Zinc-rich Primer Research Articles

Surface Modification of Composite Coating for Marine Application: A Short Review

Corrosion is one of the phenomena that affects the deterioration of materials in offshore applications. Marine corrosion is particularly aggressive, due to the high salt content and low electrical resistivity of seawater. Corrosion cannot be stopped completely, but the reaction can be slowed down. Applying coating is an effective and widely used method to protect metal surfaces from corrosion. Coatings act as a barrier between the metal and its environment, preventing or slowing down the corrosive processes. Pursuant to ISO 12944, the most commonly used generics for coating systems in marine service are alkyd, acrylic, ethyl silicate, epoxy, vinyl ester, polyurethane, polyaspartic, and polysiloxane. The latest innovations in marine coatings still use a layer-by-layer coating method (e.g. primer coats, intermediate coats, and top coats) depending on thickness. Marine structures exposed to the atmospheric zones are usually coated with one or two coats of epoxy. A slightly more costly system of one coat of zinc-rich primer, one coat of epoxy, and one coat of aliphatic polyurethane may provide better performance. Coating systems for the atmospheric zones are frequently used in the intertidal and splash zones. Immersion zones of marine structures are commonly coated with one or two coats of 100% solid epoxy or three coats of solvent-borne epoxy. A single polymer as a generic coating have limitations. Adding fillers is a common method to improve the properties of polymers to become a composite. In marine coatings, fillers are still limited to glass flakes and powder. Poor dispersion and agglomeration might reduce the effectiveness of fillers in the matrix, which decreases the adhesion properties. The fillers must be surface modification before the application. This review provides a comprehensive and critical review of the current research status of composite coatings that serve as candidates to be used in marine coating.

Low-frequency EIS interpretation with the potential to predict the durability of protective coatings

Obtaining impedance response with predictive value for coating durability is central to meeting today's protective coatings end-user requirements. Here we present a novel approach to interpreting the low-frequency impedance of industrial coatings that takes into account the relevance of the coating properties that determine their barrier and adhesion durability. Modern, high adhesion, low VOC polymer coatings utilize cross-linking chemistry with polar or hydrogen bonding materials, leading to the apparent paradox that coatings exhibit corrosion creep values that are very low and inversely related to the barrier effect derived from the EIS response. In practice, once the corrosion creep rate is negligible, the ability of a coating to act as a long-term effective barrier, especially at edges and welds, becomes a major concern, and the improvement in durability relies on the improvement of the barrier. In the present study, we investigated the barrier effect of conventional partial and full offshore coating systems with epoxy and epoxy mastic layers applied without and with zinc-rich or zinc phosphate primers and polyurethane topcoats. The panels were aged for two years in an atmospheric offshore-like conditions and subsequently exhibited defects due to inadequate coating thickness, number of layers, surface preparation and inadequate application practice. EIS measurements were performed on the panels in the laboratory in dry and wet state. EIS provided a quantitative rating of the barrier effect that can serve as a basis for informed upgrading of coating solutions, application practices or workmanship quality, particularly in structures with limited access where high durability is an imperative.

Impact of anti-corrosion coatings and maintenance on high-strength bolt friction connections in C4 marine environment

High-strength bolt friction connections (HSBFCs) in steel constructions often employ exterior anti-corrosion coatings, and some connections in steel bridges extend these coatings to their friction surfaces. However, previous studies on HSBFCs have overlooked the influence of external anti-corrosion coatings and coatings on friction surfaces. This research investigates the impact of internal and external anti-corrosion coatings on shear performance through experimental testing. Shear tests were conducted on 43 connections under 17 different conditions, varying the presence of anti-corrosion coatings on friction surfaces and external coatings, including conditions of construction and maintenance. Calibration tests revealed varying anti-slip coefficients: sandblasted surfaces measured 0.44, below specification; epoxy zinc-rich primer coatings measured 0.27; and alcohol-soluble inorganic anti-rust primers measured 0.50, both meeting or exceeding specifications. Simulated C4 atmospheric corrosion environments and dry-wet alternating copper accelerated acetic acid salt spray tests were performed. Results indicate predictable indoor corrosion acceleration and significant shear capacity degradation (4.9 % to 19 %) despite external coating use. Coatings on friction surfaces delayed degradation, while external anti-corrosion coating effectiveness declined post-construction and maintenance. Analysis shows shear capacity degradation in unprotected connections was 1.5 to 1.8 times higher than protected counterparts, attributed to reduced anti-slip coefficients and bolt pre-tension loss.

