Hydrogen Evolution Measurements Research Articles

Effect of Sn content on the mechanical properties and corrosion behavior of Mg-3Al-xSn alloys

The effect of Sn content on the mechanical properties and corrosion behavior of Mg-3Al-xSn alloys was investigated by SEM-EDXS, XRD, electrochemical measurements, and scanning Kelvin probe force microscopy (SKPFM). The results showed that when the Sn content was 1.4 wt%, Sn dissolved in the α-Mg matrix and then precipitated as an intermetallic compound (Mg2Sn). The combined results of mass loss, hydrogen evolution, and electrochemical measurements indicated that Mg-3Al-1Sn had a low corrosion rate. The SKPFM results showed that the Volta potential of Mg2Sn particles, Al-Mn, and β-Mg17Al12 phases were 100, 80, and 50 mV higher than the matrix, respectively. Therefore, the Mg2Sn phase that formed in Mg-3Al-xSn served as a local cathode due to its high potential, which accelerated microgalvanic corrosion along with the secondary local cathode (Al-Mn). The Sn solution strengthening and secondary phase strengthening (fine Mg2Sn particles) improved the mechanical properties of the Mg-3Al-xSn alloys.

Synthesis of Ag and N doped potassium tantalate perovskite nanocubes for enhanced photocatalytic hydrogen evolution

Potassium tantalate (KTaO3) was synthesized by solvothermal process and an effort has been made with the addition of Ag and N as dopants and accessed for hydrogen evolution measurements. The structural aspect and the average crystallite size were confirmed from X-ray diffraction analysis. The particle size and cubic morphology were proved from FESEM and its compositions were confirmed by Energy Dispersive Spectroscopy. The band gap and the band edge potential were evaluated from the UV–visible spectral studies. Photocatalytic H2 evolution for the undoped, Ag and N-doped KTaO3 under UV light are 375, 2072 and 752 µmolh−1g−1. The highest rate of H2 production was achieved for Ag doped KTaO3 using 450 W Xe-Hg UV lamp without co-catalyst is not yet attained. Further the reliability test of the optimized photocatalyst showed that 91% of the photocatalytic activity was retained even after three days.

Microstructure and corrosion behaviors of AZ63 magnesium alloy fabricated by accumulative roll bonding process

AZ63 magnesium alloy sheets were fabricated by accumulative roll bonding (ARB) process at 350 °C up to 5 cycles. The aim of this work is to study the effect of ARB process on the microstructure and corrosion behavior of AZ63 magnesium alloy. The ARBed sheets were investigated via microstructure observations, electrochemical tests, hydrogen evolution measurements and immersion tests. After ARB process, the average grain size decreased. The coarse Mg17Al12 phase was broken under the action of rolling force and it distributed more dispersed in the magnesium matrix. The corrosion resistance of samples increased significantly with increasing the number of ARB cycles. The influence of microstructure on the corrosion behaviors was discussed. Fine grain produced more passive oxide layers which acted as a corrosion barrier. The Mg17Al12 phase acted primarily as a micro-galvanic cathode during the corrosion process because of its low volume fraction and isolated distribution. The volume fraction of Mg17Al12 phase decreased after ARB process, which results in the reduction of the effect of galvanic corrosion.

In vitro and in vivo biodegradation and biocompatibility of an MMT/BSA composite coating upon magnesium alloy AZ31

The performance of biodegradable magnesium alloy requires special attention to rapid degradation and poor biocompatibility, which can cause the implant to fail. Here, a sodium montmorillonite (MMT)/bovine serum albumin (BSA) composite coating was prepared upon magnesium alloy AZ31 via hydrothermal synthesis, followed by dip coating. We evaluated the surface characterization and corrosion behavior in vitro, and the biocompatibility in vitro and in vivo. Biodegradation progress of the MMT-BSA coated Mg pieces was examined through hydrogen evolution, immersion tests, and electrochemical measurements in Hank’s solution. In vitro biocompatibility studies were evaluated via hemolysis tests, dynamic cruor time tests, platelet adhesion, MTT testing and live-dead stain of osteoblast cells (MC3T3-E1). It was found that the MMT-BSA coating had good corrosion resistance and a marked improvement in biocompatibility in comparison to bare Mg alloy AZ31. in vivo studies were carried out in rat model and the degradation was characterized by computed tomography scans. Results revealed that the MMT-BSA coated Mg alloy AZ31 implants maintained their structural integrity and slight degradation after 120 d of post-implantation. A 100% survival rate for the rats was observed with no obvious toxic damages on the organs and tissues. Additionally, we proposed a sound coating formation mechanism. Considering the good corrosion protection and biocompatibility, the MMT-BSA coated Mg alloy AZ31 is a promising candidate material for biomedical implants.

