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Hydrophobicity – An Innovative Measure for Corrosion Protection

Publication Date : 2019-02-12

By Frank Shu

 

Within North America, outdoor infrastructure is constantly exposed to the elements resulting in slow deterioration which costed the United States 1.1 trillion dollars in 2016 [1]. One of the major contributors is corrosion, resulting from the oxidation of water, oxygen, and a metal. Water acts as an electrolyte, which carries electrons from the metal to the dissolved oxygen. The metal oxide subsequently forms from the reaction has poor structural integrity and weakens the supports. The absence of one component renders the process as inert. As water is the main culprit in this process, the removal of it will protect metal from corrosion [2].

 

Corrosion Mechanism
Figure 1. Corrosion Mechanism [1]


The wet angle classifications resulting in hydrophobic surface
Figure 2. The wet angle classifications resulting in hydrophobic surface [2]


A handful of materials can be designed to repel water, using a property known as hydrophobicity. These coatings have a series of microscopic hills on top which reduce the surface area the water molecules can bond to, hence droplets slide off once in contact. The degree of hydrophobicity is measured using wettability calculated by the wet angle and the surface tension. When the wet angle of the droplet is greater than 90 degrees, the material is classified as hydrophobic and will effectively repel water. Initially coatings were made using chromium, but due to their harmful nature, they were banned in the year 2000 [3].


With modern technology, hydrophobic materials are created through laser treatment or chemical etching of common metals such as Aluminium [4]. One method to measure the rate of corrosion is using potentiodynamic polarization graphs. Tests were made by the Northwest A&F University using hydrophobic Aluminium submerged in a salt solution. The calculated protection efficiency of the hydrophobic Aluminium was 99.4% indicating successful protection against corrosion even in a halophilic environment [5].


A close-up of a water droplet on a hydrophobic surface
Figure 3. A close-up of a water droplet on a hydrophobic surface [3]


The province of Ontario features a distinct continental climate with four distinct seasons. Due to the presence of ice, road salt is normally used to prevent slippery conditions. Consequently, the dissolved salt increases the speed of corrosion as it makes the water more susceptible to oxidation. As this practice is prevalent within Ontario, it was included as part of the scope.

Protection against ice is not a major issue as it is a poor electrical conductor and will not effectively transport electrons, hence it is not a contributor to corrosion.

 

References:

[1] “Cost of Corrosion Estimate in United States”,G2MT Laboratories, pp. 20-21, 2019. [Online]. Available: https://www.g2mtlabs.com/corrosion/cost-of-corrosion/. [Accessed: 05- Feb- 2019].

[2] “How does rust work?”,HowStuffWorks, 2019. [Online]. Available: https://science.howstuffworks.com/question445.htm. [Accessed: 05- Feb- 2019].

[3] D. Zhang, L. Wang and H. Chan, “Superhydrophobic surfaces for corrosion protection: a review of recent progresses and future directions”,Journal of Coatings Technology and Research, vol. 13, pp. 11-29, 2019. Available:

https://www.researchgate.net/publication/284019337_Superhydrophobic_surfaces_for_corrosion_protection_a_review_of_recent_progresses_and_future_directions. [Accessed 5 February 2019].

[4] M. Rafieazad, J. Jaffer, C. Cui, X. Duan and A. Nasiri, “Nanosecond Laser Fabrication of Hydrophobic Stainless Steel Surfaces: The Impact on Microstructure and Corrosion Resistance”,Materials, vol. 11, no. 9, p. 1577, 2018. Available: 10.3390/ma11091577.

[5] Q. Zhao, T. Tang and F. Wang, “Fabrication of Superhydrophobic AA5052 Aluminum Alloy Surface with Improved Corrosion Resistance and Self Cleaning Property”, 2019.