Evaluation of disposable protective garments against epoxy resin permeation and penetration from anti-corrosion coatings.

Epoxy-based resin formulations are a frequent cause of allergic and irritant contact dermatitis in the construction and painting industries. Cases of epoxy resin contact dermatitis continue to persist across many sectors and are likely attributable to the growing use of epoxy products, including epoxy-based anti-corrosion coatings and inadequate skin protection. There are no published performance data against epoxy resins for garment materials and gloves to guide proper material selection in the workplace. The objective of this study was to evaluate the resistance of 5 protective garment materials against permeation and penetration by bisphenol A diglycidyl ether and its higher oligomers found commonly in epoxy-based anti-corrosion coatings. Five disposable garment materials were evaluated for resistance to bisphenol A diglycidyl ether monomers and oligomers during contact with epoxy-based anti-corrosion coatings, including latex gloves, nitrile gloves, Tyvek coveralls, polypropylene/polyethylene (PP/PE) coveralls, and a cotton T-shirt. A permeation test cell system was used to evaluate each garment material against an epoxy-based zinc-rich primer and an epoxy-based intermediate coating using a realistic application method. Glass fiber filters were used to collect permeating and penetrating epoxy resin during a 120-min test period. Bisphenol A diglycidyl ether quantification was performed with high-performance liquid chromatography-electrospray ionization-tandem mass spectrometry. Paint loading, coating thickness, and homogeneity were assessed on polytetrafluoroethylene filters sprayed in series in permeation test cells. Latex gloves provided the least resistance to permeation by BADGE in coating formulations, with a maximum cumulative permeation over the 2-h test interval of 21.7 ng cm-2 with the primer and 513.8 ng cm-2 with the intermediate coating product. Nitrile gloves were not permeated by either coating formulation. The Tyvek coveralls provided greater protection as compared to the PP/PE coveralls. The cotton T-shirt was penetrated by bisphenol A diglycidyl ether more frequently than any of the tested garment materials and resulted in a maximum cumulative penetration of 128 ng cm-2 with the primer and 28.0 ng cm-2 with the intermediate coating. Although all the garment materials evaluated during this study provided sufficient protection to prevent cumulative permeation in excess of the established acceptable permeation thresholds, the use of nitrile gloves and Tyvek coverall is highly recommended to minimize skin exposure to bisphenol A diglycidyl ether. We recommend cotton T-shirts to be used under Tyvek coveralls as a secondary layer of skin protection and for added comfort, but not as a primary protection layer.

Acid resistance and failure mechanism of zinc-rich primer/micaceous iron oxide/polyurethane composite coating immersed in 5 wt% sulfuric acid

In order to study the reliable resistance to sulfuric acid corrosion of epoxy zinc rich primer/micairon oxide intermediate paint/acrylic polyurethane topcoat composite coatings for power transmission and transformation equipment. In this paper, under the condition of immersion in 5 wt% sulfuric acid, the sulfuric acid resistance behaviour of zinc-rich epoxy/micaceous iron oxide/polyurethane composite coating was evaluated by performing soaking tests for 50 h, 100 h and 150 h, and the failure mechanism of the film was studied. The changes in the surface properties of the coating during sulfuric acid soaking were evaluated by testing the hardness, glossiness and adhesion, and the changes in the capacitance and resistance characteristics of the coating during acid soaking were studied by Electrochemical Impedance Spectroscopy (EIS). The micromorphology and chemical element distribution of the cross-section of the composite coatings were studied by Scanning electron microscope (SEM) and Energy-dispersive X-ray spectroscopy (EDS). The functional group changes were studied by Fourier transform infrared spectroscopy (FT-IR). The results show that the corrosive effect of sulfuric acid solution immersion on acrylic polyurethane is weak, while the hydrolysis of water molecules will lead to aging and failure of acrylic polyurethane. Sulfuric acid leads to the formation of zinc deficient areas in zinc-rich primers, which reduces the cathodic protection effect of zinc-rich primers. The service life of the zinc-rich primer/ Micaceous Iron Oxide/acrylic polyurethane composite coating is less than 150 h.

