Zinc Vapor Research Articles

Characterization of zinc vapor condensation in fly ash particles using synchrotron X-ray absorption spectroscopy

Heavy metals released from municipal solid waste incinerators have become a major environmental concern. A comprehensive knowledge of metal vapor condensation in fly ash particles during incineration is essential for alleviating heavy metal toxicity, and for optimizing incineration process parameters and flue-gas cleaning systems. In this paper, the condensation of zinc vapor during flue-gas cooling in a 200 t/d fluidized bed incinerator and a 150 t/d moving grate incinerator was characterized and comparatively studied using high resolution synchrotron X-ray absorption spectroscopy (XAS). Principal component analysis, target transformation, and linear combination fitting were employed to identify zinc species directly from size fractionated fly ash particles. The chemical reaction behaviors of different zinc species were described by thermodynamic equilibrium simulations. Consistent with previous theoretical analysis and laboratory scale tests, the condensation behavior of zinc in an industrial incineration system is mainly affected by the sulfur/chlorine ratio and the inorganic particulates. It is found that zinc chloride is the major zinc species in a moving grate incinerator but willemite dominates in the fluidized bed incinerator. The high sulfur and silica/alumina particle concentration in the fluidized bed system changes the condensation propensity of vapors of Zn compounds. Adjusting the concentrations of SO2 in flue-gas can inhibit the formation of zinc chlorides. Silica, alumina, aluminosilicates, and calcium-based compounds are potential sorbents for transforming zinc to less harmful species. To prevent toxic zinc species contained in fine particles from escaping into the atmosphere, wet scrubbers are more suitable for cleaning flue-gases in moving grate incineration systems, while improving the efficiency of dust removal is more important for fluidized bed incineration systems.

Generation of metal ions in the beam plasma produced by a forevacuum-pressure electron beam source

We report on the production of metal ions of magnesium and zinc in the beam plasma formed by a forevacuum-pressure electron source. Magnesium and zinc vapor were generated by electron beam evaporation from a crucible and subsequently ionized by electron impact from the e-beam itself. Both gaseous and metallic plasmas were separately produced and characterized using a modified RGA-100 quadrupole mass-spectrometer. The fractional composition of metal isotopes in the plasma corresponds to their fractional natural abundance.

Structural determination and gas-phase synthesis of monomeric, unsolvated IZnCH3 (X̃(1)A(1)): a model organozinc halide.

The first experimental structure of a monomeric organozinc halide, IZnCH3, has been measured using millimeter-wave direct absorption spectroscopy in the frequency range 256-293 GHz. IZnCH3 is a model compound for organozinc halides, widely used in cross-coupling reactions. The species was produced in the gas phase by reaction of zinc vapor with iodomethane in the presence of a dc discharge. IZnCH3 was identified on the basis of its pure rotational spectrum as well as those of the isotopically substituted species I(66)ZnCH3, I(64)Zn(13)CH3, and I(64)ZnCD3. IZnCH3 is unmistakably a symmetric top molecule (X̃(1)A1) belonging to the C3v point group, in agreement with DFT calculations, with the following experimentally determined structural parameters: rIZn = 2.4076(2) Å, rZnC = 1.9201(2) Å, rCH = 1.105(9) Å, and ∠H-C-H = 108.7(5)°. The basic methyl group geometry is not significantly altered in this molecule. Experimental observations suggest that IZnCH3 is synthesized in the gas phase by direct insertion of activated atomic zinc into the carbon-iodine bond of iodomethane.

