Zeta Phase Research Articles

Effect of applied magnetic field on ZnFe alloy electrodeposition

Corrosion-resistant materials for the protection of structures are of paramount importance to the industry. This research work reports on the effects of a magnetic field applied parallel to a working electrode on the electrodeposition process of the corrosion-resistant ZnFe alloy coating. The electrochemical study of ZnFe alloy coatings prepared using an acid sulfate bath was carried out in galvanostatic mode. The results indicated that the current density and magnetic field have remarkable effects on the formation kinetics of the ZnFe deposits. The diffusion rate of the Fe ferromagnetic species subjected to mass transport accelerated under the influence of the Lorentz force (applied magnetic field); moreover, these ions were deposited in large amounts under the effect of the magnetic field. The energy-dispersive X-ray (EDX) spectroscopy analysis confirmed the modification of the Fe ion atomic concentrations in the ZnFe coatings under the influence of the magneto-hydrodynamic (MHD) convection compared to those deposited without the imposition of the magnetic field. The morphological examinations revealed that the magnetic field acted positively on the deposited layers by endowing them with homogeneous surfaces. The X-ray diffraction (XRD) analysis of ZnFe deposits demonstrated the presence of delta (δ), zeta (ξ) and eta (η) phases when there was no applied magnetic field. Furthermore, depending on the magnitude of the applied magnetic field, XRD diagrams exhibited changes in crystallographic orientation, grain size, and the electro-crystallization. These changes favor the presence of certain crystallographic phases, such as (200) and (330).

The impact of Hubbard and van der Waals corrections on the DFT calculation of epsilon-zeta transition pressure in solid oxygen.

In this study, we aim to clarify the physics that governs the unique properties of the transition between epsilon and zeta phases in solid oxygen observed at 96 GPa by using density functional theory (DFT) calculations. We first conduct the calculation using various functionals, namely, LDA, PBE, BLYP, and TPSS. The results show that LDA and TPSS predict the epsilon-zeta transition pressure at 30 GPa, while PBE and BLYP show the transition at 40 GPa. Then we include the van der Waals correction (either vdW functionals or semi-empirical methods) to improve the nonlocal effects in epsilon oxygen. The transition pressure is improved to 50 GPa. Finally, the Hubbard correction is added to enhance the localization and short-range interactions. The final epsilon-zeta transition pressure is significantly improved to 80 GPa. This demonstrates that the contribution from the local interaction is higher than the nonlocal London dispersion term at the metallization point. Moreover, this approach suggests that the van der Waals correction may correctly capture the nonlocal interaction in solid oxygen. The nonlocal effect is expected to be dominant below 20 GPa. A correct treatment of the local and nonlocal interactions on an equal footing is important to study solid oxygen.

Scalable production of visible light photocatalysts with extended nanojunctions of WO3/g-C3N4 using zeta potential and phase control in sol-gel process

Semiconductor photocatalysis for water splitting is promising approach to the current energy and environmental crisis. Although heterostructure photocatalysts exhibit enhanced photoactivity, the construction of a continuous junction at the interfaces between heterogeneous substances. In this study, visible light responsive tungsten oxide/graphitic carbon nitride composite photocatalysts with extended nanojunctions (en-WO3/g-C3N4) were synthesized through a novel sol-gel process that controlled zeta potential and sol-gel phase. The rational design of porous sphere en-WO3/g-C3N4 composite photocatalyst was constructed micropores and intimate contact between WO3 nanoparticles (NPs) and 2-dimensional (2D) g-C3N4 platelet interface. The en-WO3/g-C3N4 composite photocatalyst exhibited improved UV–vis absorbance and reduced recombination rate of photogenerated electron-hole pairs. The photocatalytic activity of hydrogen production was significantly enhanced by facile mass transfer and efficient charge-carrier separation due to direct Z-scheme mechanism. As a result, the hydrogen (H2) production of optimal en-WO3/g-C3N4 photocatalyst was obtained as much as 1060 µmol h-1g-1 which is 3.8-folds higher than g-C3N4 photocatalyst (281 µmol h-1g-1). Also, the designed en-WO3/g-C3N4 showed good stability for H2 production for 12 h under visible light irradiation.