Effects of Different Coatings, Primers, and Additives on Corrosion of Steel Rebars

In this research, methods of increasing the corrosion resistance of reinforced concrete were experimentally investigated. The study used silica fume and fly ash at optimized percentages of 10 and 25% by cement weight, polypropylene fibers at a ratio of 2.5% by volume of concrete, and a commercial corrosion inhibitor, 2-dimethylaminoethanol (Ferrogard 901), at 3% by cement weight. The corrosion resistance of three types of reinforcements, mild steel (STt37), AISI 304 stainless steel, and AISI 316 stainless steel, was investigated. The effects of various coatings, including hot-dip galvanizing, alkyd-based primer, zinc-rich epoxy primer, alkyd top coating, polyamide epoxy top coating, polyamide epoxy primer, polyurethane coatings, a double layer of alkyd primer and alkyd top coating, and a double layer of epoxy primer and alkyd top coating, were evaluated on the reinforcement surface. The corrosion rate of the reinforced concrete was determined through results of accelerated corrosion and pullout tests of steel-concrete bond joints and stereographic microscope images. The samples containing pozzolanic materials, the corrosion inhibitor, and a combination of the two showed significant improvement in corrosion resistance by 7.0, 11.4, and 11.9 times, respectively, compared to the control samples. The corrosion rate of mild steel, AISI 304, and AISI 316 decreased by 1.4, 2.4, and 2.9 times, respectively, compared to the control sample; however, the presence of polypropylene fibers reduced the corrosion resistance by 2.4 times compared to the control.

Electrochemical Assessment of Galvanized Steel Corrosion in Alkaline Sulfate Solution

Corrosion of steel prestressing strand in bonded post-tensioned bridge tendons have been associated with elevated concentrations of sulfate ions in deficient grout that can develop due to grout segregation [1]. Previous research indicated that the early presence of elevated sulfate ion concentration in the deficient grout in contact with the embedded steel can impair steel passivity. Metastable pitting was observed for steel in saturated calcium hydroxide solutions with sulfate ion concentrations greater than 1,300 ppm and pitting was observed in solutions above 20,000 ppm [2-4]. In addition to steel strand corrosion, galvanized steel ducts in direct contact with the deficient grout with elevated sulfate ion concentrations were also observed to have severe localized corrosion [1]. Galvanized steel in alkaline solutions, such as in cement pore water, have been characterized to have greater resistance to chloride-induced corrosion with chloride threshold concentrations as much as 2.5 times greater than carbon steel [5]. Information relating to sulfate concentrations is less available. Electrochemical testing including the electrochemical noise (EN) technique was conducted to identify the role of early sulfate ion presence on corrosion of galvanized steel.EN provides a test method to assess the corrosion modality without the influence of an external excitation that can affect the electrode surface and electrolyte chemistry (such as metal oxidation and oxygen reduction) [6-7]. The testing aims to identify the corrosion mitigation characteristics of the galvanized steel such as zinc activity and protective barrier surface oxide layers in presence of sulfate ions as well as combined cases with chloride ion contamination below reported threshold concentrations for galvanized steel. In the testing here, steel specimen were exposed to alkaline solutions simulating pore solutions with pH 12.6 with varying sodium sulfate levels and sodium chloride. Supplemental electrochemical experiments included the steady-state condition (open circuit potential, linear polarization test, and electrochemical impedance spectroscopy). References K. Lau, and I. Lasa. "Corrosion of prestress and post-tension reinforced-concrete bridges." Corrosion of steel in concrete structures. Woodhead Publishing, 2016. 37-57. DOI: https://doi.org/10.1016/B978-1-78242-381-2.00003-1.S. Permeh, K. K . Krishna Vigneshwaran, K.Lau., and I.Lasa. “Corrosion of Post-Tensioned Tendons with Deficient Grout. Part 3: Segregated Grout with Elevated Sulfate and Vestigial Chloride Content.” Corrosion 75 (2019) pp.848-864.S. Permeh, K. Lau, M. Duncan, and R. Simmons. “Initiation of localized steel corrosion in alkaline sulfate solution.” Materials and Structures, 54 (2021), pp.1-17.S. Permeh, K. Lau, M. Duncan, and R. Simmons. “Identification of steel corrosion in alkaline sulfate solution by electrochemical noise.” Materials and Corrosion, 72(2021), pp.1456-1467.S. Yeomans. Galvanized steel reinforcement in concrete. Elsevier, 2004.S. Permeh, and K. Lau. "Electrochemical Behavior of Steel in Alkaline Sulfate Solutions with Low Level Chloride Concentrations." ECS Meeting s. No. 10. IOP Publishing, 2021.K. Lau, S. Permeh. “Assessment of durability and zinc activity of zinc-rich primer coatings by electrochemical noise technique.” Progress in Organic Coatings, 167(2022): 106840.

