Corrosion Behavior of Microarc Oxidation and Polycaprolactone Coatings Applied to AZ31 Magnesium Alloy Evaluated in Simulated Body Fluid and Balanced Salt Solution PDF Download
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Author: Benjamin M. Wilke
Publisher:
ISBN:
Category : Biomedical materials
Languages : en
Pages : 182
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Book Description
Recent research in orthopedic implant materials has focused on the use of magnesium alloys as a base material due to its mechanical properties similar to that of human bone. Rapid corrosion of magnesium materials in aqueous environments poses a significant hurdle to their application as a biomedical implant. A variety of coatings have been shown to improve the corrosion resistance of magnesium based materials in simulated body fluid environments including microarc oxidation and polymer coatings. However, formulation and corrosion rates vary significantly between solution types. Furthermore, in vivo results have shown that many common in vitro solutions over estimate corrosion rates. In addition to variations between solutions needing to be resolved, there has been little work performed to characterize large sample corrosion under stress. This is an essential step in evaluating concept performance at a macro scale, for application as a human implant. The experiments performed and presented in this thesis primarily involve the comparison of conventional simulated body fluid (c-SBF) and Earle's balanced salt solution (EBSS). Samples evaluated in these environments are microarc oxidation (MAO) coated AZ31 magnesium alloy and polycaprolactone dip-coated AZ31. MAO coated samples were created for a range of process settings to observe the effect of processing on corrosion performance. A dependence of MAO coating thickness on process voltage was found which augmented the initial corrosion resistance values observed via electrochemical testing. Both MAO and PCL coatings were found to improve the corrosion resistance of the samples as compared to uncoated AZ31. It was found that all variations (MAO, PCL, and uncoated) showed a reduced corrosion rate in EBSS as compared to c-SBF. This corrosion reduction was apparent through potentiodynamic scanning, electrochemical impedance spectroscopy, and visual inspection. Preliminary mechanical corrosion results, in the form of constant extension testing, showed no dependence of corrosion on stress level. Future work may be aimed towards expanding modes of mechanical testing and further refining simulated body fluids to fit with in vivo test results.
Author: Benjamin M. Wilke
Publisher:
ISBN:
Category : Biomedical materials
Languages : en
Pages : 182
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Book Description
Recent research in orthopedic implant materials has focused on the use of magnesium alloys as a base material due to its mechanical properties similar to that of human bone. Rapid corrosion of magnesium materials in aqueous environments poses a significant hurdle to their application as a biomedical implant. A variety of coatings have been shown to improve the corrosion resistance of magnesium based materials in simulated body fluid environments including microarc oxidation and polymer coatings. However, formulation and corrosion rates vary significantly between solution types. Furthermore, in vivo results have shown that many common in vitro solutions over estimate corrosion rates. In addition to variations between solutions needing to be resolved, there has been little work performed to characterize large sample corrosion under stress. This is an essential step in evaluating concept performance at a macro scale, for application as a human implant. The experiments performed and presented in this thesis primarily involve the comparison of conventional simulated body fluid (c-SBF) and Earle's balanced salt solution (EBSS). Samples evaluated in these environments are microarc oxidation (MAO) coated AZ31 magnesium alloy and polycaprolactone dip-coated AZ31. MAO coated samples were created for a range of process settings to observe the effect of processing on corrosion performance. A dependence of MAO coating thickness on process voltage was found which augmented the initial corrosion resistance values observed via electrochemical testing. Both MAO and PCL coatings were found to improve the corrosion resistance of the samples as compared to uncoated AZ31. It was found that all variations (MAO, PCL, and uncoated) showed a reduced corrosion rate in EBSS as compared to c-SBF. This corrosion reduction was apparent through potentiodynamic scanning, electrochemical impedance spectroscopy, and visual inspection. Preliminary mechanical corrosion results, in the form of constant extension testing, showed no dependence of corrosion on stress level. Future work may be aimed towards expanding modes of mechanical testing and further refining simulated body fluids to fit with in vivo test results.
Author: Wenli Zhao
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Author: Jiayang Liu
Publisher:
ISBN:
Category : Biomedical materials
Languages : en
Pages : 262
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Book Description
In recent years, magnesium alloys, due to their high strength and biocompatibility, have attracted significant interest in medical applications, such as cardiovascular stents, orthopedic implants, and devices. To overcome the high corrosion rate of magnesium alloys, coatings have been developed on the alloy surface. Most coating methods, such as anodic oxidation, polymer coating and chemical conversion coating, cannot produce satisfactory coating to be used in human body environment. Recent studies demonstrate that micro-arc oxidation (MAO) technique can produce hard, dense, wear-resistant and well-adherent oxide coatings for light metals such as aluminum, magnesium, and titanium. Though there are many previous studies, the understanding of processing conditions on coating performance remains elusive. Moreover, previous tests were done in simulated body fluid. No test has been done in a cell culture medium, which is much closer to human body environment than simulated body fluid. In this study, the effect of MAO processing time (1 minute, 5 minutes, 15 minutes, and 20 minutes) on the electrochemical behaviors of the coating in both conventional simulated body fluid and a cell culture medium has been investigated. Additionally a new electrolyte (12 g/L Na2SiO3, 4 g/L NaF and 4 ml/L C3H8O3) has been used in the MAO coating process. Electrochemical behaviors were measured by performing potentiodynamic polarization and electrochemical impedance spectroscopy tests. In addition to the tests in simulated body fluid, the MAO-coated and uncoated samples were immersed in a cell culture medium to investigate the corrosion behaviors and compare the difference in these two kinds of media. The results show that in the immersion tests in conventional simulated body fluid, the 20-minute MAO coated sample has the best resistance to corrosion due to the largest coating thickness. In contrast, in the cell culture medium, all MAO coated samples demonstrate a similar high corrosion resistance behavior, independent of MAO processing time. This is probably due to the organic passive layers formed on the coating surfaces. Additionally, a preliminary finite element model has been developed to simulate the immersion test of magnesium alloy in simulated body fluid. Comparison between the predicted corrosion current density and experimental data is discussed.
