Search

Porcelain enamels are silica-based inorganic coatings, which are successfully applied to different kind of metallic substrates in applications where high chemical resistance and corrosion protection are needed. The main weakness of enamel coatings is represented by the glassy and brittle nature of the matrix: therefore, it is necessary to find some solutions to address this issue effectively and improve their resistance to abrasion. Some recent papers about the production of composite enamels with Al2O3 particles showed that a high concentration of corundum particles (10–20 wt%) could improve the abrasion resistance of these coatings. This work is focused on studying the influence of micro and macro sized corundum particles on the abrasion and chemical resistance of composite enamel coatings. The Al2O3 particles are added in 20 wt % concentration and the firing treatment is optimized for every sample type. The coatings topography and morphology are mainly characterized by scanning electron microscopy measurements and Energy Dispersive X-ray (EDX) microanalysis. The abrasion resistance of the coatings is evaluated by P.E.I. abrasion test. Mass loss and roughness measurements are used to assess the coatings surface properties during the mechanical damage; in addition, Electrochemical Impedance Spectroscopy (EIS) measurements and electron microscopy observations are carried out after 5000 P E.I. abrasion cycles to evaluate the decrease of the coatings protection properties due to mechanical damage. Finally, the coatings chemical resistance is evaluated by exposure to an aggressive fog with the presence of SO2 (Kesternich test), simulating an industrial environment. The addition of macro sized alumina particles leads to an improvement of the coating abrasion resistance, without a loss in the protection properties. Differently, the addition of micro sized alumina particles produces an increase of the coating surface roughness and results to have detrimental effects on the behaviour of the coating in aggressive environments.

Vitreous enamels represent a class of coatings with different technological properties, mainly appreciated for the protection they guarantee to the covered substrates. This review introduces enamel coatings, describing their production technologies and presenting the main properties affecting the enamel’s durability. Firstly, this review article introduces the most important studies regarding the improvement in abrasion resistance, highlighting both successes and failures. Afterward, the work reveals an outlook about the resistance to chemicals, underlining the good resistance of enamels toward acidic chemicals and discussing the results of studies aimed to improve their performances toward alkaline solutions. This review also considers the corrosion protection property of enamels, highlighting the high barrier effect they provide against the absorption of aggressive substances toward metal substrates. Finally, new perspectives and possible future research paths are presented, being aware that this kind of coating offers both good product protection and functional integrity over time.

This study aims to demonstrate the remarkable features of graphene-based fillers, which are able to improve the protective performance of acrylic coatings. Furthermore, the joint application of a cataphoretic primer and a spray top coat, containing graphene and functionalized graphene oxide flakes, respectively, enables the deposition of a double-layer coating with high conductivity and abrasion resistance properties, capable of offering excellent corrosion resistance to the metal substrate. The surface morphology of the single- and double-layer coatings was investigated by optical and electron microscopies, analysing the defectiveness introduced in the polymer matrix due to the filler agglomeration. The behavior in aggressive environments was assessed by exposure of the samples in the salt spray chamber, evaluating the blister formation and the adhesion level of the coatings. Electrochemical impedance spectroscopy measurements were employed to study the corrosion protection properties of the coatings, whose conductivity and abrasion resistance features were analysed by conductivity assessment and scrub tests, respectively. The incorporation of graphene-based fillers in the cataphoretic primer improves the corrosion protection properties of the system, while the graphene flakes provide the top coat spray layer with high conductivity and excellent abrasion resistance features. Thus, this work demonstrates the possibility of employing different types of graphene-based fillers and deposition methods for the creation of multifunctional coatings.

