Barrier Properties Of Coatings Research Articles

Performance of a Magnesium-Rich Primer on Pretreated AA2024-T351 in Selected Laboratory and Field Environments: Anodization Pretreatment

The effect of anodization on the corrosion protection of AA2024-T351 by magnesium-rich primer (MgRP) was evaluated in topcoated (TC) and non-TC MgRP systems with and without defects in the form of scribes. Protection of remote scratches and global protection by the coating after exposure in selected laboratory and field environments was investigated. Exposure studies focused on the following pretreatments: anodization without sealing (ANS), anodization with hexavalent chromium sealing (ACS), and anodization with trivalent chromium pretreatment sealing (ATS). Mg pigment depletion rate, global galvanic protection potential of intact coating, and coating barrier properties were investigated. In systems without TC, all chosen environments except for full immersion resulted in complete depletion of Mg pigment resulting from high self-corrosion rates. Polyurethane TC limited the Mg metallic pigment depletion resulting in only partial Mg depletion. In the case of ANS and ATS pretreated AA2024-T351 with MgRP, there was no initial galvanic coupling as inferred by a more positive global galvanic protection potential and predicted by high-pretreatment resistances. Upon prolonged exposure in full immersion, the global galvanic protection potential decreased to more negative potentials with time indicative of gradual galvanic coupling of the AA2024-T351 substrate with the MgRP. This was interpreted as resulting from degradation of the buried anodized layer. In the case of ACS pretreated AA2024-T351 with the MgRP, there was no initial galvanic coupling. After initial lowering of global galvanic protection potential indicating active coupling, there was a shift back to more positive potential. The global galvanic protection potential was heavily mediated by the TC polymer and there was no significant galvanic coupling between AA2024-T351 and Mg in the time frame over which experiments were conducted for TC systems. Mg was preserved and available for any future sacrificial anode-based cathodic protection. The barrier properties of the MgRP pigmented coating also degraded with time at a higher rate in systems in the absence of TC. This was correlated to UV degradation of the pigmented coating resin and could be reduced with the polyurethane TC. Scanning electron microscopy/energy dispersive spectroscopy characterization after different ASTM B117 and field exposure times indicated that the Mg2+ redeposition increased as a function of exposure time in AA2024-T351/ACS/MgRP systems. TC limited the Mg2+ release by mediating both the global galvanic protection potential and Mg self-corrosion. Corrosion volume analysis by optical profilometry indicated that the scribe protection was better for sealed anodization pretreatments compared to the case of anodized without sealing-based systems.

Influence of submicron-sheet zinc phosphate synthesised by sol–gel method on anticorrosion of epoxy coating

Abstract Submicron-sheet zinc phosphate (SZP) was synthesised by sol–gel method. Anticorrosion behaviour of epoxy coating with SZP was investigated by electrochemical impedance spectroscopy, gravimetric test, adhesion test and scanning electron microscopy. Results showed that the submicron-sheet structure of SZP pigment can reduce defects in the coating, improve consistency of pigment/resin interface and lengthen diffusion pathways. SZP pigments in coating had more contact area with permeating water, ensuring PO 4 3− quickly attained the specific density to inhibit corrosion on the steel surface. Thus, SZP pigment can enhance the barrier properties of coatings and effectively inhibit the corrosion reactions at coating/metal interface.

Evaluation of Ni0.5Zn0.5Fe2O4 nanoparticles as anti-corrosion pigment in organic coatings for carbon steel