Modeling of Cold Metal Transfer Spot Welding of AA6061-T6 Aluminum Alloy and Galvanized Mild Steel

In this article, a three-dimensional (3D) transient unified model is developed to simulate the transport phenomena during the cold metal transfer (CMT) spot welding process of 1 mm thick aluminum AA6061-T6 and 1 mm thick galvanized mild steel (i.e., AISI 1009). The events of the CMT process are simulated, including arc generation and evolution; up-and-down movement of electrode, droplet formation and dipping into the weld pool; weld pool dynamics; zinc evaporation, and zinc vapor diffusion in the arc. The effects of the gap between the two workpieces and effects of zinc vapor evaporated from the steel surface on CMT process are studied. The results show that the arc temperature, velocity, and pressure keep changing during the CMT process, which is related to the variations of welding current, arc length, and zinc evaporation. It is found that the zinc evaporation leads to the extremely high arc pressure and the upward flow of zinc vapor near the steel surface, which would induce the arc instability and provide the drag force for the droplet impingement. The presence of the gap between the two workpieces can improve the expansion of the arc plasma, resulting in the smaller arc pressure and the more intensive upward flow of zinc vapor from the steel surface. The phenomena observed in the experiment are in agreement with the modeling results.

High temperature electrical conductivity in hydrothermally grown ZnO

AbstractResults of measurements of high temperature electrical conductivity (HTEC) in undoped hydrothermally grown ZnO single crystal are presented. HTEC measurements were made under the Zn component vapor pressure (up to 1 atm) and in the temperature range from 873 K to 1273 K. Reliable thermodynamic equilibrium in the ZnO crystal for HTEC measurements of isotherms and isobars was obtained at the temperatures higher than 873 K. Surprisingly slow chemical diffusion prolonged the high temperature measurement cycles continuously for several weeks. In our experiments the absolute value of HTEC in undoped hydrothermally grown ZnO was several orders of magnitude higher than HTEC in undoped ZnS. Slopes of HTEC isotherms varied with component vapor pressure and changed in the range from 0.2 to 0.4. For HTEC isobar in the temperature range from 1173 K to 1273 K it was found activation energy value 0.3‐0.4 eV at zinc vapour pressure 0.092 atm. Defect model for explanation of this high temperature experiment is discussed in connection with impurities. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Dissimilar Welding of H62 Brass-316L Stainless Steel Using Continuous-Wave Nd:YAG Laser

Continuous-wave Nd:YAG laser welding of H62 brass and 316L stainless steel was studied using welded joints made with different overlap configurations. Optical and scanning electron microscopies, energy-dispersive X-ray spectroscopy, and microhardness testing were used to analyze the microstructures and mechanical properties of the joints. The welded joints with the brass-on-steel overlap configuration exhibited better performance. Elemental diffusion and dissolution—in particular, the evaporation of zinc—were observed in the welded joints. Intermetallic compounds were absent in the joints because brass and stainless steel exhibit unlimited solid solubility. Finally, the microhardness of the joints was higher than that of the brass.

Fluxless arc weld-brazing of aluminium alloy to steel

In this work, joining of aluminium alloy AA6061-T6 to Interstitial Free steel using pulsed gas metal arc welding process has been attempted. The effect of different surface conditions of steel (viz, galvanized, galvanealed and uncoated) and gap between the sheets on braze joint formation have been investigated. Galvanized steel surface showed good bead width, joint formation and lap shear strength compared to the other two combinations. Interface gap has not affected the wetting behaviour significantly but presence of a gap of 300μm or so helped in escape of zinc vapour during the process there by avoiding formation of any crevice or macroporosity in the joint. Features and properties of the joint are characterized by metallography, fractography, energy dispersive spectroscopy (EDS) and lap shear tests. Load carrying capacity of Al-Galvanized steel was highest (222N/mm of seam length) compared to other combinations, aided by better wetting due to presence of Zn on the surface and minimum porosity due to interfacial gap provided during brazing.

Breakdown voltage of zinc and magnesium vapours

In this paper the findings of a study into the electrical breakdown of zinc and magnesium metal vapours are reported. The interest in the breakdown of these vapours lies in the fact that there is a growing interest in producing zinc–magnesium coated articles using physical vapour deposition. For commercial scale operations which require a high power input, a disturbance by electrical breakdown of the metal vapour is unacceptable. Hence, knowledge of the breakdown voltage and pressure relation of these elements is essential in the engineering of a set-up.To determine the breakdown of these metal vapours, a Knudsen effusion cell is built. It is proven that the flow through the Knudsen cell does not change the minimum breakdown voltage or location of this minimum, and is a reliable apparatus for determining the zinc and magnesium vapour data. The outcome of the experiments show that the minimum breakdown for zinc is in agreement with the reported data in the literature, around 350 V. Magnesium has a much lower minimum breakdown voltage than that found for zinc, around 110 V. Furthermore, the locations of the minimum breakdown voltages of both zinc and magnesium are found at around 4–7 Pa m and 1.5 Pa m respectively.

