Zinc Vapor Research Articles

Effects of welding current and torch position parameters on minimizing the weld porosity of zinc-coated steel

This study involves an investigation of the effects of the welding current and torch position parameters, including the travel angle, torch-aiming position, and work angle, on reducing the weld porosity in the cold metal transfer (CMT) welding of hot-dip galvannealed steel in the lap-joint configuration. The effects of the welding parameters on the weld porosity are investigated through statistical analysis, high-speed imaging of the weld pool behavior, welding signal analysis, and scanning electron microscopy (SEM) analysis. The magnitude of the welding current influences the weld porosity and weld pool behavior because the current determines the arc force, the heat input, the amount of zinc vaporization, and the weld pool viscosity. The torch position parameters also have considerable effects on the weld porosity because they determine where the arc, arc force, and heat input are concentrated. A response surface model relating the welding parameters and the amount of weld porosity is estimated, and the optimum welding conditions and a suitable welding range are determined on the basis of the estimated model to minimize the weld porosity in the CMT welding of hot-dip galvannealed steel.

Examining transition metal hydrosulfides: The pure rotational spectrum of ZnSH (X̃2A').

The pure rotational spectrum of the ZnSH (X̃2A') radical has been measured using millimeter-wave direct absorption and Fourier transform microwave (FTMW) methods across the frequency range 18-468 GHz. This work is the first gas-phase detection of ZnSH by any spectroscopic technique. Spectra of the 66ZnSH, 68ZnSH, and 64ZnSD isotopologues were also recorded. In the mm-wave study, ZnSH was synthesized in a DC discharge by the reaction of zinc vapor, generated by a Broida-type oven, with H2S; for FTMW measurements, the radical was made in a supersonic jet expansion by the same reactants but utilizing a discharge-assisted laser ablation source. Between 7 and 9 rotational transitions were recorded for each isotopologue. Asymmetry components with Ka = 0 through 6 were typically measured in the mm-wave region, each split into spin-rotation doublets. In the FTMW spectra, hyperfine interactions were also resolved, arising from the hydrogen or deuterium nuclear spins of I = 1/2 or I = 1, respectively. The data were analyzed using an asymmetric top Hamiltonian, and rotational, spin-rotation, and magnetic hyperfine parameters were determined for ZnSH, as well as the quadrupole coupling constant for ZnSD. The observed spectra clearly indicate that ZnSH has a bent geometry. The rm(1) structure was determined to be rZn-S = 2.213(5) Å, rS-H = 1.351(3) Å, and θZn-S-H = 90.6(1)°, suggesting that the bonding occurs primarily through sulfur p orbitals, analogous to H2S. The hyperfine constants indicate that the unpaired electron in ZnSH primarily resides on the zinc nucleus.

Numerical and experimental investigation of vacuum-assisted laser welding for DP590 galvanized steel lap joint without prescribed gap

The high-pressurized zinc vapor, which was developed at the interface of the two metal sheets due to the lower boiling point of zinc (around 906 °C) than the melting point of steel (over 1500 °C), led to the formation of macro-blowholes. Vacuum-assisted laser welding was a powerful approach to obtain a defect-free weld bead. The laser welding process was simulated to observe the dynamic or zinc vapor. The stability of laser welding was analyzed according to simulated results. The zinc distribution which was measured by EDS experiment also represented the influence of ambient pressure on welding stability. The bearing load for weld beads under different ambient pressure was measured by shear strength test. A defect-free continuous laser weld bead could be obtained under 3 kPa ambient pressure.

Effect of Bonding Temperature on Microstructure and Mechanical Properties of WC–Co/Steel Diffusion Brazed Joint

In this work, the diffusion brazing of AISI 4145 steel to WC–Co cemented carbide using RBCuZn-D interlayer with bonding temperature values of 930, 960, 990 and 1020 °C was studied. The microstructure of the joint zone was evaluated by scanning electron microscope (SEM) and X-ray diffraction (XRD). Vickers microhardness and shear strength tests were performed to investigate mechanical behaviors of the brazed joints. The XRD and SEM results indicated that with increase of bonding temperature, the elements readily diffused along the interface and formed various compounds such as γ, α and β and Co3W3C. The results also showed that with the increase of bonding temperature from 930 to 960 °C, a sound metallurgical bond was produced, however in higher bonding temperatures (990 and 1020 °C) a decrease in mechanical properties of the joints was observed which could be due to the excessive zinc evaporation, interface heterogeneity and voids formation. The maximum shear strength of 425 MPa was obtained for the bond made at 960 °C.