Graphene nanoplatelets-reinforced magnesium metal matrix nanocomposites with superior mechanical and corrosion performance for biomedical applications

Magnesium (Mg) metal matrix composites (MMCs) reinforced with graphene nanoplatelets (GNPs) have been developed by powder metallurgy (PM). GNPs with different concentrations (0.1, 0.2, and 0.3 wt.%), layer thicknesses (5 nm and 9 nm), and particle sizes (15 µm and 5 µm) were dispersed into Mg powder by high-energy ball-milling processes. The microstructure and mechanical properties of the fabricated composites were characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Raman spectroscopy (RS), and compression tests. The corrosion resistance was evaluated by electrochemical tests and hydrogen evolution measurements. The cytotoxicity of Mg-GNPs composites was assessed using osteoblast-like SaOS2 cells. The results indicate that GNPs are excellent candidates as reinforcements in Mg matrices for the manufacture of biodegradable Mg-based composite implants. GNP addition improved the mechanical properties of Mg via synergetic strengthening modes. Moreover, retaining the structural integrity of GNPs during processing improved the ductility, compressive strength, and corrosion resistance of the Mg-GNP composites. Cytotoxicity assessments did not reveal any significant toxicity with the addition of GNPs to Mg matrices. This study demonstrates that Mg-xGNPs with x < 0.3 wt.%, may constitute novel biodegradable implant materials for load-bearing applications.

Effect of Microstructure on the Corrosion Behavior of as-cast and Extruded Mg–Sn–Y Alloys

The effect of microstructure on the corrosion behavior of as-cast and extruded Mg–Sn–Y alloys was investigated using measurements of hydrogen evolution, weight loss, potentiodynamic polarization, electrochemical impedance spectroscopy, and scanning Kelvin probe force microscopy. The results showed that the corrosion rate increased in the following order: as-cast, transversal section of bar, and longitudinal section of bar. The higher corrosion rate was related to the refinement of grain size, the micro-galvanic corrosion between second phases and α-Mg matrix, and the micro-galvanic corrosion between different orientated grains. The Volta potentials of Sn3Y5 and MgSnY phases were more positive than that of the α-Mg matrix. Accordingly, the Sn3Y5 and MgSnY phases acted as the cathodes for micro-galvanic corrosion and accelerated the corrosion of α-Mg matrix. After extrusion, the content of second phases reduced and the grain size significantly refined. As a consequence, extrusion increased the corrosion rate of Mg–Sn–Y alloys, as the contribution of grain size refinement to increase the corrosion rate was much bigger than that of the content decrease of second phases to decrease the corrosion rate.

Corrosion of Mg alloys EV31A, WE43B, and ZE41A in chloride‐ and sulfate‐containing solutions saturated with magnesium hydroxide

AbstractThis study studied corrosion in 0.1 M Na2SO4, 0.1 M NaCl, and 0.6 M NaCl, all saturated with Mg(OH)2, using weight loss, hydrogen evolution, and electrochemical measurements. Corrosion was similar in all cases. Nevertheless, the corrosion rates were alloy‐dependent, were somewhat lower in 0.1 M Na2SO4 than in 0.1 M NaCl, and increased with NaCl concentration. The corrosion damage morphology was similar for all solutions; the extent correlated with the corrosion rate. The corrosion rates evaluated by the electrochemical methods were lower than those evaluated from hydrogen evolution, consistent with the Mg corrosion mechanism involving the unipositive Mg+ ion.

