Distribution Of Small Grains Research Articles

Bicontinuous nickel/tin oxide films with enhanced photoelectrochemical hydrogen production efficiency

Self-assembled bicontinuous NiO:SnO2 films are proposed for enhanced photoelectrochemical hydrogen production efficiency due to their high interface-to-volume ratio and three-dimensional interconnectivity. The X-ray diffraction confirms the superior crystallinity of the bicontinuous NiO:SnO2 films. Bicontinuous NiO:SnO2 films reveal a heterostructure of mixed NiO and SnO2 phases, where the NiO phase exhibits the distribution of small grains, whereas the SnO2 phase exhibits large agglomerates of SnO2 crystals embedded in the NiO structure. The bicontinuous NiO:SnO2 films exhibit lower bandgap energy and higher electrical conductivity compared to pure NiO and pure SnO2 films. The photoresponsivity of the bicontinuous oxide films is higher than pure NiO and pure SnO2 films. These results imply the presence of strong charge interactions at the three-dimensional interfaces in bicontinuous NiO:SnO2 films. The hydrogen revolution reaction analysis confirms that the bicontinuous NiO:SnO2 films exhibit higher photoelectrocatalyst hydrogen production activity compared to pure NiO and pure SnO2 films.

Crystal Plasticity Modeling to Capture Microstructural Variations in Cold-Sprayed Materials

The high-velocity impact of powder particles in cold-spray additively manufactured (CSAM) parts creates intersplat boundaries with regions of high dislocation densities and sub-grain structures. Upon microstructure and mechanical characterization, CSAM Aluminum 6061 showed non-uniformity with spatial variation in the microstructure and mechanical properties, affecting the overall response of the additively manufactured parts. Post-processing treatments are conducted in as-printed samples to improve particle bonding, relieve residual stresses, and improve mechanical properties. In this work, we attempt to implement the effects of grain size and distribution of smaller grains along the intersplat boundaries using the grain size distribution function and powder size information to accurately predict the deformation response of cold-sprayed material using a mean-field viscoplastic self-consistent (VPSC) model. The incorporation of an intersplat boundary term in the VPSC model resulted in a stress–strain response closely matching the experimental findings, preventing the superficially high stresses observed due to Hall–Petch effects from ultra-fine-grain structures. Likewise, the results from the grain analysis showed the combined effects of grain size, orientation, and intersplat mechanisms that captured the stresses experienced and strain accommodated by individual grains.

Wire arc additive manufacturing (WAAM) of nanotreated aluminum alloy 6061

PurposeAdditive manufacturing (AM) can achieve significant weight savings with only minor compromises in strength if high-performance wrought aluminum alloys are used as feedstock. Despite the advantages in strength that aluminum alloys (AA) 6061 offer, they cannot be manufactured via printing because of hot cracking and other solidification problems. The purpose of this study is to achieve high-quality printing of AA6061 with nanotreated wires.Design/methodology/approachNanotreating was used to modify the AA6061 alloy composition by adding a small fraction of nanoparticles to enhance the alloy’s manufacturability and resultant properties. Wire arc additive manufacturing (WAAM) was used to print the nanotreated AA6061 wire feedstock. The microstructure of the printed AA6061 was characterized by X-ray crystallography, optical microscopy, scanning electron microscopy and energy dispersive spectroscopy mapping. The microhardness profile, tensile behavior and fracture surface were analyzed.FindingsThis work successfully used WAAM to print nanotreated AA 6061 components. The resulting AA6061 parts were crack-free, with exceptional grain morphology and superior mechanical properties. Owing to the excellent size control capabilities of nanoparticles, a homogeneous distribution of small grains was maintained in all deposited layers, even during repeated thermal cycles.Originality/valuePrevious studies have not successfully printed AA6061 using WAAM. Conventional WAAM products exhibit anisotropic mechanical properties. The nanotreated AA6061 was successfully printed to achieve homogeneous microhardness and isotropic tensile properties. The promising results of this study reflect the great potential of nanotech metallurgy as applied to the WAAM process.