Health hazards resulting from exposure to zinc and its inorganic compounds in industry

This article deals with health risks resulting from exposure to zinc and its inorganic compounds in industry. The main source of zinc exposure are fumes generated during thermal and chemical processes, mainly zinc oxide fume formed by immediate oxidation of metallic zinc vapor formed during high-temperature processes, as well as dust generated during the mechanical processing of zinc-containing materials. It is recognized that zinc ions are responsible for health effects of exposure to dust/fumes of the majority of zinc compounds, and the final effect of exposure depends on the degree of dispersion of dusts/fumes suspended in the air. Since the effects of exposure depends on the particle size, occupational exposure limits have began to be established separately for respirable and inhalable fractions. A critical effect of acute exposure to respirable fraction is a "fume fever" which in chronic exposure occurs as an effect associated with recurrent symptoms of acute poisoning. Impaired lung function and asthma symptoms are considered to be the main effects of exposure to inhalable fraction. Due to the limited number of the available data it is not possible to assess carcinogenicity, reproductive toxicity and teratogenicity of zinc and its compounds. The aim of the study was to analyze the major health hazards resulting from occupational exposure to zinc and its inorganic compounds in the context of their physico-chemical properties, a wide range of applications and occupational exposure data. Med Pr 2017;68(6):779-794.

Electric arc furnace dust as an alternative low-cost oxygen carrier for chemical looping combustion

The relative abundance and low cost of electric arc furnace dust (EAFD) make it a viable oxygen carrier for chemical looping combustion (CLC) system. Under a reducing agent, zinc ferrite (ZnFe2O4) phase in EAFD releases zinc vapor in a complex gas-solid reaction. In an effort to suppress the emission of zinc vapor, the reaction mechanism of ZnFe2O4 prepared as an oxygen carrier in a redox cycling test is primarily discussed, as well as the issue of coupling with an inert Al2O3 support. The study focused the investigation on redox cycling behavior and CO2 conversion in ZnFe2O4/Al2O3 and EAFD/Al2O3 systems using a thermogravimetric analyzer (TGA) and fixed-bed reactor (FxBR). In a lab-scaled semi-fluidized bed reactor (semi-FzBR) of EAFD/Al2O3 as an oxygen carrier system, a high CO gas yield approximately 0.98 after fifty redox cycles is also experimentally obtained. It can be anticipated that the use of EAFD/Al2O3 system as an oxygen carrier in a reversible CLC process could be economical and environmentally beneficial.

X-Ray Diffraction Analysis of ZnO Particles Prepared by Microwave Plasma

The aim of this work is to use x-ray diffraction (XRD) technique to analyze ZnO particles prepared by the reaction between the zinc vapor and oxygen within microwave plasma. The microwave plasma was created by the interaction between the 1200-W 2.45-GHz microwave, the conductive material, and the argon-oxygen gas mixture. Due to the high effective temperature of the plasma, it was thermodynamically and kinetically possible to generate zinc vapor from the solid zinc and then reacted with the oxygen in the gas mixture to form ZnO particles. The synthesis of ZnO in the microwave plasma has been done for 10 to 15 minutes. The XRD results show that the synthesized ZnO samples have wurtzite structure. Moreover, the increasing of synthesis time from 10 to 15 minutes affects the lattice constants, the crystallite size, and the magnitude of strain in ZnO crystals.

Influence of SiC addition on the properties of andalusite brick used in EAF dust recovery kiln

The aim of this study is to determine the properties of fired andalusite brick with silicon carbide addition. Brick samples were prepared by mixing, shaping, drying, and sintering at 1300 °C in a commercial tunnel kiln. The bulk density, apparent porosity, gas permeability, and cold crushing strength of fired brick samples were determined. Slag penetration test was investigated by static cup test with electric-arc furnace (EAF) dust recovery blend. The effects of SiC additions on the penetration properties of the samples have been investigated. The addition of SiC significantly affects the reduction behavior of metallic ingredients in EAF dust recovery on the brick surface. SiC shows the self-glazing properties in the brick and behaves as an antibarrier for zinc vapor.