The vitreous enamel coatings present very interesting properties for several industrial applications due to the glassy nature of the matter. Their chemical resistance and corrosion protection properties result very high due to the glassy nature of deposits. A good wear behavior is also requested in some applications. The use of composite layer obtained by the addition of hard particles to enamel could be a possible solution to increase the deposits hardness. In literature, there are some work about the chemical nature of the added particles, but the influence of the dimension and quantity of these particles are not well studied. The aim of this work is the study of composite enamel layers deposited on low carbon steel substrate with addition of Al2O3 particles characterized by macro and micro dimensions with different concentration (5, 10 and 20 wt.%). After the microstructure characterization, the abrasion resistance behavior is evaluated by Taber Test following ASTM C501 for 1500 cycles. Mass loss, gloss and roughness changes are collected. The protection properties change is evaluated by Electrochemical Impedance Spectroscopy measurements. The addition of micro dimension particles produces the best behavior. On the contrary, the presence of macro dimension particles reduces the abrasion resistance, probably caused by the increase of porosity level during firing treatment. Finally, the corrosion protection properties are evaluated by Kesternich test (aggressive fog with the presence of SO2), simulating an industrial environment. In this case the presence of the micro- particles shows a limited resistance. Probably the presence of the particles produces an increase of surface roughness and a presence of higher quantity of particles in surface, which favor the start of enamel degradation with a loss of protection properties. Increasing the quantity of particles, a reduction of chemical resistance is observed.

This work aims to verify how the addition of graphene oxide into the cataphoretic bath goes to modify the properties of the obtained coating. Because a simple single-step deposition produced a strange morphology deposit, other combinations consisting of two deposition steps were done, in order to make the coating even more homogeneous and protective. Particular attention is therefore paid to the importance of the intermediate curing process, between the two deposition steps. The morphology of the coatings is analyzed by both optical and scanning electron microscopy, to measure the thickness of the protective layers and their defective properties. Finally, corrosion resistance properties of the coatings are evaluated by salt spray chamber exposure and electrochemical impedance spectroscopy measurements. It appears evident that the graphene oxide leads to the creation of defective layers, with the consequence of decreasing the durability of the coating. However, by depositing in two steps, with two different baths, it is possible to preserve the integrity of the coating, ensuring the protection of the substrate.

In many fields of application, the aluminium foam panels could undergo flexural loads or impact forces. The presence of a vitreous layer influences the foam's response. Four different enamel systems, deposited on aluminium closed-cell foam, are studied. The bending stiffness values are obtained using a 4-point bending test and then the Young's modulus and the strength are extrapolated using a transformed section method. To evaluate the cracking behavior an indentation test was performed. A better sintered filling increases the bending stiffness and strength, moreover the presence of a primer layer may cause an early fracture in the coating.

•Aluminum foams are a very interesting engineering materials.•The opened cells are critical for corrosion behavior.•Electrodeposited organic coating is a solution to guarantee corrosion protection properties.•The deposition parameters influence the protection performance of the paints.

The functional properties displayed by graphene oxide (GO)-polymer nanocomposites are strongly affected by the dispersion ability of GO sheets in the polymeric matrix, which can be largely improved by functionalization with organosilanes. The grafting to GO of organosilanes with the general formula RSi(OCH3)3 is generally explained by the condensation reactions of silanols with GO reactive groups. In this study, the influence of the organic group on the RSi(OCH3)3 grafting ability was analyzed in depth, taking into account the interactions of the R end chain group with GO oxidized groups. Model systems composed of commercial graphene oxide reacted with 3-aminopropyltrimethoxysilane (APTMS), 3-mercaptopropyltrimethoxysilane (MPTMS), and 3-methacryloxypropyltrimethoxysilane, (MaPTMS), respectively, were characterized by natural abundance 13C, 15N and 29Si solid state nuclear magnetic resonance (NMR), x-ray diffraction (XRD), and electron spin resonance (ESR). The silane organic tail significantly impacts the grafting, both in terms of the degree of functionalization and direct interaction with GO reactive sites. Both the NMR and XRD proved that this is particularly relevant for APTMS and to a lower extent for MPTMS. Moreover, the epoxy functional groups on the GO sheets appeared to be the preferential anchoring sites for the silane condensation reaction. The characterization approach was applied to the GO samples prepared by the nitric acid etching of graphene and functionalized with the same organosilanes, which were used as a filler in acrylic coatings obtained by cataphoresis, making it possible to correlate the structural properties and the corrosion protection ability of the layers.

