Wide Grain Size Distribution Research Articles

Morphometric analysis of pebbles in verification of transport processes and interpretation of palaeoenvironment: A case study from the Ogwashi Formation (Oligocene), Niger Delta Basin, Nigeria

The present paper discusses a palaeoenvironmental interpretation of the Oligocene Ogwashi Formation (Niger Delta Basin, Nigeria) through morphometric analysis of pebbles, a research method essentially depending on the quantitative evaluation of pebble size and shape which change during transport processes in a range of depositional environments. The relationship of bivariate and ternary-diagram plots of independent functions was determined from freshly exposed sandstone sections in quarries at Ibusa, near Asaba, Nigeria. The grain size of pebbles ranges from fine (11.00 mm) to very coarse (41.33 mm), with a mean size of 21.05 mm (coarse pebbles). A bivariate plot of the flatness index vs maximum projection sphericity index shows 37% of the pebbles to fall within a beach (marine) environment, and 33% within a fluvial environment; the remaining 30% are uncertain. The maximum projection sphericity index vs oblate-prolate index bivariate plot indicates that 47% of pebbles fall within a marine environment and 22% within a fluvial environment, while the remaining 31% are uncertain. The sphericity-form ternary diagram plot shows that the pebbles primarily comprise bladed, platy, very bladed and very platy of near-equal proportions with minor elongate and very elongate stones, which suggests that the pebbles are diverse in origin. The sphericity-form bivariate plot indicates that the pebbles are largely of disc and blade shapes with a minor number of spherical and rod shapes. The near-equal proportion of pebbles in different segments of the bivariate and ternary diagram plots, and the wide distribution of the pebble grain sizes and shapes suggest the Ogwashi Formation is composed of redeposited sediments that likely were transported and deposited in a mix of marine and fluvial settings with possible transitional environments. In other words, the pebbles can be interpreted as marine-influenced fluvial sediments in marginal-marine settings.

Estimating geoacoustic properties of sediments with a wide grain-size distribution using sediment organic content and the viscous grain shearing model

Interstitial organic matter (OM) is a ubiquitous constituent of marine sediment, particularly prevalent in sediments with significant silt/clay fractions, and is often quantified across a wide range of disciplines. OM suspends silt and clay particles in the sediment matrix, adsorbs onto mineral surfaces, and resides primarily between mineral contacts, all of which are hypothesized to alter geoacoustic properties, yet OM has not been included in sediment acoustics models. Recent studies have shown that OM content (OC) correlates well with sediment geoacoustic properties, such as porosity and index of impedance, from sediments found in the Baltic Sea to seagrass-bearing sediments in Texas to mud banks in Brazil. In Mobile Bay, Alabama, OC correlated well not only with porosity and index of impedance, but also with grain-shearing coefficients described by the viscous grain shearing (VGS) model. Using empirical regressions derived from a subset of the Mobile Bay biogeoacoustic data and VGS, OC will be used to estimate geoacoustic properties of Mobile Bay sediments with a wide grain-size distribution. The efficacy and potential of using OC to predict sediment geoacoustic properties (and vice versa) in Mobile Bay and in other sediments with similar composition will be discussed. [Work supported by ONR.]

Crossover from intrinsic to extrinsic magneto transport in La1-xPbxMnO3 perovskite systems

The intrinsic to extrinsic magneto transport of Pb doping and intermediate grinding on transport as well as magnetic properties in La1-xPbxMnO3 (x = 0, 0.15, 0.25 and 0.4) has been investigated. Double exchange related electron transport is supposed to prevail in case of highly doped samples whereas spin dependent interfacial tunneling of conduction electrons along with double exchange related electron transport dominate conduction process in case of less Pb substituted samples. It has been shown that with repeated grinding and increase in doping percentage (within the doping limit), it is possible to have relatively narrow grain size distribution, which is a major cause of gradual disappearance of the intergrain interfacial tunneling (extrinsic) resistance leaving only intragrain (intrinsic) transport properties in the high temperature region. At low temperature the existence of spin-glass insulator behaviour were observed, which get stronger with decrease in Pb content. Thus with decrease in Pb doping, it has been possible to generate relatively wide distribution of grain size with probable increase in misorientation angle in the grain boundary region. This reveal a crossover from major intrinsic to combination of extrinsic, intrinsic magnetotransport and spin-glass behaviour.

