Corrosion Of Mg Research Articles

Corrosion Resistance and Cytocompatibility of Magnesium-Calcium Alloys Modified with Zinc- or Gallium-Doped Calcium Phosphate Coatings.

In orthopedic surgery, metals are preferred to support or treat damaged bones due to their high mechanical strength. However, the necessity for a second surgery for implant removal after healing creates problems. Therefore, biodegradable metals, especially magnesium (Mg), gained importance, although their extreme susceptibility to galvanic corrosion limits their applications. The focus of this study was to control the corrosion of Mg and enhance its biocompatibility. For this purpose, surfaces of magnesium-calcium (MgCa1) alloys were modified with calcium phosphate (CaP) or CaP doped with zinc (Zn) or gallium (Ga) via microarc oxidation. The effects of surface modifications on physical, chemical, and mechanical properties and corrosion resistance of the alloys were studied using surface profilometry, goniometry, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), nanoindentation, and electrochemical impedance spectroscopy (EIS). The coating thickness was about 5-8 μm, with grain sizes of 43.1 nm for CaP coating and 28.2 and 58.1 nm for Zn- and Ga-doped coatings, respectively. According to EIS measurements, the capacitive response (Yc) decreased from 11.29 to 8.72 and 0.15 Ω-1 cm-2 sn upon doping with Zn and Ga, respectively. The Ecorr value, which was -1933 mV for CaP-coated samples, was found significantly electropositive at -275 mV for Ga-doped ones. All samples were cytocompatible according to indirect tests. In vitro culture with Saos-2 cells led to changes in the surface compositions of the alloys. The numbers of cells attached to the Zn-doped (2.6 × 104 cells/cm2) and Ga-doped (6.3 × 104 cells/cm2) coatings were higher than that on the surface of the undoped coating (1.0 × 103 cells/cm2). Decreased corrosivity and enhanced cell affinity of the modified MgCa alloys (CaP coated and Zn and Ga doped, with Ga-doped ones having the greatest positive effect) make them novel and promising candidates as biodegradable metallic implant materials for the treatment of bone damages and other orthopedic applications.

Effect of Galvanic Corrosion on the Degradability of Biomedical Magnesium

With recent progress in clinical trials and scale-up applications of biodegradable magnesium-based implants, the scenarios of transplanting biodegradable Mg with other non-degradable metals may occur inevitably. Galvanic corrosion appears between two metallic implants with different electrochemical potentials and leads to accelerated degradation. However, a quantitative measurement on the galvanic corrosion of Mg in contact with other metallic implants has not been conducted. Here we study the corrosion behaviors and mechanical attenuation of high purity magnesium (Mg)in contact with stainless steel (316L), pure titanium (TA2), and magnesium alloy (AZ91) respectively to form different galvanic couples in simulated body fluids. The results show that all of these three heterogeneous metal pairs accelerate the degradation of high purity Mg to different degrees, yielding declined tensile strength and mechanical failure after 4 days of immersion. Our observations alert the potential risk of co-implanting different metallic devices in clinical trials.

Effects of inorganic ions, organic particles, blood cells, and cyclic loading on in vitro corrosion of Mg[sbnd]Al alloys

Recently, magnesium (Mg) alloys have attracted extensive attention as biodegradable implant materials. However, cyclic loading and the corrosive environment of the body are significant challenges for the practical use of alloys, and there are few studies on this topic. In this study, we conducted a four-point bending fatigue test for 86,400 cycles (12 h) in simulated body fluid (SBF), plasma, and whole blood with an AZ series alloy Mg-9Al-0.5Zn-0.27Mn-0.12Ag, to examine the effects of inorganic ions, organic particles, blood cells, and cyclic loading on Mg alloy corrosion. The Mg2+ concentration and solution pH were measured before and after experimentation, and the sample surfaces were characterized by 3D digital microscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Fourier-transform infrared (FTIR) spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS).Our results showed that in the non-loading condition, a porous and weak inorganic product layer (mainly Mg/Ca phosphate and carbonate) formed on the surface of the Mg alloy sample immersed in SBF, which hardly had a protective effect on Mg alloy corrosion. For the samples immersed in plasma, the organic particles promoted the formation of an organic and more compact product layer, which protected the Mg alloy from severe corrosion. For the sample immersed in whole blood, the blood cells affected organic particle deposition on the product layer and thus interfered with the formation of an organic compact product layer, which slightly accelerated the corrosion process. Furthermore, cyclic loading damaged the layer integrity and significantly increased the corrosion rates of all the studied materials compared to the samples not subjected to cyclic loading. Nonetheless, under cyclic loading, blood cells adsorbed on the Mg alloy surfaces, and formed films, which protected the Mg alloy substrate and delayed Mg alloy corrosion.

