Corrosion Resistance Of Pure Magnesium Research Articles

In-situ formation of self-assembled hydrophobic Mg(OH)2/organosilane composite coatings under the driven of quadruple hydrogen bonds with enhanced corrosion properties

The close density, elastic modulus of magnesium and magnesium alloys to those of human bone, as well as their good biodegradable and bio-safety make them attractive as biomaterials. However, rapid degradation rate seriously limits their applications. In this study, an organic silanes (TES) containing quadruplet hydrogen bond structure was synthesized. In-situ formation of self-assembled Mg(OH)2 coating was prepared at first on pure magnesium surface by one-step hydrothermal method. And then self-assembled organosilane coatings was fabricated under the motivation of quadruple hydrogen bonding on Mg(OH)2 coating by sol-gel dip-coating. The dense cage-liked braided structure of Mg(OH)2 coating promotes the good bonding between the organosilane and Mg(OH)2 coatings. The contact angle of the sample with Mg(OH)2 coating is about 20.50°. The surface changes from hydrophilic to hydrophobic after the organosilane coating treatment. The contact angle increases to 113.99° and 135.49° with one and three passes dip-coating, correspondingly. The complete and dense hydrophobic composite coating could provide effectively barrier effect and improve the corrosion resistance of pure magnesium. After 3 times organosilane coating, the Mg(OH)2/organosilane composite coating shows the minimum corrosion tendency with the most positive corrosion potential (−1.27 V) and the lowest corrosion currency (1.50 ×10−4A·cm−2) in the simulated body fluids.

Investigation of anti-corrosion property of hybrid coatings fabricated by combining PEC with MAO on pure magnesium

• Novel hybrid coatings are prepared by combining PEC with MAO on pure magnesium. • PEC modified layers play a positive effect on improving corrosion resistance of PEC+MAO hybrid coatings. • PEC+MAO hybrid coatings can further enhance corrosion resistance of pure magnesium. Novel hybrid coatings on pure magnesium were prepared by combining plasma electrolytic carburizing (PEC) with micro-arc oxidation (MAO) to further enhance the anti-corrosion property in this paper. Scanning electron microscopy (SEM) was used to observe the micro-structure of the coatings, meanwhile, energy dispersive spectrometry (EDS) and X-ray diffraction (XRD) were separately used to investigate the elemental as well as phase compositions of the coatings. The anti-corrosion property of the coatings was evaluated by potentiodynamic polarization curves as well as electrochemical impedance spectroscopy (EIS).The results show that PEC process is closely related with the effects of adsorption as well as diffusion of the activated carbon atoms, and it can provide a favorable pretreatment surface with predesigned chemical composition to obtain a new kind of phase, namely SiC with superior corrosion resistance and chemical stability, in the following PEC+MAO hybrid coatings. Meanwhile, PEC preprocessing also can afford an excellent micro-structure to increase the coating thickness as well as to improve the compactness of the PEC+MAO hybrid coatings. During the fabrication process of the PEC+MAO hybrid coatings, an overlapping phenomenon in regard to coating thickness can be observed instead of heaping up layer by layer. Compared with both single PEC surface modification layers as well as single MAO coatings, the PEC+MAO hybrid coatings exhibit more superior anti-corrosion property. Especially, the EIS data reveal that the PEC+MAO hybrid coatings can act as an effective protection system to provide relatively excellent long-range anti-corrosion protection. Note also that employing same MAO technique for both single MAO treatment as well as PEC+MAO combining procedure is the key to this research.

Mechanical Behavior and In Vitro Corrosion of Cubic Scaffolds of Pure Magnesium Processed by Severe Plastic Deformation

Reports in the literature show that severe plastic deformation can improve mechanical strength, ductility, and corrosion resistance of pure magnesium, which suggests good performance for biodegradable applications. However, the reported results were based on testing of small samples on limited directions. The present study reports compression testing of larger samples, at different directions, in pure magnesium processed by hot rolling, equal channel angular pressing (ECAP), and high pressure torsion (HPT). The results show that severe plastic deformation through ECAP and HPT reduces anisotropy and increases strength and strain rate sensitivity. Also, scaffolds were fabricated from the material with different processing histories and immersed in Hank’s solution for up to 14 days. The as-cast material displays higher corrosion rate and localized corrosion and it is reported that severe plastic deformation induces uniform corrosion and reduces the corrosion rate.

