Formation Of Galvanic Cells Research Articles

Assessment of biodegradability and biocompatibility: An experimental and comparative analysis of magnesium and magnesium-(zinc-tin)/hydroxyapatite composites

This study presents the fabrication and comparative assessment of biodegradation and biocompatibility behaviors of pure Mg, Mg/HA (Hydroxyapatite), Mg-Zn/HA, and Mg-Sn/HA composites with fixed 5 wt% HA and 1 wt% each of Zn and Sn, using novel ultrasonic-assisted rheo casting technology. Characterization techniques, including X-ray diffractometry and scanning electron microscopy integrated with energy dispersive spectroscopy, were employed to analyze phase formation, surface morphology, and elemental composition. Microhardness tests were conducted to assess indentation resistance, while in vitro corrosion performance was evaluated in simulated bodily fluid to compare degradation behavior. Results indicate a uniform distribution of reinforced particles within the matrix with minimal casting defects. Intermetallic phases MgZn and Mg2Sn precipitated along grain boundaries in Mg-Zn/HA and Mg-Sn/HA composites. The Mg-Sn/HA composite exhibited peak microhardness (94.8 HV) due to precipitation strengthening. In contrast, Mg-Zn/HA samples showed a low degradation rate (0.19 mm/yr) and H2 gas evolution rate (0.035 ml/mm2), attributed to uniform distribution of secondary phases and fine grains that mitigate galvanic cell formation and control degradation. Cell viability assay results demonstrated that Mg-Zn/HA composite outperformed all other samples, showing a 94% relative cell growth rate of osteosarcoma MG-63 cells after 2 h of incubation, attributed to strong apatite formation (rich in Ca and P) on the surface post-immersion, promoting cell proliferation.

Investigation of corrosion behavior of Al–TiO2 nanocomposite produced using air plasma spray and accumulative roll bonding method

This work is an attempt to study the Al–TiO2 nanocomposite properties applying accumulative roll bonding process. For this purpose, nano Titania powder was first coated on aluminum foil by air plasma spraying process. The nanocomposite was then fabricated in one, two, three, five, and seven cycles by ARB. To investigate the effect of ARB process cycles on an Al-5% wt. TiO2 nanocomposite, characterization tests including XRD, quantitative XRD analysis by MAUD software, FESEM, EDS, electrochemical impedance, and TAFEL polarization tests were performed on the samples. The results indicate that the crystallite size reduced from 156 to 31 nm and the dislocation density quadrupled in the composite. The results of XRD analysis showed an increase in the dislocation density in the composite when the number of cycles increases. The reduction of crystallite size and increase of the grain boundaries have caused a sudden increase in the dislocation density. As the ARB cycle increases, the local porosity decreases and the local cracks due to the separation of the titanium sprayed droplets disappear in the matrix phase, and the reinforcing phase has more diffusion in the matrix. With the increase of ARB cycles, the percentage of titanium and oxygen elements on the surface was decreasing, but they remained until the last cycle. Among the non-rolled and rolled samples in different cycles, ARBed samples after 1 cycle and 5 cycles had not only the lowest and highest corrosion current densities but also the highest and lowest total resistance (Rt), respectively. This indicates max corrosion resistance due to the decrease in defect and porosity resulting from plasma spray and min corrosion resistance as a result of formation of galvanic cell between Al-matrix and Ti-reinforcing particles, respectively.

Synergistic effect of ceria-zirconia nanoparticles and hBN nanosheets incorporation on the corrosion resistance of MoS2 solid lubricant coatings

