Ag-Zn Alloys Research Articles

Advances on biodegradable zinc-silver-based alloys for biomedical applications.

The biodegradable metals have great potential for the biomedical applications, which could be gradually degraded, absorbed, or excreted in the human body, avoiding the removal though secondary surgery. Zinc-based alloys are novel series of degradable metals for medical applications, and they are gaining lots of attention in the research field of absorbable metals. Zinc-silver (Zn-Ag) alloys show superior mechanical strength, good biodegradability, biocompatibility, and antibacterial properties, which render them to be potential candidates for biomedical applications. In this paper, we reviewed the development of Zn-Ag alloys in terms of mechanical properties, degradabilities, biocompatibilities, antibacterial properties, and potential applications in dentistry.

Effects of a high-voltage pulsed magnetic field on the solidification structures of biodegradable Zn-Ag alloys

The physical and chemical properties of biodegradable zinc alloys are closely related to their microstructures. Therefore, various techniques are being attempted to change their microstructures. However, little work has been done to control the initial solidification structures of the biodegradable zinc alloys, which play an important role in determining their final properties. In view of this, Zn-Ag alloys with different compositions were solidified under a high-voltage pulsed magnetic field (HVPMF) in this work. The results show that the primary η-Zn grains in the isomorphous Zn-2.5 wt% Ag alloy are transformed from coarse dendrites to fine globular grains with increasing the HVPMFs. Also, its macrostructural homogeneity in the specimens is enhanced gradually. Moreover, the primary ε-AgZn3 dendrites in the hypoperitectic Zn-4.0 wt% Ag and hyperperitectic Zn-9.0 wt% Ag alloys are refined and “levitated” by the HVPMFs. Correspondingly, the peritectic η-Zn grains that nucleate on the fine primary ε-AgZn3 particles are also significantly refined. In addition, when applying the HVPMFs in separate solidification stages of these two alloys, it is found that the HVPMFs mainly have a crucial effect on the structures in the early stage. The modification of the solidification structures in the Zn-Ag alloys is attributed to the forced convection and the Joule heat induced in the liquid-solid two-phase zone by the HVPMFs.

Discharge Behavior of Mg–Sn–Zn–Ag Alloys with Different Sn Contents as Anodes for Mg-air Batteries

Controlling the microstructure and discharge performance of Mg-based alloys is of great importance and aimed at optimizing magnesium anode materials to the level required for power source applications. In this study, the microstructure along with discharge properties of extruded Mg–Sn–Zn–Ag alloys with Sn content ranging from 2 wt.% to 8 wt.% are investigated. The results indicate that the Mg–4Sn–1Zn–1Ag alloy exhibits the most negative discharge potential during the half-cell test than the other alloys investigated in this study. Moreover, a Mg-air battery with a Mg–4Sn–1Zn–1Ag alloy as the anode provides a relatively high cell voltage together with power density compared with the counterpart battery. Furthermore, the microscopic mechanism of an anode material exhibiting an excellent discharge performance is systematically discussed in terms of the second phase, dynamic recrystallization, crystal orientation and discharge product film.

Effect of a High Magnetic Field on Crystal Growth in the Solidification of Hypoperitectic Zn–Ag Alloy

Hypoperitectic Zn–Ag alloy was solidified under various high magnetic fields (HMFs) to investigate the crystal growth. The results show that without the HMFs the randomly aligned primary e-AgZn3 de...

