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Guest Adsorption in the Nanoporous Metal–Organic Framework Cu3(1,3,5-Benzenetricarboxylate)2: Combined In Situ X-ray Diffraction and Vapor Sorption
No full textThe structure of the nanoporous metal–organic framework Cu3(BTC)2 (BTC = 1,3,5-benzenetricarboxylate) with a variety of molecular guests was studied in situ using single crystal X-ray diffraction. By collecting crystal structure data for a series of guests within the same host crystal, insights into the molecular interactions underpinning guest adsorption processes have been gained. Adsorption behaviors are influenced strongly by both enthalpic and entropic thermodynamic, as well as interpore steric (size-exclusion) effects, and we note correlations between guest attributes and these effects. Vapor adsorption measurements revealed a guest uptake capacity inversely proportional to guest size. Correspondingly, structural results show that guests reside in the smallest pores accessible to them. Interpore steric effects for larger guests cause these to be excluded from the smallest pores, and this corresponds to lower total uptake. Both hydrophilic and lipophilic small guests adsorb favorably into the 5 Å diameter smallest pore of the material, with the number of guests in these pores dependent on guest size and their location, in turn dependent upon both guest–guest interactions and competition between hydrogen-bonding interactions at the apertures of the smallest pore and lipophilic interactions at the center of the smallest pore. Hydrophilic guests with lone electron pairs interact preferentially with the coordinatively unsaturated Cu sites of the desolvated framework, with the number of these depending on steric interactions between neighboring bound guests and guest flexibility. Guest coordination at the Cu sites has a significant effect on the framework structure, increasing the Cu···Cu distance in the dinuclear unit, with the Cu3(BTC)2 unit cell being smaller when guests that do not coordinate with the Cu are present, and in the case of cyclohexane, smaller than for the desolvated framework. Overall, our comprehensive structural study reconciles Cu3(BTC)2 adsorption properties with the underlying guest–host and guest–guest interactions that gives rise to these. © 2014, American Chemical Society
Unglaciated areas in East Antarctica during the Last Glacial (Marine Isotope Stage 3)–New evidence from Rauer Group
No full textLimited information on the East Antarctic Ice Sheet (EAIS) geometry during Marine Isotope Stage 3 (MIS 3; 60-25 ka) restricts our understanding of its behaviour during periods of climate and sea level change. Ice sheet models forced by global parameters suggest an expanded EAIS compared to the Holocene during MIS 3, but field evidence from East Antarctic coastal areas contradicts such modelling, and suggests that the ice sheet margins were no more advanced than at present. Here we present a new lake sediment record, and cosmogenic exposure results from bedrock, which confirm that Rauer Group (eastern Prydz Bay) was ice-free for much of MIS 3. We also refine the likely duration of the Last Glacial Maximum (LGM) glaciation in the region.
Lacustrine and marine sediments from Rauer Group indicate the penultimate period of ice retreat predates 50 ka. The lacustrine record indicates a change from warmer/wetter conditions to cooler/drier conditions after ca. 35 ka. Substantive ice sheet re-advance, however, may not have occurred until much closer to 20 ka.
Contemporary coastal areas were still connected to the sea during MIS 3, restricting the possible extent of grounded ice in Prydz Bay on the continental shelf. In contrast, relative sea levels (RSL) deduced from field evidence indicate an extra ice load averaging several hundred metres thicker ice across the Bay between 45 and 32 ka. Thus, ice must either have been thicker immediately inland (with a steeper ice profile), or there were additional ice domes on the shallow banks of the outer continental shelf. Further work is required to reconcile the differences between empirical evidence of past ice sheet histories, and the history predicted by ice sheet models from far-field temperature and sea level records. © 2016, Elsevier Ltd
Incorporation of Yttria particles into 410L stainless steel by a power metallurgy route
No full textAddition of yttria to steels has been proposed for the fabrication of oxide-dispersion-strengthened materials for nuclear power applications. We have investigated materials prepared from 12 Cr martensitic stainless steel, AISI 410L, produced by powder metallurgy. Materials were produced with and without yttria addition, and two different sizes of yttria were used, 0.9 µm and 50 nm. Tensile and mini-creep tests were performed to determine mechanical properties. Optical microscopy, SEM, TEM, and EDX analysis were used to investigate the microstructures and deformation mechanisms and to obtain information about non-metallic inclusion particles. SiO2, MnS, and Y2Si2O7 inclusion particles were observed. An SiO2 and Y2O3 interaction was seen to have occurred during the ball milling, which impaired the final mechanical properties. Small-angle neutron scattering experiments showed that the matrix chemistry prevented effective dissolution of the yttria. © The Author(s) 201
Dysprosium complexes with mono-/di-carboxylate ligands—From simple dimers to 2D and 3D frameworks.
