M. Fedel

Study of corrosion protection of mild steel by eco-friendly silane sol–gel coating

The effects of dipping duration in the silane solution and the sol pH on the protective performance of an eco-friendly silane sol–gel coating consisting a mixture of tetraethoxysilane, methyltriethoxysilane and glycidyloxypropyltrimethoxysilane applied on mild steel substrate were studied in this paper using electrochemical techniques and surface analysis. In consistency with the data obtained from electrochemical impedance spectroscopy and polarization curves, electrochemical current noise fluctuation analysis, appearance of the power spectral density plots and noise resistance indicated the most efficient sol pH and immersion time in the silane solution. In this regard, field emission type scanning electron microscopy images and water contact angle values revealed impact of the sol pH on the film structure. The enhancement in protective performance of the hybrid coating resulting from optimum immersion in the silane solution with appropriate pH was connected to the film homogeneity and higher cross linking and thickness as well. Moreover, a good trend correlation was observed between the noise resistance and low-frequency impedance modulus data.

Accelerated weathering and chemical resistance of polyurethane powder coatings

A study of the weathering mechanism of innovative polyurethane powder coatings has been performed. UV-B irradiation and condensation cycle accelerated tests were carried out on two different polyurethane powder coating formulations for outdoor applications. Using Fourier transform infrared spectroscopy and microscope observation, it was possible to analyze the photochemical and morphological modifications. In addition, the color and gloss changes were measured. Organic coatings are often in contact with solvents in particular during cleaning actions. The chemical resistance was then studied considering the evolution of the corrosion barrier property of the coating as a function of the solvent contact time. Electrochemical impedance spectroscopy measurements were carried out. Methylethylketone (polar) and xylene (apolar) were considered as representative solvents. Due to the strong polarity, the first solvent showed a strong interaction with the hydrogen bonds between the polyurethane chains causing the solvent uptake. The amount of solvent uptake depends on the coating chains rigidity caused by the different polyester resin monomers. The apolar xylene presented no significant interaction with the coatings.

Microstructural modification of pure Mg for improving mechanical and biocorrosion properties

In this study, the effect of microstructural modification on mechanical properties and biocorrosion resistance of pure Mg was investigated for tailoring a load-bearing orthopedic biodegradable implant material. This was performed utilizing the friction stir processing (FSP) in 1-3 passes to refine the grain size. Microstructure was examined in an optical microscope and scanning electron microscope with an electron backscatter diffraction unit. X-ray diffraction method was used to identify the texture. Mechanical properties were measured by microhardness and tensile testing. Electrochemical impedance spectroscopy was applied to evaluate corrosion behavior. The results indicate that even applying a single pass of FSP refined the grain size significantly. Increasing the number of FSP passes further refined the structure, increased the mechanical strength and intensified the dominating basal texture. The best combination of mechanical properties and corrosion resistance were achieved after three FSP passes. In this case, the yield strength was about six times higher than that of the as-cast Mg and the corrosion resistance was also improved compared to that in the as-cast condition.

On the real effectiveness of experimental silicon alkoxides based pre-treatment as adhesion promoter for different painted metals

Abstract Silicon alkoxides sol-gel pre-treatments act as coupling agents between metal substrates and organic coatings. This kind of metal finishing is widely studied pre-treatment, but relatively little study is done on the effect of this sol-gel pre-treatment on the durability and on the corrosion protection properties of the complete protection system which consist of a pre-treated and, subsequently, painted metals. In this paper the performance of a sol-gel layer produced from a mixture of silicon alkoxides precursors was applied on different metals (galvanized steel, copper, aluminum) as a pre-treatment prior the application of an organic coating. The effect of the sol-gel pre-treatment on the durability of the painted metals was investigated evaluating the dry and wet adhesion of the organic coating to the substrate as well as the corrosion resistance in the salt spray chamber and the resistance to cathodic delamination. The laboratory testing proved that the experimental sol-gel layer provides the three different painted metals with an improved corrosion resistance, thus leading to a reduced extent of delamination of the coating from the substrate after the accelerated tests.

Corrosion Protection Properties of New UV-Curable Waterborne Urethane-Acrylic Coatings

Abstract Looking to the development of sustainable and low impact chemical technologies, water based paints offer significant advantage especially for in field applications, where the problem of solvent emission is really stringent. Some water based coatings are represented by alkyd and epoxy paints, capable of cross-linking either by auto-oxidation or with polyamines. Polyurethane aqueous dispersions are finding wide acceptance due to their better durability, adhesion and mechanical properties. The research presented here describes the design, application and characterisation of well defined model structures of waterborne UV curing coatings. The waterborne resins used in this work are segmented anionomeric polyurethanes functionalised with acrylic end groups: they were prepared from polytetramethylene glycol, isophorone diisocyanate, dimethylol propionic acid, and hydroxyethylacrylate. The preliminary results concerning the corrosion protection properties of the new UV curable waterborne coatings applied onto metallic substrates are very promising and were obtained by using electrochemical techniques. Water uptake is the critical process determining the corrosion performance. In particular the necessity to formulate the coating starting from higher molecular weight polytetramethylene glycol for good barrier properties is evident from the electrochemical impedance spectroscopy data.