Zinc Anode Design for Rechargeable Aqueous High-Energy Zn Batteries

As an energy storage system, Li-ion batteries are not safe because they use flammable organic electrolytes. A safer alternative is rechargeable Zn-based batteries with aqueous electrolytes. Among them, Zn-air batteries have high theoretical volumetric energy density (4400 Wh/L), which can even compete with lithium-sulfur batteries. Alkaline electrolyte is preferable for Zn-air batteries. However, the performance of Zn anodes in alkaline electrolyte is limited by passivation, dissolution and hydrogen evolution. Through SEM investigation, critical passivation size was found to be ~ 2 µm. Sub-micron-sized Zn anodes won’t have passivation problem. As a result, we focus our research on nanoscale. However, Zn dissolution of nanosized anodes will be accelerated because of large electrode-electrolyte surface area. Thus, anode modification and protection are needed to alleviate the dissolution. We designed a (1) Zn mesh@GO anode (Fig. 1a): graphene oxide (GO) layers on the Zn mesh surface deliver electrons across insulating ZnO and can slow down the Zn dissolution; (2) lasagna-inspired ZnO@GO anode (Fig. 1b): ZnO nanoparticles encapsulated by GO can solve simultaneously the passivation and dissolution problems; (3) core-shell ZnO@TiN nanorod anode (Fig. 1c): thin and conformal TiN coating mitigates Zn dissolution, mechanically maintains the nanostructure, and delivers electron to nanorods. These coatings are ion selective, which allow permeation of OH- and water, and prevents loss of Zn active material through blocking bigger Zn(OH)4 2-. Hydrogen evolution is a competitive side reaction on the zinc anodes, which causes low efficiency of Zn based batteries. Two approaches are investigated to suppress hydrogen evolution, including (1) modify the anode with a hydrogen suppressive material: core-shell ZnO@TiO2 nanorod anode was made with hydrogen suppressive TiO2 coating, which solves hydrogen evolution, passivation and dissolution problems at the same time; (2) design a hydrogen evolution suppressive nanostructured alloy anode: Zn-Ag alloy with increased standard reduction potential was used, which is more competitive compared with hydrogen evolution and more stable in aqueous electrolyte. All of these anodes show superior performance compared with unmodified anodes. These anodes can be paired with air cathodes to make high energy Zn-air batteries. The nanoscale design principles here can potentially be applied to overcome intrinsic limitations of other battery materials. Figure 1

Silver(I) Oxide on Silver–Zinc Alloys: Anodic Formation and Properties

Anodic formation in deoxygenated 0.1 М KOH solution of Ag(I) oxide on Ag–Zn alloys with zinc atomic fraction from 5 to 30 at % and its properties were examined using cyclic voltammetry supplemented by photoelectrochemical measurements. Phase composition of the alloys is confirmed by X-ray diffraction analysis. Surface morphology is studied using scanning electron microscope. Ag(I) oxide anodically formed on silver–zinc alloys is shown possessing n-type conductance, with dominating donor defects. The donor defect concentration in the Ag(I) oxide increases, as the zinc content in the alloy grows, and this leads to a decrease in the maximum photocurrent and to narrowing of the space charge region. With the increasing of the zinc concentration in the alloy, the Ag2O particles’ size decreases and their surface density increases.

Zn-alloy provides a novel platform for mechanically stable bioresorbable vascular stents.

Metallic Zn alloys have recently gained interest as potential candidates for developing platforms of bioresorbable vascular stents (BVS). Previous studies revealed that Mg alloys used for BVS can degrade too early, whereas PLLA materials may fail to provide effective scaffolding properties. Here we report on results of a new bioresorbable, metallic stent made from a Zn-Ag alloy studied in a porcine animal model of thrombosis and restenosis. While the tensile strength (MPa) of Zn-3Ag was higher than that of PLLA and resembled Mg’s (WE43), fracture elongation (%) of Zn-3Ag was much greater (18-fold) than the PLLA’s or Mg alloy’s (WE43). Zn-3Ag exposed to HAoSMC culture medium for 30 days revealed degradation elements consisting of Zn, O, N, C, P, and Na at a 6 nm surface depth. Platelet adhesion rates and blood biocompatibility did not differ between Zn-3Ag, PLLA, Mg (WE43), and non-resorbable Nitinol (NiTi) stent materials. Balloon-expandable Zn-3Ag alloy BVS implanted into iliofemoral arteries of 15 juvenile domestic pigs were easily visible fluoroscopically at implantation, and their bioresorption was readily detectable via X-ray over time. Histologically, arteries with Zn-3Ag BVS were completely endothelialized, covered with neointima, and were patent at 1, 3, and 6 months follow-up with no signs of stent thrombosis. Zn-3Ag alloy appears to be a promising material platform for the fabrication of a new generation of bioresorbable vascular stents.

