Bulk Value Research Articles

WITHDRAWN: Controlling and testing anisotropy in additively manufactured stochastic structures

Abstract Additive manufacturing methods such as laser powder bed fusion (PBF) can produce micro-lattice structures which consist of ‘micro-struts’, which have properties that differ from the bulk metal and that can vary depending on the orientation of the strut to the build direction (the strut build angle). Characterising these mechanical and morphological changes would help explain macro-scale lattice behaviour. Individual stainless steel (SS316L) and titanium alloy (Ti6Al4V) laser PBF struts were built at 20°, 40°, 70° and 90° to the build platform, with 3 designed diameters and tested in uniaxial tension (n = 5). Micro-CT was used to quantify changes in surface roughness, eccentricity and cross-section. Average elastic modulus was 61.5 GPa and 37.5 GPa for SS316L and Ti6Al4V respectively, less than the bulk material. Yield strength was uniform over build angle for SS316L, but for Ti6Al4V varied from 40% to 98% of the bulk value from 20° to 90° build angles. All lower angle struts had worse morphology, with higher roughness and less circular cross-sections. These data should help inform micro-lattice design, especially in safety critical applications where lower mechanical performance must be compensated for.

Isotopic Composition of Noble Gases, Nitrogen, and Carbon in the Ozerki New L Chondrite

The isotopic composition of noble gases, nitrogen, and carbon in two samples of the Ozerki L chondrite, which differ in the degree of impact metamorphism, analyzed by the methods of stepwise oxidation and crushing, is reported. The data obtained indicate that the meteorite contains gases trapped on the asteroid during the impact events. The isotopic composition of trapped argon, studied by the stepwise crushing method, is dominated by radiogenic 40Ar (the average 40Ar/36Ar values are 846 in the chondrite material and 1908 in the melt with fine chondrite fragments). Most of the trapped 36Ar is located in positions inaccessible for crushing. The isotopic composition of Ne is a mixture of the solar-wind neon, cosmogenic, and most likely planetary (Q) components. The elemental composition of the trapped noble gases is formed by mixing of the solar, planetary (Q), and cosmogenic components in different proportions. Diffusion processes caused by impact events most likely influenced the elemental abundance of noble gases, primarily helium. Almost all carbon and nitrogen are chemically bound in the rock. In general, their isotopic composition corresponds to that of ordinary chondrites; however, an atypically light carbon isotopic composition with a bulk value δ13C = –47.6 ± 4.8 (‰) was detected in a sample of the chondrite material. The nitrogen released during crushing is isotopically lighter than that released during oxidation. This may indicate that in the course of impact processes, solar nitrogen is more easily mobilized and redistributed into voids than organic nitrogen enriched in the heavy isotope.

On the Difference Between the Tensile Stiffness of Bulk and Slice Samples of Microstructured Materials

Many materials with a microstructure are statistically inhomogeneous, like casting skins in polymers or grain size gradients in polycrystals. It is desirable be able to account for the structural gradient. The first step is to measure the location dependent properties, for example by tensile testing of thin slices. Unfortunately, the slices properties can differ significantly from the bulk properties, since the slices lack a scale separation in one direction. For Polypropylen, we measured that Young’s modulus of the slices is approximately 70% of the respective bulk value. We have identified three significant effects, all making the slices appear softer than the bulk material: Load path confinement: The approximate plane stress forces the load path through a softer phase where in 3D-of-plane load distribution is possible.Free lateral straining: In thin slices, small regions can contract freely, while phases have to contract concurrently in the bulk. Therefore, when two phases have very different Poisson ratios, the bulk appears stiffer than a slice.Topological changes upon slicing: Interpenetrating phases in the bulk can show features of a matrix-inclusion-structure in the slices.We examine and quantify these effects in the linear elastic range for matrix-inclusion-structures and an interpenetrating-phase-structure. Some approaches on how the slice- vs bulk difference can be estimated are given.