PurposeInorganic oxide addition can be synergistically beneficial in organic coatings if it can impart anti-corrosion properties and also act as an additive to enhance physical and/or chemical properties. The aim of this study was to evaluate the anti-corrosion benefits of nano nickel zinc ferrite (NZF) in the polymer film.Design/methodology/approachThe time-dependent anti-corrosion ability of NZF (0.12-1.0 per cent w/w NZF/binder), applied on API 5L X-80 carbon steel, was characterized by electrochemical techniques such as open circuit potential, electrochemical impedance spectroscopy, linear polarization resistance and potentiodynamic. Characterization of corrosion layer was done by removing coatings after 216 h of immersion in 3.5 per cent w/v NaCl. Optical microscopy, field emission scanning electron microscopy and X-ray diffraction techniques were used to characterize the corroded surface.FindingsCorrosion measurements confirm the electrochemical activity by metallic cations on the steel surface during corrosion process which results in improvement of anti-corrosion properties of steel. Moreover, surface techniques show compact corrosion layer coatings and presence of different metallic oxide phases for nanocomposite coatings.Originality/valueThe suggested protection mechanism was explained by the leaching and precipitation of metallic ion on the corroded surface which in turn slowed down the corrosion activity. Furthermore, improvement in barrier properties of rubber-based coatings was confirmed by the enhanced pore resistance. This work indicates that along with a wide range of applications of NZF, anti-corrosion properties can be taken as an addition.

Corrosion News

Corrosion News

Electrochemical Diagnostic Cycle Testing of Magnesium and Magnesium Oxide-Pigmented Primers on AA2024-T351

Intact Mg-rich and MgO-rich primer (MgRP and MgORP) coatings on aluminum alloy 2024-T351 substrate were evaluated for their ability to protect remote scratches (coating defects) as well as for coating barrier properties using a laboratory diagnostic cycle test. These coatings consist of a pretreated substrate and a Mg-containing pigmented primer with and without a UV-inert pigmented topcoat. For MgRP, Mg2+ and electrons are available upon Mg oxidation, while for MgORP only Mg2+ is available upon MgO chemical dissolution. The thickness and the pigment volume concentration of the MgORP was less than the MgRP as characterized with scanning electron microscopy/energy dispersive spectroscopy imaging, resulting in a larger reservoir and Mg capacity in MgRP than the Mg2+ capacity in MgORP. Diagnostic electrochemical cycle testing assessed the anode capacity of Mg pigment available for sacrificial anode-based cathodic protection of the substrate during potentiostatic holds during full-immersion testing in 5 wt% NaCl. The MgO had no capacity for sacrificial anode-based cathodic protection, but it did exhibit beneficial effects associated with the electrochemical behavior of coated and bare AA2024-T351; this was attributed to presence of Mg2+ in solution and the redeposited corrosion product. During exposure, electrochemical impedance spectroscopy monitored the barrier properties of the coatings, which were affected by primer type and the presence of topcoat. MgRP is shown to protect AA2024-T351 via both sacrificial anode-based cathodic protection and Mg2+ redeposition. MgORP is shown to function as a corrosion preventative coating for AA2024-T351 through chemical release of Mg2+, which beneficially alters the electrochemical corrosion behavior of the AA2024-T351 alloy. This investigation serves as a foundation for future investigations into MgORP and spent MgRP in the case where Mg has been oxidized as a result of long-term field exposure.

Exploring the combined effect of DC polarization and high temperature exposure on the barrier properties of organic coatings

Abstract Organic coatings are evaluated by various electrochemical, accelerated and natural exposure test methods. Among the expedited electrochemical approaches, measurements such as electrochemical impedance spectroscopy (EIS) at high temperature (HT EIS), and AC-DC-AC have been used previously. In this work, we attempted to combine these two approaches to further expedite the test and perform high temperature AC-DC-AC (HT AC-DC-AC) on organic coatings and compare the results with individual AC-DC-AC, and HT EIS measurements. A commercially available standard epoxy primer, and a formulated blank epoxy was used for the experiment. It was observed that HT AC-DC-AC can expedite the barrier changes in coating more rapidly compared to the use of only AC-DC-AC or HT EIS.