Characterization Of Nano-structured UV Cured Acrylic Coatings

This paper deals with the production and characterization of nanostructured UV curable acrylic coatings applied on mild steel substrates for corrosion protection purposes. UV curable acrylic coatings were modified in two ways: by adding pre-formed silica nanoparticles modified with MEMO molecules and by promoting an in situ formation of silica domains functionalized with MEMO molecules. The coatings were characterized by means of both chemical (FT-IR, DSC, UV-Vis absorbance, Gloss) and electrochemical techniques (EIS, Potential vs Time). The coatings showed different thermal stability as revealed by the DSC measurements. The coatings showed also different barrier properties depending on the presence of the nanoparticles or of the silica domains. It was proved that a convenient functionalization of the silica domains (or particles) lead to noticeable improvements of the barrier properties of the coating respect to the pure UV curable polymer.

Coatings to increase the corrosion behaviour of aluminium foam

The aluminium foams present very interesting properties due to their low density. However, the presence of cells and the complex geometry are critical aspects considering the corrosion behaviour. A suitable method to increase the corrosion resistance is desirable. The cataphoretic deposited paint could be a useful way due to the possibility to obtain a protective and homogenous paint layer also with complex geometry. Other solution could be the application of an enamel layer, which shows high protection properties together with a good resistance at high temperature. The aim of this paper is the evaluation of the protection performance of these kinds of coatings. The corrosion behaviour of coated samples is evaluated by acetic acid salt spray exposure test and by electrochemical measurements. Both layers, organic coating and enamel, show a high increase of corrosion behaviour in comparison of uncoated aluminium foam.

Stress corrosion cracking (SCC) failure in marine areas of fixed guards for climbing

Abstract This work studies the particular mechanism of environmental stress corrosion cracking (SCC) that has been described to interest stainless steel products, like climbing anchors, installed in sea areas. The failure analysis of several broken anchors was carried out. The samples were collected in different parts of the world, always from climbing structures close to the sea. The analysis confirmed the stress corrosion mechanism of degradation, giving also important information about the specific environments causing the metal fracture. These results are in agreement with a few previous works about this subject and are in the frame of the larger topic of SCC of austenitic stainless steel at room temperature. Moreover, some corrosion tests were carried out on stainless steel samples simulating the operation conditions, after contamination with electrolytes at different concentration. The tests are performed in order to better understand the degradation mechanism and to evaluate the influence of some environmental parameters over the susceptibility to SCC. With these experimental data, a possible interpretation model has been proposed together with some reasonable solutions for the material selection process, considering the problem’s characteristics and the multiple alternatives available nowadays for climbing materials.

Corrosion behavior of severely plastic deformed magnesium based alloys: A review

The purpose of this paper is to provide an overview of the impact of the microstructural modifications via severe plastic deformation on the corrosion behavior of magnesium and its alloys, especially when they are considered to be biodegradable materials. Mechanical processing involved in grain refinement modifies textures and residual stresses of materials which have their own impacts on corrosion behavior as reported in a large number of studies. However, the existing literature on the influence of microstructure on corrosion resistance is often contradictory, which discloses a lack of knowledge in this area. In this article the effects and contributions of critical factors such as the grain size, texture, residual stress and second phase distribution, affected by severe plastic deformation, on the magne-sium corrosion behavior is reviewed in order to find a relation between the microstructure and corrosion resistance.

Anti-Graffiti Properties of Polyurethane Powder Coatings

Graffiti in street furniture and architectural facades is an increasingly important issue. For metallic structures, anti-graffiti coatings have to guarantee excellent corrosion protection, as well as have an easy-to-remove capability. In addition, color and gloss should not be changed because of natural weathering. In this work, two anti-graffiti polyurethane powder coatings applied were studied. In particular, these layers were deposited on aluminum substrate used in architectural application. Two different surface finishes, smooth and wrinkled, were considered. The efficiency of four different removers was investigated. For this purpose graffiti were drawn on the coatings by means of blue felt-tip marker and a red acrylic spray paint. Gloss and color changes were collected. Methyl–ethyl–ketone and a remover, based on aliphatic and aromatic compounds, resulted in the most effective means, producing a limited change in the appearance. On the contrary, the wrinkled surface result was less resistant. To simulate the weathering effect, UV-B cyclic tests and the Taber abrasion test were carried out.