Limits...
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) Static water contact angles of the different microsheet layers before and after PTES modification: (1) HR 120 °C-8 h at a pH of 12, (2) HR 120 °C-12 h at a pH of 12. (b) Photograph of water contact behavior on the vertical and tilted microsheet surfaces. (c) Illustration of the patterns of the morphology-induced water contact states on the superhydrophobic surface.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4663789&req=5

f6: (a) Static water contact angles of the different microsheet layers before and after PTES modification: (1) HR 120 °C-8 h at a pH of 12, (2) HR 120 °C-12 h at a pH of 12. (b) Photograph of water contact behavior on the vertical and tilted microsheet surfaces. (c) Illustration of the patterns of the morphology-induced water contact states on the superhydrophobic surface.

Mentions: To further improve the corrosion protection, the surface energy is lowered by modification with 1H,1H,2H,2H-perfluorooctyltriethoxysilane (PTES) to obtain a unique superhydrophobic surface36. The FTIR spectrum in Figure S3 confirms successful modification of PTES on the surface. The wettability, an important feature to evaluate the relationship between the aqueous solution and substrate, is highly dependent on the surface microstructure. The wetting behavior of the hydrothermal coatings [(1) 120 °C for 8 h, (2) 12 h at a pH of 12] with and without PTES modification is evaluated using an optical water contact angle meter. The hydrothermal surface is hydrophilic showing a small water contact angle of 37 ± 2° on the uniform vertical microsheets layer and 29 ± 1° on the uniform titled microsheet surface. They are smaller than that on the pristine Mg alloy (60 ± 2°). Although the PTES modified pristine Mg alloy exhibits a larger water contact angle (123 ± 2°), surface texture plays an important role in the water repellence effect. Here, superhydrophobic properties for water contact angles over 150° on the hydrothermal samples are observed after PTES modification (Fig. 6a). However, the superhydrophobic surfaces show distinct wettability. When the morphology of the microsheets changes from being vertical to tilted, the contact angles decrease from 164 ± 3° to 153 ± 3° as a result of the increased solid/liquid contact area. The wetting states change from Cassie to Wenzel-like correspondingly (Fig. 6b). It has been shown that the microscopic scale and morphology determine the solid/liquid contact and control the adhesive strength of water droplets on the superhydrophobic surface3637. As described by the water contact angle equation proposed by Cassise and Baxter38, cos θ′ = f cos θ – (1 − f), where θ′ and θ are the apparent water contact angle on a rough and flat substrate surface respectively. The factor f is the fraction of solid/liquid interface, while (1 − f) is that of the air/liquid interface. Generally, the solid/liquid contact based on the factor f is divided into the area contact, line contact, and point contact, which decide the magnitude of the adhesive force on a superhydrophobic surface36. Here, the superhydrophobic surface comprising fine and vertical microsheets (120 °C for 8 h at a pH of 12) shows small sliding angles (<3°), whereas the water droplets on the tilted superhydrophobic microsheet surface (120 °C for 12 h at a pH of 12 or in DI water) oppose the gravitational force when the surface is tilted vertically (90°) or even turned upside down (180°). The distinct water adhesion can be attributed to the different Van der Waals attraction on the surface micro/nanostructures. The vertical microsheet surface provides the line contact with a small contact area resulting in the low adhesive force but on the other hand, the tilted microsheets offer a large contact area which dramatically increases the water adhesive force36, as illustrated in Fig. 6c. Meanwhile, there are many pits with several nanometers in diameter on the microsheets might be formed by Al dissolution at a high pH and they are believed to be an important factor of the large adhesive force because the Van der Waals interaction can be strengthened due to the strong dipole moment produced at the edge of the crystal defect3940.


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) Static water contact angles of the different microsheet layers before and after PTES modification: (1) HR 120 °C-8 h at a pH of 12, (2) HR 120 °C-12 h at a pH of 12. (b) Photograph of water contact behavior on the vertical and tilted microsheet surfaces. (c) Illustration of the patterns of the morphology-induced water contact states on the superhydrophobic surface.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f6: (a) Static water contact angles of the different microsheet layers before and after PTES modification: (1) HR 120 °C-8 h at a pH of 12, (2) HR 120 °C-12 h at a pH of 12. (b) Photograph of water contact behavior on the vertical and tilted microsheet surfaces. (c) Illustration of the patterns of the morphology-induced water contact states on the superhydrophobic surface.
Mentions: To further improve the corrosion protection, the surface energy is lowered by modification with 1H,1H,2H,2H-perfluorooctyltriethoxysilane (PTES) to obtain a unique superhydrophobic surface36. The FTIR spectrum in Figure S3 confirms successful modification of PTES on the surface. The wettability, an important feature to evaluate the relationship between the aqueous solution and substrate, is highly dependent on the surface microstructure. The wetting behavior of the hydrothermal coatings [(1) 120 °C for 8 h, (2) 12 h at a pH of 12] with and without PTES modification is evaluated using an optical water contact angle meter. The hydrothermal surface is hydrophilic showing a small water contact angle of 37 ± 2° on the uniform vertical microsheets layer and 29 ± 1° on the uniform titled microsheet surface. They are smaller than that on the pristine Mg alloy (60 ± 2°). Although the PTES modified pristine Mg alloy exhibits a larger water contact angle (123 ± 2°), surface texture plays an important role in the water repellence effect. Here, superhydrophobic properties for water contact angles over 150° on the hydrothermal samples are observed after PTES modification (Fig. 6a). However, the superhydrophobic surfaces show distinct wettability. When the morphology of the microsheets changes from being vertical to tilted, the contact angles decrease from 164 ± 3° to 153 ± 3° as a result of the increased solid/liquid contact area. The wetting states change from Cassie to Wenzel-like correspondingly (Fig. 6b). It has been shown that the microscopic scale and morphology determine the solid/liquid contact and control the adhesive strength of water droplets on the superhydrophobic surface3637. As described by the water contact angle equation proposed by Cassise and Baxter38, cos θ′ = f cos θ – (1 − f), where θ′ and θ are the apparent water contact angle on a rough and flat substrate surface respectively. The factor f is the fraction of solid/liquid interface, while (1 − f) is that of the air/liquid interface. Generally, the solid/liquid contact based on the factor f is divided into the area contact, line contact, and point contact, which decide the magnitude of the adhesive force on a superhydrophobic surface36. Here, the superhydrophobic surface comprising fine and vertical microsheets (120 °C for 8 h at a pH of 12) shows small sliding angles (<3°), whereas the water droplets on the tilted superhydrophobic microsheet surface (120 °C for 12 h at a pH of 12 or in DI water) oppose the gravitational force when the surface is tilted vertically (90°) or even turned upside down (180°). The distinct water adhesion can be attributed to the different Van der Waals attraction on the surface micro/nanostructures. The vertical microsheet surface provides the line contact with a small contact area resulting in the low adhesive force but on the other hand, the tilted microsheets offer a large contact area which dramatically increases the water adhesive force36, as illustrated in Fig. 6c. Meanwhile, there are many pits with several nanometers in diameter on the microsheets might be formed by Al dissolution at a high pH and they are believed to be an important factor of the large adhesive force because the Van der Waals interaction can be strengthened due to the strong dipole moment produced at the edge of the crystal defect3940.

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