Zn-rich Alloys Research Articles

Fabrication Of Zn4Sb3 Alloys By A Combination Of Gas-Atomization And Spark Plasma Sintering Processes

Abstract In this study, single phase polycrystalline Zn4Sb3 as well as 11 at.% Zn-rich Zn4Sb3 alloy having ε-Zn4Sb3 (majority phase) and Zn (minority phase) phases bulk samples produced by gas-atomization and subsequently consolidated by spark plasma sintering (SPS) process. The crystal structures were analyzed by X-ray diffraction (XRD) and cross-sectional microstructure were observed by the scanning electron microscopy (SEM). The internal grain microstructure of 11at.% Zn-rich Zn4Sb3 powders shows lamellar structure. Relative density, Vickers hardness and crack lengths were measured to investigate the effect of sintering temperature of Zn4Sb3 samples which are sintered at 653, 673 and 693 K. Relative density of the single phase bulk Zn4Sb3 sample reached to 99.2% of its theoretical density. The micro Vickers hardness of three different sintering temperatures were found around 2.17 – 2.236 GPa.

The effect of Al−5Ti−1B on the microstructure, hardness and tensile properties of a new Zn rich aluminium alloy

The aim of the present study is to investigate the effect of Al−5Ti−1B grain refiner on the microstructure, hardness and tensile properties of a new Zn-rich Al−Zn−Mg−Cu alloy. The microstructural observations revealed that Ti addition refines the grain size (up to 95%) and dispersion of the second phase and subsequently forms rosette-shape grains. In addition, the grain refinement by Al3Ti particles resulted in an increase in the area fraction of the recrystallized regions as compared to unrefined specimens. After grain refinement and thermomechanical processes, the improvements of the tensile strength, yield strength and elongation values were nearly 33%, 25% and 1930% respectively, when compared to as-cast specimens. Computer simulation used to determine the strain and stress patterns showed a plastic strain gradient from the edge to the center of the hot worked specimen. The microscopic examination of the fracture surfaces showed dimple-like mechanism in deformed specimens while the presence of coarse eutectic constituent in interdendritic regions was responsible for brittle fracture in not deformed ones.

Electrodeposition of Zn - Ni Alloys from Protic Ionic Liquids

Electrodeposition of metals and alloys is currently carried out from aqueous solutions despite the environmental problems associated to the complex baths needed to obtain electrodeposits with controlled properties (composition, roughness, etc). In this context, ionic Liquids (IL) are studied as an option to be used as new green solvents for electrodepositon due to their interesting properties : non volatility, low fusion temperature, conductivity, viscosity, etc. However, commercial LIs are generally toxic and highly reactive in the presence of water which limits their application in many chemical and electrochemical processes. In this work, we study the use of environmentally friendly and stable protic ionic liquids (PILs) as solvents in the electrochemical deposition of nanostructured metals (Ni and Zn) and their alloys. The studied PILs synthetized by using well-known amounts of a linear aliphatic amine and a single-chain carboxylic acid as precursors in order to get mixtures of controlled composition (e.g., pure PIL or mixture of a pure PIL and its pure acidic or basic precursor as a co-solvent) to be applied directly as the depositon bath in the electrochemical deposition of nanostructured nickel, zinc and their alloys.The electrodeposition process was studied by electrochemical techniques and the obtained deposits were characterized by optical microscopy and also by SEM and AFM techniques. For the electrodeposition of the studied single metals (Ni and Zn), results shown that nanostructured nickel and zinc deposits can be electrodeposited from these protic ILs with faradic efficiencies dependent on the composition of the IL and on the temperature; the influence of the physicochemical properties of the studied PILs and of the temperature on the morphological characteristics of the obtained deposits were also evaluated. The major effects were attributed to the influence of composition on mass and charge transfer properties of the PILs.In the case of the electrodeposited Ni-Zn alloys, results allow to evaluate the influence of the composition of the ionic liquid on the composition of the electrodeposited alloys. In these media, it is observed that Zn-rich alloys are commonly formed. The morphology of the obtained electrodeposits are strongly dependent on the temperature.These results allow conclude that the studied PILs are good as new reaction media with tunable properties for electrochemical applications, allowing to propose them as new systems for electrodeposition processes, as new single solvents without the use of organic additives.Acknowledgements: Authors gratefully acknowledge financial support from SEP–CONACyT Program (Project CB 2011-1-168032). TBGR is indebted to CONACYT for the fellowship.

