Abstract
A major challenge in materials engineering is the development of new materials and methods and/or novel combination of existing ones, all fostering innovation. For that reason, this study aims at the synergy between low-pressure cold spray (LPCS) as a tool for coating deposition and sol-gel technique for fabrication of the feedstock powder. The complementarity of both methods is important for the examined topic. On one side, the LPCS being automized and quick mean provides the solid-state of feedstock material in nondestructive conditions and hence the hydrophobicity imparted on the sol-gel route is preserved. On the other side, the sol-gel synthesis enables the production of oxide materials with enhanced deformability due to amorphous form which supports the anchoring while LPCS spraying. In the paper, several aspects including optimal fluoroalkylsilane (FOTS) concentration or substrate roughness are examined initially for altering the superhydrophobicity of produced coatings. Further, it is shown that the appropriate optimization of feedstock powder, being submicron silica matrices covered with two-layer FOTS sheath, may facilitate the anchoring process, support roughening the substrate or cause enhancement the coating hydrophobicity. All the discussion is supported by the characteristics including surface morphology, wettability and thermal behaviour examined by electron microscopy, water contact angle measurements and thermal analysis (TGA/DSC), respectively. The coatings presented in the paper are characterized by an uneven thickness of up to a few silica particles, but final hydrophobicity is provided uniformly on the surface by the formation of multi-level roughness by a detachment of outer layer from the SiO2 particles. Thus, the presented approach constitutes a simple and fast solution for the fabrication of functionalized coatings using LPCS including industrial potential and fundamental research character.
Highlights
Innovation practice contributes to global activity in science and industry by the development of new engineering solutions and altering the already existing ones
This paper shows that the conditions of spraying minimizing the heat input do not cause the decomposition of fluorinated groups (FOTS) and as a result, they allow the desired materials behaviour to be preserved
The feedstock powder was produced in a single two-step process including SiO2 formation via Stöber technique and surface functionalization by adding fluorinated groups (FOTS)
Summary
Innovation practice contributes to global activity in science and industry by the development of new engineering solutions and altering the already existing ones. In this aspect, the fairly new cold spray technique [1], 2001, accounts its extreme popularity for the relative simplicity of the concept and optional automation which can be successfully utilized for adapting to new materials and methods. The deposition sequence for composite coatings is often being discussed [6] and more and more frequently mathematical models are prepared to assist experimental data [7,8,9,10] All these activities are aimed at the development of cold spray. Polymer coatings were formed due to application of lower velocities (about 100 m·s−1 ) and even ceramic materials were employed [11,12,13,14,15] which was possible due to particle fragmentation and particle interlocking
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