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Structure of the Li4Ti5O12 anode during charge-discharge cycling
No full textThe structural evolution of the “zero-strain” Li4Ti5O12 anode within a functioning Li-ion battery during charge–discharge cycling was studied using in situ neutron powder-diffraction, allowing correlation of the anode structure to the measured charge–discharge profile. While the overall lattice response controls the “zero-strain” property, the oxygen atom is the only variable in the atomic structure and responds to the oxidation state of the titanium, resulting in distortion of the TiO6 octahedron and contributing to the anode's stability upon lithiation/delithiation. Interestingly, the trend of the octahedral distortion on charge–discharge does not reflect that of the lattice parameter, with the latter thought to be influenced by the interplay of lithium location and quantity. Here we report the details of the TiO6 octahedral distortion in terms of the O–Ti–O bond angle that ranges from 83.7(3)° to 85.4(5)°. © 2014, International Centre for Diffraction Data
Temperature- and pressure-dependent structural study of {Fe(pmd)2[Ag(CN)2]2}n spin-crossover compound by neutron Laue diffraction
No full textThe effect of pressure (up to 0.17 GPa) on the spin-crossover compound {Fe(pmd)2[Ag(CN)2]2}n [orthorhombic isomer (II), pmd = pyrimidine] has been investigated by temperature- and pressure-dependent neutron Laue diffraction and magnetometry. The cooperative high-spin [left right arrow] low-spin transition, centred at ca 180 K at ambient pressure, is shifted to higher temperatures as pressure is applied, showing a moderate sensitivity of the compound to pressure, since the spin transition is displaced by ca 140 K GPa-1. The space-group symmetry (orthorhombic Pccn) remains unchanged over the pressure-temperature (P-T) range studied. The main structural consequence of the high-spin to low-spin transition is the contraction of the distorted octahedral [FeN6] chromophores, being more marked in the axial positions (occupied by the pmd units), than in the equatorial positions (occupied by four [Ag(CN)2]- bridging ligands). © 1999-2020 John Wiley & Sons, Inc
Hardness-tensile property relationships for HAZ in 6061-T651 aluminum
Get PDFHigh-strength aluminum is used extensively in industry, with welding being a widely used fabrication method. This work focuses on welding of 6061-T651 aluminum and establishment of the hardness–tensile properties relationship in the heat-affected zone (HAZ) of a gas metal arc weld using 4043 filler material. Test welds were prepared from 12.7-mm-thick plate with a single-V weld preparation. Base plate temperatures were measured with an array of eight embedded thermocouples during welding, relating temperature to properties at intervals from the weld. Through-thickness slices 1.7 mm thick were removed, by electric discharge machining, from the plate parallel to the weld at 2-mm intervals and extending from the weld centerline to 40 mm. into the HAZ and base plate. Tensile samples were prepared from these slices, and tensile properties and hardness values measured to establish a relationship between these two parameters. Both EQUOTIP (portable hardness tester) and Vickers microhardness measurements were conducted and related to tensile properties. Although a significant body of work exists relating tensile properties to hardness, no previous study was found that used this approach. Most work appeared to use cross-weld tensile tests, which only give the point of lowest strength. Sections of base plate material having a different thickness (31.75 mm) from that of the welded samples, and from a different source, were thermally aged to four hardness values and the hardness–tensile relationship was also established for this material. These results were compared with those of the HAZ samples; the results were found to fall within the scatter band of HAZ results
Review of Commercial Electronic Ceramic Materials in Australia; 50 years onwards
No full textThis review paper will address the Australian history of electronic ceramic materials which were used primarily for their dielectric properties rather than their insulation properties. The history of these materials can be broken down into three main periods. The first period is that prior to 1950, when the electronic components industry was first set-up. The second period from approximately 1950 to 1975 involves the expansion and decline of the capacitor product lines and production capacity under the Ducon Condenser Company. The third period from approximately 1975 and continuing to the current day, involves the manufacture of piezoelectric components and devices through Ausonics Pty Ltd and a group at Plessey Ducon, which was subsequently managed in turn by its successors, Plessey Australia, GEC Marconi, Thomson Marconi and the Thales Australia companies. ©2014, The Australian Ceramic Societ
Thermal denaturation of A-DNA
