Zn Vapor Research Articles

Optical and Photoelectric Properties of Planar Structures Obtained by Thermal Annealing of Ga2S3 Plates in Zn Vapors

Ga2S3 single crystals have been obtained by chemical vapor transport (CVT) in iodine vapors. The Ga2S3 compound was synthesized from Ga and S taken in stoichiometric quantities. The compound has been subjected to long term thermal annealing (TA) at the temperatures of 850 and 1070 K for 6 to 60 h in Zn vapors. After TA the natural surface of Ga2S3 single crystals contain a cover layer. The photoluminescence, photoconductivity and electrical conductivity of this layer depend on treatment conditions (temperature and duration). Electrical conductivity of these samples is 3–5 magnitude orders higher than for untreated crystals. The treated single crystals contain both Ga2S3 and ZnS crystallites. Thermal annealing of Ga2S3 crystals in Zn vapors leads to shifting of fundamental absorption edge toward low energies and absorption coefficient increase in the spectral region of 2.4–3.0 eV.

Zinc-induced embrittlement in nickel-base superalloys by simulation and experiment

The high cost of Re has driven interest in processes for recovering Re from scrap superalloy parts. In this work thermodynamic modelling is used to study Zn-induced embrittlement of a superalloy and to direct experiments. Treating superalloy powder with Zn vapour reduces the average particle size after milling from approximately m to 0.5–10 m, vs. m for untreated powder. Simulations predict the required treatment time to increase with temperature. Agreement between predictions and experiments suggests that an embrittling liquid forms in less than an hour of Zn vapour treatment between 950–1000 C and partial pressures of Zn between 14–34 kPa (2–5 psi).

Biomass Gasification and Hot Gas Upgrading in a Decoupled Dual-Loop Gasifier

A decoupled dual-loop gasifier (DDLG) has been developed in which biomass gasification and hot gas upgrading are separated into two parallel loops so that they can be optimized individually. In the gasification loop, the gasifier is designed so that the contact between volatiles and char is restrained and, therefore, the steam gasification of char is enhanced. In the upgrading loop, both a desulfurizer and a tar-reforming catalyst are used for desulfurization and tar destruction, respectively. As the in-bed desulfurizer, an iron-bearing olivine-supported ZnO (Zn/olivine) material was prepared and tested in a fixed-bed reactor. H2S sorption over ZnO, adversely affected by H2O, was accompanied by the evident reduction of ZnO and vaporization of Zn at 550 °C. In contrast, no obvious ZnO reduction was observed under the same conditions over Zn/olivine. The reduction resistance of Zn/olivine was investigated by means of temperature-programmed reduction and powder X-ray diffraction. In DDLG tests with pine sawd...

Electronic and Geometrical Structure of Zn+ Ions Stabilized in the Porous Structure of Zn-Loaded Zeolite H-ZSM-5: A Multifrequency CW and Pulse EPR Study

Electron spin resonance and hyperfine sublevel correlation (HYSCORE) spectroscopy at X- and Q-band frequencies have been employed, in conjunction with X-ray absorption spectroscopy (XAS), to determine the geometric and electronic structure of Zn+ ions in H-ZSM-5 zeolite. Zn+ ions were generated by the direct exposure of dehydrated acid H-ZSM-5 to Zn vapors. The number of Zn+ ions is found to increase substantially upon UV irradiation. A single EPR active species is detected, indicating a single site of adsorption, characterized by the presence of an Al3+ site, as revealed by superhyperfine interactions. The full g (gx = 1.9951, gy = 1.9984, gz = 2.0015) and 27Al |A| (Ax = 2.8, Ay = 2.7, Az = 4.6) MHz tensors were resolved, allowing for a detailed description of the geometric and electronic structure of Zn+ ions stabilized in the cages of H-ZSM-5 zeolite. The dispersion and nuclearity of Zn species formed during the sublimation/irradiation process was assessed by means of XAS spectroscopy, which indicates ...