MgFe2O4/(Ba0·85Ca0.15) (Zr0·1Ti0.9)O3 lead free ceramic composite: A study on multiferroic and magnetoelectric coupling properties at room temperature

MgFe2O4 (MFO) and (Ba0·85Ca0.15) (Zr0·1Ti0.9)O3 (BCZT) was prepared by solid state route and are found to be ferromagnetic and ferroelectric at room temperature respectively. MFO/BCZT composite (50:50 M concentration of MFO and BCZT) was also prepared by solid state route. Multiferroic properties of MFO/BCZT ceramic composite were investigated. Scanning electron micrograph confirms the distribution of small grains of MFO around large grain of BCZT for proper surface interaction. MFO/BCZT composite exhibits saturated magnetization of 12 emu/gm, which reduce to 10 emu/gm on electrical poling at 2.5 kV/cm indicating magneto-electric coupling between MFO and BCZT through interface interaction. The composite also exhibits proper ferroelectric polarization, which is confirmed from I–V characteristic plot (occurrence of double minima as that of proper ferroelectric). The transverse magnetoelectric coupling coefficient (αV31) for this composite is found to be 7.97 mVcm−1Oe−1 at 10 kHz. MFO/BCZT ceramic composite exhibit multiferroic and magnetoelectric coupling properties for 50:50 M concentration at room temperature may be suitable for device applications.

Effect of RF sputtering power and vacuum annealing on the properties of AZO thin films prepared from ceramic target in confocal configuration

Aluminum-doped zinc oxide (AZO) thin films are deposited on glass substrate by radio frequency (RF) magnetron sputtering method in confocal configuration at room temperature (RT). Several techniques are used to investigate the effects of sputtering power, from 50 to 300 W, on structural, optical and electrical properties. It is found, from Grazing Incidence X-Ray Diffraction (GIXRD) analysis, that the sputtering power has a great influence on the crystalline quality of AZO films. A preferential orientation along the c-axis is obtained at lower sputtering power of 50 W. XPS analysis confirms the existence of only Zn and Al in the oxidized state in accordance with the XRD results. SEM and AFM observations of AZO films reveal dense and homogenous distribution of small grains on the surface. Analysis by UV–Vis–NIR spectroscopy at RT reveals that the average optical transmittance in the visible range (400–800 nm) of the AZO thin films is higher than 75%. Hall-effect measurements put into evidence that the electrical resistivity of the films increases with the increase of the sputtering power. A low resistivity of 1.65 × 10−3 Ω cm is obtained for the lowest sputtering power (50W). Moreover, AZO thin film deposited at 50 W and annealed for 1h at 400 °C under vacuum shows a lower resistivity of 5.75 × 10−4 Ω cm, an average optical transmission above 86% and a high figure of merit (ФTC) value of 3.4 × 10−3 Ω−1sq which suggests that the fabricated AZO thin films are promising for optoelectronic devices in the UV region.

Dust survival rates in clumps passing through the Cas A reverse shock – I. Results for a range of clump densities

ABSTRACT The reverse shock in the ejecta of core-collapse supernovae is potentially able to destroy newly formed dust material. In order to determine dust survival rates, we have performed a set of hydrodynamic simulations using the grid-based code astrobear in order to model a shock wave interacting with clumpy supernova ejecta. Dust motions and destruction rates were computed using our newly developed external, post-processing code paperboats, which includes gas drag, grain charging, sputtering, and grain–grain collisions. We have determined dust destruction rates for the oxygen-rich supernova remnant Cassiopeia A as a function of initial grain sizes and clump gas density. We found that up to $30\,\mathrm{{{\ \rm per\ cent}}}$ of the carbon dust mass is able to survive the passage of the reverse shock if the initial grain size distribution is narrow with radii around ∼10–50 nm for high gas densities, or with radii around $\sim 0.5\!-\!1.5\,\mathrm{\mu m}$ for low and medium gas densities. Silicate grains with initial radii around 10–30 nm show survival rates of up to $40\,\mathrm{{{\ \rm per\ cent}}}$ for medium- and high-density contrasts, while silicate material with micron-sized distributions is mostly destroyed. For both materials, the surviving dust mass is rearranged into a new size distribution that can be approximated by two components: a power-law distribution of small grains and a lognormal distribution of grains having the same size range as the initial distribution. Our results show that grain–grain collisions and sputtering are synergistic and that grain–grain collisions can play a crucial role in determining the surviving dust budget in supernova remnants.

