Wettability of hierarchically-textured ceramic coatings produced by suspension HVOF spraying

Abstract

A novel but simple path for the preparation of superhydrophobic and superhydrophilic coatings has been demonstrated via a recently developed technology, namely suspension high velocity oxy-fuel spraying.Potential uses for robust superhydrophobic coatings include antifouling applications such as aeroplane wings, ship hulls, offshore wind turbine blades, or the above-deck structures on ice breaker vessels.Several fabrication techniques have been reported for preparing inorganic superhydrophobic surfaces, but existing coatings either lack the necessary robustness for engineering applications and/or their deposition methods are not suitable for industrial scale-up. In this work, the industrially established HVOF coating process was adapted to use a liquid suspension of commercially available nano-particles (titania-TiO 2 , and hexagonal boron nitride-h-BN) as feedstock to produce nanostructured suspension HVOF TiO 2 /h-BN coatings for the first time on stainless steel. Results indicate that agglomerates in the nano-feedstock can be dispersed by h-BN due to poor mutual wettability between h-BN and molten TiO 2 . It also inhibits the anatase-to-rutile transformation of TiO 2 during coating deposition by inhibiting sintering of TiO 2 in the HVOF flame. The resultant coating becomes superhydrophobic when the addition of h-BN reaches 10 wt% due to the presence of hierarchical nano-texture on the surface. The superhydrophobicity (contact angle of 163-170 ) is maintained over a long period of time (>13 months, test still ongoing) and remains stable after exposure to light and tape test. A potential route for industrial preparation of robust water-repellent coatings is therefore highlighted by the study.

An electrodeposited Ni-P-WS2 coating with combined super-hydrophobicity and self-lubricating properties

“…where θ represents the contact angle on a heterogeneous surface composed of a solid and air, θ A is the contact angle of a droplet with the gas phase and can be considered up to 180 deg, f SL and f LA are the area fractions of solid and air in contact with liquid. The sum of f SL and f LA is unity if the droplet is small enough to neglect sagging and Laplace pressure is constant between the high curvature front and the smaller curvature rear [27].…”

Robust Ni/WC superhydrophobic surfaces by electrodeposition

“…3,4 The effects of hierarchical structures on wetting was reviewed by Feng et al 5 Recently, the research on superhydrophobicity is focussed on more practical uses, and various superhydrophobic surfaces have been fabricated with improved properties. These surfaces can be classied into three categories, 6 polymeric surfaces, inorganic surfaces modied by organic materials and inorganic surfaces. Due to the low surface energy of organic chemicals, most superhydrophobic surfaces are organic compounds or compounds modied by them.…”

One-step electrodeposition of a self-cleaning and corrosion resistant Ni/WS2superhydrophobic surface

“…Ceramics are particularly important due to their good mechanical strength and heat/corrosion resistances. Although ceramics are rarely used for water-repelling surfaces because of their intrinsically hydrophilic nature, our group has recently prepared a ceramic TiO 2 /BN coating with superhydrophobic contact angle of nearly 170 deg by thermal spraying 11 . Its superhydrophobicity has been maintained over a year but the process is relatively costly.…”