Molybdenum disulphide is a conventional solid lubricant material due to their layered crystal structure enabling easy shearing resulting in low coefficient of friction. Even though MoS2 is highly lubricating, the corrosive nature of this dry solid lubricant limits its application, especially in oxidizing and humid environment. The present work focuses on the improvement of corrosion resistance properties of MoS2 nanosheets coatings, while maintaining its excellent anti-friction properties by incorporating hexagonal boron nitride (hBN) nanosheets and ceria-zirconia nanoparticles (CZ NPs). A hybrid structure consisting of MoS2, hBN and CZ NPs was prepared as a composite and multilayer coating. The coatings were characterized by FE-SEM, XRD, Raman spectroscopy and XPS. The inclusion of hBN and CZ NPs did not significantly alter the coefficient of friction (CoF) and wear for the composite and multilayer coatings, as determined by the tribological investigations conducted using high frequency reciprocating rig (HFRR). The MH30-CZ composite coatings showed higher CoF compared to MH30-CZ multilayer coatings, with only 7.75 % increase as compared to pure MoS2 coating. The composite structure and multilayer structure showed high long-term corrosion resistance while the latter had the highest resistance to corrosion and oxidation. The hybrid multilayer structure had the lowest corrosion current density and corrosion rate with 167 % enhancement in total impedance. In the hybrid coating, hBN acts as a physical and insulating barrier to the flow of corrosive ions and charge transfer while CZ NPs forms insoluble precipitates which further impedes the corrosion. The galvanic cell formation of MoS2 with steel was suppressed due to the presence of insulating CZ NPs layers. The synergic effect of hBN and CZ NPs resulted in high long-term corrosion resistance of the coating.

Robust Self‐Catalytic Reactor for CO2 Methanation Fabricated by Metal 3D Printing and Selective Electrochemical Dissolution

AbstractThe methanation of CO2 has been actively pursued as a practical approach to mitigating global climate change. However, the complexity of the catalyst development process has hindered the development of new catalysts for CO2 methanation; as a result, few catalysts are commercially available. Herein, a multifunctional self‐catalytic reactor (SCR) is prepared via metal 3D printing and selective electrochemical dissolution as a method to not only simplify the catalyst development process but also fabricate active catalysts for CO2 methanation. The combination of metal 3D printing and selective electrochemical dissolution is demonstrated as a feasible method to prepare active catalysts for the methanation of CO2 in a short time. In addition, the use of an electrochemical method enables the formation of galvanic cells on the SCR; these cells continuously generate active sites via self‐dissolution during a simple refresh process, resulting in high reusability of the SCR. The proposed method represents a new facile technique to fabricate highly reusable catalysts that exhibit superior performance for CO2 methanation, and the results provide a guideline for preparing metal 3D‐printed catalysts that will satisfy industrial demand.

Enhanced reductive degradation of chloramphenicol by sulfidated microscale zero-valent iron: Sulfur-induced mechanism, competitive kinetics, and new transformation pathway

Crystalline iron sulfide (FeSx, i.e., FeS or FeS2) minerals as sulfur sources were used to prepare the mechanochemically sulfidated microscale zero-valent iron ((FeSx+ZVI)bm). Metastable FeS and FeS2 precursors were generated via aqueous coprecipitation and applied to fabricate FeSx@ZVI samples. (FeSx+ZVI)bm and FeSx@ZVI exhibited better chloramphenicol (CAP) degradation than ZVI due to the increase in specific surface areas, the decrease of electrochemical impedance, the formation of galvanic cells, and sulfur-induced pitting and local acidity. (FeSx+ZVI)bm had better CAP removal capacity than FeSx@ZVI under different S/Fe molar ratios, initial pH, and oxygen conditions. At the same time, FeSx@ZVI showed better electron utilization under oxic conditions, related to their Fe0 and sulfur spatial distribution. Nitro reduction and dechlorination of CAP by (FeSx+ZVI)bm produced nitroso, azoxy, amine, and monodechlorination products, while dechlorination was not involved in the degradation process of CAP by FeSx@ZVI. A new transformation pathway of nitroso-CAP to amine-CAP mediated by azoxy products is proposed via coupling a chain decay multispecies model and DFT calculations. The larger competitive reaction rates among O2, CAP, and its degradation products was determined by their lower LUMO energy. The contribution of direct electron transfer to nitro reduction was greater than that of atomic hydrogen, but the opposite was true for dechlorination. FeSx@ZVI had a larger DET contribution than (FeSx+ZVI)bm, and FeS2 promoted the DET contribution better than FeS. Toxicity assessment indicated that the rapid transformation of nitroso and azoxy products was crucial for eliminating the biotoxicity of CAP.