Hot-press sintering of aluminum nitride nanoceramics

The increasing interest in nanostructured ceramics and their applications highlights the need to understand the hot-press sintering of nanoscale AlN powders. We use molecular dynamics simulations to investigate the hot-press sintering of AlN nanoceramics and to clarify the underlying sintering mechanisms. We consider samples with 32 nanoparticles with diameters 8, 12, and 16 nm, arranged in a face centered cubic supercell: samples AlN-8, AlN-12, and AlN-16. Sintering simulations are performed at $T=1900\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ under 1 GPa for 6 ns. An additional simulation is performed for a sample with 8 nm sized nanoparticles at a lower pressure of 0.1 GPa, namely, sample AlN-8-0.1. After 6 ns, densifications of 99%, 96.2%, 95.6%, and 93.2% are achieved for samples AlN-8, AlN-8-0.1, AlN-12, and AlN-16, respectively. Analysis shows that the fast densification process is rooted at the high diffusivity of nanoparticles surface atoms. The AlN-8 sample undergoes intense microstructural evolution during the sintering process from 3 to 6 ns, resulting in a wide distribution of grain sizes from 4 to 15 nm and a larger, 11 nm average grain size. A slower grain growth process is observed in the AlN-8-0.1 sample from $\ensuremath{\sim}4.0\phantom{\rule{0.28em}{0ex}}\mathrm{ns}$. These results indicate a change in the densification mechanism from surface diffusion to grain boundary migration and relaxation of grain boundaries and triple junctions, resulting in a two-stage sintering process, i.e., initially the sample experiences a fast densification, which is followed by intense microstructural evolution. The densification mechanism crossover occurs at 98.7% and 95% densification for the AlN-8 and AlN-8-0.1 samples, respectively. The results indicate that the onset of the second stage depends on a densification threshold, which can be delayed by applying higher external pressure. Sintering of the AlN-16 sample indicates the presence of structural phase transformation at the nanoparticles contact points, which reach over 12 GPa of local pressure during the 1 GPa compression. These results provide atomistic insights into the hot-press sintering of nanoscale ceramics, highlighting the intrinsic swift densification and microstructural evolution processes.

Influence of grain inhomogeneity and precipitates on the stress rupture properties of Inconel 718 superalloy fabricated by selective laser melting

Abstract Optimizing the microstructure to enhance the high temperature stress rupture properties of Inconel 718 (IN718) alloy fabricated via selective laser melting (SLM) is an urgent issue. In this study, SLM-built IN718 specimens were heat-treated with hot isostatic pressing, solution and aging treatment, and their microstructure and high temperature stress rupture properties were investigated, focusing on the influence of grain structure and precipitates. The results show that the coarsening of γ″ precipitate with the aging time at 720 °C follows the Lifshitz-Slyozov-Wagner theory. As the γ″ precipitate size increases, the rupture life gradually increases, area reduction gradually decreases, and the uniform elongation first increases and then decreases. Furthermore, a wide distribution of grain size results in the fine grains regions with much higher geometrically necessary dislocations compared with coarse grain regions during deformation. Hence, the micro-cracks preferentially initiate and propagate along fine-grain boundary. The main deformation mechanisms of specimens aged at 720 °C for 4 h (HSA4) and 8 h (HSA8) with the small γ″ precipitate are dislocation slipping and micro-twinning mode during stress rupture test, while those of specimen aged at 720 °C for 32 h (HSA32) with relatively large γ″ precipitate are dislocation slipping and isolated faulting mode. The HSA8 specimen with the best comprehensive stress rupture properties has the average life of 130 h and uniform elongation of 7.5%, meeting the standard specification for wrought IN718. Finally, some potential strategies for further improving the stress rupture properties of SLM-built IN718 were proposed by comparing to forged-IN718.