Dissimilar Diffusion Brazing of WC-Co to AISI 4145 steel using RBCuZn-D interlayer

Diffusion brazing mechanism of two dissimilar alloys WC-CO and AISI 4145 steel by RBCuZn-D filler metal with different bonding times of 1, 2.5, 5, 7.5, 10 and 12.5min was investigated. Shear strength and microhardness tests were performed to evaluate mechanical properties. The microstructure and compositional changes in the joint zone was characterized using scanning electron microscopy, X-ray diffraction and energy dispersive spectroscopy. The results revealed that there are γ, α and β solid solution phases and Co3W3C intermetallic compound in the joint zone of the bonds made in 5 and 10min due to the inter-diffusion of elements across the interface. The optimum shear strength of 412MPa was achieved for the bond made in 5min. With increase of bonding time to more than 5min, a reduction in the strength occurred which may be due to the increase in formation of brittle Co3W3C compound, zinc evaporation and heterogeneity of interface. It is also indicated that hardness mapping exposed the microstructure heterogeneity very well while linear hardness measurement was incapable to show the variations accurately.

A study of keyhole behavior and weldability in zero-gap laser welding of zinc-coated steel sheets at subatmospheric pressures

Experiments were conducted to investigate how the keyhole responds to a decrease in the ambient pressure using a coaxial observation method in the laser welding of zinc-coated steel sheets. To understand the effect of zinc coating on keyhole dynamics, both zinc-coated and uncoated DP 590 steel sheets were studied using a 2kW multi-mode fiber laser in a zero-gap lap-weld configuration. Two energy density conditions (1830W, 12.5mm/s and 1230W, 21.2mm/s) and four ambient pressures (101.3, 10, 1 and 0.1kPa) were considered systematically. For these conditions, time-averaged 3-D keyhole shapes were reconstructed by analyzing top and bottom surface video images. This study showed that zinc evaporation was much more intensified than the evaporation of steel at subatmospheric pressures, which made the keyhole highly fluctuating and elongated in the welding direction for the zinc-coated steel. Also, the bottom aperture opening time increased as the ambient pressure was decreased due to the enhanced effect of evaporation, which led to less energy absorption and smaller melt pools. The weld quality became poorer as the spacing of weld chevrons were wider and more erratic, and more fumes with less light emission were observed at reduced ambient pressures.

Utilization of electric arc furnace dust as regenerable sorbents for the removal of hydrogen sulfide

Abstract The possibility of using electric arc furnace dust (EAFD) as regenerable sorbents to adsorptive hydrogen sulfide was studied. To avoid the releasing of zinc vapor and leaching of heavy metal matter, the addition of Al 2 O 3 was used as inert stabilizer to suppress the volatilization of zinc vapor and generate a more stable chemical forms in EAFD. The results of redox behavior and toxicity characteristic leaching procedure show that Al 2 O 3 are excellent stabilizers for EAFD of industrial waste. Multi-cycle tests of sulfidation/regeneration showed that the prepared EAFD/Al 2 O 3 sorbents can be regenerated and thus reused after the regeneration process. After ten sulfidation/regeneration cycles, the sulfur capacity of the tenth cycle remained approximately on a level of 79% of the sulfur capacity in the first cycle. The results based on the material characterization and sulfidation/regeneration performance evaluation showed that EAFD/Al 2 O 3 sorbent has desirable physical and chemical properties for the desulfurization of simulated syngas at high-Temperature range. Therefore, EAFD with addition of Al 2 O 3 has a potential utilization for the removal of hydrogen sulfide.

