7TH INTL. SYMP. ON SUSTAINABLE SURFACE AND INTERFACE ENGINEERING: COATINGS FOR EXTREME ENVIRONMENTS

In food processing industries, products and especially dairy products undergo thermal treatments (pasteurization, sterilization) leading to fouling formation on heat exchangers’ surfaces. These deposits can contaminate dairy products during pasteurization process and also impair heat transfer mechanism by creating a thermal resistance, thus leading to regular shut down of the processes. Therefore, periodic and drastic cleaning-in-place (CIP) procedures are implemented. These CIP involve the use of chemicals and high amount of water, thus increasing environmental burden. It has been estimated that 80% of production costs are owed to dairy fouling deposit. [1]
To reduce dairy fouling, two pathways have been considered: (i) Process conditions optimization, mainly tested by food-processing industries and (ii) Stainless steel surface anti-fouling or fouling-release coating to either inhibit attachment of depositing species or to ease their removal during cleaning respectively.
In our team, we focus on this latter approach by developing biomimetic coatings (slippery liquid-infused surfaces (SLIS) [2] and atmospheric plasma nano-structured coatings [3]) of low contact angle hysteresis to limit fouling adhesion onto stainless steel surfaces. Slippery liquid-infused surfaces are inspired by Nepenthes plant by designing slippery interface between the substrate and the fouling providing fouling-release surfaces. Slippery surfaces were elaborated in three steps: (i) femto laser surface structuring, (ii) silanization and (iii) lubricant impregnation. In order to maximize lubricant retention, laser manufacturing parameters were optimized.
Plasma nano-structured coatings intend to mimic lotus leave surfaces, by creating a dual-scale roughness preventing adhesion of denatured dairy proteins. Hydrophobic silane-based coatings were sprayed by atmospheric pressure plasma (ULS, Axcys Technologies) and conditions were optimized depending on the fouling test results obtained.

With the rapid developments in deep sea exploration, more and more metallic equipments have been employed in the deep sea environments. As compared with shallow sea and marine atmosphere, the deep sea environments are quite different, showing with relatively low temperature, high hydrostatic pressure, and variable dissolved oxygen contents, etc. However, as the metallic equipment up and down in the ocean, the equipment is subjected to the alternating loads and scours from the sea water, which are the most significant factors that may greatly affect the corrosion behavior of metallic equipment served in the deep sea.
The organic coatings are the most widely used and effective method among various anti-corrosion techniques for metals. In particular, epoxy resin based anti-corrosion coatings used in deep sea have been reported previously. In the previous works [1-3], it has been clearly discussed the failure mechanisms for coatings under alternating hydrostatic pressure in deep sea. The alternating hydrostatic pressure (AHP) changed the degradation processes and failure mechanisms, and hence accelerated the failure process. The AHP had great effects on the coating/steel interface and led to a rapid loss of adhesion at initial, then AHP accelerated water diffusion into coatings, and deteriorated the coating physical structure, including enlarging the original pores on coating surface and destroying the pigment/binder interface, both of which weakened the anti-permeability of coating against water. Based upon, our latest research direction is how to improve the problem of weakly bonded interfaces.
In this work, epoxy resin based anti-corrosion coatings used in deep sea (two kinds of coating systems were applied, basalt scale coating and the etched basalt scales coating) were studied by in situ electrochemical impedance spectroscopy (EIS), pull-off adhesion test and other coating performance tests, as well as the Fourier Transform infrared spectroscopy (FTIR) and Scanning Electron Microscopy (SEM), etc. We investigated the failure mechanisms of epoxy composited coatings under alternating hydrostatic pressure systematically, and the failure models of the pigmented coatings under alternating hydrostatic pressure were proposed. Furthermore, an alternating hydrostatic pressure accelerated test and a prediction model based on the artificial neural network were established to develop the laboratory method of fast evaluation and prediction for organic coatings used in deep sea. The aim of this study is to provide some essential theoretical and experimental guidance for the development of new organic coatings used in deep sea.