PEO coating with Ce-sealing for corrosion protection of LPSO Mg–Y–Zn alloy

Plasma Electrolytic Oxidation coatings (PEO), without and with Ce-based sealings, were developed on a Mg–Y–Zn alloy containing long period stacking order (LPSO) phases in order to improve its corrosion behaviour. Specimens were investigated in terms of morphology, composition and corrosion behaviour (polarization and hydrogen evolution measurements). PEO improved the corrosion resistance compared to the bulk material. Sealing for 5 min plugged the coating pores and cracks with Ce-rich compounds, resulting in improved long-term corrosion behaviour. Sealing for 1 h resulted in excessive dissolution of the coating and deterioration of the inner barrier layer.

One-Pot Seed-Mediated Growth of Co Nanoparticles by the Polyol Process: Unraveling the Heterogeneous Nucleation.

The one-step seed-mediated synthesis is widely used for the preparation of ferromagnetic metal nanoparticles (NPs) since it offers a good control of particle morphology. Nevertheless, this approach suffers from a lack of mechanistic studies because of the difficulties of following in real time the heterogeneous nucleation and predicting structure effects with seeds that are generated in situ. Here, we propose a complete scheme of the heteronucleation process involved in one-pot seed-mediated syntheses of cobalt nanoparticles in liquid polyols, relying on geometrical phase analysis (GPA) of high-resolution high-angle annular dark field (HAADF)-STEM images and in situ measurements of the molecular hydrogen evolution. Cobalt particles of different shapes (rods, platelets, or hourglass-like particles) were grown by reducing cobalt carboxylate in liquid polyols in the presence of iridium or ruthenium chloride as the nucleating agent. A reaction scheme was established by monitoring the H2 evolution resulting from the decomposition of metal hydrides, formed in situ by β-elimination of metal alkoxides, and from the polyol dehydrogenation, catalytically activated by the metal particles. This is a very good probe for both the noble metal nucleation and the heterogeneous nucleation of cobalt, showing a good separation of these two steps. Ir and Ru seeds with a size in the range 1-2 nm were found exactly in the center of the cobalt particles, whatever the cobalt particle shape, and high-resolution images revealed an epitaxial growth of the hcp Co on fcc Ir or hcp Ru seeds. The microstructure analysis around the seeds made evident two different ways of relaxing the lattice mismatch between the seeds and the cobalt, with the presence of dislocations around the Ir seeds and compression zones of the cobalt lattice near the Ru seeds. The relationship between the nature of the nucleating agent, the reaction steps, and the microstructure is discussed.

Enhancing the biodegradability and surface protective performance of AZ31 Mg alloy using polypyrrole/gelatin composite coatings with anodized Mg surface

The intention of the current study is to improve the biodegradability and corrosion resistant performance of AZ31 Mg substrates by anodization and electrodeposition of polypyrrole/gelatin composite coatings. The effect of anodization time, and the concentration of gelatin on the biodegradability and corrosion protective performance of coated AZ31 Mg substrates were systematically evaluated using different characterization techniques. Surface topographical and morphological studies of anodized substrates indicated that the surface roughness, distribution of pores and pore size increased with increasing the anodization time. Water contact angle studies confirmed the improved surface wettability of AZ31 Mg substrates after anodization treatment. Surface characterization results of PPy/Ge composite coatings revealed the significant influence of gelatin addition on the surface morphology of PPy coatings. Structural characterization results confirmed that intermolecular chemical interaction exists between the polypyrrole moiety and gelatin molecules. It was also found that the anodized layer has enhanced the adhesion of PPy coatings from 3B to 5B. In vitro corrosion analysis indicated that the anodization layer efficiently improved the corrosion resistance behavior of coated AZ31 Mg substrates and this performance was increased with the addition of gelatin up to 1 wt% and then slightly reduced. Hydrogen evolution measurements corroborated that the amount of hydrogen evolved is significantly reduced in the presence of anodization layer and gelatin addition into PPy coating.