Investigation of zinc recovery by hydrogen reduction assisted pyrolysis of alkaline and zinc-carbon battery waste

Zinc (Zn) recovery from alkaline and zinc-carbon (Zn-C) battery waste were studied by a laboratory scale pyrolysis process at a reaction temperature of 950°C for 15–60min residence time using 5%H2(g)-N2(g) mixture at 1.0L/min gas flow rate. The effect of different cooling rates on the properties of pyrolysis residue, manganese oxide particles, were also investigated. Morphological and structural characterization of the produced Zn particles were performed. The battery black mass was characterized with respect to the properties and chemical composition of the waste battery particles. The thermodynamics of the pyrolysis process was studied using the HSC Chemistry 5.11 software. A hydrogen reduction reaction of the battery black mass (washed with Milli-Q water) takes place at the chosen temperature and makes it possible to produce fine Zn particles by rapid condensation following the evaporation of Zn from the pyrolysis batch. The amount of Zn that can be separated from the black mass increases by extending the residence time. Recovery of 99.8% of the Zn was achieved at 950°C for 60min residence time using 1.0L/min gas flow rate. The pyrolysis residue contains MnO and Mn2O3 compounds, and the oxidation state of manganese can be controlled by cooling rate and atmosphere. The Zn particles exhibit spherical and hexagonal particle morphology with a particle size varying between 200nm and 3µm. However the particles were formed by aggregation of nanoparticles which are primarily nucleated from the gas phase.

Metal-cored welding wire for minimizing weld porosity of zinc-coated steel

Metal-cored welding (MCW) wire with an optimal chemical composition was developed to minimize the weld porosity and pits in the cold metal transfer welding of hot-dip galvannealed steel in a lap-joint configuration. The effects of the chemical composition of the welding wire (specifically, the effects of the C, Si, and Mn contents) on the weld porosity formation were investigated through statistical analysis, high-speed imaging of the weld pool behavior, and welding signal analysis. The Si and Mn contents were found to be significant factors in reducing the weld porosity and pits. As the Si and Mn contents decreased, the viscosity of the weld pool decreased and the Zn vapor emission increased. The electrical resistance of the wire also decreased with decreasing Mn content. Although the C content rarely affected the emission of Zn vapor, it affected the hardness of the welds. The response surface model between the wire elements and weld porosity was also estimated, and the chemical composition of the wire was optimized based on this model. The optimal MCW wire with low Si and Mn contents (0.08% C–0.30% Si–0.51% Mn) was fabricated, and its effectiveness in reducing weld porosity was experimentally verified.

Phase Equilibria at 600 °C of the Y-Zn-Zr System

The phase equilibria at 600 °C of the Y-Zn-Zr system were determined via investigating the reaction of Y-Zr alloy with Zn vapor and the equilibrated ternary alloys, by means of the electron probe microanalyses and x-ray diffraction. Two ternary phases, which are denoted as τ1 and τ2, were found at 600 °C. The τ1 phase was deduced to have a triclinic structure. It has a homogeneity range of Y3.6-5.8Zn88.7-89.8Zr4.8-6.6 and is located approximately between Zr5Zn39 and Y2Zn17. The τ2 phase was determined to have a homogeneity range of Y9.0-9.9Zn74.0-75.0Zr15.6-16.6 (in at.%). The solubility of Zr in YZn2 was measured to be up to 10.4 at.% Zr. Thirteen three-phase equilibria were well determined. Six of them involving the τ1 or τ2 were found. The isothermal section at 600 °C was constructed over the entire composition range of the Y-Zn-Zr system.

Chemical vapor deposition-based growth of aligned ZnO nanowires on polycrystalline Zn2GeO4:Mn substrates

ZnO nanowires have been grown on polycrystalline Zn2GeO4:Mn substrates for the first time using a chemical vapor deposition method. Both Zn and ZnO sources were used to supply Zn vapor in the growth process of ZnO nanowires. The Zn2GeO4:Mn substrates were prepared using solid-state ceramic synthesis methods, and average grain sizes of ~1 μm were achieved. The nanowires of diameters in the range of 100–200 nm and length of ~30 μm were observed. In addition to nanowires, other morphologies of ZnO nanostructures, such as ZnO tetrapods, were observed when Zn powder was used as the source for the CVD growth. The results reveal that polycrystalline substrates are also promising as novel alternative substrates for growth of ZnO nanostructures. The as-synthesized ZnO nanowire/Zn2GeO4:Mn composites are being developed for future electroluminescent devices.