Graphene coated copper in a one-year atmospheric corrosion and color preserving challenge

A one-year atmospheric corrosion study was conducted to evaluate the performance of transparent single-layer (SLG) and multilayer graphene (MLG) coating as a protective coating on copper substrate against atmospheric corrosion and color changing. Employing the CIE−L*a*b* color space, it was shown that the transparent SLG and MLG coatings can maintain the pure color of copper before exposure to the atmosphere. However, after 15 days the color change (∆E) in the SLG-coated copper (SLG/Cu) was found to be more than that in the bare copper. A scanning Kelvin probe (SKP) was used to measure the surface potential as well as corrosion behavior. The observed decrease of average surface Volta potential of SLG/Cu, from -312 mV to -830 mV, was supposed to be caused by corrosion and electron transfer during galvanic cell formation. Further examinations by Raman spectroscopy, OM, and AFM measurements were logically correlated with those from SKP. Moreover, it was revealed that the surface voltaic potential for MLG-coated copper (MLG/Cu) remains constant along one-year atmospheric exposure. The presented results strongly prove that the MLG coating could be considered an anti-corrosion coating that can fully preserve the color of copper metal after exposure to the environment for at least a year.

The effect of microstructure on corrosion behaviour and mechanical properties of friction stir welds of AA2519 and AA2219 Al-alloys

The highly weldable AA2219 Al-Cu alloy has been amended as AA2519 Al-Alloy to increase its ballistic resistance. Despite the fact that the mechanical properties of friction stir(FS) welds are improved, corrosion resistance is affected as a result of the diverse microstructural changes which occurs in different zones in the course of welding.Present work is planned to compare and correlate the effect of microstructure on mechanical and corrosion behaviour of AA2219 and AA2519 FS welds. Results of the work shown better corrosion resistance and mechanical properties of AA2519 welds when compared to that of AA2219 welds. The presence of strengthening precipitates Al 2 CuMg, Al 3 Zr and Al 3 Ti provides insulation path for galvanic cell formation between the Al 2 Cu and Al matrix, may be the reason for improved corrosion resistance in AA2519 Al-alloys and it’s welds. Overall it was found that better combination of strength and corrosion resistance was obtained for AA2519 Al-alloy welds. • For the first time a systematic comparison is made between the Microstructure, Mechanical properties and corrosion behaviour of AA2219 and AA2519 alloy friction stir welds. • Effect of precipitates like Al 2 CuMg, Al 3 Zr and Al 3 Ti on mechanical and corrosion properties of AA2519 and AA2219 alloy friction stir welds was studied. • Observed tensile properties and corrosion behaviour was correlated with the microstructure of AA2519 and AA2219 alloy friction stir welds. • Present study is proved that a good combination of tensile strength and corrosion resistance can be achieved in Friction stir welds of AA2519.

Employing conductive carrier for establishing spontaneous microbial galvanic cell and accelerating denitrification

It is well-known that metal corrosion is accelerated by formation of galvanic cell. In this study, we reported the acceleration of denitrification by using conductive carrier through formation of microbial galvanic cell (MGC). Electrically conductive graphite plate (GP) was used as biofilm carrier and compared with the non-conductive polypropylene (PP) plate carrier. Cyclic voltametric analyses showed that biofilms with bidirectional electron transfer functions of bioelectrochemical denitrification (BEDN) and acetate oxidation could be enriched spontaneously onto the GP carrier, hinting the establishment of MGC. Further analysis using differential pulse voltammetry revealed that the redox mediator related to extracellular electron transfer was detected in both media of the GP and PP carrier. Microbial community analysis showed that the biofilms in both GP and PP carrier had identical microbial composition but varied in abundance. The genus of Comamonas, Pseudomonas, Paracoccus and Thauera were the dominance of electroactive denitrifiers responsible for BEDN in both the GP and PP carrier. The GP carrier had a 75.9% higher abundant enrichment of electroactive denitrifiers than the PP carrier. Denitrification performance analyses showed that the GP carrier had a denitrification rate constant (kDN) of 1.25 and 2.66 h−1 at 15 °C and 30 °C, respectively, which was nearly 76.1% and 92.7% higher than the non-conductive PP carrier with corresponding values of about 0.71 and 1.38 h−1. Further, the result of conductive carrier accelerating denitrification was confirmed in scaled-up denitrification bioreactors with volume of 104 L using brush-like biofilm carriers. The acceleration of denitrification was attributed to the spontaneously established MGC, which promoted the direct and mediated electron transfer of the electroactive denitrifiers grown onto the conductive carriers and speeded up the BEDN. The result of this study demonstrated that the BEDN could be integrated to traditional biological denitrification system to accelerate denitrification in the form of MGC by simply employment of conductive carrier.

