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Mitigation of Corrosion on Magnesium Alloy by Predesigned Surface Corrosion.

Zhang X, Wu G, Peng X, Li L, Feng H, Gao B, Huo K, Chu PK - Sci Rep (2015)

Bottom Line: A uniform surface composed of an inner compact layer and top Mg-Al layered double hydroxide (LDH) microsheet is produced on a large area using a one-step process and excellent corrosion resistance is achieved in saline solutions.Moreover, inspired by the super-hydrophobic phenomenon in nature such as the lotus leaves effect, the orientation of the top microsheet layer is tailored by adjusting the hydrothermal temperature, time, and pH to produce a water-repellent surface after modification with fluorinated silane.The results reveal an economical and environmentally friendly means to control and use the pre-corrosion products on magnesium alloys.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong, China.

ABSTRACT
Rapid corrosion of magnesium alloys is undesirable in structural and biomedical applications and a general way to control corrosion is to form a surface barrier layer isolating the bulk materials from the external environment. Herein, based on the insights gained from the anticorrosion behavior of corrosion products, a special way to mitigate aqueous corrosion is described. The concept is based on pre-corrosion by a hydrothermal treatment of Al-enriched Mg alloys in water. A uniform surface composed of an inner compact layer and top Mg-Al layered double hydroxide (LDH) microsheet is produced on a large area using a one-step process and excellent corrosion resistance is achieved in saline solutions. Moreover, inspired by the super-hydrophobic phenomenon in nature such as the lotus leaves effect, the orientation of the top microsheet layer is tailored by adjusting the hydrothermal temperature, time, and pH to produce a water-repellent surface after modification with fluorinated silane. As a result of the trapped air pockets in the microstructure, the super-hydrophobic surface with the Cassie state shows better corrosion resistance in the immersion tests. The results reveal an economical and environmentally friendly means to control and use the pre-corrosion products on magnesium alloys.

No MeSH data available.


Related in: MedlinePlus

(a) Polarization curves of the hydrothermal samples, (b) Corresponding Nyquist plots, and (c,d) Bode plots. (e) Corresponding equivalent circuit model based on the pristine Mg alloy and hydrothermal samples. The measurement is carried out in a 3.5 wt% NaCl aqueous solution.
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f5: (a) Polarization curves of the hydrothermal samples, (b) Corresponding Nyquist plots, and (c,d) Bode plots. (e) Corresponding equivalent circuit model based on the pristine Mg alloy and hydrothermal samples. The measurement is carried out in a 3.5 wt% NaCl aqueous solution.

Mentions: The corrosion behavior of the hydrothermal coatings (120 °C for 8 h and 12 h at a pH of 12 and 12 h in DI water) is investigated in 3.5 wt% NaCl as shown in Fig. 5. The potentiodynamic polarization curves disclose the improved corrosion resistance by both cathodic hydrogen evolution and anodic dissolution24. The hydrogen evolution rate decreases significantly on the cathodic side as well as the enhanced passive region on the anodic side of the hydrothermal samples (Fig. 5a). The polarization measurements show that the corrosion current density (Icorr) of the hydrothermal samples is (0.55–1.35) × 10−7 A.cm−2 which is 100–200 times smaller than that of the untreated Mg alloy (1.22 × 10−5 A.cm−2) thus implying good corrosion resistance. Furthermore, the corrosion current density of the optimal hydrothermal sample (120 °C for 12 h at a pH of 12) demonstrates apparent corrosion resistance improvement compared to the flower-like structure and the sample prepared with a short hydrothermal time in addition to most of the corrosion resistance coatings on Mg alloys such as the Mg-Al LDH layer or Mg-Al LDH and Mg(OH)2 composite layer2730 and other magnesium oxide layer233132. The excellent corrosion resistance properties can be attributed to the uniform compact and thick inner layer. The potential differences (∆E) between the corrosion potential and transition potential in the anodic region are listed in Fig. 5a indicating a better anti-corrosion behavior for the samples with uniform thick compact inner layers (hydrothermal treatment for 12 h at a pH of 12). Figure 5b–d show the corresponding Nyquist and Bode plots. In EIS, the impedance features fitted by the corresponding equivalent circuits are denoted by Rs(CPEf(Rf(CPEdl(Rt(CPEdiffRdiff)))))3334, where Rs is the solution resistance between the reference electrode and working electrode. CPEf, CPEdl and CPEdiff are three time constant phases representing the capacitance of the whole film, electric double layer capacitance, and capacitance pertaining to the diffusion process, and Rf, Rt and Rdiff denote the resistance of the pores and other defects in the whole film, charge transfer resistance, and diffusion resistance, respectively. Usually, the capacitance CPEf, is an important parameter to reflect water absorption in coatings and the resistance Rf can be used to measure the porosity and deterioration of the coatings35. The experimental data are fitted well by the equivalent model (Fig. 5e) and the calculated values of the individual electrical components with three times replicates are listed in Table 1. Since Rs is small and similar in all the tests, it is neglected here. The thick inner compact layer covered by uniform microsheets exhibits larger sums of Rf, Rt, and Rdiff indicative of excellent corrosion resistance in the NaCl solution. The enhanced resistance is also confirmed by the Bode plots including the impendence versus frequency and phase angle versus frequency in Fig. 5c,d.