Flexible and Transparent Flexoelectric Microphone

AbstractPVDF based flexoelectric polymers imply innumerous applications, for example, in developing flexible and transparent transducers for touch screen users. Here, a prototype flexoelectric microphone is developed and characterized. A straightforward method is adopted to fabricate the microphone device in which a film of copolymer blend is sandwiched between pair of ITO coated transparent electrodes integrated at the stretched rubber substrates. In this study, the phase represented at 1337 cm−1 of FTIR reflection spectra containing 50% α and 50% ß termed as Zeta phase which is correlated to the enhancement in its flexoelectric properties, is investigated. Here, the flexoelectric coefficient (µ33) and sensitivity (S) of 6.5 cm × 5 cm flexible and transparent laminates featuring 0 ≤ φ ≤ 1.0 blends at 100SPL is examined. The study reports the µ33 = 23.5 µC m−1 and S = 15.3 V Pa−1 for φ = 0.5 blend, which is the highest reported values for P (VDF‐TrFE) and P (VDF‐TrFE‐CTFE) polymer blends. This study is helpful in developing the flexible and transparent flexoelectric microphones for potential mobile applications.

Graphs, local zeta functions, log-Coulomb gases, and phase transitions at finite temperature

We study a log-gas on a network (a finite, simple graph) confined in a bounded subset of a local field (i.e., R, C, and Qp being the field of p-adic numbers). In this gas, a log-Coulomb interaction between two charged particles occurs only when the sites of the particles are connected by an edge of the network. The partition functions of such gases turn out to be a particular class of multivariate local zeta functions attached to the network and a positive test function, which is determined by the confining potential. The methods and results of the theory of local zeta functions allow us to establish that the partition functions admit meromorphic continuations in the parameter β (the inverse of the absolute temperature). We give conditions on the charge distributions and the confining potential such that the meromorphic continuations of the partition functions have a pole at a positive value βUV, which implies the existence of phase transitions at finite temperature. In the case of p-adic fields, the meromorphic continuations of the partition functions are rational functions in the variable p−β. We give an algorithm for computing such rational functions. For this reason, we can consider the p-adic log-Coulomb gases as exact solvable models. We expect that all these models for different local fields share common properties and that they can be described by a uniform theory.

Microstructure and Electrochemical Performance Evaluation of Zn, Zn-5 wt.% Al and Zn-20 wt.% Al Alloy Coated Steels

A comparative study has been done on three coatings obtained on steel surface using pure Zn, two Zn-Al alloy baths. The coatings obtained using both Zn alloy baths are thinner than the same obtained using pure zinc bath as Al reacts with steel and forms very thin layer of Fe2Al5 phase which hinders iron-zinc reaction. Coating obtained using pure zinc bath predominantly consists of eta (~ 100 wt.% Zn) and zeta (FeZn13) phases in combination with less extent of delta (FeZn10) and gamma (Fe3Zn10) phases, whereas coatings obtained using Zn-Al alloy baths exhibit zinc-rich phase covered by aluminum rich phase with Al2O3 at the top. Al-rich phase content is higher for Zn-20 wt.% Al alloy coating. The coatings obtained on steel surfaces using both the Zn alloy baths show better ductility compared to pure zinc bath. This can be attributed to the presence of brittle Zn-Fe alloy phase in the coating obtained using pure zinc bath. The coatings obtained using both the Zn alloy baths were found to have a greater passivation characteristics compared to the coating obtained using pure zinc bath without compromising sacrificial characteristic of the coating. Electrochemical and salt spray tests results showed 3 and 6 times improved corrosion resistance properties of Zn-5 wt.% Al and Zn-20 wt.% Al alloy coatings than the pure zinc coating.