No full textFour dysprosium (Dy) single carboxylates, a formate, a propionate, a butyrate and an oxalate have been synthesized and structurally characterized. The structure of Dy(HCO2)3 (1) contains nine-fold coordinated Dy polyhedra in perfect tricapped trigonal prisms. They are linked through trigonal O atoms forming 1D pillars which are further linked together through tricapped O atoms into a 3D pillared metal organic framework. The network structure is stable up to 360 °C. The structure of [Dy2(C2O4)3(H2O)6]·2.5H2O (2) contains nine-fold coordinated Dy polyhedra linking together through μ2-bridging oxalate anions into a 2D hexagonal layered structure. Both [Dy2(Pr)6(H2O)4]·(HPr)0.5 (3) [Pr=(C2H5CO2)−1] and [Dy2(Bu)6(H2O)4] (4) [Bu=(C3H7CO2)−1] have similar di-nuclear structures. The Raman vibration modes of the complexes have been investigated. © 2016 Elsevier B.V
Residence times and mixing of water in river banks: implications for recharge and groundwater–surface water exchange
Get PDFBank exchange processes within 50 m of the Tambo River, southeast Australia, have been investigated through the combined use of 3H and 14C. Groundwater residence times increase towards the Tambo River, which suggests the absence of significant bank storage. Major ion concentrations and δ2H and δ18O values of bank water also indicate that bank infiltration does not significantly impact groundwater chemistry under baseflow and post-flood conditions, suggesting that the gaining nature of the river may be driving the return of bank storage water back into the Tambo River within days of peak flood conditions. The covariance between 3H and 14C indicates the leakage and mixing between old (~17 200 years) groundwater from a semi-confined aquifer and younger groundwater (<100 years) near the river, where confining layers are less prevalent. It is likely that the upward infiltration of deeper groundwater from the semi-confined aquifer during flooding limits bank infiltration. Furthermore, the more saline deeper groundwater likely controls the geochemistry of water in the river bank, minimising the chemical impact that bank infiltration has in this setting. These processes, coupled with the strongly gaining nature of the Tambo River are likely to be the factors reducing the chemical impact of bank storage in this setting. This study illustrates the complex nature of river groundwater interactions and the potential downfall in assuming simple or idealised conditions when conducting hydrogeological studies.© Author(s) 2014. CC Attribution 3.0 License
Magnetic structure of Sr2CuWO6
No full textMagnetic structure of the double perovskite Sr2CuWO6 was determined from neutron powder
diffraction data. At 3K the material is magnetically long-range ordered into a collinear
antiferromagnetic structure described by a propagation vector k = (0, 1/2, 1/2) with the CuII moments of 0.57(1) μB parallel to the a-axis. The result is in agreement with our previous prediction (Vasala et al 2014 Phys. Rev. B 89 134419) based on electronic structure calculations, showing that the three-dimensional magnetic long-range order is caused by relatively strong antiferromagnetic next-nearest-neighbor interactions.© 2014, IOP Publishing Ltd
Hydrological influence on the dead carbon fraction in a tropical speleothem during the Younger Dryas and the Last Millennium
No full textThe number of paleoclimate records derived from speleothems has increased significantly in recent years. In addition, speleothems have been used for calibration of the radiocarbon timescale beyond the range of the tree-ring record. One critical issue for reliable speleothem-based radiocarbon calibration and 14C dating of speleothems is constraining the temporal variations in the radioactively dead carbon (i.e. dead carbon fraction (DCF)) that is incorporated into this archive and to determine the potential mechanisms driving such changes. While some studies have shown insignificant variations in DCF through time and highlighted the potential utility of speleothems to extend/improve the radiocarbon calibration curve, others have reported significant temporal variability in speleothem DCF associated with changes in cave recharge.
To further assess the potential hydrological control on speleothem radiocarbon variability, we constructed a new high-resolution DCF record from a speleothem from Flores, Indonesia for two different time periods, the Younger Dryas (YD) chronozone and the Last Millennium. A total of thirty-four 14C analyses (twenty for the YD and fourteen for the Last Millennium) were conducted on pieces of calcite extracted from stalagmite LR06-B1, which was well-dated by ~90 U-Th ages. To better characterize the paleoclimate and environmental changes, high-resolution stable-isotope (δ18O, δ13C) and trace-element (Mg/Ca, Sr/Ca) measurements were also conducted along the same sections of stalagmite.