Solid-state additive manufacturing of aluminum and copper using additive friction stir deposition: Process-microstructure linkages

Among metal additive manufacturing technologies, additive friction stir deposition stands out for its ability to create freeform and fully-dense structures without melting and solidification. Here, we employ a comparative approach to investigate the process-microstructure linkages in additive friction stir deposition, utilizing two materials with distinct thermomechanical behavior—an Al-Mg-Si alloy and Cu—both of which are challenging to print using beam-based additive processes. The deposited Al-Mg-Si is shown to exhibit a relatively homogeneous microstructure with extensive subgrain formation and a strong shear texture, whereas the deposited Cu is characterized by a wide distribution of grain sizes and a weaker shear texture. We show evidence that the microstructure in Al-Mg-Si primarily evolves by continuous dynamic recrystallization, including geometric dynamic recrystallization and progressive lattice rotation, while the heterogeneous microstructure of Cu results from discontinuous recrystallization during both deposition and cooling. In Al-Mg-Si, the continuous recrystallization progresses with an increase of the applied strain, which correlates with the ratio between the tool rotation rate Ω and travel velocityV. Conversely, the microstructure evolution in Cu is found to be less dependent on Ω, instead varying more with changes to V. This difference originates from the absence of Cu rotation in the deposition zone, which reduces the influence of tool rotation on strain development. We attribute the distinct process-microstructure linkages and the underlying mechanisms between Al-Mg-Si and Cu to their differences in intrinsic thermomechanical properties and interactions with the tool head.

Evolución de fases de Ba<sub>1-x</sub>Eu<sub>x</sub>Ti<sub>1-x/4</sub>O<sub>3</sub> durante el proceso de sinterizado en aire con Difracción de Rayos X in situ a alta temperatura

La evolución de fases de Ba1-xEuxTi1-x/4O3 durante el proceso de sinterizado (calentamiento-enfriamiento) en aire con x = 0,0054; 0,0384; 0,1920 y 0,2689 mol% Eu2O3 fue investigada por Difracción de Rayos X in situ a alta temperatura en el rango de temperatura entre 30 y 1200 °C. Las muestras fueron preparadas mezclando BaCO3, TiO2 y Eu2O3 empleando el método de reacción en estado sólido. Los resultados para las muestras con x ≥ 0,2689 mol% Eu2O3 mostraron la fase cubica BaTiO3 dopada con Eu3+ a 900 °C. Por debajo de 500 °C fue identificada la fase tetragonal ferroeléctrica BaTiO3 dopada con Eu3+. La fase secundaria Ba2TiO4 fué identificada en las muestras durante el calentamiento a 1100 °C con x = 0.0054, 0.0384 y 0.2689 mol% Eu2O3 y a 1200 °C para x = 0.1920 mol% Eu2O3. Las fases secundarias Eu2Ti2O7 y Eu2TiO5 fueron identificadas durante el enfriamiento en el rango de temperatura de 1200 °C a temperatura ambiente para la muestra con x = 0.1920 y 0.2689 mol% Eu2O3. Los resultados de microscopía electrónica de barrido mostraron una amplia distribución de tamaño de grano, una microestructura parcialmente homogénea y altas cantidades de porosidad intergranular, así como una uniforme incorporación y distribución de Ti, Ba y Eu en cada muestra.

Remagnetization of Red Beds on the Tibetan Plateau: Mechanism and Diagnosis

AbstractRed beds are important targets for paleomagnetic studies, yet discriminating secondary chemical remanent magnetization (CRM) from primary depositional remanent magnetization (DRM) in them remains challenging. Here we reanalyze the thermal demagnetization data of and conduct comprehensive rock magnetic, Mössbauer spectroscopic and petrographic studies on red beds from four Cenozoic basins on the eastern Tibetan Plateau (China): the Gongjue, Nangqian, Shanglaxiu, and Jinggu basins. The red beds in the latter two basins are remagnetized, as are most Nangqian red beds. The Gongjue red beds and some Nangqian red beds retain a DRM. Our results reveal that detrital (titano)magnetite and hematite are well preserved in red beds retaining the DRM, whereas remagnetized red beds contain large amounts of authigenic hematite and goethite with detrital Fe‐bearing minerals strongly altered. Postdepositional diagenetic alteration induced by heating and/or fluid circulation related to magmatism and/or crustal deformation is probably the main reason for the remagnetization. Hematite carrying the CRM in remagnetized red beds has wide distribution of grain size and unblocking temperature spectra, while hematite carrying the DRM is usually coarse and has confined unblocking temperature spectrum. This can be used as a criterion for diagnosing remagnetization. Nanoscale goethite appears to occur only in remagnetized red beds: another sensitive criterion for discriminating CRM from DRM. These property‐based criteria constrain the origin of the NRM in red beds better than the classic paleomagnetic field tests. Our research emphasizes that integrated rock magnetic, Mössbauer spectroscopic and petrographic studies provide robust tools to diagnose remagnetization in red beds.

