Zinc Vapor Research Articles

X-Ray Luminescence of ZnO Whisker Microstructures

Morphology and the optical and luminescent properties of zinc oxide (ZnO) whisker microcrystal arrays grown on sapphire using gas-transport synthesis from zinc vapors in oxygen by vapor–liquid–solid (VLS) mechanism have been studied. The arrays consisted of uniaxial microcrystals with two morphologies, combining hexagonal prisms and single-crystalline microrods. Short-wavelength boundary of transparency of the whisker microcrystal arrays occurs in a region of 385−395 nm. Total transmission in the visible and near-IR spectral range is on a level of 10–20% for layer thicknesses about 15–18 μm. The X-ray luminescence spectrum displays two bands: (i) an intense narrow excitonic peak at 388.3 nm and (ii) an about 2.5 times less intense broad band in a region of 430−600 nm. The time constant of the decay of excitonic luminescence from undoped ZnO microstructures has been estimated for the first time at about 1.1 ns (with the exciting pulse width not taken into account).

On the nature of active sites in alumina-supported zinc propane dehydrogenation catalysts

Zinc-based materials are currently considered as an alternative for toxic chromium and costly platinum catalysts for propane dehydrogenation. So far however insufficient attention has been devoted to these materials in the literature. In this work we have revealed the nature of active sites in zinc-alumina (γ-alumina) catalysts. We have investigated zinc-alumina catalysts prepared by two different methods: traditional incipient wetness impregnation and zinc chemical vapor deposition (CVD) on alumina. The catalysts were characterized by infrared spectroscopy of adsorbed CO and H2 molecules, TPR measurements and tested in propane dehydrogenation. It has been shown that high-temperature interaction of zinc vapor with alumina results in the formation of surface Zn2+ cations which are active in hydrogen dissociation and propane conversion. The amount of zinc that can be introduced by this procedure depends on the alumina dehydroxylation degree. It has been found that molecular hydrogen heterolytically dissociates on Zn2+ surface cations resulting in the formation of surface zinc hydride species. The Zn2+ sites on the surface of alumina are heterogeneous and are characterized by different band positions in the IR spectra of adsorbed CO and H2 molecules. The Zn2+ sites are subjected to reduction under the reaction conditions.

X-ray Nanospectroscopy Reveals Binary Defect Populations in Sub-micrometric ZnO Crystallites

Besides its many applications in electronics, photonics, and catalysis, ZnO has also been extensively used as the pigment zinc white ever since its introduction in the first half of the 19th century. It is shown here that zinc whites (ZnO formed through zinc vapor oxidation) form a chemically binary system, with each of the sub-micrometric crystallites belonging to either of two distinct classes. The observation of the two classes is done based on X-ray absorption nanospectroscopy and was determined to be caused by differences in the populations of anisotropic crystal defects. A theoretical assessment of the vapor oxidation synthesis method is formulated that predicts that the binary distinction in crystal defect populations is caused by local variations in synthesis parameters. As the crystal defect population in ZnO has been shown to be related to its catalytic properties, these results provide fundamental insights on the link between the intrinsic properties of zinc white and its degradation issues in oil paint.

Influence of laser beam inclination angle on galvanized steel laser braze quality

Experimental and numerical methods were applied to investigate the effect of laser beam inclination angle on spatter occurrence and laser braze quality of galvanized steels. High-speed videography revealed that spatter mostly occurred at the wetting line and melt pool front where the escaping zinc vapor came into interaction with the melt material. Application of a developed thermo-fluid simulation model considering laser-material interaction, wetting dynamics, material melting, and solidification, resulted in temperature profiles during the brazing processes for given beam angles as well as both the positions of the zinc evaporation front and wetting front. It was found that negative travel angles helped to move the zinc evaporation front ahead of the wetting front and reduce the interaction between the zinc vapor and melt pool. Experimental observations confirmed that partially removing and/or evaporating the zinc layer ahead of the wetting zone contributed to a stable process and good braze quality.