Comparative Study of Carbonaceous and Polymer Conductive Additives on Anticorrosion Performance of Epoxy Zinc-Rich Primer

Zinc-rich primers are among the most promising organic coating systems for improving the corrosion resistance of metals in the marine environment. However, the high zinc content results in poor coating adhesion, high cost, insecurity and pollution. To decrease the zinc dust content, the carbonaceous and polymer conductive additives carbon black (CB), conductive graphite (CG), multiwalled carbon nanotubes (MWCNT) and polyaniline (PANI) were introduced to partially replace the zinc dust in the primers. A comparative study of the anticorrosion performance of epoxy zinc-rich primer (ZRP) is presented herein to systematically discuss and elaborate on the effects of the different conductive additives. There were no blisters, rust or corrosion products presented on the coatings of the CB-modified series due to the good dispersion and conductivity of nanosized CB clusters, while the zinc corrosion products covered the surface of the MWCNT-modified series samples, which was attributed to the excessive electrical conductivity resulting in high consumption of zinc powder. The lamellar CG provided an additional blocking barrier for the coatings based on the maze effect. The transition from the intrinsic state to the doped state of PANI resulted in corrosion protection for the coatings depending on the cathodic and barrier function. The experimental results suggested that the formula with 2 wt.% CB and 67 wt.% zinc dust had the most promising anticorrosion properties, which was also demonstrated by the high Rct and low CPEdl values calculated according to the equivalent electrical circuit analyses.

Fabrication of a Conductive Additive for the Anticorrosion Enhancement of Zinc-Rich Epoxy Coatings

In the study, a conductive polypyrrole (PPy) is deposited on the lamellar sericite powder (SCP) surfaces by an in situ oxidization growth method and the prepared PPy/SCP conductive additive is successfully applied on the zinc-rich primer (ZRP) coating. The equal mass substitution and the equal volume substitution methods of the conductive additives to zinc dusts are discussed, as well as the optimal replacing ratio to achieve the best corrosion protection effect of the ZRP coatings. The results indicate that the equal volume substitution method is in favor of corrosion resistance of coating film. The salt spray test and the electrochemical impedance spectroscopy (EIS) and polarization curves show that the prepared ZRP coating with a 66% zinc content and replacing ratio of 1:3 possesses the best corrosion-resistant performance and an optimal adhesion strength. The replacement of PPy/SCP particles to zinc dusts using the equal volume substitution method is feasible to achieve the improvement in anticorrosion ability through a synergic function of the cathodic protection effect and barrier effect.

Correlations between standard accelerated tests for protective organic coatings and field performance

Accelerated testing is widely used in development and pre-qualification of protective organic coatings. In this work 26 coating systems have been investigated in a 2-year C5 atmospheric exposure field test, ISO 9227 salt spray test, ISO 12944-9 cyclic ageing and ISO 16773 electrochemical impedance spectroscopy measurement of coating resistance. Of the 26 coating systems, 16 have epoxy mastic primers and 10 have zinc rich epoxy primers. In the field test, the zinc rich primer improved corrosion creep resistance from scribe by a factor of about 10. However, this is not reflected in any of the accelerated lab tests. The lab tests all show rather poor correlation to the field test with respect to corrosion creep. All the coatings had little corrosion creep from scribe in the field test, even the coating systems with epoxy mastic primers. The large focus on this parameter in coating pre-qualification testing, e.g. in ISO 12944-6 and 12944-9, may therefore not be justified.