A computational examination of the zeta and eta phases in the hafnium nitrides

AbstractThe hafnium‐rich portion of the of the hafnium‐nitrogen phase diagram is dominated by a substoichiometric rocksalt HfN1‐x, the ζ‐Hf4N3−x, the η‐Hf3N2−x, and the elemental Hf phase. The zeta and eta nitride phases have a close packed metal atom stacking sequence but their nitrogen atom ordering has yet to be concretely identified. With respect to the composition of these phases, recent computational studies of their phase stability using density functional theory (DFT) are not in agreement with reported experimental observations. In this work, we re‐examine the phase stability of the zeta and eta phases using DFT combined with enumerated searches using the known metal atom stacking sequences of these phases but with variable carbon concentration and ordering. We have found new structures for the zeta and eta phases that are now in better agreement with experimental findings. Furthermore, we report a new eta phase, ‐Hf12N7, which lies on the convex hull and has a nitrogen atom ordering that is substantially different from the zeta phase. This work also demonstrates the importance of configurational entropy in dictating the finite temperature phase diagrams in this system.

Experimental Investigation of PEG 6000/Tween 40/SiO2 NPs Stabilized Nanoemulsion Properties: A Versatile Oil Recovery Approach

The article presents a comprehensive oil recovery approach through experimental investigations and mechanistic descriptions of formulated nanoemulsion systems stabilized by {PEG 6000 (an amphiphilic polymer), Tween 40 (a non-ionic surfactant) and silica nanoparticles (SiO2 NPs)}. Initially, polymers were screened for emulsion preparation depending on their surface active properties and solubilization parameters. Oil droplets of nano-size (<500 nm) were measured by dynamic light scattering (DLS) in emulsion phase. The prolonged kinetic stabilities of nanoemulsions were inspected by zeta (ζ) potential and phase behavior studies. The mechanical barrier (steric hindrance + electrostatic repulsion) is strengthened at oil-aqueous interface by NPs inclusion occasioning augmented emulsion stability. Surface tension measurements quantified the air-emulsion interfacial behavior and lowest value of 6.42 mN/m at 343 K signifies the improved adsorption of polymer, surfactant and NPs at the interface in polymer-surfactant-NPs (PSN) nanoemulsion system. Viscosity analysis at varying temperatures concludes the pseudo-plastic behavior through fitting of flow parameters by Power law model. The hydrophobic connection of viscosification of nanoemulsion by formation of macromolecular and supramolecular structures is described mechanistically. The miscibility test infers the improved emulsification of crude oil by PSN nanoemulsion system with synergistic interactions among polymer, surfactant and nanoparticles. The core flood test yielded an additional oil recovery of 27.82% of original oil in place (OOIP) by PSN nanoemulsion, after conventional water flooding.

Thermal properties and elastic constants of ζ‐Ta4C3−x

AbstractThermal and elastic properties were measured for ceramics that contained as much as 96 wt% zeta phase tantalum carbide (ζ‐Ta4C3−x). The ceramics were produced from tantalum hydride that was milled to reduce particle size and then blended with carbon. Powders were reaction hot‐pressed at 1800°C for 2 hours under a flowing He environment, which resulted in ζ‐Ta4C3−x that was about 99% dense. The main secondary phases present in the reacted ceramic were TaC and Ta2O5. ζ‐Ta4C3−x had a thermal conductivity of 9.6 W/m·K and an electrical resistivity of 160 ± 4.2 μΩ‐cm, which are lower and higher than those of TaC, respectively. The Young's modulus was 379 ± 5 GPa and the hardness was 5.1 ± 0.7 GPa, which are also both lower than TaC. This study is the first to report the thermal properties and elastic moduli of high‐purity ζ‐Ta4C3−x.

The crystal structure and phase stability of the zeta phase in the group VB transition metal carbides: a computational investigation.

