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Abstract
This study has presented an efficient coating method, namely suspension high velocity oxy-fuel (SHVOF) thermal spraying, to produce large super-hydrophobic ceramic surfaces with a unique micro- and nano-scale hierarchical structures to mimic natural super-hydrophobic surfaces. CeO2 was selected as coatings material, one of a group of rare-earth oxide (REO) ceramics that have recently been found to exhibit intrinsic hydrophobicity, even after exposure to high temperatures and abrasive wear. Robust hydrophobic REO ceramic surfaces were obtained from the deposition of thin CeO2 coatings (3–5 μm) using an aqueous suspension with a solid concentration of 30 wt.% sub-micron CeO2 particles (50–200 nm) on a selection of metallic substrates. It was found that the coatings’ hydrophobicity, microstructure, surface morphology, and deposition efficiency were all determined by the metallic substrates underneath. More importantly, it was demonstrated that the near super-hydrophobicity of SHVOF sprayed CeO2 coatings was achieved not only by the intrinsic hydrophobicity of REO but also their unique hierarchically structure. In addition, the coatings’ surface hydrophobicity was sensitive to the O/Ce ratio, which could explain the ‘delayed’ hydrophobicity of REO coatings.
Highlights
® polymeric modifiers, e.g. polytetrafluoroethylene (PTFE, or Teflon ), which are used as conventional hydrophobic coatings, rare-earth oxide (REO) exhibited sustained hydrophobicity after high temperature exposure to up to 1000 °C for 2 h and abrasive-wear test[1]
In 2016, Cai et al.[23] first manufactured super-hydrophobic REO coatings with hierarchically structured topography using precursor solutions as feedstock in a plasma spray deposition process, which is known as solution precursor plasma spray (SPPS)
suspension high velocity oxy-fuel (SHVOF) was used to deposit REO coatings with intrinsic hydrophobicity and hierarchically structured surface topography on a selection of commonly used metallic substrates, i.e. aluminium, stainless steel and nickel-based alloys, which can be found in various applications but differ significantly in hardness
Summary
This study has presented an efficient coating method, namely suspension high velocity oxy-fuel (SHVOF) thermal spraying, to produce large super-hydrophobic ceramic surfaces with a unique microand nano-scale hierarchical structures to mimic natural super-hydrophobic surfaces. It was demonstrated that the near super-hydrophobicity of SHVOF sprayed CeO2 coatings was achieved by the intrinsic hydrophobicity of REO and their unique hierarchically structure. ® polymeric modifiers, e.g. polytetrafluoroethylene (PTFE, or Teflon ), which are used as conventional hydrophobic coatings, REOs exhibited sustained hydrophobicity after high temperature exposure to up to 1000 °C for 2 h and abrasive-wear test[1] These robust hydrophobic surfaces obtained from REOs ceramics are seen to be incredibly useful for a wide range of applications including anti-icing[3,4,5,6], anti-corrosion[7,8,9], drag reduction[10,11,12], and dropwise condensation[13,14,15,16], etc. SHVOF was used to deposit REO coatings with intrinsic hydrophobicity and hierarchically structured surface topography on a selection of commonly used metallic substrates, i.e. aluminium, stainless steel and nickel-based alloys, which can be found in various applications but differ significantly in hardness. We aim to demonstrate the potential of SHVOF technique for industrial preparation of robust water-repellent REO coatings on various metallic components; and find out the mechanism for the improvement in surface hydrophobicity of SHVOF sprayed REO coatings
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