Deformation of directionally solidified alloys: Evidence for microstructural hardening of Earth's inner core?

The viscosity of Earth's inner core (IC) plays a key role in its dynamics, being important for understanding IC convection, translation, super-rotation, and development of elastic anisotropy. However, estimates for the viscosity of the IC range from 1013Pa·s to 1021Pa·s. One difficulty in estimating the viscosity is that it is not simply a material property, but it depends on the rheology, i.e., the deformation mechanism, which in turns depends on factors such as the temperature, stress, grain size, and microstructure. To examine the effects of microstructure we have carried out constant strain rate torsional deformation experiments on directionally solidified hexagonal close packed (hcp) Zn-rich Sn alloys at high homologous temperature and atmospheric pressure. The directionally solidified hcp Zn-rich Sn alloys have a microstructure that consists of large, columnar, textured crystals composed of dendrites. This microstructure has been proposed for the IC, and hcp Zn at atmospheric pressure serves as an analog for hcp iron under IC conditions, including a likely basal slip (0001) <12′10>, along with some prismatic slip (101’0) <12’10> associated with twinning. The measured torque (or stress, which is a function of the geometry and deformation mechanism, which in turn depends on the grain size) continues to increase past what one would expect for steady state deformation, indicative of hardening. We are yet unclear as to the origin of the hardening, but our hypothesis is that it may involve the relatively few slip systems available in hcp systems, and the large, textured grains of directionally solidified alloys, so that not all strains are easily accommodated by the available slip systems. The semi-brittle behavior of the alloy also supports this hypothesis. An inner core with a textured, columnar microstructure might therefore be harder than estimates of its shear strength might predict.

Morphology, electrical, and optical properties of heavily doped ZnTe:Cu thin films

We report on a study of the physical properties of ZnTe:Cu films with Cu content up to ∼12 at. % prepared using rf magnetron sputtering. The composition and lateral homogeneities are studied using X-ray photoelectron spectroscopy (XPS). Atomic force microscopy measurements on films deposited at different substrate temperatures (up to 325 °C) yielded activation energy of 12 kJ/mole for the grains growth. The results of XPS and electrical and optical measurements provide evidence for the formation of the ternary zinc copper telluride alloy in films containing Cu concentration above ∼4 at. %. The XPS results suggest that copper is incorporated in the alloy with oxidation state Cu1+ so that the alloy formula can be written Zn1−yCuy Te with y = 2−x, where x is a parameter measuring the stoichiometry in the Cu site. The formation of this alloy causes appreciable shift in the binding energies of the XPS peaks besides an IR shift in the energy band gap. Detailed analysis of the optical absorption data revealed the presence of two additional transitions, besides the band gap one, originating from the Γ8 and Γ7 (spin-orbit) valence bands to a donor level at ∼0.34 eV below the Γ6 conduction band. This interpretation yields a value for the valence band splitting energy Δ ≅ 0.87 eV independent of copper concentration. On the other hand, the mechanism of formation of the alloy is tentatively explained in terms of a point defect reaction in which substitutional Cu defect CuZn is also created. Assuming that substitutional Cu is the dominant acceptor in the Zn rich alloy as in ZnTe, its formation energy was determined to be 1.7 eV close to the theoretical value (1.41 eV) in ZnTe.

