Zinc Vapor Research Articles

Processing, growth mechanism and thermodynamic calculations of carbon foam with a hollow tetrapodal morphology – Aerographite

Aerographite is a 3D interconnected carbon foam with a tetrapodal morphology. The synthesis of Aerographite is based on a two-step process: first the production of a zinc oxide (ZnO) template in a flame transport synthesis (FTS) followed by the replication into the carbon structure in a chemical vapour deposition process (CVD). This study presents a growth model of this 3D carbon foam via analyzing the newly formed carbon structure in an interrupted synthesis by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. Moreover, the Gibbs free energy of the occurred replica CVD (rCVD) process, based on the reduction of ZnO and the formation of carbon layers, was calculated. During the CVD process the injected carbon deposits on the surfaces of the ZnO tetrapods, while simultaneously the replication into the carbon structure takes place, as a result of the reduction of ZnO into gaseous zinc and water vapour, which is due to the reaction of ZnO with the hydrogen (H2) from the injected source. This replication of the ZnO template into a carbon structure is based on an epitaxial controlled process combined with a catalytic graphitization, whereby the morphology of the template structure is replicated by the carbon. Furthermore, the influence of the growth process on the arrangement of carbon in layers and formation of defects was explained.

Analytical modeling of hot gas clean up reactor

Thermal sustainability of zinc oxide was studied. Experiments were conducted in atmosphere of syngas components. Thermogravimetrical analysis was used as the main method of investigation. Zinc oxide based sorbents were tested in methane, hydrogen, carbon and hydrogen sulphide atmospheres. Experimental data has shown intensification of reactions between zinc oxide and methane, hydrogen and carbon in temperature range from 650 to 800 °C and zinc evaporation and sorbent chemical destruction. Experiments did not reveal significant change of rate constant of reaction between zinc oxide and hydrogen sulphide. Ten probable reactions were numerically analysed. Equilibrium constants were calculated for all ten reactions. The temperature influence on equilibrium constants were calculated. Some elements of hot gas clean up desulfurization unit simulation model were also presented. Experimental rate constants for both four reactions were used in the model. Outlet gas composition and efficiency factor were calculated. Sorbent mass flow was determined. Recommended temperature range was identified.

The Replacement of Resistance Welding with Laser Beam Welding

Abstract Resistance welding has long been successfully used in the automotive industry, but nowadays, there are even more advanced technologies, such as laser beam welding, which is a much faster, more economical and flexible technology. During our work, we have mapped the possibility of replacing resistance welding with laser beam welding. Furthermore, we have found a solution to the problems occurring during laser beam welding. The biggest challenge in laser beam technology is that the zinc coating on the steel plates (required to prevent corrosion) evaporates during welding, resulting in pores, and leading to a significant reduction in weld strength. We have solved that by using spacer sheets, which allow the zinc vapour to escape from the keyhole.

Recovery of Zinc From Zinc Dross Using Pyrometallurgical and Electrochemical Methods

Recovery of zinc from its dross was investigated using electrochemical and pyrometallurgical methods. Almost 100% pure zinc was obtained using these methods. A small bench scale system for the investigating the recovery of zinc using pyrometallurgical methods was developed. The system based on the evaporation of zinc (in the dross) at 1050oC and condensing zinc vapors into pure zinc in a separate crucible. Almost pure Zn (99.95%) is obtained using this method. Recovery of zinc was also performed using electrowinning from acidified zinc sulfate bath and electrorefining of zinc dross anodes in alkaline ammonia bath. In either method different parameters including current density and deposition time were addressed. Zinc powder of almost 100% purity was obtained.

Research Regarding Capacitor Discharge Stud Welding with Tip Ignition on Galvanized Thin Sheets

Arc stud welding is a widely used welding process used to fix joints like studs, screws, pins, or similar elements on a wide variety of products. The process is mainly characterized by simplicity, high welding productivity, very good welding joint quality, low cost price, easy welding equipment and easy to handle, flexibility. The process successfully replaces other assembly methods such as: threaded assembly, riveting, classic arc welding or pressure welding and soldering. The paper proposes to establish welding technology for M5 x 35 mm steel stud with tip ignition and electric charge stored in capacitors on thin galvanized steel (s <1 mm thick). The main problem of welding galvanized steel is vaporization of zinc on the surface of the sheet which produces pores, splashes and very toxic fumes. This vaporization produces also the corrosion hazard in the surface of the sheet. Welding technology will be applied to joint stud on the cover of an air filter.