The crystal structure and composition of the zeta phase in the group VB transition metal carbides are not completely understood despite decades of experimental studies. As such, the phase rarely appears on phase diagrams of the group VB transition metal carbides. There is currently renewed interest in this phase, as tantalum carbide composites exhibit high fracture toughness in the presence of this phase. This work extends the initial computational study using density functional theory of the phase stability of the zeta phase in the tantalum carbide system, where the tantalum carbide zeta-phase crystal structure and stability were determined, to the niobium and vanadium carbides. It is shown that the zeta phases in the three systems share the same crystal structure and it is an equilibrium phase at low temperatures. The carbon atom ordering in the three different phases is explored and it is demonstrated that the zeta phase in the tantalum carbides prefers to order carbon atoms differently than in the niobium and vanadium carbide zeta phases. Finally, the properties of this crystal are computed, including elastic constants, electronic densities of states and phonon dispersion curves, to illustrate that this crystal structure is similar to other transition metal carbides.

Gemini surfactant/polymer/silica stabilized oil-in-water nanoemulsions: Design and physicochemical characterization for enhanced oil recovery

The present study deals with the synthesis and characterization of oil-in-water nanoemulsion systems for application in enhanced oil recovery (EOR). Nanoemulsions stabilized by N,N′-bis((dimethyltetradecyl)-1,6-hexanediammonium bromide) gemini surfactant (14-6-14 GS), partially hydrolyzed poly-acrylamide (PHPA) polymer and/or silica (SiO2) nanoparticle were synthesized by ultrasonication technique. Nanoparticles strengthen the mechanical barrier (electrostatic repulsion + steric hindrance) at oil-aqueous interfaces, resulting in increased ionic strength and droplet stability. Dynamic light scattering (DLS) results confirmed the formation of nano-sized (<500 nm) oil droplets within bulk emulsion phase. Kinetic stabilities of nanoemulsions were investigated by zeta potential and phase behavior analyses. Surface tension of surfactant-stabilized nanoemulsions increased with PHPA addition. However, silica particles improved adsorption ability of surfactant-polymer-nanoparticle (SPN) systems, causing decrease in surface tension. Rheological experiments were conducted as screening experiment at different temperatures to identify pseudoplastic character, and flow parameters were fitted using the Power law model. Contact angle studies showed that nanoemulsions alter the wetting characteristics of rock from intermediate-wet to favorable water-wet condition. Core-flooding studies revealed tertiary oil recovery percentage of 26.25% of original oil in place (OOIP) by chemical injections of {14-6-14 GS + PHPA + SiO2} nanoemulsions, after conventional water-flooding.

Characterizing the Image Forming Particles of Modern Ungilded Daguerreotypes Using XRD and SEM.

X-ray diffraction (XRD) and high-resolution scanning electron microscopy (SEM) have been used to characterize the silver mercury amalgam particles resting on the surface that comprise the image of five daguerreotype plates that were not gilded and that were prepared by three different contemporary daguerreotype makers. The regions of interest of the surface that were examined were overexposed, solarized, and highlight (white) areas. The XRD portion of the study shows that the two main silver mercury amalgam particles identified using the International Center for Diffraction Data PF4 + database were the Schachnerite/ζ (zeta) phase amalgam, Ag1.1Hg0.9, and the mercury silver amalgam, Ag0.65Hg0.35. On one of the daguerreotypes a third silver mercury amalgam, Moschellandsbergite, Ag2Hg3, was also identified in small concentrations. High-resolution SEM images corroborate the diffraction data and show that the crystalline nature of the silver mercury amalgam particles on all five plates to be mostly hexagonal, which would correspond to the Schachnerite/ζ (zeta) phase amalgam, and fewer rectangular solid and cubic crystals corresponding to the mercury silver amalgam.

