Zinc Grains Research Articles

A Scalable Method for Improving Zn Crystallinity for Low-Gassing Alkaline Batteries

The corrosion of zinc particles in alkaline environments is an energetically parasitic process that produces hydrogen gas as a byproduct. This “gassing” phenomenon is thermodynamically favorable in standard zinc-alkaline battery chemistries. Building hydrogen pressure within these primary cells can eventually lead to cell rupture, leaking the high-pH electrolyte and slurry from the cell, often destroying the electronic device that the cell was meant to power. One of the particle-level variables that can control the gassing and corrosion rate is the particle crystallinity. As the crystallinity of the zinc particles is enhanced (larger grains and fewer grains per particle), a reduction in the rate of this undesirable gassing phenomenon is expected.In this study, we demonstrate a systematic method for enhancing zinc particle crystallinity by thermally growing zinc grains. Since thermally growing zinc grains requires temperature exposure above the melting point of metallic zinc, an oxide layer is first grown around the outside of the particle surface. Oxides tend to have significantly higher melting temperatures than their metallic counterparts and this is true in the zinc/zinc oxide case where the melting temperature of metallic zinc is 420 oC and the melting temperature of zinc oxide is 1975 oC. Forming a thin oxide layer around the particle allows the metallic zinc core to be recrystallized whilst simultaneously retaining the particle shape. Following the grain growth step, the oxide layer is easily washed away with a quick acetic acid treatment. Outlined in this work is a detailed study on the scalable three-step process for growing zinc grains and enhancing bulk zinc powder crystallinity by the following: 1) oxide layer formation, 2) grain growth, and 3) oxide layer removal. Following the treatment, both achievable capacity and the corrosion rate were tested. It will be shown that the higher crystallinity particles have superior performance and lower gassing than traditional Zn powders without the treatment.

Effects of high current density on the characteristics of zinc films electroplated in ethaline electrolyte

Abstract Zinc coatings on Cu substrates were successfully electroplated from choline chloride (ChCl) with ethylene glycol (EG) based deep eutectic solvent with the current density varied from 10 to 40 mA cm−2 in air atmosphere at a temperature of 343 K. The effects of current density on the microstructure and corrosion performance were investigated in this paper. Smooth zinc coatings were obtained at the current density of 10 mA cm−2 with a current efficiency of over 90 %. With the increase in current density, there was a declining trend in the current efficiency and the surface quality of zinc coatings. Although there was no diffusion layer between the coating and substrates, all the zinc coatings still bonded well with the copper substrates. Compared with the smooth zinc coating electroplated at 10 mA cm−2, the zinc coating obtained at 40 mA cm−2 exhibited a better corrosion resistance in 3.5 wt.% NaCl aqueous solution due to the dense packing of the large number of flake zinc grains.

The effect of grain refinement on the deformation and cracking resistance in Zn–Al–Mg coatings

The present study is dedicated to explore the effect of grain refinement on cracking resistance of hot-dip galvanized Zn–Al–Mg coatings on steel substrate. In this work, we demonstrate the enhancement of plastic deformation and cracking resistance by refining the microstructure (primary zinc grains) of the Zn–Al–Mg coatings. For this purpose, two types of Zn–Al–Mg coatings namely, fine grained and coarse grained microstructures are investigated utilizing in-situ scanning electron microscopy tensile tests. Electron backscatter diffraction technique is used to illuminate the deformation behavior at the scale of grains (and/or within grains). The results reveal that the coating with fine grained microstructure possesses higher ductility and cracking resistance, whereas the coating with coarse grain microstructure induces more transgranular cracking during deformation. Moreover, primary zinc grain refinement has been shown to decrease the fraction of coarse deformation twins that serve as undesirable sites of micro-cracking. In particular, both deformation mechanisms and cracking behavior are found to be grain size-dependent in these coatings.

Mathematical Modeling of Dielectric Permeability and Volt-Ampere Characteristics of a Semiconductor Nanocomposite Conglomerate

Mathematical computer models of the permittivity of silicon-based nanostructures upon interaction with electromagnetic radiation in a wide frequency range have been developed. To implement computer models for studying the electrophysical properties of the structures under study, algorithms and a set of programs have been developed. The results of the study of materials will not only provide fundamental information about the physical effects occurring in composite nanostructures but will also be useful for solving problems related to calculations for given electrophysical problems. For a nanocomposite based on ceramics and semiconductor oxides of zinc grains, resonant bursts of permittivity are observed within a wavelength of 300–400 nm; it has been found that this is due to the presence of electronic polarization of the nanocomposite core. The paper presents the results of modeling the current-voltage characteristics of a nanocomposite based on ceramics and semiconductor grains of zinc oxide. The obtained results show that the geometrical parameters, such as the number of layers and sample width, affect the CVC of the nanocomposite, and the operating point of the CVC shifts. This may be of interest in the development of materials with desired electrical characteristics for the creation of varistors.