Anodic and cathodic deposition of polyaniline films: a comparison between the two methods

This paper reports the comparison of polyaniline (PAni) thin films grown by anodic and cathodic electrodeposition. The growth condition, structure, optical property, thickness and morphology of the deposited layers have been characterized using cyclic voltammogram, x-ray diffraction (XRD), UV–vis spectroscopy, optical profilometry and scanning electron microscopy (SEM). The thin films grown from anodic deposition show blue-violet colour, which denotes pernigraniline fully oxidised state whereas the layers grown using cathodic deposition show pale yellow colour, which indicates leucoemeraldine fully reduced state of PAni. PAni grown from anodic deposition exhibit amorphous phase with cementing effect growth and bandgap varies from 3.90–4.08 eV. PAni layer from cathodic deposition demonstrated crystalinity based on the presence of the two XRD peaks at 2θ = 30.7° and 32.1° in the XRD pattern with random distribution of smaller grains and bandgaps in a range from 1.05 to 1.20 eV. The properties of PAni thin films electrodeposited from anodic and cathodic deposition and under a variety of deposition conditions have been compared and discussed in detail.

Micromagnetic simulation of the effect of grain boundaries and secondary phases on the magnetic properties and recoil loops of hot-deformed NdFeB magnets

Abstract Hot-deformed NdFeB magnets have attracted considerable attention due to their high thermal stability and exceptional corrosion resistance. In this study, the dependence of magnetic properties and recoil loops on the presence of a grain boundary phase (GBP) and Nd-rich secondary phases in hot-deformed NdFeB magnets was explored using micromagnetic simulations. By adjusting the parameters of the simulation model, the influence of several factors (thickness and spontaneous magnetization (Ms) of the GBP, Ms, total volume fraction and spatial distribution of the secondary phase), on the main and recoil loops was investigated. A change in thickness and in Ms of the GBP affects the coercivity (Hc) and remanence of the main loop. In particular, an increase of Ms leads to a decrease in the magnet’s Hc. The influence of the secondary phase depends on its spatial distribution. Large volume grains result in lower Hc, but the role in decreasing Hc is weaker in contrast to a random distribution of smaller grains of the same overall volume content. Open recoil loops were interpreted by analyzing the distribution of calculated magnetic moments and energy terms. Loop opening is not directly related to Hc of the main loop. Rather it is mainly due to small irreversibilities in the dipolar energy of different magnetic configurations that appear along the recoil loop.

Effect of Tungsten Doping on the Properties of In2O3 Films

Highly crystalline tungsten oxide (WO3)-doped indium oxide (In2O3) films are synthesized at room temperature by the RF magnetron sputtering technique. The structural and morphological properties of the as-deposited films and the films annealed at a temperature of 300°C are investigated in detail. X-ray diffraction analysis reveals the presence of a cubic bixbyite structure with preferred orientation along the (222) plane for both the as-deposited and annealed films. Moderate WO3 doping (1 wt.%) enhances the crystallinity of the as-deposited In2O3 films, whereas the crystallinity of the films systematically decreases with an increase in WO3 doping concentration beyond 1 wt.%. Raman spectral analysis discloses the modes of the cubic bixbyite In2O3 phase in the films. Atomic force microscopy micrographs show a smooth and dense distribution of smaller grains in the films. X-ray photoelectron spectroscopy reveals the existence of W5+ in the doped films. The undoped film is highly oxygen deficient. Variation in the concentration of oxygen vacancy can be associated with the degree of crystallinity of the films.

Properties of Au incorporated In2O3 films

Effect of gold loading on the structural, morphological, optical and electrical properties of RF magnetron sputtered In2O3 films is discussed. Annealing is done to analyse the properties of heavily Au loaded In2O3 film after thermal treatment. Au acts as a nucleation centre and improves the crystalline quality of cubic bixbyite In2O3 films with moderate Au loading concentration. FESEM and AFM images of the as-deposited films present smooth surface morphology with a dense distribution of small grains. Random distribution of Au nanorods can be seen in the FESEM image of the 10 wt% Au incorporated film annealed at a temperature of 400 °C. The present study reveals the formation of smooth, crack-free, crystalline In2O3 films with Au incorporation. XPS analysis suggests the predominance of metallic state of Au in the Au loaded films. Absorption studies show an enhanced absorption in both as-deposited and annealed Au loaded films. Transmittance of In2O3 films is considerably modified but electrical properties are not much modified by Au incorporation. Enhancement in UV luminescence emission of In2O3 films ~378 nm is observed with Au incorporation up to 3 wt%. Intense UV emission in Au incorporated films opens a possibility of using these films for UV light emission applications.