Comportamiento mecánico de la capa de zinc sobre acero al variar calidad superficial y velocidad de enfriamiento

espanolLa corrosion del acero estructural es un problema recurrente en nuestro pais, llegando a afectar a muchas edificaciones, y la forma como se aplica el revestimiento protector de zinc es la principal causa. El presente estudio analiza el comportamiento mecanico adhesivo de la capa protectora depositada sobre acero estructural, variando la calidad superficial y la velocidad de enfriamiento del recubrimiento, los datos obtenidos en este estudio serviran para corregir o mejorar la forma de aplicacion de este recubrimiento. EnglishThe corrosion of structural steel is a recurrent problem in Ecuador, affecting many buildings, and the way in which the zinc protective coating is applied is the main cause. The present study analyzes the adhesive mechanical behavior of the protective layer deposited on structural steel, varying the surface quality and cooling rate of the coating. The applied methodology consists of characterizing the raw material (structural profiles of angular type), applying surface pre-treatments to the angular profiles by polishing, sanding, grinding and as it comes from the factory, galvanizing the angular profiles in companies A and B, measuring the layer of galvanizing, identify and measure the thickness of the phases, measure surface roughness, quantify hardness of the zeta phase, and finally, measure the adhesiveness of the coating to the substrate. From the results obtained it can be seen that the roughness allows a better anchorage of the zinc layer to the metallic surface, the high cooling speeds allow to obtain a zinc layer with more brightness, greater hardness and adherence, although it sacrifices the ductility of the layer of coating when having a more fragile behavior. The presence of defects in the phases formed by the zinc influences the mechanical behavior during the pull-off test, since it can break the substrate when it is released from the steel surface. The high thicknesses of the zinc layer give the steel a longer life and resistance to corrosion. The data obtained in this study serve to correct or improve the application form of this coating.

A computational investigation into the microstructures and stability of the zeta phase in transition metal carbides and nitrides

ABSTRACTA high-volume fraction of the zeta phase in multiphase group VB transition metal tantalum carbides has been shown to dramatically increase fracture toughness. This has been attributed to its unique nanoscale lath-based microstructure. However, what governs the microstructure and how it forms is still not well understood. In this paper, we propose a precipitation model for the formation of these phases and demonstrate that the anisotropic surface energies govern the observed zeta-phase morphology. The energetics and zeta-phase microstructure for other group VB carbides were found to be similar. In contrast, multiphase hafnium nitrides can form both thin-lath-based microstructure as well as large, single zeta-phase grains. The difference between hafnium nitride and the group VB carbides is attributed to the relative bulk free energies and low-temperature stability between the phases.

Influence of Delta Phase Morphology in Galvannealed Coated Steels on Formability

It is well known that coating microstructure can affect the frictional behavior and the formability of galvannealed steels. Several studies are available in literature describing the influence of different coating phases, such as, gamma, delta and zeta phases, on press formability. In the present study, the authors have investigated the effect of the surface morphology, specifically of the delta phase of galvannealed coating on press formability. Formability tests including conditions of (a) complete metal lockdown and (b) significant metal movement in the dies were conducted. It was found that cubic delta coatings seem to perform better (reduced splitting) in forming operations which are accompanied by significant sliding in the blankholder area than rod delta coatings. This paper presents the results of the formability evaluation for samples with different delta phase morphology and correlation with traditionally used measures for evaluation of surface behavior such as the frictional behavior and surface roughness.

A computational search for the zeta phase in the tantalum carbides

AbstractA systematic electronic structure density functional theory search for the zeta phase in the tantalum carbon system has been conducted, demonstrating that the zeta phase does indeed lie on the convex hull, establishing low‐temperature thermodynamic stability, and is structurally stable. Even though the zeta phase is most oft reported as a ζ‐Ta4C3‐x structure, these new computational results reveal that the perfectly ordered zeta phase occurs at the Ta3C2 composition and belongs to the C2/m space group. Furthermore, these results suggest that the space group may be a result of an order‐disorder transition and potential deviations from ideal stoichiometry at higher temperatures. The structure of this Ta3C2 compound can be described as ordered strings of carbon vacancies on a single carbon plane, which is also the preferred plane where additional carbon vacancies or interstitials form. These defects have modest formation energies, which provides further explanation for the small homogeneity range in zeta phase.