Enhanced Dissolution of Pt from Pt–Zn Intermetallic Compounds and Underpotential Dissolution from Zn-Rich Alloys

Anodic dissolutions of Pt and Zn from Pt–Zn compounds in 5 mol L–1 hydrochloric acid have been directly monitored by the channel flow double electrode method to investigate the mechanism of enhanced dissolution of precious metals by alloying with less noble metals. The enhancement of Pt dissolution shows strong dependence on the compound composition formed during the alloying process and is more prominent from r-PtZn1.7 and γ1-Pt3Zn10 than υ-PtZn and γ-Pt2Zn11. In addition, linear sweep voltammograms of Pt–92% Zn alloys show dissolution of Pt below 0.2 V vs SHE, which is far lower than the standard potential for the reaction (0.74 V). The result is explained by an activation of Pt through the preferential dissolution of Zn from the alloys. Such theoretically proposed “underpotential dissolution” is demonstrated for Pt–Zn alloys experimentally for the first time in the present study.

Annealing of directionally solidified alloys revisited: No loss of solidification texture in Earth’s inner core

Bergman et al. (2010) found experimental evidence for recrystallization and loss of solidification texture during annealing of directionally solidified hexagonal close-packed (hcp) Zn-rich Sn alloys. They suggested that this could support the model of Alboussiere et al. (2010) and Monnereau et al. (2010), in which the Earth’s inner core translates convectively eastwards with enhanced solidification in the western hemisphere and melting in the eastern, because as inner core material translates eastwards and anneals it might lose texture, as inferred seismically. The 2010 study hypothesized that the alloys recrystallized rather than coarsened via diffusion due to the very low solubility of Sn in the Zn-rich phase. This study tests this hypothesis by annealing directionally solidified hcp Zn-rich Al alloys, in which there is greater solubility. Indeed, we find the Zn-rich Al alloys coarsen without recrystallization or fundamental change in texture. However, in contrast to the 2010 study the current study also did not find recrystallization in Zn-rich Sn alloys. This might tend to support models such as those by Cormier (2007) and Aubert et al. (2008) where long term mantle control over fluid flow near the base of the outer core might result in a weaker solidification texture in the eastern hemisphere. Although we do believe the results of the previous study are valid because they were repeatable at that time, it shows that there is something subtle that we cannot yet account for, and it remains unclear whether there is loss of solidification texture due to annealing of Earth’s inner core.

Electrodeposition of Ni-Zn Alloys on Steel from Acidic Solution in Presence of Boric Acid

The electrode position of nickel with zinc in presence of boric acid was studied in order to determine the influence of the composition of the deposition solution on the properties of the obtained electrodeposits. The Ni / Zn concentrations ratio in solution determines the deposition mechanism and thus, the chemical composition and the electrochemical activity of the electrodeposited alloys. Boric acid decreases current density which minimizes anomalous deposition. The typical results from these acidic media are the formation of Ni-rich alloys (%Ni > 90) by a normal code position mechanism with a better electrochemical activity than Ni for the hydrogen evolution reaction HER reaction. Results show that it is possible to obtain alloys rich in either zinc or nickel, from an acidic solution containing boric acid. For Ni / Zn concentration ratios in the range of 1-3, Zn-rich alloys are obtained despite Zn is the less noble element and even when it is present at lower concentrations than Ni, confirming that at these conditions alloys are deposited by an anomalous deposition mechanism as reported by many researchers1,2,3