Remote laser welding of zinc coated steels in a zero-gap lap joint configuration

Zinc coated steels have been increasingly used in the automotive industry due to their excellent corrosion resistance. However, the presence of zinc coating on the steel sheet poses significant challenges in the laser welding process. Zinc has a lower boiling point (906 °C) than the melting point of steel (>1300 °C). When zinc coated steels are laser welded in a zero-gap lap joint configuration, a highly pressurized zinc vapor is readily produced at the faying interface. Without special precaution, a large amount of spatter and blowholes can be produced, which can degrade the weld quality and mechanical performance of the welds. The state-of-the art approach to mitigate the negative impact of zinc vapor is to employ a series of dimples having an approximate height of 0.1–0.2 mm to provide a channel along the faying interface for the resulting zinc vapor to escape. In this study, an innovative remote laser welding process has been developed to directly weld zinc coated steels in a zero-gap lap joint configuration without the use of dimples. Experimental results show that high-integrity welds can be achieved with excellent mechanical performance. The new process can dramatically reduce the cycle time and manufacturing cost by eliminating the dimpling process.

Bronze Alloy Development for Zinc Vapor Capture

After gamma-emitting 65Zinc was detected in a vacuum pumping system contained in a tritium glovebox, a series of experiments were undertaken to develop a method and material to trap zinc vapors in an area that is more suitable for preventing dose to workers. In this study, bronze alloys with 0–30% tin were prepared using a powder metallurgical process and exposed to three levels of zinc vapors. All of the alloys demonstrated acceptable zinc gettering capacity; however, low tin content bronzes are considered for further testing.

Reconstruction of perfect ZnO nanowires facets with high optical quality

ZnO nanowires were grown on sapphire substrates using metalorganic chemical vapor deposition. The samples were subsequently annealed under zinc pressure in a vacuum-sealed ampoule, at temperature ranging from 500 to 800°C. The originality and the main motivation to provide a zinc–rich atmosphere were to prevent the out-diffusion of zinc from the nanowires. In doing so, the perfect structural properties and the morphology of the nanowires are kept. Interestingly, photoluminescence experiments performed on nanowires annealed in a narrow window of temperature [580–620°C] show a spectacular improvement of the optical quality, as transitions commonly observable in high quality bulk samples are found. In addition, the intensity of the so-called “surface excitons” (SX) is strongly decreased. To accurately investigate the chemical modifications of the surface, XPS experiments were carried out and show that zinc hydroxide species and/or Zn(OH)2 sublayer were partially removed from the surface. These results suggest that the annealing process in zinc vapor helps to properly reconstruct the surface of ZnO nanowires, and improves the optical quality of their core. Such a thermal treatment at moderate temperature should be beneficial to nanodevices involving surface reaction, e.g. gas sensors.

Zinc ions enhanced nacre-like chitosan/graphene oxide composite film with superior mechanical and shape memory properties

Bio-inspired by the hierarchical structure and remarkable mechanical properties of natural nacre, nacre-like N-succinyl chitosan (NSC)-graphene oxide (GO) composite film was fabricated via zinc ion cross-linking and evaporation process. NSC and GO were used as the building “mortar and bricks,” which rapidly self-assembled into composite hydrogel (NSC/GO-Zn) via zinc ions cross-linking, and the hierarchical NSC/GO-Zn composite film was obtained thereafter by evaporation. A series of NSC/GO-Zn composite films with different GO concentrations was fabricated with the layered structure, as confirmed by scanning electron microscopy. Zinc ion-enhanced hierarchical NSC/GO-Zn composite film exhibited remarkable mechanical properties (strength of 212.6±10.1MPa and toughness of 2.51±0.08MJ·m−3). Unique shape memory response to alcohols was demonstrated by the composite film due to the presence of the chitosan, which has a significant ability to desorb/absorb water. Furthermore, a remarkable broad-spectrum bactericidal property of the NSC/GO-Zn composite film was observed through E. coli and S. aureus exposure. These features indicated that NSC/GO-Zn composite film has inherent properties that can be used in protection, aerospace, and biological materials.