Graphene-Dominated Hybrid Coatings with Highly Compacted Structure on Stainless Steel Bipolar Plates.

Highly conductive corrosion protection coatings are necessary for metallic bipolar plates (BPs) of the proton-exchange membrane fuel cell. Graphene coatings have the potential of protecting metal substrates from corrosion without obscuring their excellent electrical conductivity. The electron transfer in the coatings facilitates the formation of galvanic cells, so the challenge is to block the mass transfer of the corrosion process. Here, we constructed highly compacted hybrid coatings with aligned water-dispersible graphene layers. The water-dispersible graphene (SG) held an electrical conductivity of >270 S cm-1 while providing an unprecedented dispersibility, which can be redispersed from filter cake with a concentration of 120 mg mL-1 or even dry state. The cohesion of the hybrid coatings was attributed to the interaction between highly aligned SG layers and the heterointerface between SG and polydopamine (PDA), as proven by the molecular dynamics simulations. The hybrid coatings presented a corrosion current density of 0.023 μA cm-2 and an interfacial contact resistance of 9.94 mΩ cm2, which meets the requirements of corrosion protection and electron transfer for the coatings on metallic BPs. The water-based fabrication method of the graphene-dominated hybrid coatings was a promising alternative of the vacuum-based deposition method for industrial production.

Computational design of Mg alloys with minimal galvanic corrosion

Formation of galvanic cells between constituent phases is largely responsible for corrosion in Mg-based alloys. We develop a methodology to calculate the electrochemical potentials of intermetallic compounds and alloys using a simple model based on the Born-Haber cycle. Calculated electrochemical potentials are used to predict and control the formation of galvanic cells and minimize corrosion. We demonstrate the applicability of our model by minimizing galvanic corrosion in Mg-3wt%Sr-xZn alloy by tailoring the Zn composition. The methodology proposed in this work is applicable for any general alloy system and will facilitate efficient design of corrosion resistant alloys.

Elucidation of high removal efficiency of dichlorophen wastewater in anaerobic treatment system with iron/carbon mediator

Conductive material assisted anaerobic digestion presented much interest and promising prospect in pollutant removal during wastewater treatment. The present study deeply investigated the effect iron/carbon in anaerobic digestion for dichlorophen (DCP) degradation and methane production in synthetic DCP wastewater treatment. Results showed that nano-zero valent iron/activated carbon (nZVI/AC) and zero valent iron/activated carbon (ZVI/AC) gave higher chemical oxygen demand (COD) conversion (42.18% and 42.61%) and DCP removal (98.49 wt% and 99.00 wt%) in acidification step with better methane production from anaerobic digestion of the pretreated effluent. Same phenomenon occurred in the direct anaerobic degradation process due to the formation of galvanic cells between iron and carbon. In comparison, applying iron/carbon in acidification as pretreatment strategy plus following effluent anaerobic degradation showed higher efficiency in methane production and DCP removal than that of direct anaerobic degradation. Specifically, the methane production was 253.70 mL and 253.41 mL in subsequent anaerobic digestion system after nZVI/AC and ZVI/AC acidification pre-treatment, which was higher than 224.37 mL and 246.31 mL in direct anaerobic digestion system. Microbial community analysis showed that Clostridium_sensu_stricto_1 was the dominated bacteria due to its important role in DCP wastewater treatment. Both acetoclastic and hydrogenotrophic methanogens were enhanced in iron/carbon added systems, which was also agreement with the strengthen in related genes involved in methanogenesis. In conclusion, the present work systematically investigated the enhancement role of iron/carbon system in anaerobic digestion for DCP wastewater treatment and paved way for future application.