Biofriendly nanocomposite containers with inhibition properties for the protection of metallic surfaces

An attempt to combine two 'green' compounds in nanocomposite microcontainers in order to increase protection properties of waterborne acryl-styrene copolymer (ASC) coatings has been made. N-lauroylsarcosine (NLS) served as a corrosion inhibitor, and linseed oil (LO) as a carrier-forming component. LO is compatible with this copolymer and can impart to the coating self-healing properties. For the evaluation of the protective performance, three types of coatings were compared. In the first two, NLS was introduced in the coating formulation in the forms of free powder and micro-containers filled with LO, correspondingly. The last one was a standard ASC coating without inhibitor at all. Low-carbon steel substrates were coated by these formulations by spraying and subjected subsequently to the neutral salt spray test according to DIN ISO 9227. Results of these tests as well as the data obtained by electrochemical study suggest that such containers can be used for the improvement of adhesion of ASC-based coatings to the substrate and for the enhancement of their protective performance upon integrity damage, whereas the barrier properties of intact coatings were decreased.

Effect of polyaniline/montmorillonite content on the corrosion protection of epoxy coating

PurposeThe purpose of this paper was to research the influence of polyaniline/montmorillonite (PANI/OMMT) composite powder content on the corrosion protection of epoxy (EP) coating.Design/methodology/approachThe polyaniline/montmorillonite/epoxy (PANI/OMMT/EP) coatings containing different contents of PANI/OMMT composite powder were prepared on steel. The corrosion protection performances of PANI/OMMT/EP coatings in 3.5 per cent NaCl solutions were investigated by electrochemical impedance spectroscopy. The barrier property of coatings was examined using water absorption analysis. The structure and crosslink density of coatings were examined using scanning electron microscopy and differential scanning calorimetry, respectively.FindingsThe PANI/OMMT composite powder could enhance the barrier properties of the EP coating and reduce the corrosion rate of the steel beneath the coating. The coating showed the best corrosion protection performance when 3 per cent PANI/OMMT powder was added to the coating.Originality/valueThe research clarified the influence of PANI/OMMT content on the corrosion protection of coating from two aspects: one is the barrier performance of the coating; the other is the corrosion inhibitors for metal substrate.

Effect of polyelectrolyte on the barrier efficacy of layer-by-layer nanoclay coatings

The development of effective barrier materials is becoming increasingly important, particularly as microelectronic devices and food supplies must be protected for extended periods of time from atmospheric gases and water vapor. One of the most effective, facile, eco-friendly, and inexpensive strategies introduced in this spirit is the sequential buildup of layer-by-layer (LBL) surface coatings. This technology relies on the repeated, alternating deposition of impermeable nanoclay platelets possessing a large diameter-to-thickness aspect ratio and a polyelectrolyte adhesive. Previous studies have focused extensively on the use of polycations for this purpose since they are attracted by the negative charges inherently present on the face of natural nanoclays, such as montmorillonite (MMT). In this work, we compare the barrier properties of LBL coatings prepared with a common polycation and a polyester-based polyanion, which selectively interacts with the positive charges that accumulate on the edges of nanoclay platelets. Deposition of these coatings on a hydrophobic styrenic copolymer is reported here to promote dramatic reductions in the measured permeabilities of oxygen and carbon dioxide. This study, which systematically explores the dependence of single-gas permeability on factors such as MMT suspension concentration, bilayer (BL) coating number and temperature, aims to expand the understanding of LBL coatings by also elucidating morphological considerations.

CATHODIC DISBONDING OF INDUSTRIAL CHLORINATED RUBBER-BASED PRIMER USED IN RUBBER/METAL COMPOSITES: AN ELECTROCHEMICAL IMPEDANCE SPECTROSCOPY ANALYSIS

ABSTRACT Chemlok 205 primer is a common bonding agent used together with a top coat in rubber/metal–bonded composites. Recent studies indicated that a stand-alone Chemlok 205 primer failed when its metal substrate underwent corrosion. The failure was suspected to be caused by coating degradation, followed by cathodic disbonding, induced from the corrosion reaction. Therefore, in this work, the effect of cathodic polarization on the coating delamination was further investigated. The work intends to focus on understanding the adhesion failure processes involved. Thus, electrochemical impedance spectroscopy (EIS) was employed on a stand-alone industrial coating Chemlok 205 primer on mild steel substrate subjected to cathodic polarization potential of −0.8 V versus Ag/AgCl reference electrode in 0.5 M NaCl. The coating barrier properties were interpreted through Nyquist and Bode plots of the EIS plots for a selected time interval. The data obtained were modeled against three distinguished electrical equivalent circuits representing the stages of coating degradation against time. Analysis through Nyquist and Bode plots indicated that the stand-alone Chemlok 205 primer coating experienced a significant drop in coating impedance before experiencing adhesion loss. The changes in the coating capacitance and coating resistance indicated that the coating underwent degradation first before adhesion failure.