First-principles study of phase stability of bccXZn(X=Cu, Ag, and Au) alloys

First-principles density-functional theory is used to study the phase stability/instability and anomalies in the formation of the high-temperature bcc phases of $X\mathrm{Zn}$ ($X$ = Cu, Ag, and Au) alloys. Although from perhaps a naive point of view, their properties are expected to monotonically depend on the noble-metal ($X$) column position in the periodic table, this is not the case. For example, the middle-column AgZn alloy has a lower bcc order-disorder (critical) temperature than the CuZn and AuZn alloys above and below in the column. It is shown that this and other nonmonotonic behaviors can be explained in terms of a competition between atomic-size effects and $X$-atom $d$-orbital spatial extent. For example, charge-density studies and pair-potential modeling of $X\mathrm{Zn}$ alloys show that the effective Ag-Zn bond is significantly weaker than either the Cu-Zn or Au-Zn bond at their respective equilibrium lattice constants. We find that an increased atomic-core size effect initially weakens the $X$-Zn bonding as one goes from CuZn to AgZn, but then the larger $d$-orbital spatial extent for higher principal quantum numbers becomes a more dominant effect and increases the bonding from AgZn to AuZn. This study is focused on the highly symmetric cubic high-temperature phases, where relative bond-strength magnitudes should be far more important than any bond-directionality effects; the lattice parameters, bulk moduli, elastic constants, Debye temperatures, heats of formation, and order-disorder temperatures for the bcc phases of the three $X\mathrm{Zn}$ alloys are calculated and compared with experiment.

Fabrication and properties of porous Zn-Ag alloy scaffolds as biodegradable materials

Porous Zn-xAg binary alloy scaffolds (where x = 1.0 and 3.5 wt.%) with porosity of 59.1 ± 0.7% were successfully prepared as biodegradable biomedical implant materials using air pressure infiltration method (APIM) in this work. NaCl particles of around 100–400 μm in size were used as space holders. Their morphologies and structures, compressive mechanical properties, corrosion characterizations in simulated body fluid (SBF), and antibacterial ability were studied in detail. Scanning electron microscopy imaging shows that the grain sizes of porous Zn scaffolds are refined to some extent due to the addition of Ag element. The compressive plateau stresses at 3% strain for the porous Zn-3.5Ag, Zn-1Ag and Zn scaffolds with a porosity of 59.1 ± 0.7% are around 13.7 ± 0.2 MPa, 5.5 ± 0.2 MPa and 4.0 ± 0.3 MPa, respectively. The mean weight loss rate of porous Zn-Ag alloy scaffolds is about 1.1 mg/day during immersion tests, which is much less than the tolerable limit of Zn intake (40 mg/day). XRD results suggest that the corrosion products on the degraded surface consisted mainly of ZnO, Ca3(PO4)2 and Zn(OH)2. Antibacterial tests indicate that the antibacterial ability of the porous Zn-Ag scaffolds becomes higher and higher with the increase of Ag content.

Selective laser melting of Zn–Ag alloys for bone repair: microstructure, mechanical properties and degradation behaviour

ABSTRACT Zn possesses good biodegradability and biocompatibility, but its strength and hardness are insufficient for bone implants. In this study, Ag was introduced into Zn to improve the mechanical properties by selective laser melting. The results showed that Ag was dissolved in Zn, which generated constitutional undercooling in front of the advancing solid/liquid interface during solidification, making more nucleation events occur and thus refining the grains. When Ag content exceeded its solid solubility in Zn, AgZn3 phase is formed, which acted as active nucleation sites for Zn grains, further refining the grains. The refinement of the grains effectively hindered the plastic deformation and dislocation. As a result, the compressive strength and hardness were improved by about 100% and 116%, respectively. When Ag content continued increasing and became excessive, AgZn3 phase grew rapidly, coarsening the grains. Accordingly, the mechanical properties slightly decreased. These results demonstrated that the Zn–Ag alloys are potential implant biomaterials.