Broad comparison of the DCF record with the hydrologically-controlled proxy data suggests that increases in rainfall were matched by DCF increases. In line with a previous interpretation of DCF variability for the same specimen, but during the time interval 2.4-2.8 cal kyr BP and the post-bomb period, we interpret the DCF during the YD and the Last Millennium to have been primarily controlled by limestone dissolution associated with changes in open- versus closed-system conditions, rather than other potential factors such as kinetic fractionation and/or variations in the age-spectrum of soil organic matter above the cave. American Geophysical Union, Fall Meeting 201
Growth of bainitic ferrite and carbon partitioning during the early stages of bainite transformation in a 2 mass% silicon steel studied by in situ neutron diffraction, TEM and APT
No full textIn situ neutron diffraction, transmission electron microscopy (TEM) and atom
probe tomography (APT) have been used to study the early stages of bainite
transformation in a 2 mass% Si nano-bainitic steel. It was observed that carbon
redistribution between the bainitic ferrite and retained austenite at the early
stages of the bainite transformation at low isothermal holding occurred in the
following sequence: (i) formation of bainitic ferrite nuclei within carbondepleted
regions immediately after the beginning of isothermal treatment; (ii)
carbon partitioning immediately after the formation of bainitic ferrite nuclei but
substantial carbon diffusion only after 33 min of bainite isothermal holding; (iii)
formation of the carbon-enriched remaining austenite in the vicinity of bainitic
laths at the beginning of the transformation; (iv) segregation of carbon to the
dislocations near the austenite/ferrite interface; and (v) homogeneous redistribution
of carbon within the remaining austenite with the progress of the
transformation and with the formation of bainitic ferrite colonies. Bainitic
ferrite nucleated at internal defects or bainite/austenite interfaces as well as at
the prior austenite grain boundary. Bainitic ferrite has been observed in the
form of an individual layer, a colony of layers and a layer with sideplates at the
early stages of transformation. © 2016, International Union of Crystallograph
Iron and Fire: Geoarchaeological history of a Khmer peripheral center during the decline of the Angkorian Empire, Cambodia.
No full textPreah Khan of Kompong Svay (Preah Khan) was a vast peripheral outpost of the Angkorian Khmer Empire, managed with either strong influence from the capital or semi-autonomously between the 11th and 13th centuries AD. It is believed to have held significant economic importance to the Angkorian elite given its assumed trade partnerships with the neighbouring Kuay hill tribes as well as its proximity to Phnom Dek, or “Iron Mountain”, one of Cambodia's richest known sources of iron oxide. However, the dating of a number of iron metallurgy sites found within the complex placed the heaviest period of industrial activity between the 13th and 17th centuries AD — during the decline of the Angkorian period and beyond into Cambodia's Middle Period. In this paper we present a more extensive record of occupation and use of the site, using a series of geoarchaeological and geochemical records, and show that occupation likely occurred in three stages (Stage 1, Stage 2 and Stage 3). We suggest that in Stage 1 Preah Khan was initially established as a politico-religious expression of power in this strategically important region, and during this time maintained a small, non-industrial population. By the mid-late 14th century AD (Stage 2) macrocharcoal levels increase suggesting that Preah Khan's purpose may have shifted as it became increasingly occupied or utilised for iron smelting activity, before it was finally abandoned in Stage 3, approximately half a century before the supposed abandonment of Angkor. An important question raised from this transition is whether the increased activity in the later phase represents a new wave of Khmer occupants or parasitic occupation of an abandoned temple complex by neighbouring forest-based minority groups. These results highlight the benefit of using geoarchaeological approaches in reconstructing the histories of Angkorian settlements and in increasing our understanding of the response of Khmer peripheral cities to the abandonment of the capital. © 2016 Elsevier Ltd
Structural relationships among LiNaMg[PO4]F and Na2M[PO4]F (M = Mn-Ni, and Mg), and the magnetic structure of LiNaNi[PO4]F. [10.1039/C3DT52587B]
No full textThe new compound LiNaMg[PO4]F has been synthesized by a wet chemical reaction route. Its crystal structure was determined from single-crystal X-ray diffraction data. LiNaMg[PO4]F crystallizes with the monoclinic pseudomerohedrally twinned LiNaNi[PO4]F structure, space group P21/c, a = 6.772(4), b = 11.154(6), c = 5.021(3) Å, β = 90.00(1)° and Z = 4. The structure contains [MgO3F]n chains made up of zigzag edge-sharing MgO4F2 octahedra. These chains are interlinked by PO4 tetrahedra forming 2D-Mg[PO4]F layers. The alkali metal atoms are well ordered in between these layers over two atomic positions. The use of group–subgroup transformation schemes in the Bärnighausen formalism enabled us to determine precise phase transition mechanisms from LiNaNi[PO4]F- to Na2M[PO4]F-type structures (M = Mn–Ni, and Mg) (see video clip 1 and 2). The crystal and magnetic structure and properties of the parent LiNaNi[PO4]F phase were also studied by magnetometry and neutron powder diffraction. Despite the rather long interlayer distance, dmin(Ni+2–Ni+2) ∼ 6.8 Å, the material develops a long-range magnetic order below 5 K. The magnetic structure can be viewed as antiferromagnetically coupled ferromagnetic layers with moments parallel to the b-axis