Experimental and numerical analysis of the effects of different repair mortars on the controlling factors of macro-cell corrosion in concrete patch repair

In reinforced concrete structures, the increase in the corrosion rate in the vicinity of the repair zone, due to galvanic cell formation, is known as the incipient anode effect. This study aims to investigate the effect of different repair mortars on the controlling factors of macro-cell corrosion current, induced by patch repair. Therefore, slab samples with different repair mortars, including mortar with ordinary Portland cement (OPC), repair mortar containing 5 and 9% micro-silica, and latex-modified cementitious mortar are investigated. Moreover, corrosion potential and macro-cell current between the substrate concrete and repair mortar are measured in this study, followed by determining the driving force, anodic and cathodic polarization resistance, and the ohmic drop. Using numerical simulation, a more extensive range of repair mortar resistivity and the driving force has been applied to evaluate their effects on the controlling factors of the macro-cell current. As demonstrated in the experimental results, despite the change in resistivity of the repair mortar, cathodic polarization resistance is always controlling the macro-cell current. An ohmic drop of approximately 5% will have the lowest contribution to controlling macro-cell current. In addition, simulation results illustrate that by increasing the resistivity of the repair mortars to 500 Ω m and the driving force to 500 mV, the ohmic drop contribution does will not increase significantly, while the cathodic polarization is always dominant.

On-demand hydrogen generation by the hydrolysis of ball-milled aluminum composites: A process overview

The hydrolysis of aluminum (Al) is a relatively simple method for on-demand hydrogen generation for niche (low-power, <1 kW) proton exchange membrane fuel cell applications. The hydrolysis of Al in neutral pH water and under standard ambient conditions is prevented by the presence of a thin surficial oxide layer. A promising method to enable Al's spontaneous hydrolysis is by its mechanochemical activation (ball milling) with certain metals (e.g., Bi, Sn, In, Ga). This overview presents several aspects relating to the changes occurring in Al particles during ball milling, e.g., the structural and morphological behavior of Al during ball milling procedures (with and without the presence of activation metals), and the distribution and homogenization of Al and various activation metals. The formation of galvanic cells between anodic Al and cathodic activation metals (relative to Al) is discussed. A summary of the existing Al composites for on-demand hydrogen generation is presented. The paper concludes with a discussion of activation metal recovery, and the effects thereof on the economic feasibility of Al composites for hydrogen generation.

Preparation and Properties of Zn-Cu Alloy for Potential Stent Material

Among degradable metal cardiac stent materials, zinc has great biocompatibility and corrosion properties, which make it become the most potential stent material. However, the mechanical properties of zinc cannot meet the performance requirements of stent material which severely limit its application. In this paper, Zn-xCu (x = 1, 2 and 3 wt.%) alloys were prepared, and their mechanical properties, corrosion properties and biocompatibility were studied. Tensile testing showed the tensile strength and hardness of Zn-xCu alloys both increased with the addition of copper, but the elongation decreased at first and then upturned. Since the formation of galvanic cell, the corrosion rates of Zn-xCu alloys increased. The main corrosion mechanism of Zn-xCu alloy was pitting corrosion, and the corrosion products mainly included ZnO and Zn(OH)2. The cytotoxicity evaluation showed that Cu2+ and Zn2+ would contribute to cell proliferation, while the concentrations of them reached a suitable range like the concentration of soaking solution of Zn-3Cu alloy was 25%. However, it would inhibit proliferation, while the concentrations of Zn2+ and Cu2+ were too large. In general, Zn-3Cu alloy had the best comprehensive properties.