Microstructure, Mechanical Properties and Corrosion Behavior of Extruded Mg–Zn–Ag Alloys with Single-Phase Structure

Mg–Zn–Ag alloys have been extensively studied in recent years for potential biodegradable implants due to their unique mechanical properties, biodegradability and biocompatibility. In the present study, Mg–3Zn-xAg (wt%, x = 0.2, 0.5 and 0.8) alloys with single-phase crystal structure were prepared by backward extrusion at 340 °C. The addition of Ag element into Mg–3Zn slightly influences the ultimate tensile strength and microstructure, but the elongation firstly increases from 12% to 19.8% and then decreases from 19.8% to 9.9% with the increment of Ag concentration. The tensile yield strength, ultimate tensile strength and elongation of Mg–3Zn–0.2Ag alloy reach up to 142, 234 MPa and 19.8%, respectively, which are the best mechanical performance of Mg–Zn–Ag alloys in the present work. The extruded Mg–3Zn–0.2Ag alloy also possesses the best corrosion behavior with the corresponding corrosion rate of 3.2 mm/year in immersion test, which could be explained by the single-phase and uniformly distributed grain structure, and the fewer twinning.

Investigation of the thermoelectrical properties of the Sn91.2−x–Zn8.8–Agx alloys

Sn91.2−x–Zn8.8–Agx alloys (x = 0.15–10.0 wt%) were directionally solidified upwards at a constant G (4.16 K mm−1) and V (41.5 μm s−1) in a Bridgman-type directional solidification furnace. The electrical resistivity (ρ) measurements of the alloys depending on the temperature were performed using the standard four-point probe method, and the temperature coefficients of the resistivities (α) were calculated. Composition analyses of the alloys were carried out using energy-dispersive X-ray spectroscopy. The enthalpy (∆H) and the specific heat (∆Cp) values of the alloys were determined by differential scanning calorimetry analysis. The thermal conductivity (K) values were obtained from the Wiedemann–Franz equation. According to the experimental results, electrical resistivities increased up to 3.0 mass% Ag and decreased with further increase in Ag content. Enthalpy and specific heat values decreased with the increasing content of Ag. The results were compared with the previous works for Sn–Zn–Ag alloys.

Fabrication, mechanical properties and in vitro degradation behavior of newly developed Zn[sbnd]Ag alloys for degradable implant applications

Zn and Zn-based alloys have been recognized as highly promising biodegradable materials for orthopedic implants and cardiovascular stents, due to their proved biocompatibility and, more importantly, lower corrosion rates compared to Mg alloys. However, pure Zn has poor mechanical properties. In this study, Ag is used as a promising alloying element to improve the mechanical properties of the Zn matrix as well as its biocompatibility and antibacterial properties. Accordingly, we design three ZnAg alloys with Ag content ranging from 2.5 to 7.0wt% and investigate the influence of the Ag content on mechanical and corrosion behavior of the alloys. The alloys are developed by casting process and homogenized at 410°C for 6h and 12h, followed by hot extrusion at 250°C with extrusion ratio of 14:1. Degradation behavior is assessed by electrochemical and static immersion tests in Hank's modified solution. Microstructural analysis reveals that hot extrusion significantly reduces the grain size of the alloys. Zn-7.0%Ag alloy shows a reasonably equiaxed and considerably refined microstructure with mean grain size of 1.5μm. Tensile tests at room temperature suggest that increasing the Ag content steadily enhances the tensile strength, while it does not affect the tensile ductility significantly. Zn-7.0%Ag shows high yield strength and ultimate tensile strength of 236MPa and 287MPa, respectively, which is due to the grain refinement and high volume fraction of fine AgZn3 particles precipitating along the grain boundaries during the extrusion process. Among all these alloys, Zn-7.0%Ag displayed superplasticity over a wide range of strain rates (from 5×10−4s−1 to 1.0×10−2s−1) providing the possibility of exploiting forming processes at rapid rates and/or even at lower temperatures. In addition, extruded alloys exhibit slightly faster degradation rate than pure Zn. X-ray diffraction results show the presence of ZnO and Zn(OH)2 on the degraded surfaces. Moreover, scanning electron microscopy imaging reveals that micro-galvanic corrosion is more pronounced on the alloys with higher Ag content due to the higher volume fraction of AgZn3 particles.