Continuous and discontinuous grain-boundary wetting inZnxAl1−x

Temperature dependences of the contact angle $\ensuremath{\theta}(T)$ between (i) specially grown tilt grain boundaries (GBs) in Al and the Zn-rich melt; (ii) tilt GBs in Zn and the Al-rich melt; and (iii) tilt GBs in Zn and the Al-based solid solution ${(\text{Al})}^{\ensuremath{''}}$ were measured using scanning electron microscopy and light microscopy. $\ensuremath{\theta}$ decreases with increasing $T$ in all cases and reaches zero (complete wetting) at a certain temperature ${T}_{w}$ in cases (i) and (ii). The wetting transformation for Al GBs is discontinuous (first order): $\ensuremath{\theta}(T)$ dependence is convex, $d\ensuremath{\theta}/dT$ has a break at ${T}_{w}$, and $\ensuremath{\theta}\ensuremath{\sim}{[(T\ensuremath{-}{T}_{w})/{T}_{w}]}^{1/2}$. The wetting transformation for Zn GBs is continuous: $\ensuremath{\theta}(T)$ dependence is concave, $d\ensuremath{\theta}/dT$ is continuous at ${T}_{w}$, and $\ensuremath{\theta}\ensuremath{\sim}{[(T\ensuremath{-}{T}_{w})/{T}_{w}]}^{3/2}$. For the Zn GBs in contact with a second solid phase ${(\text{Al})}^{\ensuremath{''}}$, $\ensuremath{\theta}(T)$ dependence is concave and $\ensuremath{\theta}\ensuremath{\sim}{[(T\ensuremath{-}{T}_{w})/{T}_{w}]}^{3/2}$ for the extrapolated ${T}_{w}$. The observed change from the discontinuous wetting transition for GBs in a metal with a higher melting point (Al) to the continuous one for GBs in a metal with a lower melting point (Zn) is explained using the approach proposed in [Pandit et al., Phys. Rev. B 26, 5112 (1982)]. The validity of this approach and critical exponent of 3/2 may indicate that GB wetting in the Zn-rich alloys is governed by the long-range forces.

Thermodynamic description of the Cu–Fe–Zn system

Thermodynamic description of the ternary Cu–Fe–Zn system is presented. The thermodynamic parameters of the sub-systems, Cu–Fe, Cu–Zn and Fe–Zn, are taken from earlier SGTE-based assessments, and those of the ternary Cu–Fe–Zn system are optimized in this study by using the experimental zinc activity and phase equilibrium data. Due to the lack of experimental data from iron-rich alloys, the validity of the present description is verified only for Cu–Zn-rich alloys.

Thermodynamic properties and phase relations of Zn-rich alloys in the system Pt–Zn

Abstract Zinc vapor pressures over binary Pt–Zn alloys were determined in the composition range from 63 to 84 at.% Zn for temperatures between 840–1150K using an isopiestic method. The phase boundaries of four different phase fields in this composition range could be fixed based on the experimental data. Thermodynamic activities and partial molar enthalpies of zinc within these phase fields were derived from the vapor pressure data and the composition dependence of the zinc activity was calculated for 1023 K. The integral Gibbs energy at 1273 K was derived as a function of composition by Gibbs–Duhem integration, combining the activity data of the present investigation with earlier results from the literature.

Au-catalyzed growth processes and luminescence properties of ZnO nanopillars on Si

ZnO nanopillars are often grown on various substrates by catalytic growth processes through a vapor-liquid-solid (VLS) mechanism. However, on silicon substrates, even with the catalyzed growth processes, it is still very difficult to obtain highly oriented ZnO nanopillar arrays. In this work, it was found that in most cases the actual growth process of ZnO on Si catalyzed by Au was not of real VLS character. In the initial growth stage, the substrate surface is partially melted and then oxidized into a very thin layer of SiO2. Zn-rich alloys instead of ZnO are first deposited on the SiO2∕Si substrates and form polycrystalline hillocks in an atmosphere with low O2 partial pressure. The difficulty for ZnO to nucleate on SiO2∕Si is another reason preventing ZnO nanopillars from growing epitaxially on the substrates. Defects, steps, and∕or stress on the substrate surfaces may support the nucleation process and thus may influence the initial growth stage and the control of the growth orientation of the pillars. With the help of scratches on Si substrates and by avoiding the formation of hillocks, well-aligned ZnO nanopillars were obtained both on Si (111) and (100) surfaces. Sharp photoluminescence (PL) peaks of bound exciton emissions and a free exciton emission were detected at low temperature. An unreported PL peak at about 3.367eV and in some cases a donor-acceptor-pair transition at about 3.308eV were also found. At higher temperature, a band-acceptor recombination process together with strong LO-phonon replicas occurred. A donor dopant concentration ND of about 5.7×1018cm−3 and an acceptor ionization energy of 126±2meV were evaluated from the spectra.