The effect of simulated inflammatory conditions on the corrosion of Mg, Fe and CoCrMo

For the first time, the effect of inflammation on the degradation of Mg and Fe was evaluated. The immersion test and electrochemical approaches were carried out under simulated inflammatory condition, with CoCrMo alloy selected as the reference. It turned out that H2O2, the major reactive oxygen species released in the inflammation, changed the surface film behavior of pure Mg and CoCrMo alloy for the initial exposure in PBS, but insignificantly affected their corrosion during the long-term immersion. By contrast, H2O2 actively participated in the degradation of pure Fe in a concentration-relevant manner, notably accelerated the Fe corrosion, and inhibited the corrosion product formation during 14-day immersion. It’s suggested that inflammation induced corrosion should be taken into consideration in evaluating biodegradable metals.

Modification of hydroxyapatite-based coating in the presence of polyvinylalcohol (PVA) for implant application: Corrosion, structure and surface study

Eco-friendly hydroxyapatite-based coating modified by polyvinylalcohol (PVA) was used as a protective layer for Mg AZ31 substrates. Anti-corrosion performance of coatings was examined in both sodium chloride 3.5 wt% and simulated body fluid (SBF) solutions. The best performance against corrosion was achieved in the one-step process with a PVA concentration of 0.05 wt% and an immersion time of 60 min. The FE-SEM images also have shown that the irregularity of morphology was evident for the samples treated longer than 60 min. The results showed that the HA+PVA 0.05 wt% coated AZ31 Mg alloy causes less corrosion of Mg in the SBF solution.

The Activation of Mg Powder Promoted by Chloride and Activation Mechanism

Magnesium has bright market prospects such as generating thrust for under water engines and hydrogen production. However, the passive oxide film on the surface of magnesium powder prevents the further reaction of magnesium with water at room temperature. In this paper, highly active magnesium-based materials were prepared via ball milling pure Mg with different chlorides (NiCl2, CoCl2, CuCl2, FeCl3). The activity of the as obtained powder was analyzed through Scanning Electron Microscopy (SEM), Energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), synchrotron X-ray tomography, Extended X-ray Absorption Fine Structure (EXAFS), etc. Among the various compositions, the Mg-6%CoCl2 composite exhibited the best hydrogen production performance with a hydrogen generation volume of 423 mL/(0.5 g) and a conversion yield of 96.6%. The related activation mechanism was thoroughly studied, showing that the addition of chloride during ball milling can effectively break the continuity of oxide films on Mg surfaces and introduces a large number of micro defects. In addition, the EXAFS and tomography data verified that metallic cobalt was generated during the ball milling process, subsequently forming a Mg-Co micro glance cell, and the Cl− in the system accelerates the corrosion of Mg. The active mechanism can be verified as synergistic effects of micro glance cell and as-generated surface microcracks.

Effect of surface condition on the corrosion behaviour of AZ31 magnesium alloy

Corrosion of magnesium (Mg) is generally manifested by cathodic hydrogen gas evolution and concomitant anodic Mg dissolution. The surface condition significantly modified the corrosion of Mg, especially related to the deformation. The corrosion behaviour of AZ31 Mg alloy with emphasis on surface condition effect has been investigated. Filiform-like corrosion was observed significantly along the grinding path due to surface modification by mechanical grinding. From the cross-section characterization, the corrosion attack into the crystallographic structure. The analysis of corrosion behaviour is based on the polarization behaviour during the electrochemical measurement and scanning vibration electrode technique (SVET) measurement for local electrochemical quantification. Cathodic filiform body with Mg(OH)2 formation promoted the anodic corrosion propagation. Thick non-protective corrosion product formed after a longer immersion period was associated with uniform pitting propagation tunneled underneath the alloy, confirming the autocatalytic cathodic activation.