Mitigation of Corrosion on Magnesium Alloy by Predesigned Surface Corrosion.

Zhang X, Wu G, Peng X, Li L, Feng H, Gao B, Huo K, Chu PK - Sci Rep (2015)

(a) Polarization curves of the hydrothermal samples, (b) Corresponding Nyquist plots, and (c,d) Bode plots. (e) Corresponding equivalent circuit model based on the pristine Mg alloy and hydrothermal samples. The measurement is carried out in a 3.5 wt% NaCl aqueous solution.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4663789&req=5

f5: (a) Polarization curves of the hydrothermal samples, (b) Corresponding Nyquist plots, and (c,d) Bode plots. (e) Corresponding equivalent circuit model based on the pristine Mg alloy and hydrothermal samples. The measurement is carried out in a 3.5 wt% NaCl aqueous solution.
Mentions: The corrosion behavior of the hydrothermal coatings (120 °C for 8 h and 12 h at a pH of 12 and 12 h in DI water) is investigated in 3.5 wt% NaCl as shown in Fig. 5. The potentiodynamic polarization curves disclose the improved corrosion resistance by both cathodic hydrogen evolution and anodic dissolution24. The hydrogen evolution rate decreases significantly on the cathodic side as well as the enhanced passive region on the anodic side of the hydrothermal samples (Fig. 5a). The polarization measurements show that the corrosion current density (Icorr) of the hydrothermal samples is (0.55–1.35) × 10−7 A.cm−2 which is 100–200 times smaller than that of the untreated Mg alloy (1.22 × 10−5 A.cm−2) thus implying good corrosion resistance. Furthermore, the corrosion current density of the optimal hydrothermal sample (120 °C for 12 h at a pH of 12) demonstrates apparent corrosion resistance improvement compared to the flower-like structure and the sample prepared with a short hydrothermal time in addition to most of the corrosion resistance coatings on Mg alloys such as the Mg-Al LDH layer or Mg-Al LDH and Mg(OH)2 composite layer2730 and other magnesium oxide layer233132. The excellent corrosion resistance properties can be attributed to the uniform compact and thick inner layer. The potential differences (∆E) between the corrosion potential and transition potential in the anodic region are listed in Fig. 5a indicating a better anti-corrosion behavior for the samples with uniform thick compact inner layers (hydrothermal treatment for 12 h at a pH of 12). Figure 5b–d show the corresponding Nyquist and Bode plots. In EIS, the impedance features fitted by the corresponding equivalent circuits are denoted by Rs(CPEf(Rf(CPEdl(Rt(CPEdiffRdiff)))))3334, where Rs is the solution resistance between the reference electrode and working electrode. CPEf, CPEdl and CPEdiff are three time constant phases representing the capacitance of the whole film, electric double layer capacitance, and capacitance pertaining to the diffusion process, and Rf, Rt and Rdiff denote the resistance of the pores and other defects in the whole film, charge transfer resistance, and diffusion resistance, respectively. Usually, the capacitance CPEf, is an important parameter to reflect water absorption in coatings and the resistance Rf can be used to measure the porosity and deterioration of the coatings35. The experimental data are fitted well by the equivalent model (Fig. 5e) and the calculated values of the individual electrical components with three times replicates are listed in Table 1. Since Rs is small and similar in all the tests, it is neglected here. The thick inner compact layer covered by uniform microsheets exhibits larger sums of Rf, Rt, and Rdiff indicative of excellent corrosion resistance in the NaCl solution. The enhanced resistance is also confirmed by the Bode plots including the impendence versus frequency and phase angle versus frequency in Fig. 5c,d.

Bottom Line: A uniform surface composed of an inner compact layer and top Mg-Al layered double hydroxide (LDH) microsheet is produced on a large area using a one-step process and excellent corrosion resistance is achieved in saline solutions.Moreover, inspired by the super-hydrophobic phenomenon in nature such as the lotus leaves effect, the orientation of the top microsheet layer is tailored by adjusting the hydrothermal temperature, time, and pH to produce a water-repellent surface after modification with fluorinated silane.The results reveal an economical and environmentally friendly means to control and use the pre-corrosion products on magnesium alloys.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong, China.

ABSTRACT
Rapid corrosion of magnesium alloys is undesirable in structural and biomedical applications and a general way to control corrosion is to form a surface barrier layer isolating the bulk materials from the external environment. Herein, based on the insights gained from the anticorrosion behavior of corrosion products, a special way to mitigate aqueous corrosion is described. The concept is based on pre-corrosion by a hydrothermal treatment of Al-enriched Mg alloys in water. A uniform surface composed of an inner compact layer and top Mg-Al layered double hydroxide (LDH) microsheet is produced on a large area using a one-step process and excellent corrosion resistance is achieved in saline solutions. Moreover, inspired by the super-hydrophobic phenomenon in nature such as the lotus leaves effect, the orientation of the top microsheet layer is tailored by adjusting the hydrothermal temperature, time, and pH to produce a water-repellent surface after modification with fluorinated silane. As a result of the trapped air pockets in the microstructure, the super-hydrophobic surface with the Cassie state shows better corrosion resistance in the immersion tests. The results reveal an economical and environmentally friendly means to control and use the pre-corrosion products on magnesium alloys.

No MeSH data available.


Related in: MedlinePlus