Study on the behaviour of ZnCoCu alloy electroplating

Ternary zinc–cobalt–copper alloys of wide range composition were deposited on to steel substrates from dilute metal sulphate bath. The bath consisted of 1–20 g dm −3 CuSO 4·5H 2O, 1–30 g dm −3 CoSO 4·7H 2O, 1–50 g dm −3 ZnSO 4·7H 2O, 20 g dm −3 Na 2SO 4 and 150–200 g dm −3 NH 2CH 2COOH. The effect of bath composition, current density and temperature on the cathodic potential, cathodic current efficiency and composition of the deposits were investigated. The codeposition of ZnCoCu alloys from these solutions can be classified as regular. Increasing current density enhances the rate of Zn deposition but suppresses that of Cu deposition. However, increasing the bath temperature favours Cu deposition. Co content in the deposits is hardly affected by changing these variables. Increasing Cu content in the bath or increasing the applied current density greatly improves the cathodic efficiency for the alloy deposition. X-ray diffraction studies showed that the deposits obtained at high current density (Zn-rich alloy) consisted of a cubic CuZn 2 phase, while that obtained at high temperature (Cu-rich alloy) consisted of a face, centred cubic CuCo phase. The structure and morphology of the deposited alloys were characterised by anodic stripping and SEM.

Dispersion-strengthening effect of Cu-based Mn, Al, and Zn rich alloys

In this systematic study, dispersion-strengthening effect of the Cu–25.91Mn (wt.%), Cu–26.62Mn–8.99Al (wt.%), Cu–22.17Mn–12.32Zn (wt.%) ingot alloys have been investigated. Samples were homogenized at a high fixed temperature in different periods and cooled with different cooling rates. After processes, microanalysis of the samples were interpreted by using scanning electron microscope (SEM) and weight percentages of the elements of the occurrence phases in the samples obtained by using electron dispersion spectroscopy (EDS) technique. Additionally, some characteristic properties of the heat treated samples with different conditions of Cu–Mn, Cu–Mn–Al, Cu–Mn–Zn ingot alloys were also discussed.

Anisotropic lattice distortions in random alloys from first-principles theory.

Within the framework of the exact muffin-tin orbitals (EMTO) theory we have developed a new method to calculate the total energy for random substitutional alloys. The problem of disorder is treated within the coherent potential approximation (CPA), and the total energy is obtained using the full charge density (FCD) technique. The FCD-EMTO-CPA method is suitable for determination of energy changes due to anisotropic lattice distortions in random alloys. In particular, we calculate the elastic constants of the Cu-rich face centered cubic Cu-Zn alloys ( alpha-brass) and optimize the c/a ratio for the hexagonal Zn-rich alloys for both the epsilon and eta phases.

Electrodeposition of Zn-Fe Alloys from Aqueous Acetate Baths

SUMMARYZn-Fe alloys were electrodeposited on steel substrates from baths containing zinc acetate, ferrous sulphate and acetic acid (pH∼4·5). The effects of bath composition, applied current density and temperature on current efficiency of codeposition and composition of deposits were investigated. The data showed that the current efficiencies were high and Zn-rich alloys were plated. The results were consistent with the behaviour of an anomalous plating system with zinc, the less noble metal, being deposited preferentially. The zinc content in the deposit increased with increase in concentration of zinc ion and acetic acid in the bath and applied current density but decreased with increase of iron concentration in the bath and temperature.The structure and morphology of as-deposited alloys were examined by X-ray and SEM. The results revealed that the deposits consisted of three phases namely η, Γ and ζ-phase and the morphology of the deposits was controlled by the composition of the deposits. The microhardness of the deposits increased with increase in the deposit iron content.