Anomaly of corrosion resistance of pure magnesium via soft plasma electrolysis at sub-zero temperature

The present study investigates how sub-zero temperature affects the formation of the oxide layer of pure magnesium and subsequently alters their corrosion performance. To this end, a series of plasma electrolysis is carried out in alkaline-silicate electrolyte with two different temperatures of −5 and 25 °C. In contrast to the popular findings that low temperatures during anodic oxidation promotes superior corrosion protection, the present results show that the corrosion resistance of the sample processed at sub-zero condition is inferior to that processed at room temperature. In order to discuss such anomaly of the corrosion resistance, microstructural factors, including morphologies, compactness, and composition of the oxide layer would be taken into account.

In Vitro Osteocompatibility and Enhanced Biocorrosion Resistance of Diammonium Hydrogen Phosphate-Pretreated/Poly(ether imide) Coatings on Magnesium for Orthopedic Application.

Magnesium, as a biodegradable metal, is a promising candidate for biomedical applications. To modify the degradation behavior of magnesium and improve its osteocompatibility, chemical conversion and spin coating methods were combined to develop a diammonium hydrogen phosphate-pretreated/poly(ether imide) (DAHP/PEI) co-coating system. The diammonium hydrogen phosphate pretreatment was employed to enhance the attachment between PEI coatings and the magnesium substrate; meanwhile, it could serve as another bioactive and anticorrosion layer when PEI coatings break down. Surface characterization, electrochemical tests, and short-term immersion tests in DMEM were performed to evaluate DAHP/PEI coatings. Electrochemical measurements showed that DAHP/PEI coatings significantly improved the corrosion resistance of pure magnesium. No obvious changes of the chemical compositions of DAHP/PEI coatings occurred after 72 h of immersion in DMEM. An in vitro cytocompatibility study confirmed that viability and LDH activity of human osteoblast-like cells on DAHP/PEI coatings showed higher values than those on the DAHP-pretreated layer and pure magnesium. The DAHP-pretreated layer could still enhance the ALP activity of MG-63 cells after the degradation of PEI in DAHP/PEI coatings. Besides that, the in vitro cellular response to the treated magnesium was investigated to gain knowledge on the differentiation and proliferation of human adipose-derived stem cells (hADSCs). Cell distribution and morphology were observed by fluorescence and SEM images, which demonstrated that DAHP/PEI coatings facilitated cell differentiation and proliferation. The high level of C-terminals of collagen type I production of hADSCs on DAHP/PEI coatings indicated the potential of the coating for promoting osteogenic differentiation. Positive results from long-term cytocompatibility and proliferation tests indicate that DAHP/PEI coatings can offer an excellent surface for hADSCs.

Cytotoxicity and Corrosion Behavior of Magnesium and Magnesium Alloys in Hank's Solution after Processing by High‐Pressure Torsion

It is well‐known that processing by severe plastic deformation using high‐pressure torsion (HPT) promotes grain refinement and increases the strength of magnesium and its alloys. The present research is conducted to evaluate the effect of such processing on cytotoxicity and corrosion behavior in Hank's solution by using samples of commercial purity magnesium and AZ31, AZ91, and ZK60 magnesium alloys. All samples are subjected to electrochemical testing and hydrogen evolution testing before and after processing by HPT and the results show that this processing improves the corrosion resistance of pure magnesium, has no significant effect on the AZ31 and AZ91 alloys but reduces the corrosion resistance of the ZK60 alloy. The observations support the conclusion that grain refinement improves the corrosion resistance of metals with a tendency for passivation but impedes the resistance of metals without passivation. In addition, in vitro cytotoxicity tests are performed on the processed materials and show cell viability in all samples. The results demonstrate that HPT processing may be used to improve the performance of magnesium and its alloys as biodegradable implants.

Effects of Zr Ion Implantation on Surface Mechanical Properties and Corrosion Resistance of Pure Magnesium

Zirconium (Zr) was implanted into pure Mg by metal vapor vacuum arc (MEVVA) at the dose of 2 × 1016 ions/cm2 at room temperature. The surface characteristics of Zr-implanted Mg were analyzed by the Stopping and Range of Ions in Matter software (SRIM) and x-ray photoelectron spectroscopy (XPS), the surface nanohardness and tribological behavior were measured through nanoindentation and a friction-abrasion testing machine, and the corrosion resistance of Zr-implanted Mg was evaluated by electrochemical measurement and immersion test in simulated body fluid (SBF). The results demonstrated that a gradient modified layer composed of MgO, Mg(OH)2, ZrO2 and Zr was formed on the near surface of pure Mg and the nanohardness of pure Mg was improved by 48%. Furthermore, the Zr-implanted Mg exhibited a more positive corrosion potential of − 1.43 V (versus SCE) and a lower corrosion current density of 19.9 μA/cm2, and localized corrosion was effectively retarded during 24 h immersion in SBF, suggesting that the corrosion resistance of pure Mg was remarkably improved after Zr ion implantation. The mechanisms of surface strengthening and improved corrosion resistance were also discussed in this paper.

