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Innovative heat- and corrosion-resistant coating approaches, applicable in indirect-food-contact outdoor environments, have been developed. Two systems, a direct-to-metal single-layer, polysiloxane-based, oven-dried system and a bilayer, zinc phosphate active pigment-containing, ambient-cured system were developed to overcome the shortcomings of the traditional bilayer, zinc-rich primer-based heat-resistant surface-protective solutions for outdoor cooking equipment, such as barbecue grills. This case study aims to optimize the application conditions, measure and evaluate the impact of surface preparation and compare thermo-resistant and anticorrosive properties of different coating systems focusing on eco-efficiency. The anticorrosion efficiency of the coatings was characterized using salt-spray chamber corrosion tests and electrochemical impedance spectroscopy. The thermo-resistant character of the coatings was tested by cyclic and constant heat treatment, after which the physical integrity of the coatings was evaluated by optical microscopy. In the overall performance of the coatings, the roughening of the steel substrate surface and the thickness of the coatings were also considered as influential parameters. The study revealed that the newly developed coatings have superior anticorrosion performance to the usually applied Zn-rich coating. The Single-layered Coating has excellent corrosion resistance under certain conditions and has the advantage of fast layer application. The Bilayered Coating showed excellent heat- and corrosion-resistance properties even on a surface without sand-blasting.

Carbon nanotube (CNT) layers deposited on carbon fiber cloth (CFC) materials have been studied as electrodes of electrochemical double layer capacitors (EDLCs), in particular, the electrochemical performance and cycle stability of symmetric EDLCs in an organic electrolyte (tetraethyl-ammonium-fluoroborate in acetonitrile). Due to the large surface area of carbon-fibers, the CNT mass loading can be as high as 18 mg/cm2 which is magnitudes larger than that of what can be deposited on aluminium or nickel metal sheets. The area normalized double layer capacitance of CNT/CFC electrodes in the above organic electrolytes were found to be in the range of 100–400 mF/cm2, and the specific capacitances were 18–48 F/g. These latter values are below the achievable values of single-wall CNT of 80 F/g; the lower values can be attributed to the presence of multi-walled CNTs of some quantities, having lower accessible surface area. The energy density of CNT/CFC supercapacitors is 0.8–1.5 Wh/kg, while the power density varies between 5 and 20 kW/kg calculated on electrode level. Excellent cycling stability of EDLCs built with CNT-on carbon felt electrodes has been demonstrated up to 1 million cycles, which is due to the inert nature of substrate causing the absence of corrosion process and high mass load of CNT.

Surface modification with self-assembled alkyl-phosphonic acid layers is a powerful technique for corrosion protection of different metals. In the present study, passivated, native (covered with air-formed oxide) and metallic iron surfaces were used as substrates. The influence of the oxide on the phosphonate layer formation; the corrosion protective effect of the phosphonate layer and the structure of the modified surfaces were investigated. The layer formation process was monitored directly in the phosphonate-containing solution. It was found that the phosphonate layer formation process depends on the conditions applied during iron passivation, and the oxide layer has an important role in the stability of the protective layer, while the bare metallic iron surface is disadvantageous for phosphonate bonding. Conversion electron Mossbauer spectroscopy (CEMS) and X-ray photoelectron spectroscopy (XPS) proved the presence of phosphonate layer on the top of the passive iron surface, with the thickness around monolayer.

The objective of our studies was to investigate the layer formation of 1, 5-diphosphonopentane (DPP) on zinc surface from aqueous solution. For surface treatment, water based solutions of 1, 5-diphosphono-pentane was applied with different treatment times. Evidence of the adsorption of the diphosphonic acid on the zinc surface was obtained using the Infrared Reflection Absorption Spectroscopy (IRRAS).