Performance of L-Cu&Mn-nZVFe@B nanomaterial on nitrate selective reduction under UV irradiation and persulfate activation in the presence of oxalic acid

A novel nanomaterial (L-Cu&Mn-nZVFe@B) was synthesized and was applied to nitrate selective reduction under UV irradiation and persulfate activation in the presence of oxalic acid. Results denoted the deposition of copper could prompt the nitrate conversion and improve the nitrate conversion significantly. The high nitrate conversion was on account of the formation of galvanic cells accelerating the generation of electrons, in which Fe° acted as anode and Cu° acted as cathode. Meanwhile, the coexistence of Cu2O and MnO2 exhibited excellent photocatalytic performance with the obvious improvement of N2 selectivity because of the formation of heterojunction could boost the generation of CO2−. Furthermore, the deposition of manganese could also accelerate the generation of CO2− through the activation of persulfate. The conversion of NO3− was almost 100 % and the N2 selectivity could reach 81.57 % by the S2O82―/UV/L-Cu&Mn-nZVFe@B/H2C2O4 system when the initial nitrate concentration was 100 mg /L, the L-Cu&Mn-nZVFe@B dosage was 6.0 g/L, the H2C2O4 dosage was 15 mmol/L, pH was 5.0, the reaction time was 100 min under 25 °C. Research provides an alternative approach for selective reduction nitrate into nitrogen.

Effects of structural relaxation on the dye degradation ability of FePC amorphous alloys

The effects of structural relaxation on the catalytic efficiency of FePC amorphous ribbons in the Fenton-like reactions are studied. Different from previous knowledge, the catalytic efficiency of the Fe-based amorphous ribbons doesn't decrease linearly with increased annealing temperature before glass transition. The catalytic ability of the FePC ribbons annealed at 553 and 593 K is worse than that of as-quenched ribbons, while the ribbons treated isothermally at 633 and 673 K show higher catalytic efficiency. The impacts of structural relaxation on dye degradation performance should be considered from two aspects: i) The stored energy in the metastable ribbons, which comes from the high enthalpy and residue stress, decreases with increased annealing temperature, leading to the depression of degradation performance. ii) The precipitation of nanocrystals in the amorphous matrix when annealed at temperatures close to glass transition promotes the formation of galvanic cells that improve the catalytic efficiency of the ribbons.

Experimental comparison of corrosion behavior of pure magnesium, iron coated magnesium and hydroxyapatite coated magnesium in Hanks Basic salt solution for cardiovascular application

Biomaterials (BM) research is one of the emerging fields, and much research has been carried out towards the development of new and improved BMs. The latest development in the field of biomaterials is to develop biodegradable BMs for different applications. Many attempts have been carried out with alloys of Magnesium (Mg) and Iron (Fe), and even though Mg and Fe are found to be suitable materials, each has its limitations. Problem with Mg is its high rate of degradation while Fe has a very slow degradation rate. Hydroxyapatite (HaP) is one of the naturally occurring materials found in human bones, and many research publications have discussed the utilization of HaP. In the present study, Mg has been considered as the base material, and the effect of coating Fe and HaP on Mg substrate has been studied via immersion test in Hanks Basic salt solution (HBSS). Fe and HaP were coated on pure Mg substrate using physical vapor deposition technique (PVD). Pure Mg was used as control while Fe coated and HaP coated Mg were compared against it for mass loss and corrosion rate in HBSS for 20 days. Electrochemical corrosion test was carried on a three-electrode test rig. Fe coated Mg showed very high degradation as compared to pure Mg samples due to the formation of galvanic cells. Corrosion rate for Fe coated Mg was observed as high as (42.88 ± 1.39) mm yr−1, and it was verified with the electrochemical test, while pure Mg specimen had a maximum corrosion rate of (5.8 ± 0.35)mm yr−1. HaP coated samples showed low corrosion rate as compared to pure Mg and Fe coated Mg. The maximum corrosion rate in Hap coated specimen was observed to be (5.55 ± 0.95) mm yr−1. PVD is a very good method for coating HaP and Fe on Mg substrate, but galvanic cell formation in case of Fe coating inhibits its usage while nonreactive passive layer of HaP proved to very effective in reducing the corrosion rate of Mg.