Electronic Decoupling of Graphene from Copper Induced by Deposition of ZnO: A Complex Substrate/Graphene/Deposit/Environment Interaction

AbstractThis study presents experimental data of the interactions and reactions that occur during the early stages of the growth of ZnO on graphene supported on polycrystalline copper and the subsequent changes on the electronic properties of the graphene. The combination of substrate, graphene, and intercalated species (such as oxygen and water molecules) between graphene and copper due to air exposure, together to the evaporation of metallic zinc under oxygen atmosphere, induces the electronic decoupling of the graphene from copper by the formation of a nanometric layer of copper oxide. In particular, the final stage consists in the formation of a complex interface formed by ZnO/ZnO1−x/Zn/G/Cu2O/Cu. The role of each actor is discussed in terms of a galvanic corrosion reaction of the metallic substrate where the graphene is the cathode and the initial deposition of metallic zinc accelerates the kinetics of this reaction, after which ZnO grows on the metallic zinc initially deposited. In this manner, the electronic properties of graphene can be engineered by the combination and interrelation of substrates, environment, and new‐deposited materials, revealing a more complex and realistic picture for real fabrication processes. These results may help to improve the real applicability of graphene in mass production devices.

Real-Time Detection of Weld Defects for Automated Welding Process Base on Deep Neural Network

In the process of welding zinc-coated steel, zinc vapor causes serious porosity defects. The porosity defect is an important indicator of the quality of welds and degrades the durability and productivity of the weld. Therefore, this study proposes a deep neural network (DNN)-based non-destructive testing method that can detect and predict porosity defects in real-time, based on welding voltage signal, without requiring additional device in gas metal arc welding (GMAW) process. To this end, a galvannealed hot-rolled high-strength steel sheet applied to automotive parts was used to measure process signals in real-time. Then, feature variables were extracted through preprocessing, and correlation between the feature variables and weld porosity was analyzed. The proposed DNN based framework outperformed the artificial neural network (ANN) model by 15% or more. Finally, an experiment was conducted by using the developed porosity detection and prediction system to evaluate its field application.

On the deflection behaviour of prealloyed alpha brass during sintering: in-situ bending technique and modelling

ABSTRACTDuring Supersolidus Liquid Phase Sintering the viscosity of beams affects the deflection level, thus in sintering practice also the tendency to distortion. Although the deflection value increases with decreasing viscosity, a concentration gradient from surface to centre of samples may neutralise the effect of viscosity. In this paper, the deflection behaviour of Cu-28Zn beams, manufactured from prealloyed powder, at various temperatures and times ranging from 910 to 950°C and 0–90 min, respectively, was studied. The midpoint deflection was measured by the in situ bending images. To better understand the deflection behaviour, experimental results were mathematically modelled using general deflection equations. To obtain further information, microstructural studies were performed using optical and scanning electron microscopy. It is concluded that zinc evaporation influences the chemical composition and generates a thin solid layer around the sample resulting in a parabolic deflection behaviour with temperature and non-linear with time.

Dissimilar laser brazing of aluminum alloy and galvannealed steel and defect control using interlayer

The microstructure and tensile shear strength of the joint by laser brazing between dissimilar metals of aluminum alloy and galvannealed (GA) steel were investigated. A blowhole was formed by zinc vaporization during laser brazing; the tensile shear strength was significantly affected not by intermetallic compounds (IMCs) at the filler metal/GA steel interface but by the blowhole. The vaporization of zinc was suppressed, and the blowhole was controlled by inserting a Ti interlayer. The joint strength was improved through the suppression of blowhole, the thermal deformation of the Ti interlayer, and the increase in brazed filler metal thickness by optimizing the brazing parameter. The hardness test revealed that fracture occurs preferentially in the brazed filler metal; however, as the brazed filler thickness increases, fracture begins to occur near the heat-affected zone of A5052 because the volume of filler metal increases. The maximum strength of the joint was 185 N/mm, which is about 73% of the joint efficiency to 254 N/mm of the A5052 base material, and the base material partly fractured.

Structure of the model grignard-type reagent ClZnCH3 ([formula omitted]1A1) by millimeter-wave spectroscopy