Thin films prepared by vacuum evaporation of 57Fe and subsequent low energy ion implantation were investigated by conversion electron Mossbauer spectroscopy and AFM measurements. A sextet with Mossbauer parameters of δ = 0.1 mm/s and B = 26 T appearing in the CEM spectra was identified as amorphous iron. Passivation and phosphonation of the thin films revealed the high affinity of amorphous iron in chemical reactions.

Phosphonate layer formation on passive iron surface has been investigated by electrochemical, conversion electron Mossbauer spectroscopy (CEMS) and atomic force microscopy (AFM) techniques. Electrochemical methods revealed that the prepassivation of iron surface results in stabilization of the phosphonate layer exhibiting favorable corrosion resistance. The rate of anodic dissolution is continuously decreasing due to the time-dependent formation of a protective phosphonate layer. The large R ct values of 1–20 MΩ cm 2 indicate rather high blocking effect of metal dissolution by the phosphonate layer. The phosphonate layer formation has been also followed by the decrease of capacitance. CEMS investigations were carried out to evaluate the differences in the composition of the passive layer as a result of the phosphonate treatment. Mossbauer spectroscopy indicated the presence of iron phosphonate. Changes in morphology due to the phosphonate layer formation have been observed.

Due to the toxic and carcinogenic properties of hexavalent chromium ion, the corrosion protection with chromating technique needs replacement. Several environmentally friendly alternative metal pretreatments have already been proposed. One of these methods is the application of self-assembling molecules to form mono- or multilayers on the metal surfaces. These layers can prevent metal dissolution due to their dense and stable structure. The objective of our studies was to protect zinc surface against corrosion, with a thin phosphonate layer. Aqueous solutions of diphosphonic acid with different alkyl chain lengths were applied with different treatment times. The layer formation, stability, and corrosion protection of these films were monitored by electrochemical impedance spectroscopy and the effect of 1,5-diphosphono-pentane (DPP) on zinc was studied by polarization curves. The wetting properties were determined by static contact angle measurement. 1,5-Diphosphono-pentane forms a thin layer, with a pronounced protective ability in neutral aqueous solutions. The application of self-assembling molecules can be a promising method to replace the chromating technique on zinc surface.

Protective layer formation of α,ω-diphosphono-alkane compounds on iron surface was studied. Layer formation proved to be a spontaneous process on iron, and can be accomplished by simple immersion into an aqueous solution of phosphono compounds, resulting in a thin dense multimolecular adsorption layer with a high corrosion protection effect. The mechanism of inhibition and time dependence of layer formation is presented.

Chemical surface modification of iron by 1-phosphono-alkane derivatives in aqueous solution has been studied by EIS. The phosphonate layer formation in time was followed by the change of polarization resistance and interfacial capacitance values of iron substrate. Significant corrosion protection was observed due to the spontaneous adsorption layer formation. The protective layer is supposed to have a continuous and dense structure. The inhibition mechanism is anodic type, hindering the active iron dissolution to a large extent. The kinetics of phosphonate layer formation is a complex process. Beside the fast adsorption of molecules on bare iron surface, ordering in the layer structure is taking place during long immersion time. The layer formation process of alkane-diphosphonates and monophosphonates were compared.

Dissolution of iron in the presence of inorganic and organic sulfides was investigated as a chemical model for sulfide induced microbiologically influenced corrosion processes. Sulfur species used in the model were based on the surface analysis of the biofilm and the cell wall composition of the sulfate-reducing bacteria. Oxide layer decomposition by the sulfide species in buffer solution is explained with the formation of surface complexes, promoting the reductive dissolution of iron oxide. The mixed-sulfide species in actual biofilms result in a transformation of the surface layer by the assembly of mixed-ligand complexes. This type of film modification enhances the reactivity of the corrosion product layer where accelerated redox reaction can occur, as an analogous reaction to the biochemical role of iron–sulfur clusters containing redox proteins. The possible functional role of corrosion products in the metabolic processes of hydrogen utilizing sulfate-reducing bacteria can be also considered.