Experimental Study of the Factors Influencing the Performance of the Bonding Interface between Epoxy Asphalt Concrete Pavement and a Steel Bridge Deck

The bonding between pavement and a steel bridge deck is a key component affecting the structural integrity of steel deck pavement and delamination is a major cause. The bonding interface of steel deck pavement was systematically investigated to evaluate the interactive influences of factors, such as the air void of the asphalt concrete pavement, the surface roughness of the steel deck, the thickness of the zinc-rich epoxy primer, and the waterproof bonding membrane, on the bond strength of the pavement interface, through simulated loading, brine immersion, pull-off, and interface observation experiments. The results show that a low air void (<3.0%) was a necessary condition for the corrosion resistance and bonding reliability of the steel deck pavement structure, and a zinc-rich epoxy primer provided an additional guarantee for corrosion resistance of the steel deck pavement; additionally, the combination of steel deck plate roughness in the range of 120–140 μm and zinc-rich epoxy primer thickness in the range of 80–110 μm led to a high bond strength, which was also conducive to the corrosion resistance of the steel bridge plate. The steel deck pavement structure should be designed through combinatorial optimization of multiple factors to create an integrated waterproof and anticorrosion bonding system.

Assessment of durability and zinc activity of zinc-rich primer coatings by electrochemical noise technique

The three-coat system consisting of a zinc-rich primer, epoxy midcoat, and polyurethane topcoat has been widely adopted for corrosion protection of structural steel bridges. Corrosion mitigation is afforded by the barrier characteristics of the various layers as well as beneficial galvanic coupling of the zinc pigments in the primer to the steel substrate when subjected to corrosive environments such as with moisture ingress and coating defects. The dispersed zinc pigments in the binder require adequate electronic coupling in order to provide the beneficial electrochemical coupling of the zinc to the steel. The application of the electrochemical noise (EN) technique to identify coating corrosion performance was reviewed in controlled laboratory tests. Zinc pigment activation and transition to passive-like conditions in defect and defect-free coating specimens could be identified by EN. The characteristic charge of noise events resolved by shot noise analysis was demonstrated to be related to anodic polarization of extended active zinc pigments adjacent to coating defect sites galvanically coupled to the exposed steel and passivated zinc pigments. Electrochemical noise resistance was shown to convey zinc/steel interfacial behavior in cases with sufficient activity but largely reflects coating barrier quality for intact coatings.

Study on Compatibility of Waterborne Surface Treatment Coatings

the severe corrosion of power grid equipment has always been an important factor affecting the service life of equipment. Rust transfer technology is used to treat the corroded equipment to improve the corrosion resistance of transmission grid cabinet equipment in high temperature and high humidity environment. Taking acid modified acrylic acid as the main component, the composite conversion solution was obtained by adding phosphoric acid and phytic acid. Through the surface morphology, electrochemical test and adhesion test after rust conversion, the universality and corrosion resistance of the rust conversion solution were analyzed; Combined with zinc phosphate primer and zinc rich primer, the effects of rust conversion solution on the adhesion and salt spray corrosion resistance of the two commercial primers were studied. The compound conversion solution has good rust conversion effect on atmospheric corrosion rust layer, salt spray corrosion rust layer and damp heat corrosion rust layer; The corrosion resistance and adhesion of atmospheric corrosion rust layer are obviously improved after being treated with rust conversion solution. The adhesion of zinc phosphate primer and zinc rich primer on rust conversion solution is 2.1 times and 0.8 times higher than that of atmospheric corrosion rust layer without rust conversion, respectively. The compound rust conversion solution has strong universality and can convert atmospheric corrosion, salt spray corrosion and damp heat corrosion rust layers. At the same time, it has good corrosion resistance, which can significantly improve the corrosion potential of the corroded surface and reduce the corrosion current density. In addition, the composite rust conversion solution can significantly improve the adhesion and corrosion resistance of the primer coating.

Evaluation of coating performance on carbon steel A-36 in copper concentrate environment using electrochemical impedance spectroscopy

The presence of chalcopyrite increases the corrosion rate of carbon steel through a galvanic couple. In this study, five organic coating systems were evaluated for their strength against consequent corrosion in the presence of copper concentrate by electrochemistry impedance spectroscopy (EIS) measurement. The coating system studied are a single application epoxy coating (C1); a three-layer epoxy system with zinc-rich epoxy primer base coat, surface tolerant epoxy middle layer, and a top layer polyurethane (C2); a three-layer epoxy system that has the advantages of fast dry time consist of epoxy zinc phosphate base coat primer, the middle layer of the epoxy primer containing the pigment zinc phosphate and top layer polyurethane (C3); metallic pigmented polyurethane coating (C4), and an epoxy coating which can be applied to wet surfaces or in water (C5). All those systems have been tested by the EIS. The test results showed that C2, C3, C4, and C5 coating systems maintained good barrier properties during the immersion process, the low frequency |Z| is more than 108Ω.cm2 after 30 days of immersion exposure. Epoxy modified coating (C1) had the lowest impedance with resistance under 106 Ω.cm2 provide poor corrosion protection.