Ferromagnetic Zn/ZnO nanoparticles

Spherical zinc particles ranging in average size from 275 to 760 nm and covered with platelike zinc oxide particles on the order of 10 nm in size have been prepared by levitation-jet aerosol synthesis through condensation of zinc vapor in an inert-gas flow. The nanoparticles have been characterized by transmission electron microscopy, X-ray diffraction, BET measurements, and vibrating-sample magnetometry. The results indicate that the observed ferromagnetic ordering is due to changes in unit-cell volume on the surface of the nanoparticles. High-temperature magnetization data demonstrate that the ferromagnetic ordering of the nanoparticles persists up to 750 K.

A study of fiber laser welding of galvanized steel using a suction method

In this paper, we describe a method employing a suction device adapted to provide a negative pressure zone on the surface of the keyhole to allow the highly-pressurized zinc vapor to escape. The microstructure and properties of the lap joint were studied, and the distribution of zinc element in the joints was analyzed using synchrotron radiation X-ray. A high-speed video camera was used to record the dynamic behavior of the laser-induced plasma plume and the zinc vapor. Experimental results demonstrated that this suction method can not only facilitate venting of the high pressure zinc vapor from the molten pool and the keyhole, but also stabilizes the laser-induced plasma plume during the welding process. A lap joint with a good surface quality and excellent mechanical strength was obtained using this method.

Zinc contamination cracking in stainless steel after welding

The paper presents the results of microstructure of welded joints of hot-dip zinc galvanized steels E275D+Z and stainless steels X5CrNi18-10 (AISI 304, 1.4301) examination. Obtained results show the zinc evaporation from structural steel surface, it deposition on the stainless steel and penetration of it microstructure. The process mechanism is described and illustrated.

InZnO nanorods obtained via zinc vapour phase deposition on liquid indium seeded substrates

Indium zinc oxide nanorods (IZO-NRs) have been obtained at temperatures lower than 500 °C in a conventional CVD system, with a resulting indium concentration larger than 1%. The growth of these ternary oxide nanostructures has been obtained, simply starting from the corresponding metals, thanks to the direct deposition on the growth substrate of an In layer, which in its molten state and upon mixture with Zn acts as a growth seed. The obtained In concentration corresponds to the value required to achieve metallic behaviour and makes this ternary oxide an ideal TCO (transparent conducting oxide), while the used temperature range (<500 °C) makes this vapour phase process compatible also with commercial glass substrates, without using any expensive metal–organic precursor.

Vacuum Ultraviolet Spectroscopy and Photochemistry of Zinc Dihydride and Related Molecules in Low-Temperature Matrices

Optical absorption spectra of thin film samples, formed by the codeposition of zinc vapor with D2 and CH4, have been recorded with synchrotron radiation. With sufficiently low metal vapor flux, samples deposited at 4 K were found to consist exclusively of isolated zinc atoms for both solids. The atomic absorption bands in the quantum solids D2 and CH4 were found to exhibit large bandwidths, behavior related to the high lattice frequencies of these low mass solids. The reactivity of atomic zinc was promoted with (1)P state photolysis leading to the first recording of electronic absorption spectra for the molecules ZnD2 and CH3ZnH in the vacuum ultraviolet (VUV) region. (3)P state luminescence of atomic zinc observed in the Zn/CH4 system points to the involvement of the spin triplet state in the relaxation of CH3ZnH system as it evolves into the C3v ground state. This state is not involved in the relaxation of the higher symmetry molecule ZnD2. Time dependent density functional theory (TD-DFT) calculations were conducted to predict the electronic transitions of the inserted molecular species. Comparisons with experimental data indicate the predicted transition energies are approximately 0.5 eV less than the recorded values. Possible reasons for the discrepancy are discussed. The molecular photochemistry of ZnD2 and CH3ZnH observed in the VUV was modeled successfully with a simple four-valence electron AH2 Walsh-type diagram.