The use of coating, or in a more general way surface treatment, is one of the most efficient ways to protect materials against fire. It has several advantages: it does not modify the mechanical properties of the substrates, it is easily processed and it can be used onto diverse materials such as metallic materials[1], polymers[2], foams[3] and textiles [4]. Moreover, while ignition occurs usually at the surface of a material, it is important to concentrate the protective action at this location. It is the goal of this talk to present recent approaches to make fire protective coatings for different types of plastic based substrates.
When evaluating the fire behavior of materials, the reaction to fire (contribution of the material to fire growth) and the resistance to fire (defined as the ability of materials to resist the passage of fire and/or gaseous products of combustion) have to be distinguished. It means that different scenarios should be considered and hence, different thermal constraints are applied on the protective coatings. According to the fire scenario, the flame retardant coating must be designed with the appropriate chemical composition, thickness, thermophysical and thermo-optical properties.
A well-known example of protective coating is intumescent coating. When heated beyond a critical temperature, the intumescent material begins to swell and then to expand, forming an insulative coating limiting heat and mass transfers. Intumescence is a versatile method for providing both reaction and resistance to fire to materials. Intumescent coatings can be for example applied on carbon fiber reinforced polymers used in aircraft structure for fire protection (i.e. resistance to fire) [5]. Thin intumescent coatings can also be applied on thermoplastics in a cone calorimeter scenario (i.e. reaction to fire). It provides outstanding performance on various polymers, such as polypropylene and polycarbonate [6].
Other technologies than intumescence allow designing FR coatings including laber by layer (LbL)[7,8], sol-gel[9], plasma deposit [10,11], and more recently self-stratifying coatings [12,13] and radiative fire protective coatings [14]. All those methods will be considered in the talk, and the benefit and drawback of these methodologies will be discussed.

Galvanised or Zn coated steel provides corrosion protection to underlying steel due to sacrificial effect of Zn, where Zn dissolves and Fe acts a cathodic part in the electrochemical reactions [1]. Galvanised steels are used in wide range of applications such as, constructions (rebar), beams, etc., piping industries, automobile industries, roof covers, etc. [1]. However, for many years, the galvanization of high strength steels brings a great challenge to galvanizers mainly due to selective surface oxidation of minor alloying elements (such as Si, Mn, Al etc.) present on the steel surface during annealing, which drastically reduces the wettability of liquid Zn on the steel surface [1-3].

In the present investigation, the role of copper (Cu) pre-coat has been studied for the development of good quality defect free hot dip galvanized (GI) coating on a dual phase (DP 590) steel substrate. The application of Cu pre-coating, prior to reduction annealing process, greatly influences the microstructural development of the GI coatings and corrosion behavior. The X-ray diffraction (XRD) analysis reveals the presence of hexagonal closed packed (hcp) structure in both the GI samples, with and without Cu pre-coating. Moreover, Cu pre-coated GI steel exhibits the pronounced texture coefficient (TC) of preferred high atomically dense (0002) crystal plane in comparison to without pre-coated GI steel sheet. High quality GI coating, free from any surface defects, is obtained on the Cu pre-coated steel substrate. However, coating quality is inferior on the steel substrate without Cu pre-coat due to the presence of several bare spots on the top surface of the coating. In addition, Cu pre-coated GI steel reveals the formation of a continuous iron aluminide (Fe-Al) intermetallic interfacial layer with uniform distribution of dense and equiaxed Fe-Al crystals at the interface between the substrate and the coating. It is also noted that the corrosion resistance of Cu pre-coated GI steel is superior as compared to the GI steel without pre-coat. It is concluded that the formation of a continuous compact interfacial layer along with highest atomically dense (0002) crystal plane has resulted in high quality defect free coating, facilitating to attain the lowest corrosion rate of Cu pre-coated GI steel.

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