Mechanical properties and corrosion behaviors of AZ31 alloy with dual-phase glass-crystal coating

A magnesium-based ‘supra-nanometre-sized dual-phase glass-crystal’ (SNDP-GC) coating had been fabricated on AZ31 alloy by magnetron sputtering. Surface mechanical attrition treatment (SMAT) was also introduced to form a gradient structure in order to reduce the hardness mismatch between Mg-based SNDP-GC coating and substrate. Microstructure, mechanical properties and corrosion behaviors of the as-received AZ31 (AR), AZ31 with Mg-based SNDP-GC coating (SC) and AZ31 after SMAT with Mg-based SNDP-GC coating (SSC) were investigated by optical microscope, scanning electron microscopy, transmission electron microscope, X-ray diffraction, Vickers hardness penetrator and electrochemical characterization. Results revealed the Mg-based SNDP-GC coating together with a gradient structure contributed to the improved microhardness. The decreased hardness mismatch between the coating and substrate prevented the delamination of the coating from the substrate. There is a decrease trend in Ecorr in sequence of AR, SC and SSC, while a rise in icorr in the same sequence. Corrosion uniformity was decreased in sequence of AR, SC and SSC, and corrosion cracks exhibited on corrosion products due to formation of galvanic cells and stress concentration. These results indicated the presence of gradient structure and Mg-based SNDP-GC coating led to better mechanical properties but worse corrosion resistance.

Magnetron sputtered freestanding MgAg films with ultra-low corrosion rate

Magnesium based alloys are of great interest for temporary medical applications. In order to tailor the corrosion rate, Mg is often alloyed with other elements for the envisaged application as a biodegradable medical implant. In this study 10 µm thick freestanding MgAg thin film samples with varied Ag concentrations (nominal 2–10 wt%) are presented. These films could have the potential as scaffolds, e.g. in neurological applications. The films are fabricated by a combination of UV lithography, sacrificial layer technique and magnetron sputtering, where the latter allows the fabrication of supersaturated metastable alloys. After removing the sacrificial layer, the released freestanding thin film samples are investigated. The corrosion properties are determined using potentiodynamic polarization measurements in Hanks’ balanced salt solution. The microstructure investigations are done by X-ray diffraction and scanning transmission electron microscopy. The results obtained show that it is possible using magnetron sputtering to achieve supersaturated materials with up to 6 wt% Ag which show a significant decrease in the corrosion rate compared to pure Mg by a factor of approximately three (0.04 ± 0.01 mm/yr compared to 0.12 ± 0.02 mm/yr). Statement of SignificanceIn this study magnetron sputtered freestanding MgAg films with a Ag concentration of 2–10 wt% were investigated in terms of corrosion properties and microstructure. The 10 µm thick films were produced by a combination of UV lithography and magnetron sputtering, the latter allows the fabrication of supersaturated alloys. It was possible to fabricate participate free materials up to 6 wt% Ag, which showed a decrease in the corrosion rate by the factor of 3 compared to pure Mg. For materials with 10 wt% it was not possible to obtain single phasematerials, in this case the corrosion rate was increased by a factor of approximately 20 compared to pure Mg due to the formation of galvanic cells.

Corrosion Investigation of Zinc–Aluminum Alloy (ZA-27) Matrix Reinforced with In Situ Synthesized Titanium Carbide Particle Composites

ZA-27 alloy matrix composites comprised of different volume fractions of TiC particles as reinforcement phase were synthesized by in situ technique. Microstructural, hardness and electrochemical analysis were performed on these samples along with the base ZA-27 alloy to assess any beneficial effect of making the composites over the base alloy. It was observed that hardness increases in composites as compared to the base alloy. However, hardness of the composite reduces on increasing the reinforcement percentage. Corrosion behavior was investigated by using Tafel and EIS plots in 3.5 wt.% NaCl solution at room temperature for all the samples. The results showed increase in corrosion resistance for composites than that of base alloy. However, ZA27 + 5%TiC composite showed better results as compared to that of ZA27 + 10%TiC composite. The decreased property of ZA27 + 10%TiC composite is because of the agglomeration of particles and also by the formation of galvanic cell.