Deposition of ZnO nanostructured film at room temperature on glass substrates by activated reactive evaporation

ZnO nanostructured films were deposited on glass substrates at room temperature by activated reactive evaporation technique. Thermal evaporation of zinc at high deposition rate in presence of oxygen plasma resulted in deposition of ZnO nanostructured film with different flower-like morphologies on glass substrates. The structural and morphological properties of these nanostructured films were studied by XRD, SEM and TEM. A gas phase growth mechanism has been proposed for the formation of nanostructures. The room temperature photoluminescence spectra of these films exhibited weak ultraviolet (UV) and strong broad visible emission peaks. Further, the position of visible emission peak is found to vary with morphology of the grown nanostructured films. Photocurrent measurements indicated that these ZnO nanostructured films show high sensitivity to UV light, and hence can be used as efficient UV photodetectors.

Experimental Investigation of Vortex Flow in a Two-Chamber Solar Thermochemical Reactor

Recent advances in the field of large-scale solar thermochemical processing have given rise to substantial research efforts and demonstration projects. Many applications of high-temperature solar-thermal technology employ an enclosed cavity environment, thus requiring a transparent window through which concentrated solar energy can enter. One configuration employed is a two-cavity reactor connected by a narrow aperture, where solar flux entering through the window is focused at the aperture plane before diverging into the lower chamber, where the chemical reaction occurs. For the Zn/ZnO thermochemical cycle where Zn is solar-thermally reduced from ZnO in a high-temperature cavity environment, effective removal of the product gas stream containing zinc vapor is of paramount importance to prevent fouling by condensation on the reactor window. Two argon-jet configurations, tangential and radial, located around the circumference of the upper chamber are used to control the gas flow within the reactor cavity. First, the tangential jets drive a vortex flow, and second, the radial wall jet travels across the window before converging at the reactor center line and turning downward to create a downward jet. The tangential jet-induced flow creates a rotating vortex, contributing to overall flow stability, and the radial jet-induced downward flow counters the updraft created by the vortex while actively cooling and sweeping clear the inner surface of the window. Flow visualization in a full-scale transparent model of the reactor using smoke and laser illumination is employed to characterize the effectiveness of aerodynamic window clearing and to characterize the processes by which a vortex flow develops and breaks down in a two-chamber solar reactor geometry. Based on a large dataset of flow visualization images, a metric is developed to define vortex stability over a wide range of flow conditions and identify an ideal operating range for which a vortex formation path is established that maintains stable flow patterns and removes product gases while minimizing the use of argon gas. The predominant influence of vortex instability and breakdown is identified and examined for the case of a beam-down, two-chamber solar reactor geometry.

Study of metallurgic and mechanical properties of laser welded heterogeneous joints between DP600 galvanised steel and aluminium 6082

This investigation focuses on the feasibility of heterogeneous welded joints between DP600 steel and aluminium 6082. The process adopted used a power laser in two modes: keyhole welding and laser-induced reactive wetting. All the results of the study show that the use of laser welding of galvanised sheets, in the keyhole mode, can achieve a joint shear strength of 140MPa by optimising the process parameters and controlling the penetration, which must be limited to 600μm. Another key factor with this welding method is control of the inter-sheet gap, which was achieved by using a clamping system that ensured a rigid joint while maintaining a constant gap sufficient to allow the escape of zinc vapour. This approach enabled an increase in shear strengths of 200MPa to be obtained and the zinc acted as a beneficial factor to the welding process. With the laser-induced reactive wetting mode, the joint between galvanised sheets was more brittle because of the formation of a non-uniform reaction layer. With this mode, the presence of zinc is a factor that limits the growth of the reaction layer and, at the same time, leads to a mechanical deterioration of the joint; test results indicate that mechanical strength was limited to about 80MPa.