Corrosion protection behaviour of r-GO/TiO2 hybrid composite coating on Magnesium substrate in 3.5 wt.% NaCl

The current behavioral study investigated the effect of incorporation of two nanomaterials namely reduced graphene oxide(r-GO) and Titanium di oxide (TiO2) (synthesized by chemical reduction method) upon improving the corrosion resistance of pure Magnesium (Mg). Crystalline nature of synthesized TiO2 was analyzed through x-ray diffraction; UV vis spectroscopy showed its UV absorbance peak near 300 nm. TiO2, r-GO and r-GO/TiO2 coating over Mg is done by the way of electrode position technique for different time intervals. Analysis over electrochemical corrosion behaviour reveals that Mg coated with r-GO/TiO2 showcased better corrosion resistance when compared to bare Mg. Energy-dispersive X-ray spectroscopy and element mapping results exposed for the elementary confirmation as well as uniform dispersion of nano materials. Reduction in corrosion rate is notified for samples coated at 3 min time interval. Improvement in corrosion resistance of r-GO/TiO2 coatings is mainly due to the high impermeability of r- GO to resist Mg2+ ions dissolution in chloride media.

Development of corrosion resistant surfaces via friction stir processing for bio implant applications

Current investigation presents the use of Friction Stir Processing (FSP) to improve the corrosion resistance of pure magnesium for biomedical applications. FSP has been used to incorporate hydroxyapetite (HAP) into Mg-surface so as to modify the chemical composition. FSP was done within a matrix of different parameters and conditions. Influence of various parameters on microstructure was also clearly observed. XRD analysis confirmed the presence of HAP, whereas SEM images revealed a uniform distribution of the imbedded phase. Microhardness and in-vitro corrosion studies were also performed. Influence of grain size on hardness was validated by Hall-Petch relationship. Corrosion behavior was explained on the basis of texture, which indicated better corrosion resistance in comparison to the pure Mg. Therefore, the study reveals that the proposed FSP methodology can be useful tool to improve mechanical and corrosion properties of pure Mg for biomedical applications.

Effects of grain size on the corrosion resistance of pure magnesium by cooling rate-controlled solidification

The aim of this study was to investigate the effect of grain size on the corrosion resistance of pure magnesium developed for biomedical applications. High-purity magnesium samples with different grain size were prepared by the cooling rate-controlled solidification. Electrochemical and immersion tests were employed to measure the corrosion resistance of pure magnesium with different grain size. The electrochemical polarization curves indicated that the corrosion susceptibility increased as the grain size decrease. However, the electrochemical impedance spectroscopy (EIS) and immersion tests indicated that the corrosion resistance of pure magnesium is improved as the grain size decreases. The improvement in the corrosion resistance is attributed to refine grain can produce more uniform and density film on the surface of sample.

Study on corrosion resistance of pure magnesium with CaSiO3 contained coating in NaCl solution

A composite coating was fabricated on pure magnesium by hydrothermal treatment in order to reduce its degradation in body environment. The coating was characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The XRD pattern showed that the main composition of the coating was a mixture of CaSiO3, MgSiO3 and Mg(OH)(2). Electrochemical test showed that the corrosion current density (i(corr)) of the coated magnesium was decreased by about two orders of magnitude compared with that of the bare magnesium, and the EIS measurement also showed that the corrosion resistant performance of the coated magnesium was significantly enhanced. Meanwhile, weight loss test showed that the weight loss of the coated magnesium was lower than that of the bare magnesium. Hence, the present study indicated that the composite coating could greatly slow down the degradation of pure magnesium.

Tratamientos químicos de conversión para la protección de magnesio biodegradable en aplicaciones temporales de reparación ósea

The present study was developed to improve the corrosion resistance of pure magnesium by applying chemical conversion coatings. Carbonate and fluoride layers were generated by immersion in solutions of NaHCO 3 of concentration 9 wt.%and HF of concentration 48 wt.%, respectively. Corrosion resistance of the coated samples was evaluated in comparison with that of the uncoated substrate by electrochemical techniques in a physiological solution (PBS). Results have shown that the carbonate coating is not viable to be used for protecting magnesium against corrosion.On the contrary, the fluoridemagnesiumcoating significantly increases the corrosion resistance ofmagnesium in physiological medium. The high compactness and adherence to the base metal of theMgF 2 layer produced by this simple chemical conversion treatment confer the protective properties to the coating.