Corrosion and Wear Resistance of Micro‐Arc Oxidation Composite Coatings on Magnesium Alloy AZ31—The Influence of Inclusions of Carbon Spheres

Poor corrosion and wear resistance of magnesium (Mg) alloys restrict their applications. Herein, corrosion and wear‐resistant films are formed upon Mg alloy AZ31 through a micro‐arc oxidation (MAO) process in silicate electrolyte in the presence of carbon spheres (CS). Surface morphology, chemical composition, corrosion resistance, hardness, and coefficient of friction (CoF) of the MAO coatings are investigated using field‐emission scanning electron microscopy (FE‐SEM), Fourier transform infrared spectrometry (FTIR), X‐ray diffractometer (XRD), X‐ray photoelectron spectroscopy (XPS), electrochemical and hydrogen evolution measurements, automatic micro‐hardness testing, and reciprocating tribometer, respectively. Results demonstrate that the surface morphology and hardness of MAO coatings vary with the concentration of CS. The presence of CS results in an increased coating thickness from 8.0 ± 1.8 to 12.2 ± 1.8 μm, mean pore size from 0.7 ± 0.1 to 1.9 ± 0.1 μm, open porosity of MAO coating from 4.2 ± 0.4 to 5.6% ± 1.1%, and coating hardness from 347.0 ± 59.0 to 853.0 ± 67.3 Vickers‐hardness (HV). Furthermore, CS‐modified MAO coatings lead to improved corrosion resistance in comparison with that of the neat MAO counterparts. Moreover, the high hardness and formation of SiC of CS‐modified coatings lead to a low and stabilized CoF, which implies an enhanced wear resistance.

Degradation Behaviour of Mg0.6Ca and Mg0.6Ca2Ag Alloys with Bioactive Plasma Electrolytic Oxidation Coatings

Bioactive Plasma Electrolytic Oxidation (PEO) coatings enriched in Ca, P and F were developed on Mg0.6Ca and Mg0.6Ca2Ag alloys with the aim to impede their fast degradation rate. Different characterization techniques (SEM, TEM, EDX, SKPFM, XRD) were used to analyze the surface characteristics and chemical composition of the bulk and/or coated materials. The corrosion behaviour was evaluated using hydrogen evolution measurements in Simulated Body Fluid (SBF) at 37 °C for up to 60 days of immersion. PEO-coated Mg0.6Ca showed a 2–3-fold improved corrosion resistance compared with the bulk alloy, which was more relevant to the initial 4 weeks of the degradation process. In the case of the Mg0.6Ag2Ag alloy, the obtained corrosion rates were very high for both non-coated and PEO-coated specimens, which would compromise their application as resorbable implants. The amount of F− ions released from PEO-coated Mg0.6Ca during 24 h of immersion in 0.9% NaCl was also measured due to the importance of F− in antibacterial processes, yielding 33.7 μg/cm2, which is well within the daily recommended limit of F− consumption.

Improved Corrosion Resistance in AZ61 Magnesium Alloys Induced by Impurity Reduction

The effect of impurity element Fe on corrosion behavior of AZ61 magnesium alloys in various states has been investigated by immersion test and hydrogen evolution measurements in 3.5% sodium chloride solution. The corrosion rate is found to relay on the impurity Fe concentration in the alloys and decreases with decreasing Fe content. When Fe content drops from 150 ppm to 10 ppm, the corresponding corrosion rates under as-cast and solution treatment conditions are reduced from 8.54 mm/a and 8.61 mm/a to 2.54 mm/a and 0.21 mm/a, respectively. The corrosion pattern of the AZ61 alloys is the localized corrosion, and the galvanic couples are formed among the impurity particles, second-phase particles and the matrix. The Fe impurity particles tend to act as main cathodic to form micro-galvanic cell with the α-Mg matrix, which is harmful for corrosion resistance of AZ61 alloy.

Effect of nano zirconia on electrochemical performance, corrosion behavior and microstructure of Al-Mg-Sn-Ga anode for aluminum batteries