Zn vacancy formation, Zn evaporation and decomposition of ZnSb at elevated temperatures: Influence on the microstructure and the electrical properties

Abstract The influence of annealing on the microstructure and electrical properties of undoped polycrystalline ZnSb samples has been investigated by different experimental techniques. In situ XRD in an argon atmosphere showed that ZnSb powders decompose at 300 °C, which is attributed to Zn evaporation. In situ SEM in a moist atmosphere showed fast surface deterioration at 450 °C and above, reflecting decomposition of ZnSb and the formation of metallic Sb precipitates. The rate of Zn loss in a reducing atmosphere was determined by thermogravimetry and related to the Zn partial vapor pressure. The increase of the hole carrier concentration of ZnSb measured at room temperature after heat treatment was correlated with Zn evaporation at elevated temperature. The carrier concentration after annealing at 400 °C is consistent with an activation energy for Zn vacancy formation of 0.4 eV and a maximum Zn deficiency x of Zn1-xSb of 1 × 10−3.

Vapor–liquid–solid synthesis of ZnSnN2

A series of experiments was carried out to explore the conditions under which ZnSnN2 would form by vapor–liquid–solid synthesis from a Zn–Sn melt exposed to a nitrogen plasma. ZnSnN2 precipitated at melt temperatures between 455 and 560 °C for melt compositions between 1.5 and 15 at.% Zn. Sn3N4 formed for temperatures between 440 and 560 °C for melt compositions below 1 at.% Zn. Zn3N2 apparently grew only in the vapor phase, and only at melt temperatures between 409 and 463 °C. Each of the materials was identified by its characteristic Raman spectrum and by Auger chemical analysis. The composition profiles of the melts were modeled as a function of time using the measured temperature profiles. The results were compared with post‐growth measurements of the melt compositions. These comparisons support the visual observation that exposure of the melt to the nitrogen plasma suppressed Zn evaporation substantially even prior to the formation of a solid crust of precipitate. This work helps define the range of growth conditions available for synthesis of ZnSnN2 by this vapor–liquid–solid method.Material yielded as a function of synthesis temperature and the composition of the melt, measured post‐synthesis by EDS. The two ZnSnN2 samples labeled with asterisks were grown with a plasma power of 60 W. All others were grown using a plasma power of 240 W.

Experimental investigation of heterogeneous hydrolysis with Zn vapor under a temperature gradient

The hydrolysis step of the Zn/ZnO thermochemical cycle for hydrogen production is experimentally investigated in a laboratory-scale tube-reactor. The current work uses a new approach in which the heterogeneous oxidation of gaseous Zn with steam is carried out under a negative axial temperature gradient in order to improve cycle efficiency by reducing the proportion of steam and inert carrier gas used. It is shown that complete conversion of Zn to ZnO is possible at steam-to-Zn stoichiometries greater than 5.0. As the steam-to-Zn stoichiometry approaches unity at reduced inert gas fractions, condensation of Zn on the reactor walls becomes more likely. In addition, the observed gas-phase equilibrium shift toward increased production of ZnO at temperatures under 800 K is consistent with earlier theoretical predictions. While complete conversion with low inert gas and steam usage was not achieved, our approach shows great improvement over previous aerosol-based approaches when considering the total amounts of steam and inert gas used per unit of hydrogen produced. Therefore, the current temperature gradient approach is promising for the design of an efficient reactor for water splitting via Zn vapor.