The formation and control of porosity during laser DP780 dual-phase galvanized steels

DP780 dual-phase galvanized steels with 0.8mm thickness were lap welded by 4kw continuous fiber lasers to investigate the formation of porosity. By observing the welding parameters and recording the welding process with high speed cameras, the formation mechanism of internal porosity and external porosity was proposed. Based on the formation mechanism of porosity, we established the escape channel model of zinc vapor leaving the molten pool during the welding process, by controlling the dynamic balance of the pores of each channel to reduce the welding internal pores and external porosity defects, improve the welding quality.

Recycling Zinc and Preparing High-Value-Added Nanozinc Oxide from Waste Zinc–Manganese Batteries by High-Temperature Evaporation-Separation and Oxygen Control Oxidation

In this work, zinc was recycled and nanozinc oxide with high added values was prepared from waste zinc–manganese batteries by high-temperature evaporation-separation and oxygen control oxidation. Air was used as both the oxidant and the carrier gas. Because of the relatively fast oxidation rate of zinc, this Article attempts to balance the evaporation rate and oxidation rate of zinc by adding foreign materials to contend for the oxygen or covering the zinc with porous materials to isolate the oxygen. The results showed that the oxidation rate was still fast and the effect of contending for the oxygen by adding carbon powder or lead powder was not satisfied. The zinc hull was oxidized fast in the crucible and mixed with other oxides together, while covering the porous material (wire mesh, fiber felt) can accomplish the purpose of oxygen controlling. Zinc can be evaporated and separated from the zinc hull and oxidized during the zinc evaporation process, which is a benefit for producing pure nanozinc oxides. Under the experimental condition of 1123 K heating temperature, 3 kPa air pressure, and blowing air at 723 K, using fiber mat to cover the zinc hull, the recovery efficiency of zinc is ∼98.99%, and the uniform morphology of tetrapod-shaped nanozinc oxide was prepared successfully. This study provides a novel and environmentally friendly method for the resource utilization of zinc from waste zinc–manganese batteries.

New Process Concepts Towards Area-Selective Atomic Layer Deposition and Atomic Layer Etching of Zinc Oxide

Area-Selective Atomic Layer Deposition, AS-ALD, can be initiated by local area-activation1,2 or -deactivation.3 We studied the maskless growth of ZnO from diethyl zinc and water. The method is based on the different nucleation delays that arise from precursor adsorption on OH-terminated versus that on H-terminated Si-substrate. TEOS (tetraethyl orthosilicate) and H2O were used to deposit a SiO2 seed layer by EBID (e-beam-induced deposition) in a pattern of 500x500 nm2 dots on H-terminated a-Si:H substrate. After this local activation the substrate was coated with a ZnO film in a conventional ALD reactor using 80 cycles of diethyl zinc and water vapor. In situ spectroscopic ellipsometry (Fig. 1), SEM, cross-sectional TEM and energy dispersive X-ray spectroscopy (EDX) showed good areal selectivity with ZnO growth only occurring on the SiO2 dots. This observation was corroborated by Density functional theory calculations suggesting a kinetically hindered surface reaction between diethyl zinc and H-terminated Si. Atomic Layer Etching, ALE, was also tested on a ZnO case. Current ALE technology is emerging in both thermal, isotropic and plasma-based, anisotropic approaches.4 In this presentation we will demonstrate a plasma-assisted ALE-process driven by radicals, and therefore being isotropic. The ALE-process was tested at temperatures between 150 and 250 °C. We used alternating doses of acetylacetone (Hacac) and O2-plasma intermitted by Ar-purging. The ZnO-layer thickness as measured by spectroscopic ellipsometry decreased linearly with the number of cycles. In a synergy test, we proved that only the alternated dosing of Hacac and O2-plasma caused ZnO etching, whereas Hacac and O2-plasma alone did not (Fig. 2). Preliminary infrared studies suggest that Hacac forms volatile complexes by metal oxide surface chelation (e.g. Zn(acac)2), whereas the O2-plasma step removes non-reactive Hacac fragments to refresh the surface for the next etching cycle.5 TEM- and XPS-inspection indicated no damage of the ZnO surface, good preservation of the ZnO-stoichiometry throughout the etching process, and no distinct contamination. Furthermore, we demonstrated this ALE-process to be selective over SiO2. We believe that this novel plasma-assisted ALE-concept can be extended to several other materials. [1] A. J. M. Mackus et al., Nanoscale, 4, 4477 (2012). [2] R. Chen et al., Adv. Mater., 18, 1086 (2006). [3] A. Mameli et al., Chem. Mater. 29, 921 (2017). [4] D. R. Zywotko, et al., Chem. Mater. 29, 1183 (2017). [5] M. A. George, et al., J. Electrochem. Soc., 143, 3257 (1996). Figure 1