High-resolution neutron depolarization microscopy of the ferromagnetic transitions in Ni3Al and HgCr2Se4 under pressure

We performed neutron imaging of ferromagnetic transitions in Ni3Al and HgCr2Se4 crystals. These neutron depolarization measurements revealed bulk magnetic inhomogeneities in the ferromagnetic transition temperature with spatial resolution of about 100 μm. To obtain such spatial resolution, we employed a novel neutron microscope equipped with Wolter mirrors as a neutron image-forming lens and a focusing neutron guide as a neutron condenser lens. The images of Ni3Al show that the sample does not homogeneously go through the ferromagnetic transition; the improved resolution allowed us to identify a distribution of small grains with slightly off-stoichiometric composition. Additionally, neutron depolarization imaging experiments on the chrome spinel, HgCr2Se4, under pressures up to 15 kbar highlight the advantages of the new technique especially for small samples or sample environments with restricted sample space. The improved spatial resolution enables one to observe domain formation in the sample while decreasing the acquisition time despite having a bulky pressure cell in the beam.

Preparation of p-NiO/n-SiC heterojunction on 4H-SiC substrate

In this work, nickel oxide (NiO) film was prepared on 4H-SiC (0001) by radio frequency magnetron sputtering to form NiO/4H-SiC p-n heterojunction for the first time. XRD results indicated NiO film had (200), (220), and (020) oriented crystal structures and SEM results showed homogeneous distribution of small grains on 4H-SiC substrate. The optical band gap for NiO was calculated as 3.75 eV by UV-visible absorption spectra. The current-voltage characteristic of the NiO/4H-SiC p-n heterojunction showed a typical rectification behavior with a turn-on voltage of 1.4 V. The discontinuities of the valence band edge and the conduction band edge were estimated to be 1.15 eV and 1.64 eV, respectively. The differences in barrier heights for holes and electrons indicated an improved hole injection capacity of NiO/4H-SiC p-n heterojunction.

Ferroelectric and optical properties of ‘Ba-doped’ new double perovskites

ABSTRACTSolid solution of Pb1.5Ba0.5BiNbO6 ceramic is explored here to obtain its ferroelectric and optical properties. The polycrystalline sample was prepared by a standard solid state reaction route. Room temperature XRD and FTIR spectra of the compound exhibit an appreciable change in its crystal structure of Pb2BiNbO6 on addition of ‘Ba’ in A site. The surface morphology of the gold-plated sintered pellet sample recorded by SEM exhibits a uniform distribution of small grains with well-defined grain boundaries. Detailed studies on the nature of polarization and variation of dielectric constant, tangent loss with temperature as well as frequency indicate the existence of Ferro-electricity in the sample. Using UV-Vis spectroscopy, the optical band gap of the studied sample has been estimated as 2.1 eV, which is useful for photo catalytic devices. Photoluminescence analysis of the powder sample shows a strong red photoluminescence with blue excitation, which is basically useful for LED.

The grain boundary pinning effect of the μ phase in an advanced polycrystalline γ/γ′ Co-base superalloy

A grain boundary pinning phase was introduced into a γ/γ′ Co-base superalloy by the addition of Mo. The intermetallic phase was identified as μ phase (Co,Ni,Cr)7(W,Mo)6 by high-energy X-ray diffraction and energy-dispersive X-ray spectroscopy in the transmission electron microscope. Synchrotron radiation in-situ heating experiments confirmed the stability of the grain structure up to 1050 °C and therefore the grain boundary pinning effect of this phase. Recrystallization heat treatments at different temperatures resulted in varying amounts of μ phase. The grain size analysis revealed that at least 1% of the phase is necessary to maintain a pinning effect during recrystallization. Atom probe tomography confirmed that Mo partitioned predominantly to the γ phase. Since the μ phase and the γʹ phase are competing for W, a lower γ′ volume fraction was formed in comparison to a Mo-free polycrystalline γ/γʹ Co-base superalloy variant. However, the homogeneous distribution of small grains resulted in a higher strength compared to the Mo-free alloy without grain boundary pinning phases. The creep resistance at 750 °C was similar to the Mo-free alloy as well as the polycrystalline Ni-base superalloy U720Li with a creep rate minimum of 1.5 × 10−7 s−1 at 620 MPa.