The role of surface morphology in the barrier properties of epoxy coatings in different corrosion environments

Abstract Hydrophobic epoxy coatings with particulated surfaces were prepared via soft lithography using different abrasive papers as the templates. With the increasing surface roughness, the hydrophobicity of these surfaces first increased and then decreased and a maximum water contact angle of ∼136° was obtained by using a P2000 abrasive paper as the template. Electrochemical impedance spectroscopy (EIS) was used to study the role of surface morphology in the coatings’ barrier properties under wet–dry cyclic immersion and in salt-spray environments. The results demonstrated that the hydrophobicity induced by the trapped air in the surface microstructures produced stronger-barrier properties than that produced by a smooth coating when exposed to wet–dry cyclic immersion. The strongest barrier performance was achieved by the coating templated with the P2000 abrasive paper. However, these microstructured hydrophobic coatings deteriorated faster in the salt-spray tests because of the direct deposition of salt electrolyte particles on the coating surfaces and the increased coating surface area. Under the salt spray condition, the coating obtained from P6000 abrasive paper exhibited the fastest deterioration.

Performance of a Magnesium-Rich Primer on Pretreated AA2024-T351 in Selected Laboratory and Field Environments: Conversion Coating Pretreatments

The effect of conversion coatings on the corrosion protection of AA2024-T351 by magnesium-rich primer (MgRP) was evaluated in topcoated and non-topcoated, scribed conditions. Protection of remote scratches and global protection by the coating after exposure in selected laboratory and field environments was investigated. Exposure studies focused on chromate conversion coating, trivalent chromium pretreatment (TCP), and non-chromium pretreatment, and compared to non-film forming (NFF) surface pretreatment. Exposures were conducted in the field under two different environments: at a coastal marine site and at an inland rural site. ASTM B117 with 5 wt% NaCl, modified ASTM B117 with acidified ASTM substitute ocean water and UV light, as well as full immersion in ambiently aerated 5 wt% NaCl solution were compared to field environments. Mg pigment depletion rate, global galvanic protection potential, coating barrier properties, and scribe protection were investigated. In systems without a topcoat, full immersio...

Preparation, adhesion and barrier properties of bituminous composite coatings on steel 37

A series of bitumen/nano clay nanocomposite have been prepared through solvent intercalation technique by using mechanical agitation and sonication process. The structure of nanocomposite coatings was investigated by TEM, low angle X-ray diffraction and Fourier-transform infrared spectroscopy. To investigate barrier properties of nanocomposite coatings, polarization, salt fog test and pull-off adhesion tests have been employed. The results showed that bitumen/MMT nanocomposite coatings were superior to the pristine bitumen coating in corrosion protection effects. Also, it was observed that the corrosion protection of bitumen/clay nanocomposite coatings improved as the clay loading is increased up to 4 wt.%

Development of an ecofriendly silane sol-gel coating with zinc acetylacetonate corrosion inhibitor for active protection of mild steel in sodium chloride solution

This work intends to develop an ecofriendly silane sol-gel coating with zinc acetylacetonate for active protection of mild steel. This water-based silane coating was composed of γ-glycidoxypropyltrimethoxysilane, tetraethoxysilane and methyltriethoxysilane. The optimum inhibitor concentration was determined using electrochemical impedance spectroscopy. The electrochemical impedance spectroscopy data indicated no effect of zinc acetylacetonate on the coating barrier properties, which was confirmed by field emission scanning electron microscope (field emission scanning electron microscope), energy dispersive X-ray spectroscopy and fourier transform infrared spectroscopy surface analysis. From the charge transfer resistance, the superiority of inhibitor-doped films was associated with the function of zinc acetylacetonate at the interface. The electrochemical measurements showed an increase in the corrosion resistance of bare metal in sodium chloride solution with zinc acetylacetonate. From the results of field emission scanning electron microscope, energy dispersive X-ray spectroscopy, and atomic-force microscopy surface analysis, the corrosion control was suggested to be attributed to formation of a protective layer on the surface with contribution of zinc acetylacetonate.