This study aims to assess the synergic effect of graphene-based filler and thermochromic pigments on the protective and aesthetical performances of cataphoretic acrylic coatings. The nature of the thermochromic pigments was investigated by electron microscopy observations and infrared spectroscopy analysis. The aesthetical features of the coatings were evaluated by colorimetric measurements, estimating the colour change with temperature due to the filler addition. The corrosion protection properties were assessed by means of salt spray chamber exposure and electrochemical impedance spectroscopy measurements, which evidenced a negative contribution of the combined presence of functionalized graphene oxide flakes and thermochromic pigments. Otherwise, the incorporation of both the two fillers improved the abrasion resistance of the cataphoretic coating, as observed thanks to scrub test, as well as its aesthetical performances after chemical degradation due to UV-B exposure. Thus, this work highlighted both the positive and the negative effects caused by the synergy of reinforcing graphene-based fillers and functional pigments on the properties of cataphoretic coatings.

Restrictive regulations concerning the toxicity of certain compounds and the use and disposal of solvents present in the liquid epoxy protection system have been analyzed in this work to evaluate powder coatings as an alternative in the protection of aerosol aluminum cans, which are employed in cosmetics and pharmaceutical product packaging. In this paper, the chemical resistance of polyester and mixed epoxy-polyester powder coatings is assessed, considering different aggressive environments employed in healthcare commercial products. The samples&rsquo, performances are also compared with the currently used liquid organic coatings. The pack test has been used to evaluate the protective system behavior in contact with both the liquid and the gaseous part of the cosmetic product. However, the visual observation, required by the test, enabled the highlight of only very evident degradation phenomena. The chemical resistance of the powder coatings has proved to be appropriate only for less aggressive environment, where the critical compounds are propellants, propane, butane and isobutane. When exposed to other environments containing alcohol, water and dimethyl ether, most samples have been susceptible to layer degradation phenomena. Polyester layers lose their corrosion protection properties. Epoxy systems, instead, result more performant than polyester resins, but they particularly suffer from the contact with dimethyl ether.

In this work, functionalized graphene oxide (fGO) flakes have been added into an acrylic cataphoretic bath, studying the effect of fGO different concentration on the properties of the coatings deposited on carbon steel substrate. The samples were characterized by optical and electron microscopy, analyzing the distribution of the fGO flakes within the polymer matrix. The corrosion resistance properties were evaluated by salt spray chamber exposure and electrochemical impedance spectroscopy measurements. Finally, coatings’ conductivity was measured, in order to study the barrier effect performed by the flakes. The optimized fGO concentration, equal to 0.2 wt%, greatly increase the coating resistance in the aggressive environment.

The multiple properties of graphene can be exploited in the production of composite coatings to obtain multifunctional layers. To homogeneously disperse graphene in a polymer matrix, its sheets must be oxidised and properly functionalised. In this study, a fast, simple, and alternative method for the oxidation of graphene with nitric acid was studied. The obtained product was functionalised with three different organoalkoxysilanes. The obtained graphene flakes were subjected to infrared and X-ray analyses to study the oxidation grade and organosilane grafting. Several samples were produced by adding functionalised graphene oxide powder to an acrylic-based cataphoretic bath operating at four voltage values to evaluate the effective protective role of the powders. The morphology of the coatings was observed via optical and scanning electron microscopy (SEM) whereas their corrosion resistance properties were evaluated via salt spray chamber exposure and electrochemical impedance measurements. Although the oxidation level of graphene was low, the functionalisation was successful. The differences among the samples depended on the chemical properties of silane. By using (3-aminopropyl)trimethoxysilane (at sufficiently high voltages during the electrodeposition process), coatings with excellent properties, owing to the presence of functionalised graphene oxide sheets, were obtained.