Efeito da oxidação eletrolítica assistida a plasma sobre a resistência à corrosão do magnésio em solução simulada de fluido corpóreo
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Data
2019-09-30
Autores
Gonçalves, Thaís Matiello [UNESP]
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
O magnésio e suas ligas são materiais metálicos com elevado potencial de aplicação como biomaterial na produção de parafusos e implantes. Entretanto, suas baixas resistências a corrosão comprometem suas aplicabilidades, e a oxidação eletrolítica assistida a plasma (PEO) se mostra uma técnica viável na otimização das propriedades anticorrosivas do magnésio. Neste trabalho, a liga AZ31 foi tratada por PEO, utilizando solução de fosfato de potássio monobásico anidro e hidróxido de potássio, garantindo um aumento significativo na resistência à corrosão em fluido corpóreo simulado (SBF). Os parâmetros elétricos do sistema foram variados, com o intuito de promover a formação de um revestimento mais homogêneo, com baixa densidade de poros e menos defeitos estruturais. A polarização da corrente também foi estudada, sendo todos os experimentos realizados em ambos os modos, unipolar (tensão anódica) e bipolar (tensões anódica e catódica). Os parâmetros foram variados na seguinte ordem: frequência, tensão, ciclo de trabalho e tempo de tratamento. A frequência foi variada entre 300 e 3000 Hz, enquanto que a tensão variou entre 200 e 400 V, para modo unipolar e -60 e -200 V para bipolar. Espectroscopia de impedância eletroquímica (EIS) e polarização potenciostática foram empregadas nas análises de corrosão das amostras quando imersas em SBF. Um microscópio eletrônico de varredura (MEV) permitiu a determinação da morfologia, enquanto que o espectrômetro de energia dispersiva de raios- X (EDS) analisou a composição química dos revestimentos. A espessura dos filmes foi determinada pelo método de inspeção por corrente parasita. Altos valores de frequência de pulsos levaram à formação de revestimentos mais resistentes aos ataques de eletrólitos corrosivos, sendo 3000 Hz e 2000 Hz as melhores opções para ambas correntes unipolar e bipolar, respectivamente. A propriedade de barreira foi otimizada para amostras com tensão de tratamento de 300 V para modo unipolar e 300 V e -60 V para regime bipolar, aumentando a resistência à corrosão da liga em 17.000% e 9.000%, respectivamente. Testes de imersão em SBF foram realizados para os revestimentos produzidos tanto em modo unipolar como bipolar, seguindo os parâmetros de tratamento das melhores condições. A resistência à corrosão dos revestimentos diminuiu nos estágios iniciais de imersão, seguido de um considerável aumento no 7º dia. A integridade das amostras foi comprometida ao longo do tempo de exposição ao SBF, sendo que os filmes bipolares se mostraram mais estáveis durante os testes. Ao final das análises, apesar dos efeitos negativos inerentes ao SBF, as amostras se mostraram ainda resistentes aos ataques químicos. Este comportamento sugere a possibilidade de emprego da liga AZ31, tratada por uma técnica simples e econômica, como biomaterial, uma vez que os compostos liberados durante a dissolução são biocompátiveis. Além do mais, nenhum efeito negativo sobre as propriedades mecânicas foi observado, sendo que em 30 dias de imersão, os eletrólitos de SBF não comprometeram o substrato, apenas os revestimentos.