Laser dimpling process parameters selection and optimization using surrogate-driven process capability space

Remote laser welding technology offers opportunities for high production throughput at a competitive cost. However, the remote laser welding process of zinc-coated sheet metal parts in lap joint configuration poses a challenge due to the difference between the melting temperature of the steel (∼1500°C) and the vapourizing temperature of the zinc (∼907°C). In fact, the zinc layer at the faying surface is vapourized and the vapour might be trapped within the melting pool leading to weld defects. Various solutions have been proposed to overcome this problem over the years. Among them, laser dimpling has been adopted by manufacturers because of its flexibility and effectiveness along with its cost advantages. In essence, the dimple works as a spacer between the two sheets in lap joint and allows the zinc vapour escape during welding process, thereby preventing weld defects. However, there is a lack of comprehensive characterization of dimpling process for effective implementation in real manufacturing system taking into consideration inherent changes in variability of process parameters. This paper introduces a methodology to develop (i) surrogate model for dimpling process characterization considering multiple–inputs (i.e. key control characteristics) and multiple–outputs (i.e. key performance indicators) system by conducting physical experimentation and using multivariate adaptive regression splines; (ii) process capability space (Cp–Space) based on the developed surrogate model that allows the estimation of a desired process fallout rate in the case of violation of process requirements in the presence of stochastic variation; and, (iii) selection and optimization of the process parameters based on the process capability space. The proposed methodology provides a unique capability to: (i) simulate the effect of process variation as generated by manufacturing process; (ii) model quality requirements with multiple and coupled quality requirements; and (iii) optimize process parameters under competing quality requirements such as maximizing the dimple height while minimizing the dimple lower surface area.

Preparation of nanosized zinc oxide by vacuum oxidation and kinetic study of oxidation

Nanosized zinc oxide was prepared with a vacuum oxidation method by using hot-dip galvanizing slag as the raw material and air as the oxygen source. The oxidation kinetics curves of zinc vapor at different pressures were plotted by thermogravimetry, and the morphology of ZnO was observed by scanning electron microscopy. The nanosized ZnO products were hexagonal wurtzite crystals with the purity ≥99.98. When parabolic kinetics occurred, the ZnO products were granular, amorphous, tetra-needle-like or single needle-like. In the case of linear kinetics, the products were short tetra-needle-like or needle-like crystals. Zinc oxidation was controlled by the contracting spherical model R3 initially and the three-dimensional diffusion model D4 thereafter, with the apparent activation energies of 101.3–122.1 kJ/mol and 111.2–143.4 kJ/mol respectively.

Processing of converter slurry by coking with coal

Processing of the industrial waste formed at steel plants is of great importance. In the converter production of steel, 12–25 kg of fine dust is formed in the production of 1 t of steel, depending on the composition of the raw materials, the furnace design, and the smelting conditions. Wet cleaning of the waste gases converts the dust into a slurry containing 46–50% Fe2O3. It is difficult to process such slurry because of its high water content, the small particle size, and the presence of zinc oxides. Standard dehydration technology is complex. It is also associated with thermal drying, which poses an explosion risk, while briquetting or granulation does not resolve the problem posed by the presence of zinc oxides and is complicated by a lack of acceptable binders. Researchers at Siberian State Industrial University have developed complex conditioning of iron-bearing slurry by nonthermal adsorptive dehydration and subsequent thermochemical agglomeration, with simultaneous reduction of the iron and zinc oxides. Adsorptive dehydration to a moisture content of 2‒3% is possible by contact with porous lignite semicoke produced by Termokoks technology. Then the lignite semicoke is pneumatically separated and sent for use in energy systems, while the iron-bearing product is mixed with GZh or Zh coal and sent for thermooxidative coking in a furnace of special design (an annular furnace with a rotating hearth), where large and strong pieces of ferrocoke are obtained at 1050–1100°C. The ferrocoke contains 55–60% of the iron-bearing product. The oxides of iron and zinc are almost completely reduced. The zinc passes to the vapor phase and is removed with the combustion products of the volatile coking components. On cooling to 850°C, the zinc vapor condenses. The ferrocoke obtained is suitable for blastfurnace use, thereby reducing the consumption of sinter and coke. The heat obtained on cooling the ferrocoke and the energy of the combustion products after the deposition of zinc are utilized in a gas-turbine system.