Synthesis of porous thin silver films and their application for hydrogen peroxide sensing

Porous thin silver films were fabricated by electrochemical deposition of Ag-Zn alloys followed by a selective dealloying of zinc component. The Ag-Zn alloys were synthesized at various operating conditions including: different Ag+/Zn2+ molar ratio in the electrolyte (1:1 and 1:3), current density (0.2–20mAcm−2), and time of electrodeposition (5–60min). The deposited thin alloy films were characterized with scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The effect of dealloying time on morphology of resulting films was studied. The formation of alloys and their chemical composition were confirmed by XRD and EDS spectra. The developed porous thin Ag film electrode showed good electrocatalytic activity toward reduction of hydrogen peroxide. The influence of interfering compounds such as ascorbic acid, uric acid and glucose was studied. The proposed method with amperometric detection was applied with success, satisfying accuracy and precision to determination of hydrogen peroxide in real samples.

Ammoniacal leaching and recovery of copper from alloyed low-grade e-waste

The paper concerns a hydrometallurgical method for selective recovery of copper from low-grade electric and electronic wastes. The following consecutive stages were proposed: smelting of the scraps to produce Cu–Zn–Ag alloy, leaching of the alloy in ammoniacal solution, and selective copper electrowinning. Cu–Zn–Ag alloy was a polymetallic and five-phase system. It was leached in chloride, carbonate, sulfate and thiosulfate solutions. This resulted in the separation of the metals, wherein metallic tin and silver as well as lead salts remained in the slimes, while copper and zinc were transferred to the electrolyte. Copper was selectively recovered from the ammoniacal solutions by the electrolysis, leaving zinc ions in the electrolyte. The best conditions of the alloy treatment were obtained in the ammonia–carbonate system, where the final product was copper of high purity (99.9 %) at the current efficiency of 60 %. Thiosulfate solution was not applicable for the leaching of the copper alloy due to secondary reactions of the formation of copper(I) thiosulfate complexes and precipitation of copper(I) sulfide, both inhibiting dissolution of the metallic material.

Transmission electron microscopy investigation and interpretation of the morphology and interfacial structure of the ∊′-Mg54Ag17precipitates in an Mg–Sn–Mn–Ag–Zn alloy

The morphology and interfacial structure of the ∊′-Mg54Ag17precipitates in a peak-aged Mg–Sn–Mn–Ag–Zn alloy have been investigated using transmission electron microscopy. A typical ∊′-Mg54Ag17precipitate exhibits a (0001)αhabit plane and three pairs of side facets, with two major pairs of facets being in irrational orientations. The orientation of each preferred interface is normal to a vector connecting two adjacent diffraction spots from different phases (Δg). Using the constrained coincidence site lattice (CCSL) model, the interface orientations have been interpreted according to the degree of matching on the interfaces. The detailed stepped structures in the irrational facets and dislocation configurations in the side facets have been predicted using the secondary CCSL (II-CCSL) and the secondary O-lattice model. Both the calculated terrace/ledge and dislocation configurations in side facets are in good agreement with the high-resolution transmission microscopy observations.