Nano-additively manufactured gold thin films with high adhesion and near-bulk electrical resistivity via jet-assisted, nanoparticle-dominated, room-temperature microsputtering

Abstract Microsputtering is a novel additive manufacturing technique that takes a completely new approach to the printing of conductors, directly writing on an arbitrary substrate with the use of a microplasma, i.e., a plasma generated at atmospheric pressure by an arrangement of electrodes with millimeter-scale or smaller spacing. Conductors deposited via microsputtering promise significantly improved electrical conductivity over traditional extrusion ink-based methods. This study investigates, via a design of experiments, the deposits created by a 3D printer-compatible write head that encompasses an atmospheric-pressure gold microsputterer with strong coaxial gas flow. In addition to attaining 1 nm/s deposition rates—on par with traditional (i.e., vacuum) sputtering, the microplasma sputterer creates ~100 nm-thick gold films with near-bulk electrical resistivity (down to 2.9 µΩ cm, i.e., 120% the bulk value) and excellent adhesion—without employing an adhesion layer, annealing, or any other pre/post-processing steps. It is concluded that the strong gas flow promotes the formation of nanoparticles in the plasma plume out of the originally microsputtered gold atoms, which in turn, deposit and create films with excellent adhesion and conductivity.

Enhanced critical current density in Nb3Al superconductor by optimizing mechanical alloying and subsequent sintering process

The critical current density (Jc) is one of the most important properties for the practical application of Nb3Al superconductors. In this work, Nb3Al bulk superconductors were synthesized by mechanical alloying (MA) and subsequent sintering process. And its Jc performance is improved through optimizing the process parameters including ball milling time, sintering temperature and holding time. The results show that the optimal ball milling time to acquire high Jc performance was 20 h. Excessive ball milling worsened Nb3Al's Jc performance because some impurities were introduced into sintered sample. The holding time during sintering process mainly affected the grain size of Nb3Al. Some fine grains coalesce into larger ones after long time sintering. Besides, the sintering temperature and the holding time were all of significance to the grain connectivity in Nb3Al. Higher sintering temperature and longer holding time made a better grain connectivity. The highest Jc value of Nb3Al bulk was 2.5 × 104 A/cm2 (4.2 K, 6 T) with the sintering condition of 850 °C for 5 h. Our work raises some valuable discussions for the following studies on Nb3Al superconductor.

Strain Rate and Thickness Dependences of Elastic Modulus of Free-Standing Polymer Nanometer Films.

Elastic moduli, E, of free-standing polystyrene (PS) single-layers and polystyrene-polydimethylsiloxane (PS-PDMS) bilayers are measured by uniaxial tensile testing at room temperature under different strain rates, γ̇, and for PS thicknesses, h, from 8 to 130 nm. As γ̇ increases, E increases initially, then approaches the bulk value, Ebulk, when γ̇ exceeds a characteristic value (≡ τ-1) that decreases with increasing h. The noted variation of E with γ̇ shows that stress relaxation occurs in the films during measurement when γ̇τ ≪ 1, while the noted variation of τ-1 with h shows that thinner films relax faster. Consequently, E decreases with decreasing h if γ̇ is small, but displays independence of h if γ̇ is large. Visually, the crossover takes place at around γ̇ = 0.0015 s-1, where at γ̇τ > 1 for all films.

Application of the agglomeration process on spinach juice powders obtained using spray drying method

In this study, wet agglomeration process was applied at selected conditions (at 60 °C air inlet temperature and 1.6 m/s air velocity) to improve the functional properties of the spinach juice powders produced by the spray drying technique and distilled water, maltodextrin, whey protein isolate, and gum Arabic solutions were used as the binder agents. The moisture content and the water activity values of the obtained spinach juice agglomerates were in the range of 6.44%–11.68% and 0.254–0.412, respectively. Further a decrease in lightness (L*) values and an increase in yellowness/blueness (b*) values were observed in the agglomeration process. The agglomeration process increased the mean particle diameters, and decreased the wettability and solubility times. The calculated bulk and tapped density values for spinach juice agglomerates are in the range of 380–510 and 490–618 kg/m3, respectively. The agglomeration process improved the values of cohesiveness, flowability, porosity, and hygroscopicity. Low friability and high solubility values were also obtained after agglomeration. The microstructure of powders changed depending on binder agents, and the glass transition temperature of the powders increased from 110.72 to 117.32–127.38 °C for the agglomerates. As a result, the agglomeration process of the spray dried spinach juice powders was successfully carried out in the fluidized bed. The moisture content and water activity values were in safe limits and their powder properties were improved.