Tensile properties of three-dimensionally interconnected graphene-networked Cu composite and changes in its microstructure in relation to heat treatment temperature

An investigation of microstructure changes in a new, in situ-fabricated, three-dimensionally interconnected graphene-networked Cu composite was performed in relation to the heat treatment temperature in H2 and in air. Heat-treated in H2 revealed that recrystallization commenced at ~ 300 ℃ and the crystal grew afterward. However, the crystal growth was constrained within the initial Cu grains and inhibited due to Cu grains being wrapped by the stable graphene, even at 1000 ℃. This resulted in similar or narrower grain-size distribution. Meanwhile heat treatment in air resulted in the oxidation of carbon, instability of graphene, and crystal growth over the grain boundaries, which resulted in a wider grain-size distribution. Increases in tensile and plastic deformation (30% and 144%, respectively) were observed due to the grain size refinement and the strong interfacial bonds between graphene and the Cu matrix. The result was greater load bearing and toleration of a substantial load during plastic deformation.

Experimental study on the performance characteristics of viscous debris flows with a grid-type dam for debris flow hazards mitigation

A grid-type dam, which is an open-type dam, is an active structural countermeasure employed to mitigate the potential risk from and damage by debris flows. Although grid-type dams are widely used to control water-stone flows in Japan and other countries, they are not used in China due to the lack of knowledge regarding their suitability for controlling viscous debris flows. Viscous debris flows with a wide grain-size distribution are common in southwestern China. Using the known characteristics of such debris flows, we performed a series of flume tests designed to take three main factors into account: debris flow bulk density, channel gradient, and grid size. The goal of these tests was to investigate the dynamic processes and the performance of a grid-type dam in controlling viscous debris flows. The results of our analysis indicated that grid-type dams could effectively trap and regulate viscous debris flows. The sediment storage rate increased with the bulk density, concomitantly with a decrease in the reduction rate of bulk density and peak discharge; however, all parameters decreased with grid opening size. Additionally, based on theoretical analyses and experimental results, dimensionless relationship equations for grid-type dams were established that considered sediment storage rate, bulk density reduction rate, and peak discharge reduction rate. These equations make it possible to predict the effectiveness of controlling transported sediment using a grid-type dam. Moreover, they represent a reference for designing grid opening size, which could provide technical support for further practical engineering. Finally, we applied these equations to a case study of the Sandaoqiao Gully, where they were shown to be effective as a guideline in designing a grid-type dam to control a viscous debris flow.

Microfabrics of omphacite and garnet in eclogite from the Lanterman Range, northern Victoria Land, Antarctica

We examined the microfabrics of omphacite and garnet in foliated eclogite to determine the influence of the layered structure on seismic observations in subduction zone. The analyzed eclogite, from the Lanterman Range, northern Victoria Land, Antarctica, is characterized by layering in which the modal abundances of garnet and omphacite vary. For garnet, the low aspect ratios, similar angular distribution of long axes relative to the foliation in both layers, uniform grain size distribution, near-random crystallographic preferred orientations (CPOs), and misorientation angle distributions are indicative of passive behavior during deformation. In contrast, omphacite shows relatively high aspect ratios, a low angle between the long axes of crystals and the foliation, a wide grain-size distribution, and distinctive CPOs, suggesting dislocation creep as the main deformation mechanism. The results of fabric analyses are consistent with strain localization into omphacite or omphacite-rich layers rather than garnet or garnet- rich layers. The single-crystal seismic anisotropy of garnet is very weak (AVP = 0.2%, AVS = 0.5–0.6%), whereas that of omphacite is much stronger (AVP = 3.7–5.9% and AVS = 2.9–3.8%). Seismic anisotropy of the omphacite-rich layers shows an increase of 329% for AVP and 146% for AVS relative to the garnet-rich layers. Our results demonstrate the importance of the layered structure in strain localization and in the development of the seismic anisotropies of subducting oceanic crust.