Effect of pH on the degradation kinetics of a Mg–0.8Ca alloy for orthopedic implants

Abstract One of the promising applications of magnesium and magnesium alloys is their use as biodegradable implants in biomedical applications. The pH around an orthopedic implant greatly affects the degradation kinetics of biodegradable Mg–Ca alloys. At the location of a fracture, local pH changes, and this has to be considered in the optimization of implant materials. In this study, the effect of the pH of a physiological buffer on degradation of a Mg–0.8Ca alloy was studied. The pH of Hank’s balanced salt solution (HBSS) was adjusted to 1.8, 5.3 and 8.1. Degradation of a Mg–0.8Ca implant was tested using immersion test and electrochemical techniques. Immersion tests revealed an initial weight gain for all samples followed by weight loss at extended immersion time. Weight gain was highest at acidic pH (1.8) and lowest at alkaline pH (8.1). This was in agreement with results from electrochemical polarization tests where the degradation rate was highest (7.29 ± 2.2 mm/year) at pH 1.8 and lowest (0.31 ± 0.06 mm/year) in alkaline medium of pH 8.1. The pH of all HBSS buffers except the most acidic (pH 1.8) reached a steady state of ∼pH 10 at the end of the two-month immersion period, independent of the initial pH of the solution. Corrosion products formed on the sample surfaces were investigated by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDX) and X-ray diffractometry (XRD), revealing the formation of magnesium and calcium phosphates with distinct morphologies that were different for each of the pH conditions. Thus, pH of physiological buffers has a significant effect on the degradation and corrosion of Mg–Ca alloys used for biomedical applications.

Enhanced hydrogen generation via hydrolysis of Mg–Mg2NiH4 system

Producing hydrogen via hydrolysis of light weighted metal-based materials is a promising technology for exploiting portable hydrogen–air fuel cells. Various additives have been designed to catalyze the hydrolysis behavior of Mg-based materials. In most cases, however, the kinetic promotion is in the expense of the systematic hydrogen generation yield. In this work, Mg–Mg2NiH4 system with extraordinary hydrolysis property is explored for hydrogen generation in 3.5% NaCl aqueous solution for the first time. The Mg-10 wt% Mg2NiH4 composite releases 845.1 mL g−1 (yield of 94.7%) hydrogen in just 20 s, with a maximum hydrogen generation rate (mHGR) of 6391 mL g−1 min−1. Our results have experimentally shown the synergistic effect between Mg and Mg2NiH4 on hydrolysis reaction. The in-situ ultrafine Ni particles derived from the rapid hydrolysis of Mg2NiH4 form a large amount of micro-galvanic cells with Mg, accelerating the electrochemical corrosion of Mg efficiently. In turn, the hydrolysis reaction of Mg2NiH4 can be dramatically driven by the local solution heat due to the violent exothermic reaction of Mg. The cooperative effect provides fresh strategy designing high-property hydrolysis materials with no substantial loss of the hydrogen supply capacity.

Pure magnesium laser surface modification using Nd:YAG laser

ABSTRACT Magnesium (Mg) and its alloys are promising materials for a wide range of biomedical applications due to its biodegradability. Nevertheless, their rapid corrosion dictates the need to develop strategies to control these materials’ corrosion rate. In fact, several surface modification techniques have been used to retard the corrosion of Mg and its alloys. Laser technology can be used to tailor Mg surfaces aiming to modify exposed area/roughness and thus control the biocorrosion process. This work presents a detailed study on pure Mg surface texturing by an Nd:YAG laser and their morphological characterisation, aiming to create either localised texturing or remelted areas. The characterisation of the textured and remelted surfaces was carried out by scanning electron microscopy and analysed using image analysis software (Image J) for obtaining their depth and width. Results show that higher scan speed (400 mm/s) and lower laser power (1.5 W) were unsuitable for machining pure Mg. The parameters to perform texturing and remelting are discussed herein.

