various characterization techniques. In order to tune the ordering degree, various speeds were used to prepare Fe-6.5wt%Si samples via melt spinning. The varying wheel speed changes the cooling rate, which was confirmed by thermal imaging. In addition to the widely used TEM and normal theta-2theta X-ray diffraction methods, two quantitative methods were adopted for this Fe-6.5wt%Si system to study the ordering degree. One method is based on rotating crystal XRD technique, and the other is magnetic thermal analysis technique. These two methods effectively quantified the varying degree of ordering presented in the samples and were deemed more suitable than the TEM, normal theta-2theta XRD methods for Fe-Si due to their ease of sample preparation and short turn-around time.</p