Influence mechanism of zinc on the solution loss reaction of coke used in blast furnace

The influence mechanism of zinc on the solution loss reaction of coke at high temperature was studied using the method of liquid phase adsorption. The microcrystalline structure, pore structure, micro morphology and optical texture of coke were analyzed by X-Ray diffraction (XRD), BET, scanning electron microscopy (SEM) and optical microscopy in present research. The results show that zinc can increase the coke reactivity index (CRI) and decrease the coke strength after reaction (CSR). Furthermore, the CRI is the highest, as well as the CSR is lowest and the coke structure is severely damaged when the enriched zinc content in coke reaches to 1.17%. The results of XRD and polarizing microscopy show that the zinc catalysis on the solution loss reaction of anisotropic texture with higher degree of graphitization is larger than that of the isotropic texture. Combined with BET and optical panorama, it can be reveals that zinc can promote the generation and combination of coke pores during its catalysis process on gasification reaction, resulting in the increase of specific surface area and volume of micropores, which in turn provides favorable conditions for the permeation of zinc vapor and the kinetics condition of gasification reaction, thereby the reaction is further intensified. Meanwhile, large connected pores and honeycomb cavern caused by catalysis reduce the coke strength greatly. A compound phase containing zinc was not found in the reacted Zn-enrich coke after careful inspection through SEM/EDS and XRD, which reveals that the catalysis is derived from zinc. The zinc catalysis on the solution loss reaction of coke is mainly attributed to accelerating the decomposition of the ketone group, promoting the formation of CO gas.

Oxidation and Condensation of Zinc Fume From Zn-CO2-CO-H2O Streams Relevant to Steelmaking Off-Gas Systems

The objective of this research was to study the condensation of zinc vapor to metallic zinc and zinc oxide solid under varying environments to investigate the feasibility of in-process separation of zinc from steelmaking off-gas dusts. Water vapor content, temperature, degree of cooling, gas composition, and initial zinc partial pressure were varied to simulate the possible conditions that can occur within steelmaking off-gas systems, limited to Zn-CO2-CO-H2O gas compositions. The temperature of deposition and the effect of rapidly quenching the gas were specifically studied. A homogeneous nucleation model for applicable experiments was applied to the analysis of the experimental data. It was determined that under the experimental conditions, oxidation of zinc vapor by H2O or CO2 does not occur above 1108 K (835 °C) even for highly oxidizing streams (CO2/CO = 40/7). Rate expressions that correlate CO2 and H2O oxidation rates to gas composition, partial pressure of water vapor, temperature, and zinc partial pressure were determined to be as follows: $$ {\text{Rate}}\left( {\frac{\text{mol}}{{{\text{m}}^{2} {\text{s}}}}} \right) = 406 \exp \left( {\frac{{ - 50.2 \,{\text{kJ}}/{\text{mol}}}}{RT}} \right)\left( {p_{\text{Zn}} p_{{{\text{CO}}_{2} }} - p_{\text{CO}} /K_{{{\text{eq}},{\text{CO}}_{2} }} } \right)\,\frac{\text{mol}}{{{\text{m}}^{2} \times {\text{s}}}} $$ $$ {\text{Rate}}\left( {\frac{\text{mol}}{{{\text{m}}^{2} {\text{s}}}}} \right) = 32.9 \exp \left( {\frac{{ - 13.7\, {\text{kJ}}/{\text{mol}}}}{RT}} \right)\left( {p_{\text{Zn}} p_{{{\text{H}}_{2} {\text{O}}}} - p_{{{\text{H}}_{2} }} /K_{{{\text{eq}},{\text{H}}_{2} {\text{O}}}} } \right)\,\frac{\text{mol}}{{{\text{m}}^{2} \times {\text{s}}}} $$ It was proven that a rapid cooling rate (500 K/s) significantly increases the ratio of metallic zinc to zinc oxide as opposed to a slow cooling rate (250 K/s). SEM analysis found evidence of heterogeneous growth of ZnO as well as of homogeneous formation of metallic zinc. The homogeneous nucleation model fit well with experiments where only metallic zinc deposited. An expanded model with rates of oxidation by CO2 and H2O as shown was combined with the homogenous nucleation model and then compared with experimental data. The calculated results based on the model gave a reasonable fit to the measured data. For the conditions used in this study, the rate equations for the oxidation of zinc by carbon dioxide and water vapor as well as the homogeneous nucleation model of metallic zinc were applicable for various temperatures, zinc partial pressures, CO2:CO ratios, and H2O partial pressures.