Microstructure quantification of Cu–4.7Sn alloys prepared by two-phase zone continuous casting and a BP artificial neural network model for microstructure prediction

Microstructures of Cu–4.7Sn (%) alloys prepared by two-phase zone continuous casting (TZCC) technology contain large columnar grains and small grains. A compound grain structure, composed of a large columnar grain and at least one small grain within it, is observed and called as grain-covered grains (GCGs). Distribution of small grains, their numbers and sizes as well as numbers and sizes of columnar grains were characterized quantitatively by metallographic microscope. Back propagation (BP) artificial neural network was employed to build a model to predict microstructures produced by different processing parameters. Inputs of the model are five processing parameters, which are temperatures of melt, mold and cooling water, speed of TZCC, and cooling distance. Outputs of the model are nine microstructure quantities, which are numbers of small grains within columnar grains, at the boundaries of the columnar grains, or at the surface of the alloy, the maximum and the minimum numbers of small grains within a columnar grain, numbers of columnar grains with or without small grains, and sizes of small grains and columnar grains. The model yields precise prediction, which lays foundation for controlling microstructures of alloys prepared by TZCC.

Grain boundary engineering parameters for ultrafine grained microstructures: Proof of principles by a systematic composition variation in the Cu-Ni system

The main principles of grain boundary engineering of an ultrafine grained microstructure are studied via a systematic variation of the stacking fault energy (γSFE), solid solution effects (SSEs) and the homologous deformation/annealing temperatures choosing the Cu-Ni system as a model case for non-segregating alloys. Cu and Ni are completely miscible and the γSFE varies strongly with the alloy composition. Ultrafine grained microstructures are produced by high-pressure torsion and their evolution upon annealing is investigated. The thermal stability and the saturation grain sizes after deformation are determined by SSEs. The fraction of deformation twins varies in accordance with the γSFE. The increase of the length fraction of Σ3 grain boundaries versus the grain size is found to be governed by the SSEs, whereas the increase of the length fraction of Σ9 grain boundaries versus the grain size depends on the γSFE. The results indicate that grain boundary engineering may lead to an optimum ultrafine grained structure, i.e. with a high length fraction of Σ3 and Σ9 grain boundaries of approximately 40%. This is a significantly large fraction in comparison to a not-engineered microstructure and achieved for grain sizes below 1000 nm in alloys close to the equiatomic composition having a low γSFE and a high melting temperature. This high fraction of Σ3n grain boundaries (including their conjunctions) proved itself most effective for microstructure stabilization in this virtually non-segregating system. Thus, for Cu50Ni50 and Cu65Ni35, a narrow grain size distribution of small grains, a high hardness and a high fraction of special grain boundaries can be adjusted.

Spontaneous, high temperature and spectroscopic characterization of K0.5Bi0.5TiO3-NaVO3 ceramic

Ferroelectric, optical and impedance properties of polycrystalline K0.5Bi0.5TiO3-NaVO3 (KBT-NV) ceramic prepared by solid state reaction technique has been investigated. Field Emission Scanning Electron Microscope (FESEM) study of the gold coated sintered pellet of the sample exhibits uniform distribution of small grains with well-defined grain boundaries. The Fourier Transform Infrared (FTIR) spectra show that the compound exhibits an appreciable change in its vibrational phonon modes of KBT on addition of NaVO3. The X-ray diffraction (XRD) reveals an orthorhombic structure where the crystallites preferentially grows along (6 2 0) face. Studies on nature of polarization, variation of dielectric constant, and tangent loss with temperature as well as frequency indicate the possible existence of ferroelectricity. The temperature variation of hysteresis loop confirms the ferroelectric nature in the studied compound. The sample is found to be photoluminescent in the wavelength range of 540–570 nm with a strong greenish-red emission which originates from defects. The optical band gap of the KBT-NV sample has been estimated from diffused reflectance and absorbance spectra to be 2.68 eV, which can be useful for photocatalytic application.