Effect of modified flux on MIG arc brazing-fusion welding of aluminum alloy to steel butt joint

Pulsed MIG arc brazing-fusion welding process was applied to realize the butt joining of galvanized steel and 5052 aluminum alloy with no enclosed slot or groove adopted. A modified flux mixture was developed to improve the butt joint performance. After applying the modified flux, weld appearance became better and the spreadability of filler metal was also greatly improved. During brazing-fusion welding process, flux floating on the surface of welding pool weakened the surface tension between filler metal and Fe and reduced the evaporation of Zn, which both led to the greatly enhanced spreadability. The analysis of intermetallic compounds (IMCs) at brazed interface showed that Fe3Al was formed at upper side of steel plate, while Fe2Al5 was formed at other areas with the consideration of its lowest Gibbs free energy under certain temperature range. With modified flux, the tensile strength of the joint could reach up to 120MPa, which was about 60% of that of 5052 aluminum alloy base metal. From the fractured surface, two different fracture modes were identified, tear fracture and intergranular fracture, which confirmed that joint fractured in a brittle mode. The crack initiated at the front side of brazed interface due to the thicker IMCs layer, then propagated to the surface before the whole joint failed. The improved spreadability of filler metal on the top and back sides of steel plate due to the application of flux, contributed to the improvement of joint strength.

Zinc-nanosystem-structure formation using anodic-oxidized aluminum membranes

We propose a new method for the formation of zinc nanosystems by condensation of a weakly supersaturated Zn vapor in pores of the anodic-oxidized aluminum membrane (AOA)–silicon substrate system. For this purpose, a weak Zn vapor flow is created by magnetron sputtering of Zn target in a high-purity inert gas atmosphere and maintaining a temperature of the porous AOA membrane outer surface higher than that of the substrate. This drives a directional Zn vapor flow inward membrane parallel to the pore generatrix and favors effective penetration of Zn vapor into the membrane.

Reactive wetting of TiC-Ni cermet by Ag-Cu-Zn alloy during evaporation

In order to investigate the effect of the evaporation on wetting, reactive wetting of TiC-Ni cermet by molten Ag-Cu-Zn alloys with different Zn contents was studied at 810 °C using a sessile drop method in vacuum. The vapor recoil force induced by the strong evaporation of Zn in the Ag-Cu-25Zn alloy drove the spreading of the molten Ag-Cu-25Zn alloy. Furthermore, the sequential evaporation of Zn in the Ag-Cu-25Zn alloy caused the formation of a (Cu, Ni) solid-solution layer at the interface between the TiC-Ni cermet and the Ag-Cu-Zn alloy. Thus, the (Cu, Ni) solid-solution layer could serve as a metallization layer on the surface of the TiC-Ni cermet, which promoted the non-wetting to wetting transition of the TiC-Ni cermet by the Ag-Cu-25Zn alloy. The equilibrium contact angle of the Ag-Cu-25Zn alloy on the TiC-Ni cermet was 19.9°, approximately equal to that of a Ag-28Cu eutectic alloy on a Cu-Ni alloy surface. The final contact angle of the Ag-Cu-Zn liquid alloy on the TiC-Ni cermet first decreased and then increased as the Zn content in the liquid was increased from 0% to 30%. It reached a minimum value in the Ag-Cu-25Zn alloy.

Characterization and control of ZnGeN2 cation lattice ordering

ZnGeN2 and other heterovalent ternary semiconductors have important potential applications in optoelectronics, but ordering of the cation sublattice, which can affect the band gap, lattice parameters, and phonons, is not yet well understood. Here the effects of growth and processing conditions on the ordering of the ZnGeN2 cation sublattice were investigated using x-ray diffraction and Raman spectroscopy. Polycrystalline ZnGeN2 was grown by exposing solid Ge to Zn and NH3 vapors at temperatures between 758°C and 914°C. Crystallites tended to be rod-shaped, with growth rates higher along the c-axis. The degree of ordering, from disordered, wurtzite-like x-ray diffraction spectra to orthorhombic, with space group Pna21, increased with increasing growth temperature, as evidenced by the appearance of superstructure peaks and peak splittings in the diffraction patterns. Annealing disordered, low-temperature-grown ZnGeN2 at 850°C resulted in increased cation ordering. Growth of ZnGeN2 on a liquid Sn–Ge–Zn alloy at 758°C showed an increase in the tendency for cation ordering at a lower growth temperature, and resulted in hexagonal platelet-shaped crystals. The trends shown here may help to guide understanding of the synthesis and characterization of other heterovalent ternary nitride semiconductors as well as ZnGeN2.

