Full Length ArticleSteady anti-icing coatings on weathering steel fabricated by HVOF spraying
Introduction
Ice accumulation on critical area of equipment may cause serious problems, take the brake disc of high speed rail as an example, clamp action will be affected by ice, meanwhile mixed ice slag will abrade the brake disc abnormally, which may reduce the service life. Also, icing will make transmission line overload, which may cause security risks [1], [2].
As we all know, lotus leaves repel water droplets due to their intrinsic hierarchical micro/nanostructure, which reducing actual contact area between water and solid surface [3]. Also, the micro/nanostructure of super-hydrophobic surface like lotus structure provides a vapor pockets at the solid-liquid interface [4] to reduce the loss of heat quantity [5], which may delay the freezing time. Therefore, numerous researchers focused on super-hydrophobic surface, which show excellent anti-icing and de-icing properties. Shen et al. proposed that super-hydrophobic surfaces fabricated on titanium alloy displayed a robust icing-delay performance with a delay time of approximate 750 s at −10 °C [6]. Also, it has been reported that the ice adhesion on the super-hydrophobic surface was only 13% of that on the super-hydrophilic surface under −10 °C (relative humidity of 85–90%) [7].
Generally speaking, there are two ways to fabricate super-hydrophobic surfaces: one is to prepare a rough structure on hydrophobic substrates, and the other is to modify low surface energy materials on a rough surface. Some researches show that ice accumulation is dependent on the ice nucleation speed of overcooled water droplets as soon as they contact with a surface [8], [9]. An ice repelling surface means that water droplets under overcooled condition could roll from the surface rapidly before ice formation with the help of external forces, such as wind or gravity [10], [11], or the adhesion strength is small between ice and surface. However, it is still a great challenge to obtain steady anti-icing, de-icing abilities on as-prepared coatings because of the severe decrease in the super-hydrophobic properties at low temperature [12].
In recent years, various method of preparing super-hydrophobic surface have been proposed, such as plasma treatment [13], sol gel method [14], laser etching [15], etc. Most approach can obtain excellent hydrophobic properties, but there are few researchers prepare the super-hydrophobic surface on a surface with high wear resistance and corrosion resistance to obtain steady anti-icing properties.
Nanostructured WC-12Co coating prepared by HVOF possesses excellent wear resistance and corrosion resistance which reported by our previous work [16], [17]. The wear rate of HVOF-sprayed nanostructure WC-12Co coating is only 0.0977 g/(m2·h) under rigorous experimental conditions [17]. Therefore, the coating prepared by HVOF possesses high structural stability and comprehensive properties. ln this work, A category of nanostructured WC-12Co coating with rough structure was prepared by HVOF. And then low surface energy material was modified on it to obtain super-hydrophobic coating with excellent anti-icing performance.
Section snippets
Experimental materials and equipment
SMA490BW weather steel (≤0.16 wt% C, ≤0.50 wt% Si, 0.50–1.50 wt% Mn, ≤0.03 wt% P, ≤0.03 wt% S, 0.20–0.50 wt% Cu, 0.40–0.80 wt% Cr, ≤0.65 wt% Ni, with balance being Fe) with the size of 55 × 50 × 5mm was used as the substrate. Ethanol (Analytical reagent) and acetone (Analytical reagent) were purchased from Chengdu Chemical Factory. The nano-modified WC-12Co powder obtained from Inframat Ltd, Famington, USA. The hydrophobic SiO2 nanoparticles (R974) were obtained from King Chemical, Dongguan,
Surface morphologies and wettability of HVOF-sprayed coatings
The different magnification SEM images of nano-modified WC-12Co powder are shown in Fig. 3(a) and (b), whose average particle size is about 15–45 μm, and the WC size is about 50–500 nm. The SEM image of HVOF-sprayed coatings is presented as seen in Fig. 3(c). Combined with Fig. 3(e), the molten or semi molten WC-12Co particles were continuously stacked into layers during the spraying process, which formed conglomerate micron structure, on the other hand, it could be observed that there are many
Conclusions
- (1)
Steady super-hydrophobic coatings can be obtained by HVOF thermal spraying and low surface energy modification, whose contact angle is about 154.3 ± 3.0°, and the sliding angle is about 4.1 ± 0.1°.
- (2)
As-prepared super-hydrophobic coatings exhibit memorable promotion in max freezing delay time of 1206.4 s in static situation, which is about 8 times higher than steel substrate.
- (3)
Droplets on the steel substrate froze from every direction in overcooled environment, on the contrary, ice crystal upper
Acknowledgements
This project is supported by the National Key Research and Development Plan of China (Grant No. 2016YFB1200403).
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Preparation methods and research progress of super-hydrophobic anti-icing surface
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