Root cause analysis of an uncommon surface defect on galvannealed steel sheet

Abstract The galvannealed coating has been extensively used in automotive industries because of its superior performance for weldability, paintability and corrosion resistance. However, surface defect of the galvannealed coating is a major concern for the steel manufacturers and the automotive industries. The galvannealing coating process comprises several process steps and each process step may incorporate different types of defects on the coated surface. In the present study, an uncommon surface defect which looks like an indentation mark on the coating surface has been investigated. Scanning Electron Microscopy (SEM) coupled Energy Dispersive X-ray Spectroscopy (EDS) has been used to analyse the morphology and the chemical compositions. Confocal Laser Scanning Microscopy (CLSM) has been used to measure the depth and the morphology of the defect. It was found that the defect was developed on the steel sheet at the end section of the annealing furnace because of mechanical abrasion with rolls. In-depth analysis suggested that zinc vapour from zinc bath were forming zinc oxide particles in the snout region. Zinc oxide particles were able to travel to the end section of the annealing furnace due to improper snout operation. These particles were getting entrapped in-between the roll surface and the steel strip and forming the surface defect on the galvannealed steel surface.

Effect of Porosity on the Fatigue Behavior of Gas Metal Arc Welding Lap Fillet Joint in GA 590 MPa Steel Sheets

Weld defects such as blowholes and surface pores occur due to zinc vaporization during the gas metal arc welding of lap fillet joints of Zn-coated steel. In this study, the effect of porosity on fatigue behavior was investigated. A Zn-coated steel sheet with the strength of 590 MPa and a thickness of 2.3 mm was used as the base material. Three kinds of specimens with weld pore defects, such as blowholes and surface pores, were prepared and the tensile shear strength, hardness and fatigue behavior were investigated. The pore defects in the welds reduced the tensile shear strength. In the fatigue test, at higher load stresses between 122 and 366 MPa, pore defects reduced the fatigue life of the weld. However, the pore defects in the welds did not significantly affect the fatigue life of the welds at stresses below 92 MPa.

Porosity reduction through a Ti particle based gap-paste in arc welding of zinc coated steel

Gap-paste is used to create gaps, for zinc vapor release, between the zinc coated steel sheets during the arc welding process. In-depth morphology analysis of the gap after the welding is presented which shows zinc oxide formation patterns are consistent with zinc vapor release through the formed gaps. Porosity analysis for four different mask configuration shows that the porosity of the sample, with 120 μm gaps created by the paste, is reduced from ∼15% to a near zero value. The tensile shear stress test reveals that the strength of the welded samples increased by ∼30% compared to that of the samples with no gaps. High-speed camera images are also presented showing the changes in the zinc vapor release mechanism when the paste is applied, and the various stages of zinc vapor release during the welding process are discussed.

Microstructure and Mechanical Characterization of Friction-Stir-Welded Dual-Phase Brass

Friction stir welding (FSW) is an ideal process to join brass to avoid the evaporation of zinc. In the present investigation, 6-mm-thick dual-phase brass plates were joined efficiently using FSW at various tool rotational speeds. The microstructures were studied using optical microscopy, electron backscattered diffraction and transmission electron microscopy. The optical micrographs revealed the evolution of various zones across the joint line. The microstructure of the heat-affected zone was similar to that of base metal. The weld zone exhibited finer grains due to dynamic recrystallization. The recrystallization was inhomogeneous and the inhomogeneity reduced with increased tool rotational speed. The dual phase was preserved in the weld zone due to the retention of zinc. The severe plastic deformation created a lot of dislocations in the weld zone. The weld zone was strengthened after welding. The role of tool rotational speed on the joint strength is further reported.