Strain rate dependence of tensile strength and ductility of nano and ultrafine grained coppers

An ultrafine grained Cu with a wide distribution of grain size and an average grain size of d= 110nm was prepared by electric brush-plating technique. Tensile properties, microstructure and deformation surface morphologies of this ultrafine grained Cu were compared with two results on an electric brush-plated nanocrystalline Cu (d= 59nm) and an electrodeposited ultrafine grained Cu (d= 200nm) previously prepared by our group. Based on these comparisons, the strain rate dependences of strength and ductility of these three materials and underlying mechanisms were studied. It was revealed that the pronounced strain rate sensitivity (larger m value) of these three materials is a result of the competition between the dislocation and grain boundary mediated deformations. The grain boundary mediated deformation plays a very important role in controlling the tensile ductility of these three materials, which affects the deformation accommodation by promoting different modes of strain localization and hence leads to the completely different strain rate dependences of tensile ductility (the elongations decrease, remains unchangeable and increase with increasing strain rate).

Climatic and limnological changes at Lake Karakul (Tajikistan) during the last ~29 cal ka

We present results of analyses on a sediment core from Lake Karakul, located in the eastern Pamir Mountains, Tajikistan. The core spans the last ~29 cal ka. We investigated and assessed processes internal and external to the lake to infer changes in past moisture availability. Among the variables used to infer lake-external processes, high values of grain-size end-member (EM) 3 (wide grain-size distribution that reflects fluvial input) and high Sr/Rb and Zr/Rb ratios (coinciding with coarse grain sizes), are indicative of moister conditions. High values in EM1, EM2 (peaks of small grain sizes that reflect long-distance dust transport or fine, glacially derived clastic input) and TiO2 (terrigenous input) are thought to reflect greater influence of dry air masses, most likely of Westerly origin. High input of dust from distant sources, beginning before the Last Glacial Maximum (LGM) and continuing to the late glacial, reflects the influence of dry Westerlies, whereas peaks in fluvial input suggest increased moisture availability. The early to early-middle Holocene is characterised by coarse mean grain sizes, indicating constant, high fluvial input and moister conditions in the region. A steady increase in terrigenous dust and a decrease in fluvial input from 6.6 cal ka BP onwards points to the Westerlies as the predominant atmospheric circulation through to present, and marks a return to drier and even arid conditions in the area. Proxies for productivity (TOC, TOC/TN, TOC Br ), redox potential (Fe/Mn) and changes in the endogenic carbonate precipitation (TIC, δ18O Carb ) indicate changes within the lake. Low productivity characterised the lake from the late Pleistocene until 6.6 cal ka BP, and increased rapidly afterwards. Lake level remained low until the LGM, but water depth increased to a maximum during the late glacial and remained high into the early Holocene. Subsequently, the water level decreased to its present stage. Today the lake system is mainly climatically controlled, but the depositional regime is also driven by internal limnogeological processes.

Characterization of a Block Copolymer with a Wide Distribution of Grain Sizes

Block copolymer/lithium salt mixtures are an emerging class of lithium battery electrolytes. Previous studies have shown that the ionic conductivity of these materials is a sensitive function of grain size. Both depolarized light scattering (DPLS) and small-angle X-ray scattering (SAXS) have proven to be effective techniques for elucidating the grain structure of block copolymer (BCP) materials. DPLS is particularly useful for the characterization of samples with grain sizes larger than 1 μm, whereas SAXS is particularly well suited for samples with grain sizes smaller than 0.1 μm. We present the results of both DPLS and SAXS measurements of grain structure in a BCP/lithium salt mixture that was annealed after being initially prepared by freeze-drying from solution. The combination of the two techniques demonstrates that our sample is characterized by an extremely wide distribution of grain sizes. In particular, the sample has a large population of small sub-micrometer-sized grains that cannot be detected...