In this research, stir cast Al-0.65Mg-0.15Sn-0.05Ga-xZrO2 (wt.%) reinforced alloys containing micro-additives of ZrO2 nanoparticles are fabricated to be used as an anode in aluminum batteries. The mean size of the ZrO2 particles was 40 nm and the amount of addition varies from 0.05 to 0.8 wt.%. Electrochemical characterization of the reinforced alloys was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy and corrosion behavior were evaluated using self-corrosion rate, hydrogen evolution, and anode efficiency measurements in 3 wt.% NaCl solution. The microstructure of the reinforced alloys was also studied using field emission scanning electron microscope (FESEM) and undissolved particles were analyzed by energy dispersive spectrometer (EDS). Since a portion of the ZrO2 nano-particles enters the grain boundaries during solidification of the alloy, the improper dissolution of the anode is reduced by suppression of non-coulombic loss in these points. Hence, the hydrogen evolution and corrosion current density of the reinforced alloys decreased and the anode efficiency increased by the addition of ZrO2 nano-particles to the Al-0.65Mg-0.15Sn-0.05Ga (wt.%) alloy which in case of using reinforced anodes in an aluminum battery, energy dissipation would be reduced. In general, the addition of ZrO2 nanoparticles resulted in a reduced non-coulombic loss, which occurs due to self-corrosion and enhances the efficiency of the reinforced anodic alloys, especially in higher current densities. The severity of these changes is augmeted by increasing the amount of ZrO2 nano-particles in the reinforced alloys.

Corrosion resistance of Mg(OH)2/Mg–Al-layered double hydroxide coatings on magnesium alloy AZ31: influence of hydrolysis degree of silane

Mg(OH)2/Mg–Al-layered double hydroxide (LDH) coatings were modified with methyltrimethoxysilane (MTMS) on magnesium alloys. Effect of hydrolysis degree of silane solution on coating formation was investigated. Chemical compositions and surface morphologies of the coatings were examined using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and field-emission scanning electronic microscopy (FESEM). Results indicated that the composite coatings consisted of polymethyltrimethoxysilane (PMTMS), LDH and Mg(OH)2. Electrochemical and hydrogen evolution measurements revealed that the composite coatings possessed good corrosion resistance, especially the ones prepared in a high hydrolysis degree of silane. The optimum corrosion resistance of the composite coating was LDH/PMTMS-3 coating, which had the lowest value of corrosion current density (5.537 × 10−9 A·cm−2) and a dense surface. Plausible mechanism for coating formation and corrosion process of MTMS-modified Mg(OH)2/Mg–Al-LDH coatings were discussed.

Corrosion resistance of nanostructured magnesium hydroxide coating on magnesium alloy AZ31: influence of EDTA

A hexagonal nanosheet Mg(OH)2 coating was prepared through a one-step hydrothermal method using LiOH solution as mineralizer and then modified by ethylenediaminetetraacetic acid (EDTA) to minimize the rapid corrosion of AZ31 Mg alloy. The performance of the coating was evaluated using electrochemical technique, hydrogen evolution measurements, nanoscratch test, Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) patterns and field-emission scanning electron microscopy (FESEM). The results suggested that the corrosion rate of bare AZ31 Mg alloys was significantly reduced by one and two orders of magnitude through the protection from Mg(OH)2 coating and modification with EDTA (i.e., EDTA-Mg(OH)2 coating), respectively. FESEM micrographs indicated that the modification in EDTA elicits to the formation of an EDTA-Mg(OH)2 composite with a thickness as twice as that of as-prepared Mg(OH)2 coating. Nanoscratch tests revealed strong adhesion between the composite or Mg(OH)2 coating and the substrate. The study of formation and corrosion mechanisms of the coatings manifested that Mg(OH)2 was first formed near the intermetallic compound AlMn particles and gradually covered the entire surface, wherein the AlMn particles played an important role in the coating growth process. And it also proved that EDTA accelerated the formation of Mg(OH)2.

Comparison of Corrosion Resistance and Cytocompatibility of MgO and ZrO2 Coatings on AZ31 Magnesium Alloy Formed via Plasma Electrolytic Oxidation

In this work, one coating is comprised of ZrO2 and the other consists of MgO as main phase composition was produced on AZ31 magnesium alloy using one-step plasma electrolytic oxidation (PEO). The purpose of this work was to study the corrosion resistance and cytocompatibility of the above-coated AZ31 magnesium alloys in order to provide a basis for AZ31 Mg alloy’s clinical applications of biomedical use. The morphology and phase composition of the coatings were studied using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The corrosion properties were examined using electrochemical testing, hydrogen evolution measurements, and immersion tests in a simulated body fluid (SBF). Compared with bare magnesium and the MgO coating, the ZrO2-containing coating exhibited an improved corrosion resistance. Cell proliferation assays and cell morphology observations showed that the ZrO2-containing coating was not toxic to the L-929 cells. The ZrO2 coating was much denser and more homogeneous than the MgO coating, hence the corrosion resistance of the ZrO2-coated AZ31 Mg alloy was superior and more stable than the MgO-coated AZ31 Mg alloy, and ZrO2/AZ31 did not induce a cytotoxic reaction to L-929 cells and promote cell growth.