Heterogeneous oxidation of zinc vapor by steam and mixtures of steam and carbon dioxide

The kinetics of the heterogeneous oxidation of zinc vapor by water vapor were measured in a tube flow reactor for temperatures from 800 to 1100 K, zinc vapor partial pressures up to 0.39 atm, and water vapor partial pressures up to 1.0 atm. The results extend the prior data for oxidation of zinc by water vapor from zinc partial pressures on the order of 0.01 atm to higher values appropriate for fuel production via the Zn/ZnO thermochemical cycle. Measured oxidation rates span 10−7–10−5 mol cm−2 s−1. A second order, reversible reaction rate expression r″=kZn-H2OpZn(g)pH2O-pH2Keq is developed from regression of the data and a numerical model of advective and diffusive mass transfer. The kinetic parameter kZn-H2O is a non-monotonic function of temperature with a negative activation energy for temperatures between 800 and 1050 K, consistent with prior studies. In a second set of experiments, the rate of the heterogeneous oxidation of zinc vapor by mixtures of water vapor and carbon dioxide was measured. The product gas is hydrogen rich due to faster surface reaction kinetics for oxidation with water vapor than with carbon dioxide. We conclude that it is preferable to split water and carbon dioxide in separate reactors rather than co-produce H2 and CO in a single reactor for production of synthesis gas in the Zn/ZnO solar thermochemical redox cycle.

Producing and properties of zinc dust flames

ABSTRACTPremixed and diffusion dust flames of zinc particles dispersed in the gas (particle size d10 = 4.4 µm; metal mass concentration Cf = 0.40 kg/m3) with propane additives of molar concentration Cg = (2–8)% are studied. Two different burning modes of zinc gas suspension are found. The conditions of formation of these modes depend on the burning temperature of such systems. Two-zone structure of the flame—a zinc evaporation and combustion zone and a zinc vapor condensation zone—is observed. Its origin is explained by the unique specificity of a zinc burning process in contrast to other metals—zinc vapor does not react with oxygen in the gaseous phase, therefore, ZnO molecules and zinc oxide clusters are absent in the combustion zone. The morphology and dispersive composition of the condensed zinc oxide also depend on the gas suspension’s burning mode. In a low-temperature burning mode of zinc dust, the combustion products mostly contain tetrapods, needles and nanorods of zinc oxide. At higher temperatures of the flame, zinc oxide nanorods prevail.

Kinetics of Zinc Evaporation in Inert and Reducing Gases

Kinetics of Zinc Evaporation in Inert and Reducing Gases

Effect of Annealing Atmosphere on Chromium Diffusion in CVD ZnSe

This paper examines the effect of high-temperature doping conditions on Cr2+ diffusion in polycrystalline zinc selenide. The activation energy for the diffusion process is determined in the temperature range 900–1100°C for annealing in an argon atmosphere and zinc vapor, and the mechanism responsible for the enhanced chromium diffusion in the case of doping in zinc vapor is discussed.

Microstructure development in Pulsed Laser Welding of Dual Phase Steel to Aluminium Alloy

Lap joining of aluminium 6061 and dual phase (DP 600) steel was carried out in pulse welding mode using a high power diode laser. The effect of laser parameters (laser power, scanning speed and pulse duration) on the microstructural evolution during conduction welding was studied. The large difference in thermal and physical properties of DP 600 and Al 6061 alloy results in the formation of brittle intermetallic phases along the interface of the weld zone. At a laser power of 4 kW, scanning speed of 5 mm/s and pulse duration of 10 ms the thickness of the intermetallic phase formed was found to be reduced i.e. in the range of 1- 7 µm. The porosity in the weld zone were mainly due to the entrapment of the zinc vapors during welding because of its low vaporization temperature compared to DP 600 and Al 6061 alloy. Microstructural characterization of the intermetallic phases was done using scanning electron microscopy, X-ray diffraction and the phase composition were characterized using energy dispersive spectroscopy. The micro-hardness testing was to evaluate the mechanical properties of the lap joint. A maximum hardness of 461 HV was observed along the weld- aluminium interface owing to the presence of hard and brittle Fe2Al5 and FeAl3 intermetallic phases.

