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Article: Characterization and corrosion studies of fluoride conversion coating on degradable Mg implants

TitleCharacterization and corrosion studies of fluoride conversion coating on degradable Mg implants
Authors
KeywordsConversion Coating
Corrosion Resistance
Degradable Implant Material
Magnesium
Magnesium Fluoride
Issue Date2007
PublisherElsevier SA. The Journal's web site is located at http://www.elsevier.com/locate/surfcoat
Citation
Surface And Coatings Technology, 2007, v. 202 n. 3, p. 590-598 How to Cite?
AbstractFluoride conversion coating was synthesized on magnesium (Mg) by immersion treatment in hydrofluoric acid (HF) at room temperature, with the aim of improving the corrosion resistance of Mg in applications as degradable implant material. After an immersion period of 24 h in 48% HF, the samples carried a bronze color, and the conversion coating was dense and free of cracks. Field-emission scanning-electron microscopy (FE-SEM) of the cross-section revealed a coating thickness of about 1.5 μm. Atomic-force microscopy (AFM) recorded an average surface roughness of ∼ 21 nm for the coated sample, similar to that of the untreated one (∼ 17 nm). The coating was mainly composed of magnesium fluoride (MgF2) as identified by thin-film X-ray diffractometry (TF-XRD), consistent with compositional analysis using X-ray photoelectron spectroscopy (XPS). The MgF2 was in the form of crystallites of a few nm. A small amount of oxygen was present inside the coating, suggesting that some F- ions are replaced by hydroxyl (OH-) ions in the MgF2 structure, or that a small amount of Mg(OH)2 was present. The corrosion resistance of untreated and conversion coated Mg in Hanks' solution was studied using electrochemical impedance spectroscopy (EIS), potentiodynamic polarization tests, and immersion tests. EIS results showed a polarization resistance of 0.18 kΩ cm2 for the untreated Mg and 5.2 kΩ cm2 for the coated sample, giving an improvement of about 30 times. Polarization tests also recorded a reduction in corrosion current density from 400 μA/cm2 to 10 μA/cm2, showing an improvement of about 40 times. The galvanic effect between untreated and fluoride-coated Mg samples was small. Immersion tests in Hanks' solution also resulted in a much milder and more uniform corrosion damage on the fluoride-coated samples. The results of the present study showed that fluoride coating by conversion treatment is a simple and promising way of enhancing the corrosion resistance of Mg in Hanks' solution, or that it may be employed as a pretreatment step for subsequent coating. © 2007 Elsevier B.V. All rights reserved.
Persistent Identifierhttp://hdl.handle.net/10722/170119
ISSN
2015 Impact Factor: 2.139
2015 SCImago Journal Rankings: 0.872
ISI Accession Number ID
References

 

DC FieldValueLanguage
dc.contributor.authorChiu, KYen_US
dc.contributor.authorWong, MHen_US
dc.contributor.authorCheng, FTen_US
dc.contributor.authorMan, HCen_US
dc.date.accessioned2012-10-30T06:05:26Z-
dc.date.available2012-10-30T06:05:26Z-
dc.date.issued2007en_US
dc.identifier.citationSurface And Coatings Technology, 2007, v. 202 n. 3, p. 590-598en_US
dc.identifier.issn0257-8972en_US
dc.identifier.urihttp://hdl.handle.net/10722/170119-
dc.description.abstractFluoride conversion coating was synthesized on magnesium (Mg) by immersion treatment in hydrofluoric acid (HF) at room temperature, with the aim of improving the corrosion resistance of Mg in applications as degradable implant material. After an immersion period of 24 h in 48% HF, the samples carried a bronze color, and the conversion coating was dense and free of cracks. Field-emission scanning-electron microscopy (FE-SEM) of the cross-section revealed a coating thickness of about 1.5 μm. Atomic-force microscopy (AFM) recorded an average surface roughness of ∼ 21 nm for the coated sample, similar to that of the untreated one (∼ 17 nm). The coating was mainly composed of magnesium fluoride (MgF2) as identified by thin-film X-ray diffractometry (TF-XRD), consistent with compositional analysis using X-ray photoelectron spectroscopy (XPS). The MgF2 was in the form of crystallites of a few nm. A small amount of oxygen was present inside the coating, suggesting that some F- ions are replaced by hydroxyl (OH-) ions in the MgF2 structure, or that a small amount of Mg(OH)2 was present. The corrosion resistance of untreated and conversion coated Mg in Hanks' solution was studied using electrochemical impedance spectroscopy (EIS), potentiodynamic polarization tests, and immersion tests. EIS results showed a polarization resistance of 0.18 kΩ cm2 for the untreated Mg and 5.2 kΩ cm2 for the coated sample, giving an improvement of about 30 times. Polarization tests also recorded a reduction in corrosion current density from 400 μA/cm2 to 10 μA/cm2, showing an improvement of about 40 times. The galvanic effect between untreated and fluoride-coated Mg samples was small. Immersion tests in Hanks' solution also resulted in a much milder and more uniform corrosion damage on the fluoride-coated samples. The results of the present study showed that fluoride coating by conversion treatment is a simple and promising way of enhancing the corrosion resistance of Mg in Hanks' solution, or that it may be employed as a pretreatment step for subsequent coating. © 2007 Elsevier B.V. All rights reserved.en_US
dc.languageengen_US
dc.publisherElsevier SA. The Journal's web site is located at http://www.elsevier.com/locate/surfcoaten_US
dc.relation.ispartofSurface and Coatings Technologyen_US
dc.subjectConversion Coatingen_US
dc.subjectCorrosion Resistanceen_US
dc.subjectDegradable Implant Materialen_US
dc.subjectMagnesiumen_US
dc.subjectMagnesium Fluorideen_US
dc.titleCharacterization and corrosion studies of fluoride conversion coating on degradable Mg implantsen_US
dc.typeArticleen_US
dc.identifier.emailChiu, KY:pkychiu@hkucc.hku.hken_US
dc.identifier.authorityChiu, KY=rp00379en_US
dc.description.naturelink_to_subscribed_fulltexten_US
dc.identifier.doi10.1016/j.surfcoat.2007.06.035en_US
dc.identifier.scopuseid_2-s2.0-35549006316en_US
dc.relation.referenceshttp://www.scopus.com/mlt/select.url?eid=2-s2.0-35549006316&selection=ref&src=s&origin=recordpageen_US
dc.identifier.volume202en_US
dc.identifier.issue3en_US
dc.identifier.spage590en_US
dc.identifier.epage598en_US
dc.identifier.isiWOS:000251464300023-
dc.publisher.placeSwitzerlanden_US
dc.identifier.scopusauthoridChiu, KY=7202988127en_US
dc.identifier.scopusauthoridWong, MH=25651162500en_US
dc.identifier.scopusauthoridCheng, FT=7202811219en_US
dc.identifier.scopusauthoridMan, HC=7102326766en_US

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