Concepts of steel protection by coatings with a reduced content of zinc pigments

In zinc-rich primers Zn acts in the initial stage as sacrificial anode (cathodic protection). During lifetime Zn is transformed into its corrosion products, which seal the coating's pores (barrier protection). Such coatings are typically very highly pigmented which could cause the deterioration of cohesion and/or adhesion as well as mechanical properties. The formulations of different Zn pigments in epoxy matrices were developed with concentration of zinc particles reduced to about 50 wt% in the dry coatings. As Zn pigments were used: mixtures of zinc pigments with different particle size and particle shape (dust, flakes), zinc dust with organic surface treatment, zinc alloy pigments – ZnMg and ZnSn as well as Zn dust with an addition of graphene or carbon nanotubes.The mechanisms of protection by coatings with a reduced content of zinc pigments were studied in comparison with that of commercial zinc rich primers – epoxy and ethyl silicate – by the following methods: Scanning Kelvin Probe (SKP) detection of artificially inflicted samples after impact of salt spray test (SST), polarization experiments and EOC detections in combination with different corrosive impact, as well as by SST and the exposure to the natural marine environment (sea water splash zone).It was found that cathodic protection is shown by primer pigmented with Zn flakes, with zinc phosphate and barium sulphate addition as well as by primer containing Zn dust and graphene. They reach an open circuit potential (EOC) significantly below −0.86 V. Primers pigmented with ZnSn or Zn dust with an addition of carbon nanotubes (CNT) keep their EOC in the transition phase between −0.7 V and −0.86 V. Other primers with a reduced content of zinc pigments show only barrier protection.Coatings characterized by EOC in the range of cathodic protection or in the transition phase have very good protective properties in the corrosive environment. However, good anticorrosive properties were found also in the case of primers which do not show any cathodic protection, such as the primer pigmented with a mixture of Zn particles with different size and the primer containing Zn dust with chemical surface treatment. This shows that good anticorrosive properties can be obtained even if cathodic protection is not observed.

Results of paint coating full-scale tests for coastal and ship structures in the tropical climate of Vietnam

Full-scale tests are widely used to reliably evaluation the service life of paint and varnish coatings by assessing changes of their protective and decorative properties. Four-year exposure program was carried out in the tropical marine climate in South Vietnam (Dam Bay climate station of the Tre island, Nha Trang) of alkyd, chlorinated rubber coatings on low carbon steel, as well as epoxy coatings of various thicknesses with zinc-rich primer, urethane and acrylic outer layers. The tests were conducted on the base of the existing standards in the field of paints and varnishes intended for coastal and ship structures and were accompanied by the data collection and analysis of the meteorological factors for the classification of the area according to the degree of corrosiveness of the atmosphere. The change in the decorative properties of paint coating was assessed by visual and instrumental methods. The protective efficiency of the coatings was assessed by the time of occurrence of the first local defects or complete destruction of coating layers. According to the results of the conducted field tests, it was found that paint coating combinations correspond to expected lifetime in tropical climate from 2 to 5 years. A typical group suitable for a given climate is a two-component epoxy paint with an acrylic topcoat. A zinc-containing primer is recommended as an anticorrosive undercoat.

Corrosion resistance evaluation of rebars with various primers and coatings in concrete modified with different additives