The Circumstellar Disk HD 169142: Gas, Dust, and Planets Acting in Concert?*

Abstract HD 169142 is an excellent target for investigating signs of planet–disk interaction due to previous evidence of gap structures. We perform J-band (∼1.2 μm) polarized intensity imaging of HD 169142 with VLT/SPHERE. We observe polarized scattered light down to 0.″16 (∼19 au) and find an inner gap with a significantly reduced scattered-light flux. We confirm the previously detected double-ring structure peaking at 0.″18 (∼21 au) and 0.″56 (∼66 au) and marginally detect a faint third gap at 0.″70–0.″73 (∼82–85 au). We explore dust evolution models in a disk perturbed by two giant planets, as well as models with a parameterized dust size distribution. The dust evolution model is able to reproduce the ring locations and gap widths in polarized intensity but fails to reproduce their depths. However, it gives a good match with the ALMA dust continuum image at 1.3 mm. Models with a parameterized dust size distribution better reproduce the gap depth in scattered light, suggesting that dust filtration at the outer edges of the gaps is less effective. The pileup of millimeter grains in a dust trap and the continuous distribution of small grains throughout the gap likely require more efficient dust fragmentation and dust diffusion in the dust trap. Alternatively, turbulence or charging effects might lead to a reservoir of small grains at the surface layer that is not affected by the dust growth and fragmentation cycle dominating the dense disk midplane. The exploration of models shows that extracting planet properties such as mass from observed gap profiles is highly degenerate.

Multi-ferroic and optical spectroscopy properties of (Bi0.5Sr0.5) (Fe0.5Ti0.5) O3 solid solution

Solid solution of (Bi0.5Sr0.5) (Fe0.5Ti0.5) O3 (BFST) ceramic is explored here to obtain multiferroic and optical properties of the sample. The polycrystalline sample BFST was prepared by a standard solid state reaction route. Room temperature XRD, Raman and FTIR spectra of the compound exhibit an appreciable change in its crystal structure of SrTiO3 on addition of BiFeO3 in equal ratio. The surface morphology of the gold-plated sintered pellet sample recorded by SEM and EDX exhibits a uniform distribution of small grains with well defined grain boundaries. Detailed studies on nature of polarization, magnetization and variation of dielectric constant, tangent loss with temperature as well as frequency indicate the existence of multiferroicity in the studied compound. The optical property of the sample has been studied by using UV–vis spectroscopy technique. Using diffuse reflectance and absorbance data, the optical band gap of the studied sample has been estimated as 2.87 eV which is useful for photo catalytic application.

Multiple rings in the transition disk and companion candidates around RX J1615.3-3255

We search for signs of ongoing planet-disk interaction and study the distribution of small grains at the surface of the transition disk around RXJ1615.3-3255 (RX J1615). We observed RXJ1615 with VLT/SPHERE. We image the disk for the first time in scattered light and detect two arcs, two rings, a gap and an inner disk with marginal evidence for an inner cavity. The shapes of the arcs suggest that they probably are segments of full rings. Ellipse fitting for the two rings and inner disk yield a disk inclination i = 47 \pm 2 degrees and find semi-major axes of 1.50 \pm 0.01" (278 au), 1.06 \pm 0.01" (196 au) and 0.30 \pm 0.01" (56 au), respectively. We determine the scattering surface height above the midplane, based on the projected ring center offsets. Nine point sources are detected between 2.1" and 8.0" separation and considered as companion candidates. With NACO data we recover four of the nine point sources, which we determine not to be co-moving, and therefore unbound to the system. We present the first detection of the transition disk of RXJ1615 in scattered light. The height of the rings indicate limited flaring of the disk surface, which enables partial self-shadowing in the disk. The outermost arc either traces the bottom of the disk or it is another ring with semi-major axis > 2.35" (435 au). We explore both scenarios, extrapolating the complete shape of the feature, which will allow to distinguish between the two in future observations. The most interesting scenario, where the arc traces the bottom of the outer ring, requires the disk truncated at r ~ 360 au. The closest companion candidate, if indeed orbiting the disk at 540 au, would then be the most likely cause for such truncation. This companion candidate, as well as the remaining four, require follow up observations to determine if they are bound to the system.