Coupled application of a version of the in-situ radiotracer ‘foil’ method and voltammetry provided information on the time-, potential-, concentration- and pH-dependent adsorption of 1-hydroxy-ethane-1,1-diphosphonic acid (HEDP) on a polycrystalline gold electrode, and on the effect of Zn 2+ ions on the adsorption phenomena. Adsorption processes on the oxide-free surface of gold were observed to be potential-dependent in the potential range 0.05–1.00 V (versus RHE), while formation and irreversible accumulation of oxidation products of HEDP could be detected at E >1.00 V. The relative adsorption strength of HEDP (its dissociation and/or oxidation products) was found to be higher on an oxide-free gold surface than on an oxide-covered one. The surface excess of HEDP increased with increasing pH. Addition of Zn 2+ ions to the solution exerted a substantial effect on the HEDP accumulation. Namely, significant differences in the surface coverage, as well as in the kinetics and mechanism of HEDP adsorption could be detected in the potential regions below and above E =0.2 V. Reduction of Zn(II) species at E ≤0.1 V is probably coupled with the induced adsorption of HEDP on an Au electrode, leading to the formation of a polymolecular HEDP–Zn surface complex layer.

The influence of calcium and zinc ions on the corrosion inhibition effect of 1‐hydroxyethane‐1,1‐diphosphonic acid (HEDP) on carbon steel has been investigated by electrochemical techniques, X‐ray photoelectron spectroscopy, and atomic force microscopy. Addition of calcium or zinc ions greatly increased the inhibition efficiency of HEDP in a synergistic manner. The highest inhibition effect was obtained for molar ratios of Ca/HEDP = 0.5 and Zn/HEDP = 3 for . The corrosion inhibition mechanism in the presence of these additives proved to be different from that with HEDP alone and was related to the formation of different complex species between HEDP and cation additives. The frequency response of the studied system was described by a transfer function containing two relaxation time constants corresponding to the charge‐transfer process and the porous oxide layer. Higher zinc and phosphorous content in the inhibitor layer and a continuous change in the O‒Fe and HO‒Fe ratio were achieved by increasing zinc concentration in the solution (in the range Zn/HEDP = 0.5–3) as supported by XPS measurements. Changes in the chemical structure were established in the oxide‐hydroxide layer developed spontaneously on the steel surface. The synergistic effect of inhibitor compounds appeared also in surface morphology, leading to the development of smooth, i.e., dense, protective layers as revealed by atomic force microscopy. © 1999 The Electrochemical Society. All rights reserved.

Impedance spectra of carbon steel in the presence of 1-hydroxy-ethane-1,1-diphosphonic acid (HEDP) has been investigated in neutral solutions. The aim of the measurements was to study the effect of HEDP on the carbon steel corrosion as a function of inhibitor concentration. An optimal inhibitor concentration was found. A two-time constant equivalent circuit model including a constant phase element was consistent with experimental data in the frequency range studied. The system parameters, obtained by a nonlinear fit procedure are discussed in terms of the model used. Inhibitor efficiencies derived from impedance data are compared with those obtained from polarization and weight loss measurements. Results of these investigations show that a low concentrations, HEDP inhibits carbon steel corrosion by a precipitation mechanism forming insoluble iron complexes and repairing the porous oxide layer formed n the metal surface. Increasing HEDP concentration beyond the optimal value decreases its inhibition efficiency due to the dissolution of the oxide layer.

Phosphonate layer formation on passive iron surface has been investigated by electrochemical and atomic force microscopy techniques. It was found that phosphonate groups bond more strongly to oxide surface, while metallic iron surface is disadvantageous for phosphonate layer formation in aqueous solutions. The rate of anodic dissolution is continually decreasing due to the time-dependent formation of protective phosphonate layer. The kinetics of phosphonate layer formation on passive iron is determined by the potential applied for preceding passive film formation. The size and shape of iron oxide grains depends slightly on the potential of passivation. Changes in morphology due to the phosphonate layer formation have been recorded by AFM.