Factors that influence the quality constant of the manufacturing process for asphalt milling knifes

The quality constant for mill knifes used to strip asphalt is significantly influenced by the quality of the reinforcement which, in its turn, is influenced by the thermic brazing process and by manufacturing the protection system at blockage through welding when it spins around its axis. It’s also influenced by the quality of the intelligent wear and blocking self-protection systems that in their turn are influenced by oxidation and diffusion processes of W and C that make simmered carbides from the reinforcement and brazed joints. Overheating during welding and brazing of the knife reinforcement and/or blockage self-protection reinforcement favours the oxidation of the W carbides leading to a fast degradation of the affected zones, even in exploitation. Exceeding optimum temperature during brazing of the reinforcement in the low chromium alloyed steel support leads to Zn evaporation in certain areas from the brazing material and lowers the brazed joint resistance to wear this causes the knife reinforcement to detach from the support. Taking into consideration the above mentioned facts it is recommended that the production stages of the mill knifes are done mechanized and/or automatic constantly monitoring the execution parameters.

Microstructure evolution of a Zn-Al coating co-deposited on low-carbon steel by pack cementation

In this study, Zn–Al coatings were co-deposited on AISI 1020 steel by pack cementation. The as-prepared coatings were characterised by scanning electron microscopy, energy–dispersive X–ray spectroscopy, and X–ray diffraction. The evolution mechanism of the coating was modelled and analysed in detail. Furthermore, the corrosion resistance of the as-received coatings was investigated by a potentiodynamic polarisation test in a 3.5% NaCl solution. We observed that the relatively loose and porous structure of those coatings was a function of the Al content in the packed powders. The regions with a natural porous structure evidently increase with an increase in Al concentration. The Zn-rich layer was formed because of the dominant inward diffusion of Zn with a small diffusion of Fe in the substrate. Thus, the Zn-rich layer/substrate interface moved into the ferrous substrate. As the reaction continued, the deposition of Al dominated. The interdiffusion of Al and Zn in the Zn-rich layer and the diffusion of Fe into the Zn-rich layer towards the Al-rich layer led to the nucleation and growth of the Fe–Al phases and the consumption of the Zn-rich layer. As a consequence, the Al-rich layer/Zn-rich layer interface moved inside the Zn-rich layer. At higher deposition temperatures, when the heat was released because of the Fe–Al phase formation, the evaporation of Zn resulted in void formation in the Al-rich layer. The potentiodynamic polarisation test results show that both Zn and Zn–Al coatings significantly enhance the corrosion resistance of a ferrous substrate, but Zn–Al coatings seem to be more efficient.

Fabrication of controllable mesh layers above SiNx micro pores with ZnO nanostructures

Ultra-long and laterally aligned Zinc Oxide (ZnO) nanorod arrays were directly synthesized around the edges of SiNx micro pores by using a facile and effective chemical vapour deposition process without any catalysts or additives. ZnO nanorods can grow controllably with a preferential orientation as a bridge beyond the edges and gradually seal into a planar free-standing mesh layer. The optimized growth parameters have been thoroughly investigated and identified. A vapour solid synthesis mechanism with source vapour flow rate control has been tentatively proposed on the basis of the experimental data to explain the synthesis: ZnO nanodots first form around the edges of pores due to the local large binding energy and high Zinc (Zn) vapour concentration, and subsequently nanorods grow epitaxially from the nanodots. This precisely-controlled micro pore sealing approach is an important step toward a coherent mechanism for applications in DNA extraction, separation and the next generation DNA sequencing.