Author: Yanhong Gu
Publisher:
ISBN:
Category : Bone substitutes
Languages : en
Pages : 248
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Book Description
Author: Wenxue Lin
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Dingchuan Xue
Publisher:
ISBN:
Category :
Languages : en
Pages : 163
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Book Description
Magnesium (Mg) and its alloys are emerging as a possible biodegradable implant material. The corrosion behavior of pure Mg, AZ31, and AZ91D were evaluated in various In Vitro and In Vivo environments to investigate their potential application of being biomaterials. Mg implants may degrade too quickly in the body, before the natural healing process is complete. Anodization is known to be an effective approach for slowing down the initial corrosion rate of magnesium (Mg) and its alloys. Anodization was investigated to slow down the initial corrosion of Mg in a simulated body corrosive environment. Pure Mg and AZ91D alloy were anodized and their corrosion resistance was compared in terms of anodization behavior and parameters such as applied voltage and current with different anodization time. Electrochemical impedance spectroscopy, DC polarization, and immersion testing were used to evaluate the corrosion resistance of Mg samples and further optimize anodization parameters. The results showed that anodization increased the corrosion resistance of both pure Mg and AZ91D samples. Further characterization showed the anodized layers on both pure Mg and AZ91D consisted of Mg, O and Si, in the mixture of MgO and Mg2SiO4. The anodization of AZ91D was further investigated by studying the specific use of oxy-salts to improve the corrosion resistance of anodization coatings. Oxy-salts of silicate, phosphate, and carbonate were added separately to a sodium hydroxide alkaline electrolyte used for anodization. This modified process was investigated in terms of anodizing behavior, the surface properties of the film, and enhanced corrosion protection of the metal. Anodization of AZ91D using the silicate containing electrolyte generated sparks and increased the electrolyte temperature, and produced a thicker and more corrosion resistant layer than the other oxy-salts. In this process, MgO and SiO2 formed Mg2SiO4 at high temperature and silicon (Si) in the anodized coating was mainly presented in Mg2SiO4. Phosphorus (P) and carbon (C) were not found in the coatings from the phosphate and carbonate containing electrolyte anodizations. The effects of silicate concentration and anodizing time on the surface properties and corrosion resistance were studied in detail. A detailed chemical structure of the Si-containing anodized coating was postulated. Moreover, this paper described the water-based bis-[triethoxysilyl] ethane (BTSE) silane modification on the surface of Magnesium-Yttrium (Mg-Y) alloy for adhesion promoting, crosslinking of resins, and corrosion protection. Surface characterization of ESEM, FTIR, and EDX showed the hydrolysis and condensation of silane resulted in a strong covalent bonding. In Vivo corrosion behaviors of the uncoated and coated Mg-Y alloy were evaluated in the acute implantation by using novel self-developed corrosion probes which were inserted into the body cavity and subcutaneous tissue of the mice. In Vitro experiments, compared to In Vivo results, artificial simulated body solutions were more corrosive. Based on the electrochemical experiments of potentio-dynamics polarization and electrochemical impedance spectroscopy (EIS), the epoxy-modified BTSE silane coating successfully increased corrosion resistance at the initial stage of implantation.
Author: B.L. Jiang
Publisher: Elsevier Inc. Chapters
ISBN: 0128089466
Category : Technology & Engineering
Languages : en
Pages : 43
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Book Description
Micro-arc oxidation (MAO) is a novel and attractive surface engineering process for magnesium (Mg) alloys. In an electrolytic bath with high electric energy, the surface of a magnesium alloy can be converted into a dense and hard ceramic oxide coating. The MAO process can be used in diverse applications as a corrosion control technique. Due to its simplified pre-treatment, superior corrosion resistance performance and environmentally safe coating process, MAO technology has emerged as an important alternative to anodizing techniques in certain areas. This chapter presents a review of MAO techniques for Mg alloys from the scientific, technological and application points of view.
Author: G.-L. Song
Publisher: Elsevier Inc. Chapters
ISBN: 0128089482
Category : Technology & Engineering
Languages : en
Pages : 61
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Book Description
Anodization is one of the most important and effective surface pre-treatments for Mg alloys. This chapter systematically summarizes Mg alloy anodizing behavior, the compositions and microstructures of anodized films on Mg alloys and the anodization-influencing factors. Based on the anodizing voltage variation, gas evolution and sparking behavior in a typical anodizing process and the characteristic composition and microstructure of an anodized coating, a four-stage anodizing mechanism is postulated. Moreover, the corrosion performance of anodized Mg alloys is systematically reviewed and a corrosion model is proposed to explain the corrosion performance and electrochemical behavior. It is believed that some of the measured electrochemical features can be utilized to rapidly evaluate or compare the corrosion resistance of anodized Mg alloys.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Author: G.-L. Song
Publisher: Elsevier Inc. Chapters
ISBN: 0128089407
Category : Technology & Engineering
Languages : en
Pages : 42
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Book Description
Magnesium (Mg) alloys have low corrosion resistance and exhibit unusual corrosion behavior in aqueous environments. Because of this unique corrosion performance, some special corrosion prevention techniques have to be employed for Mg alloys in their applications. This chapter briefly summarizes the corrosion characteristics of Mg alloys, and also presents a strategy and methodologies to mitigate the corrosion damage of Mg alloys in applications.