Pure rotational spectra of the 37ClZnCH3, ClZnCD3, and ClZn13CH3 isotopologues of monomeric ClZnCH3 (X̃1A1) have been recorded using millimeter-wave direct absorption techniques in the frequency range 263–303 GHz. These species were synthesized in the gas phase in a DC discharge by the reaction of zinc vapor, produced in a Broida-type oven, with 37ClCH3 (in natural chlorine abundance), ClCD3, or Cl13CH3. Five to eight rotational transitions J + 1 ← J consisting of K ladder structure were measured for each isotopologue, identifying all three species as prolate symmetric tops. The data for each isotopologue were analyzed with a symmetric top Hamiltonian and rotational and centrifugal constants determined. In combination with previous measurements of Cl64ZnCH3, Cl66ZnCH3, and Cl68ZnCH3, an rm(2) structure was determined for this organozinc compound. The bond lengths in ClZnCH3 were calculated to be rCl-Zn = 2.0831(1) Å, rZn-C = 1.9085(1) Å, and rC-H = 1.1806(5) Å, considerably different from those established from crystal structures of related species ClZnCH2CH3 and ClZnEtTMEDA. The HCH bond angle was found to be 110.5° – slightly larger than that in methane. These data serve to benchmark future structure calculations of organozinc compounds, which are widely used in organic synthesis.

Investigations on the occurrence of different wetting regimes in laser brazing of zinc-coated steel sheets

In the automotive industry, the seam edge quality of laser brazed seams is a crucial factor for the required high optical quality standards of customer-visible connections of zinc-coated car body parts. The type of zinc coating is decisive for the resulting geometry of the seam edges, which are aspired to be straight. Especially brazing of hot-dip galvanised steel with conventional brazing setup is not resulting in seam edges which fulfil the required optical quality. In this study, the wetting of copper-based filler wire on electrogalvanised and hot-dip galvanised steel sheets is analysed to increase the understanding of the influence of the wetting fronts on the seam edge quality. For this, the wetting fronts are determined in high-speed camera images and the resulting seam edges are captured by microscopic pictures. The results show that two major wetting regimes occur on both types of zinc coatings but with a different occurrence probability: one with a steep wetting front and zinc evaporation in front of wetting (“steep-angle-wetting”) and one where liquid zinc connects with the wetting front and creates a flat wetting angle (“flat-angle-wetting”). It is found that the resulting seam edge quality is mainly depending on the present wetting regime. However, for flat-angle-wetting, in the regime with insufficient seam edge quality, a self-stabilising effect is identified, which is responsible for a missing process window for brazing of hot-dip galvanised steel with sufficient seam edge quality.

Effectiveness of pre-scanning on zinc evaporation in laser spot welding of zinc-coated steels

To prevent zinc vapor–induced spatter, pre-scanning was proposed as a means to evaporate the zinc coating prior to the welding process. This paper studied the effectiveness of various pre-scanning parameters such as beam defocusing distance, beam power, scanning velocity, and geometric scanning path. The gap conditions during pre-scanning were also studied in regard to outgassing of zinc vapor during pre-scanning. To complement the experimental testing, a thermomechanical numerical model was developed and validated by comparing the size of the predicted versus the physical fusion zone. The effectiveness of the pre-scanning process was evaluated by examining the temperature distribution at both the top and faying surfaces of the stack-up under the condition that the temperature at the faying interface is greater than the zinc boiling point through the entire pre-scanning process to prevent condensation of the zinc vapor back onto the faying interface. The study found that no gap at the faying interface should be allowed with the use of pre-scanning to ensure an effective heat conduction across the faying interface. When the pre-scanning path is spiral or circular, the beam translation should initiate at the center and work outward towards the periphery. The line energy is suggested to decrease as the radius increases to avoid excessive accumulation of heat in the path center.

Novel g-C3N4 assisted metal organic frameworks derived high efficiency oxygen reduction catalyst in microbial fuel cells

The usage of efficient electrocatalyst in an appropriate way can significantly improve the oxygen reduction performance of microbial fuel cells (MFCs) cathode, which may accelerate its commercial application. In this work, isoreticular metal organic framework-3 (IRMOF-3) that modified with g-C3N4 and pyrolyzed at 850 °C (IR/CN-x%), exhibits a superior catalytic activity in alkaline electrolytes for oxygen reduction reaction (ORR). At high temperatures, after zinc evaporation, IRMOF-3 converts to a metal-free carbon skeleton that has large specific surface area. As a nitrogen source and supporting template, g-C3N4 introduces more activated nitrogen, and forms a new metal-free hierarchically porous nitrogen-doped carbon structure. As-synthesized IR/CN-50% as cathode catalyst displays a half-wave potential of 0.89 V (vs. RHE) and limit current density of 6.35 mA cm−2 in 0.1 M KOH, which is superior to commercial Pt/C (0.86 V@5.51 mA cm−2). Furthermore, IR/CN-50% shows approximately four-electron pathway and a yield of less than 4% hydrogen peroxide. Results from electrochemical tests further confirm IR/CN-50% possesses better durability and higher methanol tolerance than Pt/C. Besides, MFCs modified with IR/CN-50% present maximum power density (1402.8 mW m−3) better than the MFCs equipping with Pt/C catalyst (1292.8 mW m−3), which is a promising alternative electrocatalyst for MFCs.