Anomaly of the dielectric function of water under confinement and its role in van der Waals interactions.

We present a theoretical calculation of the changes in the Hamaker constant due to the anomalous reduction of the static dielectric function of water. Under confinement, the dielectric function of water decreases from a bulk value of 80 down to 2. If the confining walls are made of a dielectric material, the Hamaker constant reduces by almost 90%. However, if the confinement is realized with metallic plates, there is little change in the Hamaker constant. Additionally, we show that confinement can be used to decreases the Debye screening length without changing the salt concentration. This in turn is used to change the Hamaker constant in the presence of electrolytes.

Optical properties of tungsten trioxide, palladium, and platinum thin films for functional nanostructures engineering.

In recent years, we have been witnessing the intensive development of optical gas sensors. Thin palladium and platinum films as well as tungsten trioxide films with palladium or platinum catalysts are widely used for hydrogen detection, and the optical constants of these materials are required for sensor development. We report the optical parameters retrieved from a set of ellipsometric and transmission spectra for electron-beam evaporated palladium, platinum, and tungsten trioxide films. The tungsten trioxide films were 81 nm, 162 nm, and 515 nm thick and the metal films were as thin as 5-7 nm. Ultrathin palladium and platinum films were shown to be successfully described by local and isotropic permittivity, which is quite different from known bulk values. However, this permittivity showed a strong dependence on adjacent materials, thus illustrating that the ultrathin metallic films can be considered composites characterized by effective permittivity. With the obtained refractive indices and permittivities, the optical spectra of fabricated WO3/Pd and WO3/Pt nanostructures incorporating 1D grating of Al2O3 were in an excellent agreement with the calculated ones without requiring any additional fitting procedures or inclusion of surface roughness layers in numerical models.

Molecular dynamics simulations of energy accommodation between gases and polymers for ultra-low thermal conductivity insulation

Determining the energy accommodation between gases and solids is essential to developing porous thermal insulation materials with ultra-low effective thermal conductivity that reduce energy use, greenhouse gas emissions, and fossil fuel consumption. The energy accommodation coefficients of most gases, however, have been rarely studied, especially with respect to solids that have relatively high thermal resistivity, e.g., polymers. In this work, by using all-atom nonequilibrium molecular dynamics simulations, we reveal the accommodation coefficients of He, Ar, N2, and O2 with polymers, mainly polystyrene. We find that their values are around 0.51, 0.72, 0.79, and 0.90, respectively, suggesting a critical reexamination of the commonly used theoretical maximum value of 1. We have also conducted experiments and validated the value for air, which is about 0.81. Such a change in accommodation coefficients can lead to a reduction of about 70%, 50%, 35%, and 20% in the thermal conductivity of He, Ar, N2, and O2 gases in nano pores (below 100 nm) or at low pressures (below 1 millibar). With these new accommodation coefficients, we find that in a 10 nm pore with ambient pressure at 300 K, the gas thermal conductivity of He, Ar, N2, and O2 in porous polystyrene can be as low as 9.7 × 10−4, 3.4 × 10−4, 7.3 × 10−4, and 8.5 × 10−4 W·m−1·K−1, respectively, which are two to three orders of magnitude lower than their bulk values, promising higher thermal resistivity of insulation materials. This work reveals the fundamental energy exchange between gases and polymers, providing important guidance for designing high-performance thermal insulation materials for various applications.