Investigation into Heat Treatment and Residual Stress in Laser Clad AA7075 Powder on AA7075 Substrate

The laser cladding of AA7075 powder onto a AA7075 substrate was conducted to evaluate the effect of heat treatment and to measure residual stress between the clad layer and substrate to better understand the effect of laser cladding. The microstructure formed in the clad region was characteristic of a high cooling rate, which is typical for laser cladding. The heat-affected zone (HAZ) showed coarser precipitates when compared with the substrate and was attributed to the heating from the laser. A solution heat treatment followed by aging was employed to restore the strength in the HAZ. Nanohardness traverses of the clad and substrate was performed and it was shown the hardness in the 7075 clad layer was lower than the substrate both pre- and post-heat treatment and was attributed to the vaporization of zinc and magnesium. Neutron diffraction was employed to measure the residual stress both before and after heat treatment. The residual stresses formed in the clad layer were tensile and about 50 MPa in magnitude; heat treatment increased the stress level to approximately 100 MPa.

JOINING THE COMBINATION OF AHSS STEEL AND HSLA STEEL BY RESISTANCE SPOT WELDING

Abstract The paper deals with the optimization of parameters of resistance spot welding and quality analysis of welded joints made by combination of galvanized Advanced High Strength Steel and High Strength Low Alloy steel. It is an advanced material combination utilized in automotive industry to reduce weight of the vehicle body and consequently lowering the fuel consumption to achieve the lowest possible fuel consumption, high active and passive safety of passengers while decreasing the amount of emission. The quality of welded joints was evaluated by destructive tests and non-destructive tests. The shear tensile test according to STN 05 1122 standard was used. Some samples were prepared for metallographic analysis, where the influence of the welding parameters on the structure of welded joint and occurrence of pores in the weld metal caused by evaporation of zinc from the coating was observed.

Weldability and keyhole behavior of Zn-coated steel in remote welding using disk laser with scanner head

Zinc-coated steels are widely used in automobile bodies. Laser welding, which offers a lot of advantages over the conventional welding with metal active gas welding, CO2 arc, etc. in terms of improved weld quality, high-speed, and easy automation, has been developed for cars. However, in laser lap welding of zinc-coated steel sheets without gaps, defects such as underfilled beads or porosity were easily formed due to higher pressure of zinc vapor trapped in the molten pool because of the lower boiling point of zinc (1180 K) with respect to the melting point of steel (Fe, 1803 K). Laser lap welding results of two Zn-coated steel sheets have been reported. However, there are not enough data for welding of three Zn-coated steel sheets. Therefore, to understand laser lap weldability of three Zn-coated steel sheets, lap welding of two or three sheets with and without gaps was performed using 16 kW disk laser apparatus with a scanner head, and molten pool motions, spattering, and keyhole behavior during welding were observed by high-speed video cameras and x-ray transmission real-time imaging apparatus. Lap welding of three steel sheets was difficult but acceptably good welds were produced in sheets with upper and lower gaps of 0.1 and 0.1 mm, 0.1 and 0.2 mm, or 0.2 and 0.1 mm, respectively. Bubble generation leading to porosity formation was observed, and it was confirmed that welding phenomena were different depending upon the gap levels.

Modeling the Formation and Chemical Composition of Partially Oxidized Zn/ZnO Particles Formed by Rapid Cooling of a Mixture of Zn(g) and O2

A model and its numerical implementation are presented which describe the formation of mixed Zn/ZnO droplets by rapid cooling of a mixture of zinc vapor and oxygen. The model incorporates a nucleation step producing pure metal droplets of a fixed size and three condensation-like processes determining the further growth of the droplets by adding metal atoms and oxygen. Properties to characterize the resulting droplet population are obtained from the model. Examples such as the number density of particles, their average chemical composition and surface area, or the particle mass distribution are presented. The model is verified on a qualitative level by comparing with experimental data the influence of the quench rate and the initial partial pressures of the reactants on the average chemical composition of the product. The model predicts, conforming qualitatively with experimental findings, that increasing the quench rate has little influence on the chemical composition of the products but that decreasing the initial partial pressures of zinc results in less oxidized products, thus, a higher average zinc content.