Thermal curing of para -phenylenediamine benzoxazine for barrier coating applications on 1050 aluminum alloys

Abstract Polybenzoxazine coatings have been applied by spin coating of a solution, prepared from a laboratory synthesized phenol, para -phenylenediamine benzoxazine (P-pPDA), on 1050 aluminum alloy. A heat treatment was performed on the coating to polymerize the benzoxazine monomer by a ring opening mechanism attested for by Fourier Transform Infrared spectroscopy (FT-IR) and followed by Differential Scanning Calorimetry (DSC). Dielectric Analysis (DEA) showed curing to proceed at a temperature range up to 230 °C, without thermal decomposition taking place, as has already been reported in the literature for commercial bisphenol-a benzoxazines (Ba-A). The barrier protection has been evaluated by Electrochemical Impedance Spectroscopy (EIS) for 30 days in a sodium chloride solution (0.1 M). The results were fitted with equivalent electrical circuits in order to understand the electrochemical behavior of such a system. The initial barrier properties of both precursor and polymerized coatings appear to be excellent for coatings having a thickness of only 5 μm. Though delamination occurs in the polymerized coating during saline tests after several days of immersion, such kind of coatings have remarkable properties with respect to epoxy coatings as they show a high geometrical stability during curing and a very low water uptake during saline tests.

Inhibitor encapsulated, self-healable and cytocompatible chitosan multilayer coating on biodegradable Mg alloy: a pH-responsive design.

The design of functional biomaterials that respond intelligently to external stimuli has become a rapidly growing area with widespread interest. This work contributes to the development of a feedback-active anticorrosion system with intriguing self-healing ability to protect magnesium (Mg) from biocorrosion. The system was constituted by an inner micro/nano-porous, ceramic-like pre-coating developed readily from the substrate, and an outermost inhibitor (nanosized cerium (Ce) oxides) containing chitosan (CS) multilayers. Here, the pre-coating acted as both an "anchoring" and a "barrier" layer to acquire structural integrity and improved impedance, respectively. Green CS served as cargo for Ce to be entrapped, harnessing Ce-NH2 complexation chemistry. The coating barrier properties were evaluated by electrochemical impedance spectroscopy. The active corrosion inhibition was assessed by immersion degradation tests with respect to Mg2+ release, pH alteration, crack development, and scanning Kelvin potential. To our delight, the coatings effectively protected the substrate from biocorrosion in vitro compared with bare alloys. Putatively, the pH-triggered formation of Ce oxide precipitation, along with the pH-buffering activity and movable swelling capacity of CS macromolecules, should have contributed to restraining the anodic activity and healing the cracks/defects dynamically. Furthermore, the coated substrate had the biocompatibility to elicit better attachment and growth of osteoblasts.

Robust Superhydrophobic Graphene-Based Composite Coatings with Self-Cleaning and Corrosion Barrier Properties.

Superhydrophobic surfaces for self-cleaning applications often suffer from mechanical instability and do not function well after abrasion/scratching. To address this problem, we present a method to prepare graphene-based superhydrophobic composite coatings with robust mechanical strength, self-cleaning, and barrier properties. A suspension has been formulated that contains a mixture of reduced graphene oxide (rGO) and diatomaceous earth (DE) modified with polydimethylsiloxane (PDMS) that can be applied on any surface using common coating methods such as spraying, brush painting, and dip coating. Inclusion of TiO2 nanoparticles to the formulation shows further increase in water contact angle (WCA) from 159 ± 2° to 170 ± 2° due to the structural improvement with hierarchical surface roughness. Mechanical stability and durability of the coatings has been achieved by using a commercial adhesive to bond the superhydrophobic "paint" to various substrates. Excellent retention of superhydrophobicity was observed even after sandpaper abrasion and crosscut scratching. A potentiodynamic polarization study revealed excellent corrosion resistance (96.78%) properties, and an acid was used to provide further insight into coating barrier properties. The ease of application and remarkable properties of this graphene-based composite coating show considerable potential for broad application as a self-cleaning and protective layer.