Nanoparticle Treated Stainless Steel Filters for Metal Vapor Sequestration

The ability to sequester vapor phase radioactive compounds during industrial processes reduces the exposure of workers and the environment to dangerous radioactive materials. Nanomaterials have a lot of potential in this area because they typically demonstrate size- and shape-dependent properties with higher reactivity than bulk. This is due to the increased surface area-to-volume ratio and quantum size effects. In this report, we developed a gold nanomaterial-treated stainless steel filter, namely wools and coupons, that can be efficiently used for zinc vapor sequestration. Without nanoparticle modification, stainless steel coupons do not react or alloy with Zn. Gold nanomaterials were grown onto various stainless steel filters using solution chemistry that is amenable to scaling up. Materials were characterized by electron microscopy, inductively coupled plasma mass spectroscopy and dynamic light scattering before and after exposure to zinc vapors. X-ray diffraction, high-resolution transmission electron microscopy, energy dispersive x-ray spectroscopy mapping and ultraviolet-visible spectroscopy confirm the formation of gold-zinc alloys after Zn vapor exposure. The effect of surface topography on nanoparticle morphology, size and loading density were also investigated, and stainless steel surface defects were found to have an impact on the Au NP growth and subsequently Zn sequestration.

Zinc-Derived Microporous Structure in Non-Precious Metal Catalysts for Polymer Electrolyte Fuel Cell Cathodes

The kinetically sluggish oxygen reduction reaction (ORR) at the cathode of polymer electrolyte membrane fuel cells (PEFCs) requires higher content of platinum at the cathode than the facile hydrogen oxidation at the anode. Due to the scarcity and high cost of platinum, the development of inexpensive platinum group metal-free (PGM-free) ORR catalyst is one of the most urgent needs in the PEFC field. Transition metal-nitrogen-carbon (M-N-C) catalysts obtained by heat-treating transition metals, nitrogen, and carbon precursors have been viewed as the promising PGM-free catalysts for PEFC cathodes though not yet meeting all the performance characteristics required. High ORR activity, excellent mass-transport properties and practical long-term durability must be achieved simultaneously for PGM-free catalyst to replace platinum-based catalysts in the PEFC system. Specific catalyst precursors and heat-treatment conditions are critical to obtaining PGM-free catalysts with the desired structure. Iron- and cobalt-based zeolitic imidazolate frameworks (ZIFs), with uniformly distributed transition metals coordinated by N-containing ligands, have been viewed as highly suitable precursors for ORR catalysts. However, catalysts derived from these ZIFs often have low surface area and porosity, which are not conducive to efficient mass transport. On the contrary, ZIF-8, a zinc based ZIF, yields carbon with high surface area and porosity. Dodelet et al. used ZIF-8 as a microporous host for Fe and N precursors [1]. Following a heat-treatment at a relatively high temperature of 1050 ºC, they obtained an ORR catalyst with enhanced fuel cell performance. Unlike Fe and Co in Fe- and Co-based ZIFs, zinc in ZIF-8 is volatile during high-temperature treatment, likely acting as pore-forming agent. Base on that assumption, we used in this work a zinc salt instead of zinc ZIF as a precursor responsible for the formation of micropores in the catalyst. By using high heat-treatment temperature we also achieved more corrosion-resistant catalysts, while increasing the porosity and specific surface area from 315 m2 g-1 to 910 m2 g-1due to Zn evaporation. Fe-CM-PANI(Zn) catalyst was synthesized using the two nitrogen-precursor (cyanamide and PANI) approach, developed previously by LANL[2]. ZnCl2 was mixed with nitrogen precursors and heat-treated at 1000 ºC to ensure complete removal of Zn. The resulting CM-PANI-Fe(Zn) catalyst had much higher surface area than the catalyst obtained without Zn under the same conditions. The half-wave potential (E½ ) for CM-PANI-Fe(Zn) in RDE testing in acidic electrolyte, 0.79 V vs. RHE, was similar to that obtained with Zn-free CM-PANI-Fe heat-treated at 900 ºC (optimal heat-treatment temperature for the Zn-free system), but by 0.16 V higher than E½ measured with the Zn-free catalyst heat-treated at 1000 ºC (Figure 1). While no immediate increase in the activity can be demonstrated with CM-PANI-Fe(Zn), this catalyst promises to have much improved stability thanks to being treated at a much higher temperature. Electrochemical and fuel cell testing of the Zn-derived catalyst, focusing in particular on the durability, is underway, as is the catalyst structure optimization. The results will be present at the meeting.