No full textThe DNA molecule can take various conformational forms. Investigations focus mainly on the so-called 'B-form', schematically drawn in the famous paper by Watson and Crick [1]. This is the usual form of DNA in a biological environment and is the only form that is stable in an aqueous environment. Other forms, however, can teach us much about DNA. They have the same nucleotide base pairs for 'building blocks' as B-DNA, but with different relative positions, and studying these forms gives insight into the interactions between elements under conditions far from equilibrium in the B-form. Studying the thermal denaturation is particularly interesting because it provides a direct probe of those interactions which control the growth of the fluctuations when the 'melting' temperature is approached. Here we report such a study on the 'A-form' using calorimetry and neutron scattering. We show that it can be carried further than a similar study on B-DNA, requiring the improvement of thermodynamic models for DNA.© 2014 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft
Metal distribution and disorder in the crystal structure of [NH2Et2][Cr7MF8(tBuCO2)16] wheel molecules for M = Mn, Fe, Co, Ni, Cu, Zn and Cd
No full textThe homometallic wheel compound [Cr8F8(O2CCMe3)16] formed with fluorine and pivalic acid ligands can be modified by introducing in the synthesis process a divalent cation M capable of octahedral coordination instead of one of the trivalent Cr centres in the ring. Heterometallic mono-anionic species [Cr7MF8(O2CCMe3)16]− can form diethylammonium salts and be crystallized from ethylacetate solution as compounds with the general formula [NH2Et2][Cr7MF8(tBuCO2)16][C4H8O2]0.5 for M = Mn, Fe, Co, Ni, Cu, Zn and Cd. Their structures are isomorphous, belonging to the space group P21/c. The study has determined the degree of order for the individual M heterometal over the possible metal positions of the ring in the crystal structure by modelling based on X-ray diffraction data. The model took into account disorder in tert-butyl groups of the pivalate ligands and in the position and orientation of the ethylacetate solvent molecule. The heterometal turned out to be partly ordered in the crystal structure. © 2014, International Union of Crystallography
Lithium Migration in Li4Ti5O12 Studied Using in Situ Neutron Powder Diffraction
No full textWe used in situ neutron powder diffraction (NPD) to study the migration of Li in Li4Ti5O12 anodes with different particle sizes during battery cycling. The motivation of this work was to uncover the mechanism of the increased capacity of the battery made with a smaller-particle-sized anode. In real time, we monitored the anode lattice parameter, Li distribution, and oxidation state of the Ti atom, and these suggested an increase in the rate of Li incorporation into the anode rather than a change in the migration pathway as a result of the particle size reduction. The lattice of these anodes during continuous lithiation undergoes expansion followed by a gradual contraction and then expansion again. The measured lattice parameter changes were reconciled with Li occupation at specific sites within the Li4Ti5O12 crystal structure, where Li migrates from the 8a to 16c sites. Despite these similar Li-diffusion pathways, in larger-particle-sized Li4Ti5O12 the population of Li at the 16c site is accompanied by Li depopulation from the 8a site, which is in contrast to the smaller-particle-sized anode where our results suggest that Li at the 8a site is replenished faster than the rate of transfer of Li to the 16c site. Fourier-difference nuclear density maps of both anodes suggest that 32e sites are involved in the diffusion pathway of Li. NPD is again shown to be an excellent tool for the study of electrode materials for Li-ion batteries, particularly when it is used to probe real-time crystallographic changes of the materials in an operating battery during charge–discharge cycling. © 2014, American Chemical Society
Magnetic transitions and site-disordered induced weak ferromagnetism in (1-x )BiFeO 3 -x BaTiO 3
No full textWe present evidence for weak ferromagnetism in both the rhombohedral and cubic compositions of BF-x BT solid solutions for x < 0.55. Rietveld refinement of nuclear and magnetic structures reveals that the G -type antiferromagnetic ordering of the Fe 3+ magnetic sublattice survives up to x ∼ 0.50. We address the issue of weak ferromagnetism due to spin canting, which is allowed by the symmetry in the R 3c space group but not in the cubic Pm3 ¯ m space group. It is shown that the local symmetry of the average cubic compositions of BF-x BT for 0.35 < x < 0.55 is broken due to off-centering of Bi 3+ in the (1-10) plane and O 2− along the ⟨110⟩ direction from their special Wyckoff positions at (0,0,0) and (1/2,1/2,0), respectively. The local O 2− disorder is shown to be equivalent to local antiferrodistortive rotation, leading to deviation of the Fe 3+ -O 2− -Fe 3+ bond angle from 180° that allows spin canting due to Dzyaloshinskii-Moriya interaction D ⃗ i,j ⋅(S ⃗ i ×S ⃗ j ) , which is otherwise irreconcilable with the ideal cubic symmetry. The magnetization and neutron powder diffraction measurements confirm the absence of magnetic ordering at room temperature for x ≳ 0.5
Modeling the global emission, transport and deposition of trace elements associated with mineral dust.