Wurtzite ZnxCd1 − xS layers grown by combining MBE and hot-wall beam epitaxy

ZnxCd1 − xS alloy layers revealing the wurtzite modification have been successfully grown by molecular beam epitaxy for the first time. The hexagonal crystal structure is achieved by using a wurtzite CdS buffer layer deposited by hot-wall beam epitaxy on a GaAs(1̄1̄1̄)B substrate. Characterization of the alloy films includes in situ RHEED investigations, X-ray diffraction and optical measurements. TEM diffraction patterns and reflection spectra are used to confirm the ZnxCd1 − xS alloys to be of the wurtzite type. Photoluminescence is dominated by localized exciton emission. For layers with high Zn content (x > 0.4), film quality decreases due to the increased mismatch to the CdS buffer and the fact, that the stable bulk phase for Zn-rich alloys is cubic.

Zn-Al合金における加工中の析出，回復再結晶と加工軟化

In Zn-Al alloys, work-hardening in Al-rich alloys and work-softening in Zn-rich alloys were observed respectively. The micro-Vickers hardness of work-softened specimens was increased and, on the contrary, that of work-hardened-specimens was decreased by solution treatments. The electrical resistivity was increased by solution treatments in both work-softened and work-hardened specimens. The structures of cold-rolled textures and those in the midst of recovery and recrystallization were observed in the work-hardened and work-softened specimens, respectively. In the work-softened alloys, the lattice parameters of the Al-rich phase were determined by X-ray diffraction to be in approximate agreement with that of pure Al, and those of the Zn-rich phase, in agreement with that of pure Zn. Age-hardening was observed and the electrical resistivity increased in the work-hardening Al-rich alloys when aged at room temperature after solution treatments. On the other hand, age-softening was observed and the electrical resistivity decreased in the work-softening Zn-rich alloys. These experimental results provided the evidence for the precipitation, recovery and recrystallization during working. Based upon these discussions, the mechanism of work-softening in Zn-Al alloys is as follows: Cold-working causes the precipitation of dissolved Al, which results in the lowering of recrystallization temperature and the work-softening occurs due to the recovery and recrystallization at room temperature.

Kinetics of discontinuous precipitation in a Zn-2.5 at % Cu alloy

The morphology and growth kinetics of discontinuous precipitation in a Zn-2.5 at % Cu alloy have been studied in the temperature range 383–583 K by optical and scanning electron microscopy. The precipitate phase has a lamellar morphology, and maintains a statistically constant interlamellar spacing under isothermal growth conditions. The interlamellar spacing increases with an increase in temperature. The isothermal growth kinetics in terms of reaction front migration rate is maximum at 523 K. The upper temperature limit for the occurrence of reaction in this alloy has been predicted to be 643 K. A detailed kinetic analysis of the experimental data using several analytical models has confirmed discontinuous precipitation in this system to be a boundary diffusion controlled reaction, and enabled the determination of the grain boundary chemical diffusivity of Cu in a Zn-rich Zn-Cu alloy in the temperature range studied. The corresponding activation energy values determined in this study, range between 65 to 86 kJ/mol−1, which compare well with the relevant data in the literature.

SnZn system. Correlation between thermodynamic properties, physical properties, structure and phase diagram

There is a good deal of ambiguity in the thermodynamic data for SnZn alloys reported by various authors. Thermodynamic studies for this system have shown that ΔH > 0, and also a negative deviation of ΔC p from the Neumann-Kopp rule. These facts indicate a transitional character of the SnZn alloys between systems with a miscibility gap and those with a compound-forming tendency. However, the calculated structural parameters of Bhatia-Thornton, S cc(0) and S(0) thermodynamic, do not exhibit any extrema. The isothermal relations of the viscosity and of the surface tension are similar, and decrease for Zn-rich alloys. The surface ‘phase’ is characterized by a pronounced tin enrichment by comparison with the bulk phase. In addition, the thermodynamic properties of the surface ‘phase’ indicate a negative deviation from ideality, while the bulk phase exhibits a positive deviation.