Corrosion behavior and mechanical properties of cold metal transfer welded dissimilar AA7075-AA5754 alloys

Cold metal transfer (CMT) welding is a brand-new arc welding technique which shows adequate results for welding of thin sheets and dissimilar materials. Corrosion behavior of dissimilar aluminum joints should be determined in terms of predicting the effect of welding process on the possible failures in their constructions caused by corrosive agents. The present study investigates the effect of heat input on mechanical properties and corrosion rate of AA5754-AA7075 joints welded by CMT using ER5356 filler wire. Pore formation was observed not only in the weld metal but also in the partially melted zone of AA7075 base metal due to the vaporization of zinc. Increased heat input caused over aging and zinc vaporization in AA7075 base metal, and grain coarsening in AA5754 base metal consequently decreased the tensile strength. The average tensile strength of AA7075-AA5754 joints varies between 235 and 240 MPa. The ductile fracture occurred at the AA5754 base metal side in all samples. Pitting was observed as the dominant corrosion mechanism. Corrosion resistance tended to increase with increasing heat input. Heat input values between 95 and 110 J/mm are recommended for the optimization of corrosion resistance and strength.

Рентгенолюминесценция нитевидных микроструктур ZnO

The morphology, optical and luminescent properties of an ensemble of ZnO whisker microcrystals on sapphire substrate obtained by gas transport synthesis from zinc and oxygen vapors by the vapor – liquid – crystal mechanism are studied. The ensemble is formed by uniaxial ZnO microcrystallites of two morphologies: a combination of a hexagonal prism and single crystal microrods. The absorption edge of the ensemble of whisker microstructures is located in the 385-395 nm region. The total transmittance of the sample in the visible and near-infrared regions is around 10–20% with a layer thickness around 15–18 μm. The X-ray luminescence spectrum is represented by two bands: narrow peak of excitonic emission with a maximum at 388.3 nm and wide peak of defect-related luminescence in the region of 430–600 nm. The decay time constant for excitonic luminescence is around 1.1 ns (not accounted for the width of the excitation pulse), which was obtained for the first time in undoped ZnO microstructures.

Влияние отжига в газообразном цинке на люминесценцию в видимом и среднем ИК диапазонах ZnSe : Fe-=SUP=-2+-=/SUP=-

The study results of the effect of annealing in a zinc vapor atmosphere on the defect and impurity composition of iron diffusion-doped ZnSe:Te plates on the characteristics of cathodoluminescence (CL) in the IR range are described. The formation of precipitates at the boundaries of twin faults was found. It is shown that in structures with a surface iron concentration of more than 1 at%, a significant increase in the CL intensity in the IR range is observed as a result of annealing in a zinc vapor atmosphere. A partial recovery of interband luminescence in regions with a high iron concentration as a result of annealing was found.

Highly dispersed Co nanoparticles decorated on a N-doped defective carbon nano-framework for a hybrid Na-air battery.

Efficient and low-cost bifunctional electrocatalysts for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) are of vital importance in energy conversion. Herein, an excellent highly dispersed Co nanoparticle decorated N-doped defective carbon nano-framework (Co-N-C) derived from a ZnCo bimetal organic framework (bi-MOF) is reported. A high specific surface area originating from zinc evaporation facilitates the adsorption and desorption of oxygen, which promotes the accessibility of catalytic sites. The abundant Co-N-C species act as strong bridging bonds between Co nanoparticles and carbon materials which facilitate interfacial electron transfer. Co-N-C-0.5 (0.5 represents the molar ratio of Zn in the initial ZIF-67) exhibits a low overpotential gap of 0.94 V due to the number of active sites (e.g. N-doped defective carbon and the CoNx/Co composite) and fast interfacial electron transfer. In addition, a hybrid Na-air battery with the Co-N-C-0.5 material displays a low voltage gap of 0.31 V and a high round-trip efficiency of 90.0% at a current density of 0.1 mA cm-2. More importantly, the hybrid Na-air battery shows fantastic cyclability for charging and discharging due to its stable structure. Our results confirm Co-N-C materials derived from a bi-MOF as alternatives to high-cost Pt/C catalysts for ORR and OER activities in metal-air batteries.