Effects of gelatin and polyoxyethylene ether on zinc electrowinning in a Zn(II)-NH4Cl-H2O system

Zinc-electrowinning in Zn(II)-NH4Cl-H2O systems has many advantages, such as a high current efficiency and insensitivity to F−, Cl− and metallic impurities. Additives in electrowinning are important because they influence the growth and structure of the resulting deposits and current efficiency. The effect of gelatin and polyoxyethylene ether (PEO) on the nucleation, growth mechanism, and morphology of samples are investigated through cathodic polarization, chronoamperometry, X-ray diffraction (XRD), and scanning electron microscopy (SEM) analyses during the electrowinning of Zn from an ammonium solution. The fraction-temperature diagram shows that the dominant species is ZnNH3Cl3− in the 5 M NH4Cl electrolyte when the temperature is between 298 K and 373 K. The average current efficiency reaches 95.48% in samples containing both gelatin and PEO. The surface morphology of samples with both gelatin and PEO is basically free of dendrites and shows a dense, layer-by-layer, stacked structure. The preferred growth orientation of zinc is enhanced by the presence of PEO and gelatin. The reduction kinetics of zinc are inhibited by the addition of gelatin. In the presence of gelatin and PEO, Zn nucleation and growth can be explained by the 3D growth characteristics of zinc nuclei under diffusion-limited nucleation. The arrangement and size of zinc grains are characterized through front and cross-section SEM.

Mineralogical Characterization for Selection of Possible Beneficiation Route for Low-Grade Lead–Zinc Ore of Rampura Agucha, India

Mineralogical and morphological characterization of a low-grade lead–zinc ore is carried out prior to the selection of beneficiation strategy using the combination of XRD, XRF, SEM, EPMA, microscopic, and liberation studies. Mineralogical studies indicate that the ore primarily consists of base metal sulfides (galena and sphalerite), ferruginous mineral (pyrrhotite), silicate minerals (quartz, mica, and feldspar), and graphite. Lead–zinc grains are mostly present in an interlocked state with silicate and other sulfide minerals. The sample shows an assay value of 12.14% Zn, 1.77% Pb, 57.6% ISM, 6.47% Fe, 4.19% C, and 40 ppm Ag. Based on the liberation studies, it can be predicted that beneficiation may be opted at − 75 µm as 85% liberation of value minerals is envisaged at this size range. As the ore exhibits high interlocking pattern with low-grade valuable minerals, pre-concentration is necessitated prior to flotation for further downstream operation.

Genesis and mechanism of microstructural scale deformation and cracking in ZnAlMg coatings

In-depth investigation of the microscale deformation behavior of ZnAlMg coatings is essential to reveal the origin and mechanism of cracking in these coatings. In this work anisotropic microstructural damage and cracking of multiphase Zn1.8Al1.8Mg alloy coatings produced by hot-dip galvanization process on a steel substrate have been studied extensively. Nanoindentation coupled with orientation image microscopy (OIM) is utilized to determine the local micro ductility/strength of the existing phases as well as the orientation dependent micromechanical properties of primary zinc grains. Plastic deformation and damage behavior of the coating are evaluated through in-situ tensile/bending tests, micro-digital image correlation and in-situ OIM analyses. Stress distribution fields and nucleation sites of cracks within the coating microstructure are investigated using extended finite element method. Three quantitative plastic deformation-based criteria are revealed to correlate the coating microstructure to micro-mechanical properties to comprehend the cracking phenomenon. In particular, the binary eutectic is identified as the most detrimental constituent for compatible plastic deformation. Local strain hardening exponent and Schmid factor of primary zinc grains are found to play a significant role in clarifying the cracking behavior. The results of this study are considered as an important step towards designing microstructure controlled ZnAlMg coatings with superior formability.