Determination of Thermal Conductivities for Thin-Film Materials in CMOS MEMS Process

The determination of thermal conductivities for complementary metal-oxide-semiconductor (CMOS) thin-film materials is very important as the operation and failure of integrated circuits (ICs) and CMOS microelectromechanical systems (MEMS) devices are most likely limited by thermal issues, that is, heat transfer. In this article, we present four micro thermal conductivity measurement (μTCM) devices for silicon oxide, polysilicon, and aluminum thin films using CMOS MEMS technology. To determine the thermal conductivities of those thin-film materials from the μTCM devices, a linear thermal resistance model was proposed and validated by the computational fluid dynamics (CFD) study, which showed an error of less than 5.5%. The thermal conductivities of thin-film materials were then measured over a temperature range of 210-362 K, while the measured results for silicon oxide, polysilicon, and aluminum at room temperature were 1.32, 21.22, and 70.2 W/mK, respectively. Those measured thermal conductivities were significantly smaller than the available bulk values. The discrepancies between the thin film and bulk materials are consistent with the reported data and trends, which reveals the importance of determining the thermal conductivities for thin-film materials in the CMOS MEMS process.

Effect of ultrasound pretreatment on the physicochemical properties and simulated gastrointestinal digestibility of micellar casein concentrates

In this study, microfiltered casein micelle retentates were treated with sonication within 15 min prior to spray drying, and the impact of ultrasound pretreatment on the physicochemical, functional, and digestion properties of the resultant micellar casein concentrates were investigated. The results showed that the intrinsic fluorescence intensities of casein samples increased after extending the ultrasound pretreatment time from 2 to 6 min, but decreased if pretreatment time was further prolonged; this was also true for the oil absorption capacity. Additionally, there was a reduction in particle size and thermal stability and an increase in the solubility of pretreated samples in the pH range of 4–8 compared with controls. Bulk and tapped density values decreased after extending the sonication time from 2 to 4 min, but increased if sonication time was further prolonged. No significant changes in the secondary structure of the samples were observed after sonication. An obvious disintegration of micellar casein particles was observed by scanning electron microscopy following ultrasound pretreatment times up to 10 min, resulting in improved digestibility in simulated intestinal fluid. Thus, we concluded that prolonged ultrasound pretreatment facilitates enhanced digestion of micellar casein concentrate and its products.

Microstructure, Tensile Flow and Work Hardening Behavior of W–Ni–Fe Alloys: Effect of Co and Co + Mo Additions

Present work describes the effect of additions of Co and Co + Mo in ternary (W–Ni–Fe) tungsten heavy alloys (WHAs) on the microstructures, mechanical properties, tensile flow and work hardening behavior. In present work, four ternary with different Ni/Fe ratios, one quaternary (containing Co) and one quinary (containing Co + Mo) WHAs based on 92 wt.% W have been investigated. Additions of Co and Co + Mo result in a slight decrease in W-grain size and volume fraction of matrix phase and increase in contiguity for a given Ni/Fe ratio. This has resulted in an increase of σYS and σUTS values which are attributed to higher W solubility in the matrix phase in both the heat treated as well as swaged conditions. On the other hand, the Co and Co + Mo containing alloys exhibit decrease in elongation and impact toughness values due to increase in W–W contiguity as well as decrease in the matrix volume fraction in both the heat treated and swaged conditions. Bulk and micro-hardness values of W-grains and matrix phase have enhanced in Co and Co + Mo containing alloys in swaged condition as a result of substantial solid solution strengthening of matrix phase. True stress–true plastic strain curves of present alloys exhibit single slope on log–log scale in swaged condition. The instantaneous work hardening curves reveal the presence of three distinctive regimes (I, II and III). The second derivatives of true stress–true plastic strain curves are parabola.