Corrosion resistance of glucose-induced hydrothermal calcium phosphate coating on pure magnesium

Glucose-induced composite coatings containing crystalline calcium phosphate and Mg(OH)2 interlayer were prepared on pure Mg substrate through hydrothermal deposition from alkaline solution. Surface composition, morphology and corrosion resistance of the coatings were characterized through XRD, FTIR, SEM, XPS, electrochemical and hydrogen evolution measurements. Results reveal that calcium phosphate coatings were composed of dicalcium phosphate anhydrous, calcium-deficient hydroxyapatite and hydroxyapatite. Corrosion resistance of pure Mg specimens was improved by the formation of such a calcium phosphate coating. The findings provide a novel strategy to design calcium phosphate conversion coatings with satisfactory corrosion resistance for biodegradable Mg implants.

Continuous Studies on Using Camel’s Urine as Nontoxic Corrosion Inhibitor–Corrosion Inhibition of Al–Cu Alloy in Alkaline Solutions

The corrosion inhibition of Al–Cu alloy in 0.5 M NaOH using various concentrations of camel urine (CU) was investigated using hydrogen evolution, weight loss, electrochemical impedance spectroscopy and potentiodynamic polarization measurements. Analysis of impedance spectra revealed that CU inhibits the corrosion of the studied alloy effectively through the formation of a protective film on its surface with a resistance increasing with increasing CU concentration. Polarization studies indicated that CU was a mixed-type inhibitor except for CU concentrations > 3 mL% where it behaves predominantly as an anodic inhibitor. Hydrogen evolution plots were analyzed using shrinking core models for solid–liquid heterogeneous systems. The resultant data revealed that after certain induction period, hydrogen evolution occurs by fast reaction followed by slow reaction and the latter is controlled by diffusion. The values of IE% obtained from hydrogen evolution and weight loss measurements were temperature dependent. Generally, the inhibitor performance decreased at relatively high temperature (60 $$^{\circ }$$ C) except for low CU concentrations (< 3 mL%) the inhibition efficiency improved with temperature increase. The apparent activation energy for Al–Cu alloy corrosion in the inhibited solutions was calculated and compared with that in the uninhibited solution. El-Awady and Temkin adsorption isotherms fit well the adsorption data obtained from weight loss at 30 $$^{\circ }$$ C and 60 $$^{\circ }$$ C. Based on El-Awady and Temkin isotherms, multilayer film formation with repulsive forces between the adsorbed molecules was suggested. Various thermodynamic parameters for the adsorption process were calculated and discussed. Thermodynamic data indicated comprehensive adsorption (chemisorptions and physical adsorption). Good assessment to correlate the inhibition mechanism with the CU composition was obtained.

In vitro corrosion resistance of a layer-by-layer assembled DNA coating on magnesium alloy

A (polyvinylpyrrolidone (PVP)/deoxyribonucleic acid (DNA))n coating was fabricated via layer-by-layer (LbL) assembly dip coating method. The surface morphologies, chemical compositions and corrosion resistances of the coatings were investigated using field-emission scanning electron microscopy, X-ray photoelectron spectrometer, Fourier transform infrared, X-ray diffractometer and electrochemical and hydrogen evolution measurements. The results indicated that the (PVP/DNA)n coating shows a smooth surface with shallow scratches and some corrosion cracks, which possesses a good corrosion resistance in simulated body fluid, especially for n = 20. The (PVP/DNA)n coating can be used as a inducer to construct a biomimetic biocompatible Ca-P coating on Mg alloys. Additionally, we suggest and discuss a corrosion mechanism for the coating.