Evaluation of surface activity of hot-dip galvanized steel after alkaline cleaning

The surface activity of hot-dip galvanized steel was evaluated after alkaline cleaning by exposing the cleaned specimens in humid supercritical carbon dioxide, followed by extraction and quantification of the formed corrosion products. Different free alkalinities of the cleaning bath were studied to obtain information on the evolution of zinc surface activity at different levels of surface etching. Surface reactivity of uncleaned galvanized steel is restricted and local, with major contributions from grain boundaries and intermetallic particles. Formation of zinc corrosion products took place in uncleaned samples exclusively on and around these sites. Al2O3 removal by alkaline cleaning gradually increased the surface activity. The major increase in surface activity was achieved when increasing the free alkalinity from 0.5 to 4.0 mEq/L, which was shown by formation of zinc corrosion products within zinc grains. The surface activity was confirmed by applying a titanium hexafluoride pretreatment on the cleaned panels and measuring the lateral microscale uniformity of the formed layer. The uniformity increased when larger areas of galvanized steel became activated by alkaline cleaning. Reactivity of zinc is rather difficult to quantify when setting up an industrial cleaning sequence for galvanized steel. Controlled exposure of cleaned samples in humid supercritical carbon dioxide, followed by quantification of oxidized zinc, provides a straightforward method to evaluate zinc reactivity.

A unique combination of in-situ and multi-scale methodologies to analyze damage mechanisms of temper rolled zinc coating

Coated sheets for car body are assembled by spot-welding and, more and more, by adhesive bonding. Thus, during life time, the coating endures stresses which can lead to the failure of the whole bonded assembly. The behavior of the zinc coating has then to be primarily studied during tension of flat samples. Several investigation techniques, including in-situ characterizations and 3D observations, are combined to observe and understand the damage mechanisms of the zinc coating during plastic deformation. A specific attention is paid to the influence of temper rolling which is usually applied on low-carbon steel sheets after annealing and hot-dip coating. Damage is mainly observed at the boundary of large zinc grains lying on the surface plateaus, non-deformed by rolling, and often nucleates at the defects due to dendritic zinc solidification.

The Effect of Microstructural Refinement on the Localized Corrosion of Model Zn-Al-Mg Alloy Coatings on Steel

A combination of in-situ Scanning Vibrating Electrode Technique (SVET) and time-lapse immersion optical microscopy (TLM) is used to investigate the effect of microstructural refinement on patterns of localized corrosion affecting zinc-aluminum-magnesium (ZAM) galvanized coatings on steel. Model ZAM coatings comprising Zn-2.7 wt% Al-1.5 wt% Mg are produced on 0.7 mm mild steel sheet by hot dipping, and the resulting coating microstructure is systematically refined by increasing the cooling (solidification) rate from 5°C.sec−1 to 1000°C.sec−1. The intact ZAM coated surface is immersed in 0.17 M aqueous NaCl, and SVET and TLM are used to follow the resulting localized corrosive attack. TLM shows that corrosion initiates preferentially within MgZn2 and spreads laterally over the ZAM surface by preferentially following MgZn2 rich phases. In coarse microstructures, large primary zinc grains tend to deflect and constrain lateral spreading whereas in fine microstructures the smaller primary zinc grains do not. Consequently, lateral spreading rate increases with microstructural refinement. SVET shows that global corrosion rates are similar for all the ZAM coatings but that increased lateral spreading results in lower rates of through-coating penetration for the refined microstructures. These findings are explained in terms of the lateral diffusion of aggressive anolyte species.

Corrosion behavior of zinc coating electroplated at high current from a deep eutectic solvent

A Zinc coating was electroplated in choline chloride-ethylene glycol system at high current density in atmosphere. The crystal structure, surface and cross-section morphologies, chemical elements of electroplated zinc coating were analyzed by x-ray diffraction and scanning electron microscopy with line analysis, respectively. The bending and corrosion performances were also discussed in this study. The results indicate that the zinc coating presents a highly (110) texture with small flake zinc grains stacked on the surface. The zinc coating exhibits well bonding with the copper substrate though no obvious diffusion layer was observed. The corrosion performance of zinc coating displays a combine system of the electrode process and diffusion process without passivation process.

QUALITY REINFORCEMENT OF ELECTROPLATING ZINC COATINGSELECTRODEPOSITED FROM CYANIDE FREE ALKALINE SOLUTION BY POLYAMINE 70.000 AND POLYVINYL ALCOHOL 16.000

Zinc coatings have been deposited electrochemically from cyanine free alkaline solutions containing zinc ions with the presence of polyamine 70.000 and polyvinyl alcohol at different contents. The scanning electron microscope (SEM) images showed that the size of zinc grains decreased with the presence of polyamine 70.000 and polyvinyl alcohol with smoother surface of zinc coating. The polarization measurements also revealed that the coatings with the presence of polyamine or polyvinyl alcohol possessed higher value of polarity degree. This result is in good agreement with the result obtained from SEM images.