Hot Extruded Polycrystalline Mg2Si with Embedded XS2 Nano-particles (X: Mo, W)

Due to their abundant, inexpensive and non-toxic constituent elements, magnesium silicide and related alloys are attractive for large-scale thermoelectric (TE) applications in the 500–800 K temperature range, in particular for energy conversion. In this work, we propose a hot extrusion method favorable for large-scale production, where the starting materials (Mg2Si and XS2, X: W, Mo) are milled together in a sealed vial. The MoS2 nano-particles (0.5–2 at.%) act as solid lubricant during the extrusion process, thus facilitating material densification, as confirmed by density measurements based on Archimedes’ method. Scanning electron microscopy images of bulk extruded specimens show a wide distribution of grain size, covering the range from 0.1 μm to 10 μm, and energy dispersive spectroscopy shows oxygen preferentially distributed at the grain boundaries. X-ray diffraction analysis shows that the major phase is the expected cubic structure of Mg2Si. The TE properties of these extruded alloys have been measured by the Harman method between 300 K and 700 K. Resistivity values at 700 K vary between 370 μΩ m and 530 μΩ m. The ZT value reaches a maximum of 0.26 for a sample with 2 at.% MoS2. Heat conductivity is reduced for extruded samples containing MoS2, which most likely behave as scattering centers for phonons. The reason why the WS2 particles do not bring any enhancement, for either densification or heat transfer reduction, might be linked to their tendency to agglomerate. These results open the way for further investigation to optimize the processing parameters for this family of TE alloys.

Rock-magnetic and geochemical characteristics of relict Vertisols—signs of past climate and recent pedogenic development

Rock-magnetic and geochemical characteristics of three Vertisol profiles with different degree of textural differentiation have been studied. Thermomagnetic analyses, thermal demagnetization of laboratory remanences and acquisition of isothermal remanence curves are applied for identification of iron oxide mineralogy. The main magnetic minerals in Vertisols are ferrihydrite, single-domain magnetite, maghemite and hematite. Variations in magnetic susceptibility, anhysteretic remanent magnetization, isothermal remanent magnetization, as well as different ratios (Xarm/X, ARM/SIRM, S-ratio) along depth are studied. Concentration of magnetic minerals in Vertisols is low, influenced by the intense reductomorphic processes. The lowest magnetic susceptibility is found in the most texturally differentiated soil. However, rock-magnetic data suggest the presence of small, but well defined fraction of single domain-like magnetite with relatively wide grain-size distribution found in those parts of the profiles, which are subjected to most intense and frequent seasonal changes in oxidation-reduction conditions. It is suggested that this fraction is formed as a result of transformations of ferrihydrite under repeated cycles of anaerobic/aerobic conditions. Based on geochemical data, CALMAG weathering index was calculated for the three Vertisols. Using the established relation between CALMAG and mean annual precipitation (MAP), palaeo-MAP was evaluated for the studied profiles. The obtained MAP estimations fall in the range 1000–1200 mm and are much higher compared to contemporary precipitation in the area (MAP in the interval 540–770 mm). This finding confirms the relict character of Vertisols on Bulgarian territory and gives more information about the palaeoclimate during the initial stages of Vertisol formation.

On the pressure effect in energetic deposition of Cu thin films by modulated pulsed power magnetron sputtering: A global plasma model and experiments

The modulated pulsed power magnetron sputtering (MPPMS) discharge processes are numerically modeled and experimentally investigated, in order to explore the effect of the pressure on MPPMS discharges as well as on the microstructure of the deposited thin films. A global plasma model has been developed based on a volume-averaged global description of the ionization region, considering the loss of electrons by cross-B diffusion. The temporal variations of internal plasma parameters at different pressures from 0.1 to 0.7 Pa are obtained by fitting the model to duplicate the experimental discharge data, and Cu thin films are deposited by MPPMS at the corresponding pressures. The surface morphology, grain size and orientation, and microstructure of the deposited thin films are investigated by scanning electron microscopy, transmission electron microscopy, and x-ray diffraction. By increasing the pressure from 0.1 to 0.7 Pa, both the ion bombardment energy and substrate temperature which are estimated by the modeled plasma parameters decrease, corresponding to the observed transition of the deposited thin films from a void free structure with a wide distribution of grain size (zone T) into an underdense structure with a fine fiber texture (zone 1) in the extended structure zone diagram (SZD). The microstructure and texture transition of Cu thin films are well-explained by the extended SZD, suggesting that the primary plasma processes are properly incorporated in the model. The results contribute to the understanding of the characteristics of MPPMS discharges, as well as its correlation with the microstructure and texture of deposited Cu thin films.