Porous cobalt@N-doped carbon derived from chitosan for oxidative esterification of 5-Hydroxymethylfurfural: The roles of zinc in the synthetic and catalytic process

A newly developed, facile and sustainable self-sacrifice template strategy, in which zinc and chitosan were used as the sacrificial template and carbon source respectively, has been disclosed for the synthesis of a hollow Co-embedded in nitrogen-doped graphite (Co@CN) structure. This material exhibits excellent catalytic efficiency in the oxidative esterification of 5-hydroxymethylfurfural to 2,5-furandicarboxylicacid dimethyl ester that is a significant raw material for polymer synthesis. According to the experimental and calculation results, zinc as the self-sacrificial template and acid-base site regulator has significantly improved the performance of the catalyst. The high specific surface area owing to the partial evaporation of zinc and the optimization of basic and acid sites in the catalyst prove to be the main reasons for its high activity.

Zinc removal from basic oxygen steelmaking (BOS) filter cake by sintering

Zinc removal from basic oxygen steelmaking filter cake was studied by tablet testing and in a millipot under different conditions. The results from tablet testing show that coke and metallic iron in filter cake play the role of reductants to remove zinc during sintering. Zinc removal increased with increasing temperature and decreasing partial pressure of oxygen. Zinc removal reached 24.6% when a tablet of filter cake without addition of coke was sintered at 1300 °C in a nitrogen atmosphere. Addition of 3 to 9 wt% of coke breeze into filter cake enhanced the zinc removal to 60.6 to 91.4%, in an atmosphere with 0.5 vol% oxygen. The results from millipot sintering show that adding filter cake in the form of tablets was effective in removing zinc, especially when additional coke was added into the tableted filter cake. Zinc vapour generated at high temperature in the reducing atmosphere diffused out of the tablets and was carried with flowing gas, and then re-oxidized and deposited on the lower layer of sintering material in the bed. Positioning the filter cake in the form of tablets at the bottom of the sinter bed is therefore suggested as a possibility for zinc removal from filter cake.

Attempts of braze welding galvanized steel with a trifocal multi-beam laser system

The paper presents the evaluation of the brazing capabilities of the multi-beam Trifocal laser joint system made of galvanized steel DX51D with a thickness of 3 mm, covered with a protective coating of Magnelis type. The brazed joints obtained have been subjected to metallographic, strength and corrosion resistance tests in the Ascott CCIP450 salt cell. The tests have shown that there is a certain range of brazing process parameters that allow to make the correct overlap joints of high quality with small welding distortions and a narrow heat affected zone. The obtained joints are characterized by a slightly worse corrosion resistance than the basic material, and zinc evaporation by means of additional low-power laser beams improves the solder's flow.

Reversible Multiphase Transition in a BioMOF and Its Distinctive Luminescence Turn-On in Alcohol Vapor.

Solvothermal reaction of zinc meso-tetra(4-carboxyphenyl)porphyrin and 2,6-diaminopurine with zinc salt in DMF affords a three-dimensional bioMOF (1-α). Its infinite rod-shaped building block features an alternation of octahedral Zn4O and paddle-wheel Zn2 clusters bridged by 2,6-diaminopurines. The paddle-wheel Zn2 cluster undergoes reversible transformation with half into quasi-paddle-wheel Zn2 cluster and the other half into two tetrahedral mononuclear clusters upon release/uptake of guest molecules, resulting in a new phase 1-β. This single-crystal to single-crystal transformation is accompanied by luminescence on/off switching, possibly associated with the structural conversion between the porphyrin-ligand-based photoactive 1-α and the porphyrin-stacking-caused non-photoactive 1-β. Interestingly, 1-β exhibits quick luminescence turn-on in alcohol vapor instead of other volatile organic solvents by transforming into an intermediate phase 1-γ, which shows a partial luminescence enhancing likely due to the intermittent porphyrin π-π stacking. In view of experimental results and theoretical calculations, this distinctive alcohol-vapor-induced luminescence turn-on is attributed to the coordination ability to porphyrin-bound zinc ion, molecular size, and vapor pressure, in which methanol and ethanol are particularly favored.