Reduction of dross in galvanized sheets through automatic control of snout positioning in continuous operation

Hot-dip galvanizing is a common industrial process in which sheet steel is immersed in a molten zinc alloy bath. After solidification, a thin zinc-rich layer is formed on the steel surface, which protects the substrate in corrosive environments. A rectangular metallic structure known as a snout is used for the transfer of the steel sheet from the furnace to the bath. In this study, an automatic control is implemented for the angular and linear position of the snout aiming to reduce surface defects in sheets (zinc grain) due to top and bottom dross. A mathematical model is developed for set point calculations, and on–off controllers are used and tested for industrial continuous operation. The results confirm the effectiveness of the positioning of the equipment enabling reduction of the transition time from around 5 min to a few seconds, resulting in a 24.57 % reduction in non-conformances due to zinc grains and 4.56 % reduction in non-conformances due to dross in the processed materials.

Micro-friction stir welding of titan zinc sheets

Aim of this research is first to evaluate the applicability of micro-friction stir welding (μFSW) to wrought zinc alloy sheets and then to improve the structural integrity of such joints. μFSW tool design was based on an algorithm that considers material and process limitations. Joining trials were performed at different feed rates. It is proven that joining by μFSW thin ZnTiCu sheets is possible and it offers extremely fine microstructures and β-phase distribution due to the mechanical fragmentation which is the outcome of the stirring. The β-phase particles were homogenized and precipitated inside deformed zinc grains and not at the grain boundaries, where they used to be in fusion welds. Electron microscopy showed that its size was limited to 150nm, which is in average 13 times smaller than the size of the 2μm that they get when sheets are TIG welded. Macroscopically, the μFSW joint mechanical properties are comparable with industrially fusion-welded material. The relative low elongation achieved, similar to fusion-welded sheets, is explained by the occurrence of three main defects: root opening, thinning and kissing bond.

Effect of Process Variables on the Grain Size and Crystallographic Texture of Hot-Dip Galvanized Coatings

A galvanizing simulator was used to determine the effect of galvanizing bath antimony (Sb) content, substrate surface roughness, and cooling rate on the microstructural development of metallic zinc coatings. Substrate surface roughness was varied through the use of relatively rough hot-rolled and relatively smooth bright-rolled steels, cooling rates were varied from 0.1 to 10 K/s, and bulk bath Sb levels were varied from 0 to 0.1 wt pct. In general, it was found that increasing bath Sb content resulted in coatings with a larger grain size and strongly promoted the development of coatings with the close-packed {0002} basal plane parallel to the substrate surface. Increasing substrate surface roughness tended to decrease the coating grain size and promoted a more random coating crystallographic texture, except in the case of the highest Sb content bath (0.1 wt pct Sb), where substrate roughness had no significant effect on grain size except at higher cooling rates (10 K/s). Increased cooling rates tended to decrease the coating grain size and promote the {0002} basal orientation. Calculations showed that increasing the bath Sb content from 0 to 0.1 wt pct Sb increased the dendrite tip growth velocity from 0.06 to 0.11 cm/s by decreasing the solid–liquid interface surface energy from 0.77 to 0.45 J/m2. Increased dendrite tip velocity only partially explains the formation of larger zinc grains at higher Sb levels. It was also found that the classic nucleation theory cannot completely explain the present experimental observations, particularly the effect of increasing the bath Sb, where the classical theory predicts increased nucleation and a finer grain size. In this case, the “poisoning” theory of nucleation sites by segregated Sb may provide a partial explanation. However, any analysis is greatly hampered by the lack of fundamental thermodynamic information such as partition coefficients and surface energies and by a lack of fundamental structural studies. Overall, it was concluded that the fundamental mechanisms behind the microstructural development of solidified metallic zinc coatings have yet to be completely elucidated and require further investigation.