Improvement of electrical conductivity in Pb0.96−yMn0.04SnyTe alloys for high temperature thermoelectric applications

Lead–tin–telluride is a well-known thermoelectric material in the temperature range 350–750 K. Here, this alloy doped with manganese (Pb0.96−yMn0.04SnyTe) was prepared for different amounts of tin. X-ray diffraction showed a decrease of the lattice constant with increasing tin content, which indicated solid solution formation. Microstructural analysis showed a wide distribution of grain sizes from <1 μm to 10 μm and the presence of a SnTe rich phase. All the transport properties were measured in the range of 300−720 K. The Seebeck coefficient showed that all the samples were p-type indicating holes as dominant carriers in the measurement range. The magnitude increased systematically on reduction of the Sn content due to possible decreasing hole concentration. Electrical conductivity showed the degenerate nature of the samples. Large values of the electrical conductivity could have possibly resulted from a large hole concentration due to a high Sn content and secondly, due to increased mobility by sp–d orbital interaction between the Pb1−ySnyTe sublattice and the Mn2+ ions. High thermal conductivity was observed due to higher electronic contribution, which decreased systematically with decreasing Sn content. The highest zT = 0.82 at 720 K was obtained for the alloy with the lowest Sn content (y = 0.56) due to the optimum doping level.

Flow processes and sedimentation associated with erosion and filling of sinuous submarine channels

This article uses measurements from a three-dimensional exposure of a sinuous submarine channel and its fill to document, for the first time, how flow properties and sedimentation differ between erosional and filling stages. Two units, recording this sequential evolution, are documented. Unit 1 records gravity flows that deepened and laterally migrated the channel, resulting in the deposition of point bars, with coarsening-upward profiles, on the inner part of channel bends. These gravity flows were mud-rich with a wide grain-size distribution. Flow heights exceeded the depth of the channel resulting in the deposition of levees. Strong secondary flow is evident with a helical pattern reversed to their subaerial counterparts. Strata in point bars and levees are inclined and deposited primarily by tractive processes. Unit 2 records gravity flows that filled the channel. These gravity flows were sand-rich with a relatively narrow grain-size distribution. Flow heights scaled to the depth of the channel, and they contain no evidence for secondary flow. Associated strata are horizontal and deposited primarily from suspension.

Microstructure dependence of the magnetic properties of sintered Ni–Zn ferrites by solid-state reaction doped with V2O3

In order to improve the frequency range operation of Ni–Zn ferrites with the Ni0.7Zn0.3Fe2O4 stoichiometry in this study, they were doped with V2O3 at different concentrations (0, 0.25, 0.50, and 0.75 wt%). The samples were prepared by the solid-state reaction at 1250 °C for 24 h. The content and location of Vanadium in these ferrites allow us to determine its influence on their microstructure and magnetic properties. A single cubic spinel phase with lattice parameter variation was determined by the refinement of X-ray diffraction patterns. This refinement was achieved using the Rietveld method. The lattice parameter presents a slight enhancement with increasing Vanadium content up to 0.50 wt% of V2O3. The increase of intragrain porosity and the segregation of Vanadium at the grain boundary in samples with higher concentration of Vanadium show a narrow grain-size distribution that leads to a resonant character of the magnetic domain wall. A wide grain-size distribution determined in lower concentration of Vanadium results in a mixed resonant-relaxation dispersion. The use of V2O3 as a dopant in Ni–Zn ferrites increases the frequency operation and coercivity, Hc, without abruptly degrading the saturation magnetization, Ms. We, therefore conclude, that Vanadium may be used as a strong dopant for the preparation of ferrites for any particular high-frequency application.