Corrosion of steel rebars in concrete can reduce the durability of concrete structures in coastal environments. The corrosion rate of these concrete structures can be reduced by using suitable concrete additives and coating on rebars. This paper investigates the corrosion resistance of steel rebars by the addition of pozzolanic materials including fly ash, silica fume, polypropylene fibers, and industrial 2-dimethylaminoethanol (FerroGard 901) inhibitors to the concrete mixture. Three different types of rebars including mild steel rebar st37, and two stainless steel reinforcements, AISI 304 and AISI 316, were used. Various types of primer and coating including alkyd based primer, hot-dip galvanized coatings, alkyd top coating, zinc-rich epoxy primer, polyamide epoxy primer, polyamide epoxy top coating, polyurethane coatings, double layer of epoxy primer and alkyd top coating, and double layer of alkyd primer and alkyd top coating were applied on steel rebars to investigate the effect of coating type on the corrosion resistance of steel rebars in concrete. Polarization tests, electrochemical impedance spectroscopy, compressive strength and color adhesion tests were conducted. The best reinforced concrete mix design for corrosion resistance was the one including the rebar with zinc-rich epoxy primer and 25% fly ash, 10% silica fume, and 3% FerroGard 901 inhibitors by cementitious material weight. Polyurethane was the best coating due to the highest strength and the lowest corrosion rate. Alkyd primer was the weakest coating, although it was the most economical coating system.

Study of the physical and electrochemical properties of hybrid paint system based on zinc-rich primer for mild steel protection

PurposeThis paper aims to study the corrosion performance and physical properties of hybrid paint systems based on zinc-rich primer (ZRP) and to determine the optimum modification approach that guarantees the most overall performance enhancement for the developed coating films that have been fabricated based on the usage of ZRP.Design/methodology/approachFour different approaches were applied to enhance the corrosion protection performance and the physical properties of ZRP-based paint systems, namely, incorporation with TiO2 pigment, introducing SiO2 nanoparticles, usage of polyamide curing agent and application of epoxy base coating as a second layer. The physico-mechanical properties were examined using pull-off test, glossiness test, pencil hardness test and cross-cut adhesion tape test. Moreover, the contact angle measurement was used to study the wettability of the developed coated surfaces and the corrosion protection performances were evaluated by using electrochemical impedance spectroscopy and salt spray test.FindingsThe obtained results revealed the ability of a certain approach to enhance the physical and corrosion protection properties of the ZRP paint system. Moreover, developing an intact hydrophobic nanocomposite paint system based on the usage of ZRP as the host matrix and SiO2 nanoparticles as the reinforcing agent was confirmed without altering the cathodic protection mechanism or the other desired characteristics of ZRP paint system.Originality/valueThe innovation of this work can be clearly observed by the ability to enhance the physical and corrosion protection properties of ZRP with four different approaches.

Anticorrosive effectiveness of coatings with reduced content of Zn pigments in comparison with zinc-rich primers

ABSTRACTTypically, an anticorrosive coating system for long-term protection consists of a primer, one or several intermediate coats, and a topcoat. In such systems, zinc-rich primers are often used as they ensure good adhesion to the substrate and protect it from corrosion. Such coatings are very highly pigmented, which sometimes leads to losses in cohesive strength and deterioration of mechanical properties. Furthermore, Zn is known to be harmful to the environment. In this work we present Zn primers with reduced Zn content and better protective properties than traditional zinc-rich primers. The formulations of different Zn pigments in the epoxy matrix were developed with the concentration of zinc particles reduced to about 50% in the dry coating. To evaluate the distribution of pigments scanning electron microscopy has been employed. The anticorrosive properties were tested using the salt spray test and electrochemical impedance spectroscopy. The mechanical properties of the coatings were also tested.

Application of Scanning Kelvin Probe in the Study of Protective Paints

Industrial coatings are composed of layers of different polymers (top coats, primers) containing pigments, corrosion inhibitors, and fillers as well as additives. For corrosion protection, it is vitally important to preserve the strong adhesion and long-term stability of the metal-polymer interface in corrosive environments. In recent decades, the performance of painted materials increased, which requires the application of advanced methods for quick assessing, ranking and predicting corrosion stability. Scanning Kelvin probe (SKP) is a highly sensitive and non-invasive technique to analyze in situ the metal-polymer interface of high-performance industrial coatings. SKP is able to monitor the adhesion and corrosion underneath different kinds of paints without the need for long-term corrosion tests. SKP is a localized electrochemical technique with a spatial resolution in the range of 70-100 µm. Hence, it is possible to obtain information about the intact and corroding portions of the interface at defect sites, corrosion blisters, contaminants and intermetallics, quality of pretreatments, and the development of galvanic couples that lead to corrosion de-adhesion of the polymeric coatings. This article reviews the application of SKP to the determination of the mechanisms of corrosion de-adhesion of model paints, thick marine paints, coatings with zinc rich primers, automotive paints and coil coatings applied on galvanized steel substrates.