The marine atmospheric corrosion of pure Mg and Mg alloys in field exposure and lab simulation

ABSTRACT It is of great significance to establish a reliable correlation between the field exposure damage and lab simulation measurements for marine atmospheric corrosion of Mg alloys. In this study, the corrosion behaviour of pure Mg, AM60, ZE41 and AZ91D was investigated in the real marine atmosphere and the simulated environments, such as salt spray and simulated sea wave impact by means of weight-loss measurement, morphology observation and corrosion product analysis. The simulated sea wave impact test appeared to be a suitable lab technique that can better simulate and reliably accelerate the marine atmospheric corrosion for Mg alloys. Based on the results, the individual influences of the environmental factors relative humidity, temperature, drying and wetting cycle and solution concentration, on the overall corrosion damage were compared, and a general damage process was proposed for the marine atmospheric corrosion of Mg alloys under different test conditions.

Corrosion Rate Investigation of Magnesium and Some of Its Alloys in 0.9% NaCl Solution

Magnesium(Mg)-based biomaterials are candidates for use as biodegradable metals. Mg can dissolve in body fluids, which means that implanted Mg can decompose during the healing process and it will not leave debris after healing is completed. However, uncontrolled degradation can destroy the scaffolds, leading to premature failure of the implant. The rate of magnesium degradation can be controlled by various impurities. Here, the corrosion of Mg and some of its alloys is investigated by electrochemical impedance and voltammetry methods. In the Figure, for example, the voltammogram (a) and impedance hodograph (b) are shown for an alloy containing 6.0 mass % Zn and 0.5 mass % Zr. In the Table, the corrosion rates are given from impedance measurements as the closest to stationary corrosion conditions. The corrosion rate is determined by the chemical composition and structure of the oxidation product layer. The shift of the corrosion potential in the anodic direction after cathodic polarization is explained by kinetic difficulties of electrode reactions in the presence of the reaction product layer. Figure 1

In vitro crevice corrosion of biodegradable magnesium in different solutions

Magnesium (Mg) is a promising biomedical metal because of its biodegradability. The crevice between tissue and Mg implant can not be neglected in some implantation sites due to inducing crevice corrosion of Mg. In this paper, a new single mold was designed to build the in vitro experimental setup and four kinds of solutions, i.e. the deionized water (DW), the 0.9 wt.% sodium chloride solution (NaCl), the phosphate buffer saline (PBS) and the modified simulated body fluid (m-SBF) were used to explore necessary factors of crevice corrosion in Mg. It was observed that crevice corrosion in Mg sheets would occur in NaCl and PBS solution under 0.2, 0.5 and 0.8 mm crevice thickness. And it was found that there were two necessary factors, i.e. chloride ion and crevice dimension, in crevice corrosion. For the high-purity Mg cannulated screws, crevice corrosion could occur inside tunnel when immersed in PBS.

Synthesis of Polypyrrole/V2O5 Composite Film on the Surface of Magnesium Using a Mild Vapor Phase Polymerization (VPP) Method for Corrosion Resistance

The vapor phase polymerization (VPP) method is a conventional strategy for synthesizing conducting polymers (CPs) on the surfaces of various materials. However, the current VPP method performed on a metal surface usually requires harsh reaction conditions, such as high temperature and low vacuum. In this paper, a polypyrrole (PPy) and vanadium pentoxide (V2O5) composite film was synthesized on the surface of Mg using a mild VPP method. Here, V2O5 was used as an oxidant, and it was found that the oxidation of pyrrole (Py) vapor on the surface of V2O5, which had been previously coated on the surface of Mg, could be performed at room temperature under normal atmospheric pressure. The formation of the PPy/V2O5 composite was verified by Fourier transform infrared spectroscopy (FTIR) and energy dispersive X-ray (EDX) spectroscopy. A thermogravimetric analyzer (TGA) was used to study the thermal stability of the composite. Subsequent corrosion tests showed that the PPy/V2O5 composite film could slow down the corrosion of Mg in 3.5 wt% NaCl. It is expected that the mild VPP method may find great potential in the fields of synthesis of CPs and the corrosion protection of reactive metals.

