Chemical modifications for water-repellent coatings on engineering metals

Gao, Boyang (2018) Chemical modifications for water-repellent coatings on engineering metals. Masters thesis, Memorial University of Newfoundland.

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Abstract

Hydrophobic surfaces have drawn lots of attention for use in applications such as selfcleaning surfaces, anti-icing in harsh environments and corrosion resistance. Generally speaking, the prerequisite for hydrophobic surface synthesis is the combination of micro-scale and nano-scale surface structures along with a low surface energy coating. In my research work, chemical methods were investigated to produce hydrophobic carbon steel and stainless steel, which are important engineering metals. Simple chemical etching and organic coatings were applied to carbon steel and stainless steel. Although the hydrophobicity of the modified surface increased, the degree of water repellency didn’t reach our expectation. Furthermore, the heterogeneous etching and coating caused large uncertainty in terms of wettability. The most promising system is a zinc electrodeposit with a stearic acid coating. We showed that mildly alkaline electrolytes can be used for the fabrication of zinc coatings that give rise to remarkably low adhesion surfaces. Various parameters (pH, applied potential, electrolyte composition) during zinc electrodeposition influenced the homogeneity of zinc coverage and the topography of zinc crystalites, which consequently impacted the hydrophobicity of the surface. Moreover, the two important roles of stearic acid, preventing the oxidation of zinc surface and decreasing the surface energy, were also studied. In conclusion, the zinc layer not only increases the roughness of the surface, but also provide excellent adhesion to the organic coating.

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