Characterization of the failure behavior of zinc coating on dual phase steel under tensile deformation

► The microcracks and voids at the zinc grain boundaries are the initial sites for the coating cracking. ► The crack spacing of the fragmentally fractured zinc coating is mainly determined by the zinc grain size. ► Small zinc grain size and the c -axis direction of zinc grain parallel to the zinc surface are beneficial to the mitigation of the zinc coating delamination. The failure behavior of hot-dip galvanized zinc coatings on dual phase steels under tensile deformation is characterized with in situ scanning electron microscopy (SEM). Under tension, the pre-existed microcracks and voids at the zinc grain boundaries propagate along the zinc grain boundaries to form crack nets within the coating, leading to a segmented fracture of the zinc coating with the crack spacing approximately equal to the zinc grain size. With further loading, the coating segments partially delaminated along the interface between the top zinc layer and the inhibition layer instead of the interface between the inhibition layer and steel substrate. As the c -axis of zinc grains trends to be normal to the tensile loading direction, the twinning deformation became more noticeable, and meanwhile the coating delamination was diminished. The transverse and incline tunneling cracks occurred in the inhibition layer with tensile deformation. The existence of the brittle FeZn 13 particles on top of the inhibition layer was unfavorable to the coating adhesion.

Variable Temperature Laser Light Scattering Microscopy (VTLLSM) Studies on 10-100 μm Size High Purity Gold and Commercial Grade Zinc Grains

The VTLLS microscopy studies were made on high purity gold and commercial grade zinc grains in a temperature range of 30-230?C. Differential area ω and surface activity Sa were estimated from photomicrographs. The ω vs dT/dt (rate of heating) curve was seen to differ from those of silver and titanium. The nature of curve between normalized ω and dT/dt was seen to be non-exponential. The characteristic relation between sectorized differential area ωsec and mean temperature was examined. The present study further establishes the simplicity and versatility of the VTLLS technique, in studying the defect-sub-structure of metal particles such as Au and Zn in presence of an imposed temperature gradient in a reasonable way. As such an attempt was made to connect the ω and defect-sub-structure related parameters.

A methodology to determine anisotropy effects in non-cubic coatings

Nanoindentation in combination with orientation imaging microscopy (OIM) has been employed to quantify the anisotropic linear elastic behavior in non-cubic thin films. In particular this novel approach has been tested on zinc coatings. It is shown that the indentation modulus notably increases from 39 GPa to 124 GPa, and the hardness from 0.60 GPa to 1.54 GPa upon increasing the angle between the direction of indentation and the hexagonal [0001] normal from 3° to 84°. The method can be extended to estimate the elastic compliances of crystallites. The following elastic compliances of hexagonal zinc grains have been found: s 11 = 81.7, s 12 = 5.0, s 13 = − 60.7, s 33 = 259, s 44 = 263, all in units of 10 − 13 m 2/N.

PL enhancement at the ends/junctions of ZnO micro-rods

Enhanced photoluminescence (PL) phenomena have been observed at the ends/junctions of the hexagonal ZnO micro-rods prepared from zinc grains by the thermal evaporation method. In order to study the origin of the phenomena, finite difference time domain (FDTD) method was employed here for simulation. This enhanced PL was analysed to be attributed to the waveguide effect, and a good agreement with the enhanced PL phenomena was obtained.

工業用純アルミニウムへの亜鉛置換条件と無電解ニッケル‐りんめっき皮膜の密着性

The present authors have conducted characterization of zincate films formed as a pretreatment for electroless nickel-phosphorus coatings on commercial pure aluminum substrate (JIS A1050P-H24, 99.5 mass%Al). By using a basic solution which consisted of sodium hydroxide and zinc oxide, a zincate film formed by single zincate treatment showed coarse zinc grains of 1–2 μm in size whose (0001) planes were mainly parallel to the surface of the substrate. A double zincate treatment by using the basic solution reduced the coarse grains, and the thickness of the uniform zincate film was 30–40 nm. A commercial zincate solution which contained iron decreased the number and the size of coarse zinc grains for the single zincate treatment compared with the case of the basic solution, and the double zincate treatment formed a further thin zincate film of 10–20 nm in thickness. The single zincate treatment by using the basic zincate solution resulted in such poor adhesive strength of the electroless nickel–phosphorus plated film as to peel off the substrate due to its residual stress. Quantication of adhesive strength by 90° peeling test showed the double zincate treatment increased the adhesive strength of the plated film up to 30 N/m. In the case of the commercial zincate solution, the adhesive strength obtained by the single zincate treatment was 125 N/m. Furthermore, the adhesive strength of the plated nickel–phosphorus film was too high to conduct the peeling test in the case of the double zincate treatment by the commercial solution, where dimple patterns were observed due to ductile fracture of the substrate. Observation by transmission electron microscopy of the interface between the nickel–phosphorus plated film and the substrate showed gaps in the case of the double zincate treatment by the basic zincate solution. On the other hand, the double zincate treatment by the commercial solution eliminated gaps and a strong interface was obtained.