Covalently-grafted graphene oxide nanosheets to improve barrier and corrosion protection properties of polyurethane coatings

Surface modification of graphene oxide (GO) has been performed by grafting of polyisocyanate (PI) resin. Results obtained from X-ray photo electron spectroscopy, thermal gravimetric analysis and X-ray diffraction analysis revealed that the PI resin chains were successfully attached onto the surface of GO nanosheets through covalent bonding with hydroxyl and carboxylic groups leading to amides and carbamate esters bonds formation. Subsequently, the PI functionalized GO sheets were incorporated into the polyurethane (PU) matrix. The X-ray diffraction analysis showed that surface modification of GO nanosheets with PI enhanced the level of exfoliation of PI–GO in the PU matrix. Scanning electron microscope analysis showed the enhanced interaction between GO and PU matrix after functionalization by PI resin. The electrochemical impedance spectroscopy and salt spray tests were performed to reveal the effects of addition of 0.1wt.% GO and PI–GO nanosheets on the corrosion protection properties of the PU coating. Also, the adhesion loss of the coatings was obtained by pull-off adhesion test after 30days immersion in 3.5wt.% NaCl solution. It was found that incorporation of 0.1wt.% surface modified GO nanosheets into the PU matrix resulted in significant improvement of the coating corrosion protection properties and ionic resistance.

Effect of surface modified TiO2 nanoparticles on thermal, barrier and mechanical properties of long oil alkyd resin-based coatings

Novel soy alkyd-based nanocomposites (NCs) were prepared using TiO2 nanoparticles (NPs) surface modified with different gallates, and for the first time with imine obtained from 3,4-dihydroxybenzaldehyde and oleylamine (DHBAOA). Unmodified and surface modified anatase TiO2 NPs were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and ultraviolet-visible (UV-Vis) spectroscopy, while the amount of adsorbed ligands was calculated from thermogravimetric analysis (TGA) results. Surface modification of TiO2 NPs was confirmed by FTIR and UV-Vis spectra. The influence of the TiO2 surface modification on the dispersion of TiO2 NPs in alkyd resin, thermal, barrier and mechanical properties and chemical resistance of alkyd resin/ TiO2 NC coatings was investigated. The obtained results revealed that glass transition temperature of all investigated NCs is lower than for pure resin, that the presence of TiO2 NPs surface modified with gallates had no significant influence on the thermooxidative stability of alkyd resin, while TiO2-DHBAOA NPs slightly improved alkyd resin thermooxidative stability. Also, the presence of surface modified TiO2 NPs improved barrier properties, increased stress and strain at break and hardness and chemical resistance and decreased modulus of elasticity and abrasion resistance of alkyd resin.

Flow accelerated degradation of organic clear coat: The effect of fluid shear

Flow accelerated organic coating degradation has been received attention, but the degradation mechanism is still not completely understood. In this study, we focus on investigating the influence of fluid shear on the degradation of organic coatings. A commercially available epoxy based clear coating was exposed to the laminar flow, and a 3.5 wt% NaCl solution was employed as the working fluid with a variety of flow rates. The change in the composition of the working fluid during the coating immersion was characterized by Fourier Transform Infrared Spectrometer (FTIR) and conductivity measurement. The effect of fluid shear is also demonstrated by the change in coating thickness. The barrier properties of organic coatings were monitored inline by Electrochemical Impedance Spectroscopy (EIS) measurement. The time evolution of coating resistance, capacitance, and permittivity obtained from the equivalent circuit model was studied to demonstrate the internal composition change of the coatings due to the flowing fluid. In this study, the experiments and analysis confirmed that flowing fluid promotes the release of coating materials from the coating into the surrounding working fluid while it accelerates the transport of water and ions into the coating.