Fabrication and characterization of dicalcium phosphate coatings deposited on magnesium substrates by a chemical conversion route

It is well established that magnesium (Mg) is a promising material for use in biomedical applications. Nonetheless, it exhibits an accelerated corrosion rate when present in physiological media, which may lead to premature degradation of the implant in the body. As a result, it is necessary to slow down the corrosion of Mg in order to ensure that the implant is able to maintain its mechanical integrity during the whole healing period. In this work, dicalcium phosphate dihydrate (DCPD) coatings were formed on hot-rolled Mg substrates by a chemical conversion route aiming to increase the corrosion resistance and biointegration of the latter. The materials prepared herein were examined by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, electrochemical impedance spectroscopy, and in vitro assays. The sample obtained after immersing Mg in the phosphating bath for 24 h and with no heat treatment was the one with the highest corrosion resistance. This sample also exhibited the formation of a hydroxyapatite layer on its surface after soaking in Hank's balanced salt solution for times as short as 1 day. Moreover, this specimen showed no toxicity to rat mesenchymal stem cells, suggesting that it is a promising material for biomedical applications.

Stabilized Loading of Hyaluronic Acid-Containing Hydrogels into Magnesium-Based Cannulated Screws.

Cannulated screws have a structure for inserting a guide wire inside them to effectively correct complicated fractures. Magnesium, an absorbable metal used to manufacture cannulated screws, may decompose in the body after a certain period of implantation. The hydrogel formed by hyaluronic acid (HA) and polygalacturonic acid (PGA) has been used into Mg-based cannulated screws to prevent bone resorption owing to the rapid corrosion of Mg with unfavorable mechanical properties and a high ambient pH. In addition, Ca ions were added to the gel for cross-linking the carboxyl groups to modify the gelation rate and physical properties of the gel. The developed hydrogels were injected into the Mg-based cannulated screws, after which they released HA and Ca. The possibility of the application of this system as a cannulated screw was evaluated based on the corrosion resistance, gel degradation rate, HA release, toxicity toward osteocytes, and experiments involving the implantation of the screws into the femurs of rats. Ca ions first bound to PGA and delayed the gelation time and dissolution rate. However, they interfered with HA binding and increased the elution of HA at the beginning of gel degradation. Ca(NO3)2 concentrations higher than 0.01 M and low pH environments inhibited osteoblast differentiation and proliferation, owing to the elution of HA from the hydrogel. On the other hand, when the HA hydrogel with a proper amount of Ca was inserted into a magnesium screw, the degradation of Mg was delayed, and the presence of the gel contributed to new bone formation and osteocyte expansion.

Improvement in electrochemical corrosion resistance of Mg–Al–Zn alloy by 250 keV carbon ions irradiation

Mg–Al–Zn alloy (AZ91D) was irradiated with carbon ions at different doses (1 × 1013, 5 × 1013, 1 × 1014, 5 × 1014 and 1 × 1015 ions cm−2) by using Pelletron Accelerator. Ion energy was kept constant at 250 keV for all the irradiated samples. The range of carbon ions inside the alloy was found to be 0.67 μm. X-ray diffraction results indicated that the carbon ions irradiation of Mg alloy increases the intensity of Mg (002) plane. The average crystallite size of Mg alloy was decreased at 1 × 1013 ions cm−2 whereas an increase in the crystallite size was observed by further increasing the ion dose. The FTIR data indicated C–H, C–O, C=O and C-C vibrational modes in the irradiated samples. The electrochemical corrosion of Mg–Al–Zn alloy was investigated through potentiondynamic polarization tests in 0.9% NaCl solution. The open circuit potential (OCP) did not change at lower ion doses (up to 1 × 1014 ions cm−2), however, the OCP became more positive as the ion dose was increased to 1 × 1015 ions cm−2. Similarly, corrosion current density and corrosion rate were significantly decreased after carbon irradiation at 1 × 1015 ions cm−2. The SEM results revealed severe surface pitting of the unirradiated alloy that was reduced after the carbon ions irradiation.