Atomic structure and properties of a perovskite/spinel (111) interface

Perovskite and spinel structures are widely found in ferroelectric and magnetic oxides, respectively, making their combination important for multiferroic composites. In this study, the (111) interface between perovskite-type $\mathrm{Bi}\mathrm{Fe}{\mathrm{O}}_{3}$ and spinel-type $\mathrm{Ni}{\mathrm{Fe}}_{2}{\mathrm{O}}_{4}$, has been systematically investigated at the atomic scale combining aberration-corrected scanning transmission electron microscopy and first-principles calculations. The atomic terminations at the interface were determined to be the $\mathrm{Bi}{\mathrm{O}}_{3}$ layer on the $\mathrm{Bi}\mathrm{Fe}{\mathrm{O}}_{3}$ side and the tetrahedral Fe layer on the $\mathrm{Ni}{\mathrm{Fe}}_{2}{\mathrm{O}}_{4}$ side. The lattice mismatch between $\mathrm{Bi}\mathrm{Fe}{\mathrm{O}}_{3}$ and $\mathrm{Ni}{\mathrm{Fe}}_{2}{\mathrm{O}}_{4}$ is primarily accommodated by the first and second $\mathrm{Bi}{\mathrm{O}}_{3}$ layers inside $\mathrm{Bi}\mathrm{Fe}{\mathrm{O}}_{3}$, indicating a stand-off of misfit dislocations in $\mathrm{Bi}\mathrm{Fe}{\mathrm{O}}_{3}$. A metallic interface is formed between the two insulating phases, with the $\mathrm{Bi}{\mathrm{O}}_{3}$ and tetrahedral Fe layer coupled antiferromagnetically across the interface. The magnetic moment in $\mathrm{Ni}{\mathrm{Fe}}_{2}{\mathrm{O}}_{4}$ and the ferroelectric polarization in $\mathrm{Bi}\mathrm{Fe}{\mathrm{O}}_{3}$ drop slightly at the interface and return to the bulk values within two atomic layers from the interface.

Nanocellulose reinforcement in paper produced from fiber blending

This study aimed to evaluate the effect of nanocellulose addition on the physical–mechanical properties of the paper produced from different fiber blends, besides comparing two nanocellulose addition methods. Three different fibers were used for fiber blending (eucalyptus, sisal, and pine). Handsheets were formed based on the mixing of all possible combinations at a 45/55 ratio in 2% consistency and 60 g/m2. Handsheet reinforcements were performed by two methods: The mixture method (MT) was a mixture of nanocellulose along with pulp during paper formation in 3, 5, and 10% addition; the coating method (CT) was the superficial coating of dry formed papers in 10% addition. Nanocellulose was produced by mechanical microfibrillation of sisal pulp. Handsheets were evaluated by physical and strength properties. Nanocellulose addition increased thickness, volume, grammage, apparent density, opacity, roughness, tensile strength, tensile index, stretch, bursting index, tear index, and fold endurance by 8.7, 8.8, 10.4, 2.1, 4.1, 23.2, 45.7, 31.8, 20.1, 14.2, 21.1, and 271.6% but reduced bulk, brightness, and air permeance by 1.9, 3.4, and 71.7%, respectively. The reinforcement methods presented distinct results. In physical properties, an increasing tendency toward nanocellulose (MT) increase was observed in thickness, grammage, and apparent density despite the decreasing trend in air permeance. No tendency was observed in other physical properties. In general, CT presented higher values of thickness, grammage, bulk, and brightness but lower values of apparent density and opacity, compared to MT. The mixture method showed an increasing tendency in strength properties with the increase of nanocellulose content. CT obtained fewer strength properties compared to MT.

Spatially resolving heterogeneous thermal conductivity of BiCuSeO based thermoelectric nanostructures via scanning thermal microscopy

Oxyselenide BiCuSeO is a promising thermoelectric material in the moderate temperature range, and nanostructuring is often adopted to enhance its thermoelectric properties. In these processes, secondary phases can be either induced inadvertently via doping or intentionally processed through nanocomposites, and their effects on local thermal transport remain unresolved from the experimental point of view. In this Letter, we take Pb-doped BiCuSeO and BiCuSeO embedded with rGO (BiCuSeO-rGO) as examples, and we reveal the effect of the secondary phase on local thermal conduction via quantitative scanning thermal microscopy in combination with finite element simulation. It is found that Pb-doping effectively reduces the thermal conductivity of BiCuSeO, while the rGO secondary phase slightly increases its thermal conductivity. Good quantitative agreement is observed between our nanoscale measurement and bulk values reported in the literature. Our work thus not only offers guidance for tuning the thermal transport properties of BiCuSeO but also provides an effective method to spatially resolve heterogenous thermal conductivity at the nanoscale.