Interconnection of thermal parameters, microstructure, macrosegregation and microhardness of unidirectionally solidified Zn-rich Zn–Ag peritectic alloys

In this work, the microstructural evolution of Zn–3.2wt%Ag (hypoperitectic) and Zn–8wt%Ag (hyperperitectic) alloys during transient unidirectional solidification is investigated. The experimental results include solidification thermal parameters such as the growth rate (VL), thermal gradient (GL) and tip cooling rate (Ṫ), which are related to the microstructural interphase spacing (λ) by proposed experimental growth laws. It is shown that, the classical lamellar eutectic growth law λ2V=constant, applies to the growth of the peritectic Zn–Ag alloys examined, despite the different values of the constant associated with each alloy composition. In contrast, it is shown that identical functions of the form λ=constant (GL)−14 (VL)−1/8, and λ=constant (Ṫ-1/3) can be applied to both alloys examined. Positive solute macrosegregation was observed in regions close to the bottom of the castings. The dependence of microhardness (HV) on the length scale of the microstructures (including that of a single phase Zn 0.8wt%Ag alloy: λC− cellular spacing) is examined. An experimental Hall–Petch type power law is proposed relating the resulting microhardness to λC for the single phase alloy, and despite the segregation profiles and the alloying differences of the hypoperitectic and hyperperitectic alloys, the average microhardnesses of these alloys is shown to be essentially constant and similar along the castings lengths.

Characterization and interpretation of interfacial structure of the Mg2Sn laths in an Mg–Sn–Mn–Ag–Zn alloy

Interfacial structures in facets of the basal Mg2Sn lath approximately along were characterized using high-resolution transmission electron microscopy. A set of periodic misfit-compensating ledges is observed along the irrational major facet, which deviates from by an angle of around 5°. The observation is interpreted quantitatively using a constrained secondary coincidence-site lattice model. The calculation results reveal a favourable singular structure with a specific configuration of steps, showing good agreement with the experimental observations.

Cellular growth of single-phase Zn–Ag alloys unidirectionally solidified

Transient unidirectional solidification experiments have been carried out with a single-phase Zn–Ag alloy under cooling rates in the range of 0.1–40 K s−1. The resulting macrostructure is shown to be typified by columnar grains aligned along the heat flow direction and the microstructure is characterized by a cellular morphology along the entire casting length with no evidence of cellular/dendritic transition. A regular to plate-like cells transition is shown to occur for cooling rates higher than 10K s−1. Experimental results from the literature on the cellular growth of single-phase Zn–Ag alloys in steady-state solidification conditions are compared with the results of the present investigation. An experimental growth law relating the cell spacing with the cooling rate is proposed, which is shown to be able to represent both the steady-state and transient growth regimes of single-phase Zn–Ag alloys. The Bouchard–Kirkaldy model is shown to be the only theoretical growth model that matches the cellular experimental scatters in both solidification regimes.

Inhomogeneity of bulk nanoporous silver fabricated via dealloying Ag-Zn alloy in sulphuric acid

Described is an approach to fabricate bulk nanoporous silver with a diameter of 12 mm and thickness of 5.4 mm via dealloying Ag25Zn75 alloy in 0.1 mol/l sulphuric acid at 0.4 V for 100 h at room temperature. The volume of the bulk nanoporous contracts 14.2% compared with the starting alloy. Meanwhile, crystal structure switches from close-packed hexagonal to face-centred cubic, which can be considered as a type of phase transition during dealloying. An intrinsically inhomogeneous morphology in microscale exists in bulk nanoporous silver by dealloying, which is caused by coarsening of the ligament width via surface diffusion of silver atoms in the electrolyte for different times. Moreover, parallel orientation structures and cracks have been found in the specimen, which could be related to the columnar crystal of starting alloy during solidification. The lattice defects such as stacking faults, lattice distortions and twins can be seen in the ligaments.