Corrosion Behavior of Magnesium with Hydroxyapatite Coatings Formed by Hydrothermal Treatment

Corrosion resistance of magnesium alloys must be improved for their applications to orthopaedic bioabsorbable devices. Since hydroxyapatite (HAp) is chemically stable in the body and is the main component of bones, HAp coatings have been well studied to improve the corrosion resistance and osteoconductivity of magnesium alloys. In this study, highly crystallized HAp coatings were formed on pure magnesium with a single-step hydrothermal treatment using a C 10 H 12 CaN 2 Na 2 O 8 solution with various pH values. Morphology of the HAp coating varied depending on the pH value. Corrosion behavior of the HAp-coated magnesium was investigated by anodic polarization, impedance and immersion tests in a simulated body fluid. It was revealed that the corrosion resistance of pure magnesium was improved more than 10 times with the HAp coatings. Stable localized corrosion was prevented with the HAp coatings although the occurrence and moderation of unstable localized corrosion appeared to take place at the defects of the HAp coatings. The initial protectiveness of the HAp coating depended on the treatment condition. During 4-day immersion, the precipitated HAp sealed the defects of the HAp coatings, resulting in the negligible release of magnesium ions regardless of the treatment conditions.

Influence of <i>In Situ</i> MgO Coating on Corrosion Resistance of Pure Magnesium in Normal Saline

Magnesium and its alloys are potential biodegradable materials due to their outstanding biological performance, but their poor corrosion resistance greatly limits their applications as bone implants. This paper investigates the influence of in situ magnesium oxide coating on corrosion resistance of pure magnesium in normal saline. It was discovered by SEM that rough and porous oxide coatings were obtained on the surface of the pure magnesium after heat-treated at 400~500°C and the samples were severely corroded after immersion in 0.9 wt.% NaCl solution for 3 days. It also showed that the weight loss rates of the treated pure magnesium (TPM) samples were about 5~6 times higher than that of the untreated pure magnesium (UPM) sample. Electrochemical measurements showed that the corrosion current density (icorr) of the TPM samples was one order of magnitude higher than that of the UPM sample.

Effect of alternating voltage treatment on the corrosion resistance of pure magnesium

Pure magnesium was treated by alternating voltage (AV) treatment technique. The optimal AV-treatment parameters for greatly improving corrosion resistance were determined by the orthogonal experiments. Polarization curves, electrochemical impedance spectroscopy (EIS), and scanning electrochemical microscopy (SECM) were performed to understand the effect of AV-treatment on the corrosion resistance of pure magnesium. AFM, contact angle measurement and XPS were employed to further investigate the influence of AV-treatment on the properties of the surface film formed on pure magnesium after AV-treatment. The results showed that a uniform and stable film was formed and the corrosion resistance of pure magnesium was greatly improved after AV-treatment. This was caused by the noticeable change of chemical structure and semi conducting properties of surface film after AV-treatment.

Corrosion of pure magnesium under thin electrolyte layers

The corrosion behavior of pure magnesium was investigated by means of cathodic polarization curve, electrochemical impedance spectroscopy (EIS) and electrochemical noise (EN) under aerated and deaerated thin electrolyte layers (TEL) with various thicknesses. Based on shot noise theory and stochastic theory, the EN results were quantitatively analyzed by using the Weibull and Gumbel distribution function, respectively. The results show that the cathodic process of pure magnesium under thin electrolyte layer was dominated by hydrogen reduction. With the decreasing of thin electrolyte layer thickness, cathodic process was retarded slightly while the anodic process was inhibited significantly, which indicated that both the cathodic and anodic process were inhibited in the presence of oxygen. The absence of oxygen decreased the corrosion resistance of pure magnesium in case of thin electrolyte layer. The corrosion was more localized under thin electrolyte layer than that in bulk solution. The results also demonstrate that there exist two kinds of effects for thin electrolyte layer on the corrosion behavior of pure magnesium: (1) the rate of pit initiation was evidently retarded compared to that in bulk solution; (2) the probability of pit growth oppositely increased. The corrosion model of pure magnesium under thin electrolyte layer was suggested in the paper.