Zno Micro/Nanostructures Grown on Sapphire Substrates Using Low-Temperature Vapor-Trapped Thermal Chemical Vapor Deposition: Structural and Optical Properties.

In this research, the Zn(C5H7O2)2·xH2O-based growth of ZnO micro/nanostructures in a low temperature, vapor-trapped chemical vapor deposition system was attempted to optimize structural and optical properties for potential biomedical applications. By trapping in-flow gas molecules and Zinc vapor inside a chamber tube by partially obstructing a chamber outlet, a high pressure condition can be achieved, and this experimental setup has the advantages of ease of synthesis, being a low temperature process, and cost effectiveness. Empirically, the growth process proceeded under a chamber condition of an atmospheric pressure of 730 torr, a controlled volume flow rate of input gas, N2/O2, of 500/500 Standard Cubic Centimeters per Minute (SCCM), and a designated oven temperature of 500 °C. Specifically, the dependence of structural and optical properties of the structures on growth duration and spatially dependent temperature were investigated utilizing scanning electron microscopy, X-ray diffraction (XRD), photoluminescence (PL), and ultraviolet-visible transmission spectroscopy. The experimental results indicate that the grown thin film observed with hexagonal structures and higher structural uniformity enables more prominent structural and optical signatures. XRD spectra present the dominant peaks along crystal planes of (002) and (101) as the main direction of crystallization. In addition, while the structures excited with laser wavelength of 325 nm emit a signature radiation around 380 nm, an ultraviolet lamp with a wavelength of 254 nm revealed distinctive photoluminescence peaks at 363.96 nm and 403.52 nm, elucidating different degrees of structural correlation as functions of growth duration and the spatial gradient of temperature. Transmittance spectra of the structures illustrate typical variation in the wavelength range of 200 nm to 400 nm, and its structural correlation is less significant when compared with PL.

Effects of Welding Parameters on Strength and Corrosion Behavior of Dissimilar Galvanized Q&amp;P and TRIP Spot Welds

This study investigates the effects of the main welding parameters on mechanical strength and corrosion behavior of galvanized quenching and partitioning and transformation induced plasticity spot welds, which are proposed to assemble advanced structural car elements for the automotive industry. Steel sheets have been welded with different current, clamping force, and welding time settings. The quality of the spot welds has been assessed through lap-shear and salt spray corrosion tests, also evaluating the effects of metal expulsion on strength and corrosion resistance of the joints. An energy dispersive spectrometry elemental mapping has been used to assess the damage of the galvanized zinc coating and the nature of the corrosive products. Welding current and time have the strongest influence on the shear strength of the spot welds, whereas clamping force is of minor importance. However, clamping force has the primary effect on avoiding expulsion of molten metal from the nugget during the joining process. Furthermore, clamping force has a beneficial influence on the corrosion resistance because it mainly hinders the permeation of the corrosive environment towards the spot welds. Although the welded samples can exhibit high shear strength also when a metal expulsion occurs, this phenomenon should be avoided because it enhances the damage and vaporization of the protective zinc coating.

Temperature Dependence of the Seebeck Coefficient in Zinc Oxide Thin Films

Thermoelectric devices are reliable tools for converting waste heat into electricity as they last long, produce no noise or vibration, have no moving elements, and their light weight makes them suitable for the outer space usage. Materials with high thermoelectric figure of merit (zT) have the most important role in the fabrication of efficient thermoelectric devices. Metal oxide semiconductors, specially zinc oxide has recently received attention as a material suitable for sensor, optoelectronic and thermoelectric device applications because of their wide direct bandgap, chemical stability, high-energy radiation endurance, transparency and acceptable zT. Understanding the thermoelectric properties of the undoped ZnO thin films can help design better ZnO-based devices. Here, we report the results of our experimental work on the thermoelectric properties of the undoped polycrystalline ZnO thin films. These films are deposited on alumina substrates by thermal evaporation of zinc in vacuum followed by a controlled oxidation process in air carried out at the 350-500 °C temperature range. The experimental setup including gradient heaters, thermometry system and Seebeck voltage measurement equipment for high resistance samples is described. Seebeck voltage and electrical resistivity of the samples are measured at different conditions. The observed temperature dependence of the Seebeck coefficient is discussed.