The magnesium and its alloys are metallic materials with high potential application as biomaterials in the production of screws and implants. However, their low corrosion resistance compromises their applicability. The plasma oxidation electrolytic (PEO) is a viable technique in the optimization of anticorrosive properties of magnesium. In this work, the AZ31 alloy was treated by PEO, using a solution of potassium dihydrogen phosphate and potassium hydroxide, ensuring a significant increase in corrosion resistance in simulated body fluid solution (SBF). The electrical parameters of the PEO system were varied, to promote the formation of a more homogeneous coating, with low density of pores and less structural defects. The current polarization was also studied, and all the experiments were accomplished in both, unipolar (anodic voltage) and bipolar (anodic and cathodic voltages) modes. The parameters were varied in the following order: frequency, voltage, duty cycle and treatment time. The pulse frequency was varied between 300 and 3000 Hz, while the voltage range was 200- 400 V for unipolar mode, and -60 and -200 V for bipolar mode. Electrochemical impedance spectroscopy (EIS) and potentiostatic polarization were used for corrosion analysis of the samples immersed in SBF. A scanning electron microscope (MEV) allowed the determination of morphology, while the ray - X energy dispersive spectroscopy (EDS) analysed the chemical composition of the coatings. The coating thickness was determined by eddy current. High values of pulse frequency produced more resistant coatings and frequencies of 3000 Hz and 2000 Hz were the best options for both unipolar and bipolar currents, respectively. The barrier property was enhanced for samples treated using voltages of 300 V for unipolar mode and 300 V and -60 V for bipolar regime, increasing the corrosion resistance of AZ31 alloy in 17,000% and 9,000%, respectively. Immersion tests on SBF were performed for coatings created by unipolar and bipolar regime, following the treatment parameters of the best conditions. Corrosion resistance of coatings decreased at the earlier stages of immersion, followed by considerable improvement on the seventh day. The integrity of the samples was affected throughout the exposure in SBF, and bipolar films were more stable during the tests. At the end of the analysis, despite the negative effects of SBF, the samples appeared to be still resistant to chemical attack. This behaviour suggests the possibility of using the AZ31 alloy, treated by a simple and economical technique, as biomaterial, since the compounds released during dissolution are biocompatible. Moreover, no negative effects on mechanical properties were observed, and within 30 days of immersion, the SBF electrolyte did not significantly changed the substrate, only the coating were affected.
The magnesium and its alloys are metallic materials with high potential application as biomaterials in the production of screws and implants. However, their low corrosion resistance compromises their applicability. The plasma oxidation electrolytic (PEO) is a viable technique in the optimization of anticorrosive properties of magnesium. In this work, the AZ31 alloy was treated by PEO, using a solution of potassium dihydrogen phosphate and potassium hydroxide, ensuring a significant increase in corrosion resistance in simulated body fluid solution (SBF). The electrical parameters of the PEO system were varied, to promote the formation of a more homogeneous coating, with low density of pores and less structural defects. The current polarization was also studied, and all the experiments were accomplished in both, unipolar (anodic voltage) and bipolar (anodic and cathodic voltages) modes. The parameters were varied in the following order: frequency, voltage, duty cycle and treatment time. The pulse frequency was varied between 300 and 3000 Hz, while the voltage range was 200- 400 V for unipolar mode, and -60 and -200 V for bipolar mode. Electrochemical impedance spectroscopy (EIS) and potentiostatic polarization were used for corrosion analysis of the samples immersed in SBF. A scanning electron microscope (MEV) allowed the determination of morphology, while the ray - X energy dispersive spectroscopy (EDS) analysed the chemical composition of the coatings. The coating thickness was determined by eddy current. High values of pulse frequency produced more resistant coatings and frequencies of 3000 Hz and 2000 Hz were the best options for both unipolar and bipolar currents, respectively. The barrier property was enhanced for samples treated using voltages of 300 V for unipolar mode and 300 V and -60 V for bipolar regime, increasing the corrosion resistance of AZ31 alloy in 17,000% and 9,000%, respectively. Immersion tests on SBF were performed for coatings created by unipolar and bipolar regime, following the treatment parameters of the best conditions. Corrosion resistance of coatings decreased at the earlier stages of immersion, followed by considerable improvement on the seventh day. The integrity of the samples was affected throughout the exposure in SBF, and bipolar films were more stable during the tests. At the end of the analysis, despite the negative effects of SBF, the samples appeared to be still resistant to chemical attack. This behaviour suggests the possibility of using the AZ31 alloy, treated by a simple and economical technique, as biomaterial, since the compounds released during dissolution are biocompatible. Moreover, no negative effects on mechanical properties were observed, and within 30 days of immersion, the SBF electrolyte did not significantly changed the substrate, only the coating were affected.
Descrição
Palavras-chave
Biomaterial, Magnésio, Biocorrão, Implantes bioabssorvíveis, Oxidação eletrolítica assistida a plasma (PEO), Implantes, Magnesium, Biocorrosion, Bioabsorbable implants, Plasma electrolytic oxidation (PEO), Implant