Improvement of corrosion resistance of pure magnesium in Hanks’ solution by microarc oxidation with sol–gel TiO2 sealing

Abstract A composite coating was prepared on degradable magnesium (Mg) implant for improving its corrosion resistance in Hanks’ solution (a simulated body fluid). The composite coating was fabricated using a two-step process: (i) a thick and porous oxide layer (with pore size of a few μm) was first formed by microarc oxidation (MAO) in a silicate/fluoride containing electrolyte, and (ii) a top TiO2 sealing layer was formed on the porous layer by sol–gel dip coating followed by hydrothermal treatment. SEM imaging and EDS mapping revealed an average overall thickness of about 12 μm. XRD analysis showed that the MAO layer was composed of magnesium oxide and fluoride and the TiO2 was present as an amorphous phase. Both electrochemical impedance spectroscopic (EIS) and anodic polarization measurements consistently recorded an increase in the initial corrosion resistance of about 30 times due to the composite coating. Immersion tests also showed that the corrosion behavior of the coated samples was more stable over time, and the degree of corroded damage was much reduced compared with bare Mg. The porous MAO layer provided anchorage sites for the subsequent TiO2 sol–gel coating, which sealed the pores and hence significantly enhanced the corrosion resistance while direct sol–gel coating on bare Mg was not successful. The present results indicate that the corrosion resistance of Mg implants could be significantly improved by a simple method using non-toxic materials. The increase in corrosion resistance implies the possibility of using less bulky fixation plates, thus enhancing the potential of using Mg as degradable implants.

Improvement of corrosion resistance of pure magnesium via vacuum pack treatment

An aluminized coating on pure magnesium was conducted by vacuum pack aluminizing in order to improve its corrosion resistance. XRD and SEM/EDS analysis show that the alloying coating could be divided into two layers: the inner layer is mainly composed of β-Mg 17Al 12 phase and the outer layer is mainly composed of α-Al. This coating is different from that obtained by diffusion alloying under protective atmosphere in its structure and phase constituents. A visible transition layer of aluminum in magnesium was found between the alloying layer and the magnesium substrate. The electrochemical testing results showed that the corrosion resistance of Mg was significantly improved due to the formation of the Al-rich layer and the large quantity of β-Mg 17Al 12 on the surface. The bonding between the alloying layer and the substrate is metallurgical, and the micro-hardness of this layer is increased significantly.

Effects of treatment time on corrosion of diffusion-alloyed coatings of pure magnesium

The corrosion resistance of pure magnesium with surface alloying layer obtained by a solid diffusion alloying technique has been analyzed. To establish the optimum treatment time, the experiments were performed at 480°C for different solid diffusion time (8, 16, and 24h). The diffusion interaction effectiveness between Zn, Al mix powder and the sample surface, depending on the treatment time for diffusion at given temperatures, has an obvious influence on corrosion resistance and corrosion mechanism. Corrosion properties were studied using the constant immersion test (in 3.0% NaCl solution, temperature is (28±1)°C, and time is 96h). Optical microscopy (OM) and EDS (energy dispersive spectrum) composition analysis were used to examine the cross-sectional microstructural characteristics of alloyed layer of treated samples. It is shown that in comparison with the untreated samples, the treated ones possess a better corrosion resistance. The Al5Mg11Zn4 phase, which formed as a continuous phase due to the diffusion of Al, Zn, and Mg elements and subsequent interaction on the outermost layer of diffusion alloying zones (especially the samples treated for 24h at 480°C), was inert to the chloride solution compared with pure magnesium and acted as a corrosion barrier, and therefore the best corrosion resistance was obtained. This protective action of Al5Mg11Zn4 phase was found to change with its amount, which was controlled by the diffusion time at given temperature. It was concluded that the continuous Al5Mg11Zn4 phase (WP-zone) of the reacted layer in pure magnesium was beneficial from the point of view of corrosion resistance.

Surface Modification of Magnesium by NaHCO<SUB>3</SUB> and Corrosion Behavior in Hank’s solution for New Biomaterial Applications

The present study was carried out to improve the corrosion resistance of pure magnesium in Hank's Balanced Salt Solution (HBSS) through the surface modification. Three kinds of alkaline compounds, such as sodium hydrogen carbonate, sodium carbonate, and lithium hydroxide, were used for treatment. Only magnesium treated with aqueous sodium hydrogen carbonate solution gave a good corrosion resistance in HBSS solution at 25°C up to 75 days, while almost no effect in sodium carbonate and lithium hydroxide. It was likely that hydrogen carbonate ions were essential for the surface improvement of magnesium. X-ray diffraction patterns of modified magnesium showed new peaks of magnesium carbonate and others on the surface. New surface structure of needle-shaped crystals was observed by scanning electron microscopy (SEM). Both elemental mapping, and energy dispersive (EDX) techniques in SEM showed the precipitation of calcium magnesium phosphate (low crystallinity whitlockite:(Ca,Mg)3(PO 4 ) 2 ) on the surface of magnesium specimen. It could be concluded that surface modification with sodium hydrogen carbonate made it possible to apply metal magnesium in biomedical, dental, and other industrial usage.