Cover Image, Volume 101, Issue 10

Cover Photograph: The complex phase equilibria in the tantalum carbide system allows for the development of varied microstructures with associated interfacial structures between the phases. The top‐left image is a backscattered scanning electron image of a multiphase TaC, ζ‐Ta4C3‐x, and Ta2C microstructure. The top‐right image is an atom probe reconstruction of the zeta phase laths (green) in a TaC matrix (purple). The blue regions in this atom probe reconstruction represent complex Ta‐C ion combinations that were field evaporated. The bottom left image is a focus ion beam‐serial sliced, reconstructed image of a singular TaC grain (blue) with two zeta laths (red) encased within the grain. Finally, the bottom right image is an HRTEM micrograph of an interface between the ζ‐Ta4C3‐x and Ta2C phases highlighting the stacking fault shear that creates each phase from the other. Image Credits: Robert A. Morris, Florian Vogel, Christopher R. Weinberger, and Gregory B. Thompson. DOI: 10.1111/jace.15768. image

The effect of immersion time to low carbon steel hardness and microstructure with hot dip galvanizing coating method

Along with developing necessities of metal materials, these rise demands of quality improvements and material protections especially the mechanical properties of the material. This research used hot dip galvanizing coating method. The objectives of this research were to find out Rockwell hardness (HRb), layer thickness, micro structure and observation with Scanning Electron Microscope (SEM) from result of coating by using Hot Dip Galvanizing coating method with immersion time of 3, 6, 9, and 12 minutes at 460°C. The result shows that Highest Rockwell hardness test (HRb) was at 3 minutes immersion time with 76.012 HRb. Highest thickness result was 217.3 μm at 12 minutes immersion. Microstructure test result showed that coating was formed at eta, zeta, delta and gamma phases, while Scanning Electron Microscope (SEM) showed Fe, Zn, Mn, Si and S elements at the specimens after coating.

Study of rapid thermal treatment on the microstructural evolution and surface characteristics of the electrodeposited modify Zn/TiO2 composite coatings on AISI 1015 steel

In this study, the effect of systematic homogenising annealing heat treatment on the morphology and hardness property of modified Zn-TiO2 nano-composite coatings, coated via electrocodeposition process was investigated. The morphological characteristics of the composite coatings were characterised by scanning electron microscope (SEM) equipped with energy dispersive spectrometer (EDS) and the hardness examination was carried out using Dura-scan hardness tester. The result showed that the coatings systems were homogenised with refined microstructure after annealing at 250°C and 500°C. Three different inter-metallic structures; zeta, delta and gamma phase were observed after systematic homogenising annealing at 500°C. The hardness performance of the nano-composite coatings was better after the annealing at 250°C for five hours and showed outstanding improvement after systematically annealed at 500°C.

Study of rapid thermal treatment on the microstructural evolution and surface characteristics of the electrodeposited modify Zn/TiO&lt;SUB align="right"&gt;2 composite coatings on AISI 1015 steel

In this study, the effect of systematic homogenising annealing heat treatment on the morphology and hardness property of modified Zn-TiO2 nano-composite coatings, coated via electrocodeposition process was investigated. The morphological characteristics of the composite coatings were characterised by scanning electron microscope (SEM) equipped with energy dispersive spectrometer (EDS) and the hardness examination was carried out using Dura-scan hardness tester. The result showed that the coatings systems were homogenised with refined microstructure after annealing at 250°C and 500°C. Three different inter-metallic structures; zeta, delta and gamma phase were observed after systematic homogenising annealing at 500°C. The hardness performance of the nano-composite coatings was better after the annealing at 250°C for five hours and showed outstanding improvement after systematically annealed at 500°C.