First-principles modeling of the hydrogen evolution reaction and its application in electrochemical corrosion of Mg

By means of first-principles calculations, we have proposed an ab initio modeling to establish a formula between the hydrogen evolution rate and its overpotential of hydrogen evolution reaction (HER), relating with three different rate determining mechanisms, when Volmer reaction, Tafel reaction and Heyrowsky reaction are the rate determining steps of the entire reaction, respectively. Within this modeling, the free energy (ΔGH*) of the adsorbed hydrogen atom and the concentration of hydrogen ions in the solution have been correlated to the exchange current density. The hydrogen evolution modeling has been validated by available experimental results. Furthermore, by combining the previously proposed first-principles modeling of the anodic dissolution and this modeling of the HER in the electrochemical corrosion, the polarization curves of the 18 crystallographic surfaces of pure Mg have been theoretically derived. It has been found that in a neutral solution (pH=7) the corrosion current densities (icorr) of the 18 crystallographic surfaces range from 10−3.477 to 10−0.455 A/cm2 and their corresponding corrosion potentials (Ecorr) range from −1.36 to −0.892 VSHE, respectively. The base (0001) surface exhibits a lower corrosion rate of 10−3.345 A/cm2, whereas the crystal (213¯0) surface has a fast corrosion rate of 10−0.455A/cm2. The calculations even reveal that except for Ag, all the other alloying elements considered here accelerate the rates of the cathodic HER. In agreement with theoretical results, the experimentally measured polarization curves of the Mg-1Zn and Mg-2Sn alloys verify that both Zn and Sn additions accelerate the rate of the HER of Mg.

Biodegradable Surgical Staple Composed of Magnesium Alloy

Currently, surgical staples are composed of non–biodegradable titanium (Ti) that can cause allergic reactions and interfere with imaging. This paper proposes a novel biodegradable magnesium (Mg) alloy staple and discusses analyses conducted to evaluate its safety and feasibility. Specifically, finite element analysis revealed that the proposed staple has a suitable stress distribution while stapling and maintaining closure. Further, an immersion test using artificial intestinal juice produced satisfactory biodegradable behavior, mechanical durability, and biocompatibility in vitro. Hydrogen resulting from rapid corrosion of Mg was observed in small quantities only in the first week of immersion, and most staples maintained their shapes until at least the fourth week. Further, the tensile force was maintained for more than a week and was reduced to approximately one-half by the fourth week. In addition, the Mg concentration of the intestinal artificial juice was at a low cytotoxic level. In porcine intestinal anastomoses, the Mg alloy staples caused neither technical failure nor such complications as anastomotic leakage, hematoma, or adhesion. No necrosis or serious inflammation reaction was histopathologically recognized. Thus, the proposed Mg alloy staple offers a promising alternative to Ti alloy staples.

Reducing the electrochemical capacity decay of milled Mg–Ni alloys: The role of stabilizing amorphous phase by Ti-substitution

MgNi-based alloys have high electrochemical capacity as anode of nickel-metal hydride (Ni/MH) battery (≥500 mAh g−1). However the capacity decay seriously in charge-discharge cycling, which is previously ascribed to the corrosion of Mg. To solve this problem and reveal the related mechanism, the electrochemcial properties of Mg0.50Ni0.50, Mg0.45Ti0.05Ni0.05 and Mg0.40Ti0.10Ni0.50 alloys are studied in combination with their hydrogen storage properties and microstuctural evolution during cycling. This work demonstrates the amorphous phase in milled Mg0.45Ti0.05Ni0.50 and Mg0.40Ti0.10Ni0.50 alloys has higher resistance to hydrogenation-induced crystallization than milled Mg0.50Ni0.50 alloy. Thus, they show better hydrogen absorption/desorption reversibility and contribute to the reversible electrochemical capacity. Therefore, the cycle performance of the Mg0.50Ni0.50 alloy electrodes shows obvious improvement after partially substituting Mg by Ti. The capacity retention rate increases from 24.0% (Mg0.50Ni0.50) to 55.7% (Mg0.40Ti0.10Ni0.50) after 30 cycles. In addition, the Ti addition results in the formation of TiNi phase, and thus, the alloys show better electrochemical reaction kinetics and their high-rate dischargeability (HRD) is significantly improved. At 300 mA g−1, the HRD values of Mg0.50Ni0.50, Mg0.45Ti0.05Ni0.50 and Mg0.40Ti0.10Ni0.50 alloys are 41.7%, 83.7% and 90.3%, respectively. At higher discharge current density of 1200 mA g−1, the HRD values are 26.7%, 34.8% and 46.2%, respectively.