Ferromagnetic Resonance Study of the Verwey Phase Transition of Magnetite Thin Film on MgGa₂O₄(001) Substrate

We report on temperature-dependent broadband ferromagnetic resonance studies of magnetite (Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> ) film of thickness 30 nm grown on magnesium gallate [MgGa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> (001)] single crystal substrate by pulsed laser deposition. The isotropic point, i.e., the temperature at which magnetocrystalline anisotropy vanishes, is found to be approximately 120 K, which is 10 K lower than the bulk value. The Verwey transition is close to 110 K, again about 10 K lower than the bulk crystal value. Below the Verwey transition temperature, the uniaxial anisotropy of the monoclinic phase increases gradually and asymptotically approaches a constant value indicating a smooth structural transition rather than a sudden change. Resonance linewidth and effective damping increase abruptly below 110 K. The effective damping constant is determined to be ~0.01 and is independent of temperature from 300 K to 120 K.

Shallow Iodine Defects Accelerate the Degradation of α-Phase Formamidinium Perovskite

Summary Shallow defects are mostly benign in covalent semiconductors, such as silicon, given that they do not constitute non-radiative recombination sites. In contrast, the existence of shallow defects in ionic perovskite crystals might have significant repercussions on the long-term stability of perovskite solar cells (PSCs) because of the metastability of the ubiquitous formamidinium lead triiodide (FAPbI3) perovskite and the migration of charged point defects. Here, we show that shallow iodine interstitial defects ( I i ) can be generated unintentionally during commonly used post-fabrication treatments, which can lower the cubic-to-hexagonal transformation barrier of FAPbI3-based perovskites to accelerate its phase degradation. We demonstrate that concurrently avoiding the generation of I i and the more effective passivation of iodine vacancies ( V I ) can improve the thermodynamic stability of the films and operational stability of the PSCs. Our most stable PSC retained 92.1 % of its initial performance after nearly 1,000 h of continuous illumination operational stability testing.

Dietary diversity of Bronze-Iron Age populations of Kazakhstan quantitatively estimated through the compound-specific nitrogen analysis of amino acids

The identification of which food sources were important to the diets of Central Asian populations during the Bronze and Iron Age has been heavily debated over the past decade. Stable isotope studies of human bulk collagen have often reported elevated nitrogen isotopic compositions (δ15N) that were more than one step higher in the food chain than consumed terrestrial animals, suggesting the additional contribution of fish to human diets. On the other hand, both fish and C4 plants, possibly millets, could have influenced the elevated carbon isotopic compositions (δ13C) in human bone collagen. Here we report the results of the first compound-specific nitrogen isotopic analysis of amino acids conducted on human and faunal remains from Bronze and Iron Age sites of Kazakhstan. In this paper, we examine the possible role of millet in leading to high δ15N values of human bone collagen, in addition to fish. Typically, high δ15N bulk values in humans, are linked to the consumption of particular resources such as fish and C4 plants, or extreme carnivorous diets. However, the δ15N of individual amino acids of the populations of the Kazakh steppe demonstrate trophic positions lower than what we expect in bulk collagen irrespective of δ15N and δ13C. Besides, hardly any evidence of fish consumption is identified by also the δ15N of phenylalanine. The high δ15N in human bulk collagen which obscure reconstruction of prehistoric diets may be coming from complex and diverse factors such as aridity or other dietary factors beyond fish consumption.

Ultra-low magnetic damping in epitaxial Li0.5Fe2.5O4 thin films

The realization of more energy efficient nanomagnetic information devices relies on the existence of magnetic insulators capable of supporting pure spin currents in the absence of a dissipative charge current. Currently, there is a limited number of thin-film magnetic insulators with low magnetic damping. Li0.5Fe2.5O4 (LFO) is well known to possess the lowest damping among the bulk spinel structure oxides, but, thus far, LFO thin films have not lived up to these expectations. Here, we demonstrate low magnetic damping (even lower than typical bulk values) and bulk magnetization in 3 nm thick epitaxial LFO thin films. At room temperature, SQUID magnetometry shows a high saturation magnetization of 320 kA/m, and broadband ferromagnetic resonance measurements yield an effective Gilbert damping parameter of 1.3×10−3, which is among the lowest reported for ferro-/ferrimagnetic films of comparable thickness. Our results show the promise of LFO as a candidate material for spin current-based spintronics.