Get PDFTrace element deposition from desert dust has important impacts on ocean primary productivity, the quantification of which could be useful in determining the magnitude
and sign of the biogeochemical feedback on radiative forcing. However, the impact of elemental deposition to remote ocean regions is not well understood and is not currently
included in global climate models. In this study, emission inventories for eight lements primarily of soil origin, Mg, P, Ca, Mn, Fe, K, Al, and Si are determined based on
a global mineral data set and a soil data set. The resulting elemental fractions are used to drive the desert dust model
in the Community Earth System Model (CESM) in order to simulate the elemental concentrations of atmospheric dust.
Spatial variability of mineral dust elemental fractions is evident on a global scale, particularly for Ca. Simulations of
global variations in the Ca = Al ratio, which typically range from around 0.1 to 5.0 in soils, are consistent with observations,
suggesting that this ratio is a good signature for dust source regions. The simulated variable fractions of chemical
elements are sufficiently different; estimates of deposition should include elemental variations, especially for Ca, Al
and Fe. The model results have been valuated with observations of elemental aerosol concentrations from desert regions and dust events in non-dust regions, providing sights into uncertainties in the modeling approach. The ratios between modeled and observed elemental fractions range from 0.7 to
1.6, except for Mg and Mn (3.4 and 3.5, respectively). Using the soil database improves the correspondence of the spatial
heterogeneity in the modeling of several elements (Ca, Al and Fe) compared to observations. Total and soluble dust element
fluxes to different ocean basins and ice sheet regions have been estimated, based on the model results. The annual inputs of soluble Mg, P, Ca, Mn, Fe and K associated
with dust using the mineral data set are 0.30 Tg, 16.89 Gg, 1.32 Tg, 22.84 Gg, 0.068 Tg, and 0.15 Tg to global oceans and ice sheets. © Author(s) 201
Fundamentals of Silico-Ferrite of Calcium and Aluminum (SFCA) and SFCA-I Iron Ore Sinter Bonding Phase Formation: Effects of CaO:SiO2 Ratio
No full textEffects of basicity, B (CaO:SiO2 ratio) on the thermal range, concentration, and formation mechanisms of silico-ferrite of calcium and aluminum (SFCA) and SFCA-I iron ore sinter bonding phases have been investigated using an in situ synchrotron X-ray diffraction-based methodology with subsequent Rietveld refinement-based quantitative phase analysis. SFCA and SFCA-I phases are the key bonding materials in iron ore sinter, and improved understanding of the effects of processing parameters such as basicity on their formation and decomposition may assist in improving efficiency of industrial iron ore sintering operations. Increasing basicity significantly increased the thermal range of SFCA-I, from 1363 K to 1533 K (1090 °C to 1260 °C) for a mixture with B = 2.48, to ~1339 K to 1535 K (1066 °C to 1262 °C) for a mixture with B = 3.96, and to ~1323 K to 1593 K (1050 °C to 1320 °C) at B = 4.94. Increasing basicity also increased the amount of SFCA-I formed, from 18 wt pct for the mixture with B = 2.48 to 25 wt pct for the B = 4.94 mixture. Higher basicity of the starting sinter mixture will, therefore, increase the amount of SFCA-I, considered to be more desirable of the two phases. Basicity did not appear to significantly influence the formation mechanism of SFCA-I. It did, however, affect the formation mechanism of SFCA, with the decomposition of SFCA-I coinciding with the formation of a significant amount of additional SFCA in the B = 2.48 and 3.96 mixtures but only a minor amount in the highest basicity mixture. In situ neutron diffraction enabled characterization of the behavior of magnetite after melting of SFCA produced a magnetite plus melt phase assemblage. © 2014, The Minerals, Metals & Materials Society and ASM International