The effect of surface modification on the cathodic disbondment rate of epoxy and alkyd coatings

Surface modification of carbon steel substrates using appropriate functionalised silanes was carried out to investigate their effect on the dry and wet adhesion strength, and the cathodic disbondment rate, of coating binders based on epoxy and alkyd chemistries. Results show that pre-treatment of the steel substrate with 3-glycidoxypropyltrimethoxy silane (3-GPS) enhanced the dry and wet adhesion of an epoxy-based coating. Similarly, pre-treatment with 3-aminopropyltriethoxy silane (3-APS) enhanced the dry and wet adhesion of alkyd-based systems. However, although pre-treatment with 3-GPS reduced the cathodic disbondment rate for epoxy by a factor of 3, no effect on the disbondment rate for alkyd-based binders on substrates pre-treated with 3-APS was found. This strongly suggests that cathodic disbondment of epoxy proceeds by disruption of interfacial bonds (i.e. at the binder/substrate interface) but that disbondment of alkyds proceeds by direct degradation of the binder and that the interface plays little part in the process.     

A new pigment for smart anticorrosive coatings

The purpose of this paper was to evaluate the performance of a modified zeolite as an anticorrosive pigment for paints. A procedure to prepare the pigment was outlined and its anticorrosive properties assessed following the electrochemical behavior of a steel electrode in pigment suspension. In a second stage, alkyd paints were formulated employing different anticorrosive pigments: (1) 30% by volume (v/v) of the modified zeolitic rock, (2) 10% (v/v) of zinc phosphate, and (3) a mixture of 10% (v/v) zinc phosphate plus 20% (v/v) of the modified zeolitic rock. In every case, percentages were referred to the total pigment content. Titanium dioxide, zinc oxide, and barium sulfate were incorporated to complete the pigment formula. The pigment volume concentration/critical pigment volume concentration (PVC/CPVC) ratio was 0.8. The performance of the resulting anticorrosive paints was assessed by accelerated (salt spray and humidity chambers) tests and electrochemical (corrosion potential, ionic resistance, and polarization resistance) essays. It was demonstrated that the modified zeolite is effective in protecting steel from corrosion when it is used in combination with zinc phosphate. There exists a synergism between the modified zeolite and zinc phosphate that allows the zinc phosphate content in anticorrosive paints to be reduced.     

Study of the anticorrosive behaviour of epoxy binders containing non-toxic inorganic corrosion inhibitor pigments

The anticorrosive performance of epoxy coatings pigmented with non-toxic corrosion inhibitors pigments was investigated in this work. The coatings used contained the following pigments: zinc phosphate (ZP), zinc phosphomolybdate (ZPM) and zinc calcium phosphomolybdate (ZCPM). For comparative studies epoxy coatings with the following compositions were made up: one only with filler (CRG); one without pigments, varnish (VR) and other with zinc chromate (ZC) pigment. The corrosion inhibitor performance of the coatings was evaluated by immersion tests in 0.01 mol L⁻¹ NaCl aqueous solutions and accelerated tests in a salt spray chamber. The corrosion inhibitor performance of the samples was monitored using open-circuit potential (E_oc) measurements and electrochemical impedance spectroscopy (EIS) technique. Complementary tests were carried out using water vapour permeability of free-standing films and thermogravimetric (TG) analysis. The permeability test showed that the addition of the studied pigments did not modify the barrier properties of the free-films in comparison that pigmented with chromate. Thermal analysis indicated that the addition of the pigments improved the thermal stability of the coatings and it suggested a resin/pigment interaction. The total immersion tests and salt spray tests demonstrated that the barrier properties of the coatings pigmented with the inhibitors were not degrading as much as that pigmented with ZC. Therefore, all the three pigments could replace ZC as an anticorrosive pigment in similar conditions to those described here. The best corrosion inhibitor performance in the total immersion test was presented by the ZPM and ZCPM coatings while in the salt spray test the corrosion inhibitor performance of all the three pigmented coatings was similar, suggesting that only in the less aggressive test is possible to detect any difference between the coatings with the non-toxic pigments.     

Evaluation of an environmentally friendly anticorrosive pigment for alkyd primer

An alkyd formulation containing zinc phosphate (10 wt.%) was prepared and subsequently modified replacing the latter anticorrosive additive by a very low concentration of conducting polymer. Specifically, three modified paints, which contain polyaniline emeraldine base (undoped form), polyaniline emeraldine salt (doped form) and an eco-friendly polythiophene derivative (partially oxidized), were formulated. The properties and corrosion resistance of the four alkyd coatings have been characterized. Among the three modified paints, the one containing polythiophene shows the best adherence and the highest corrosion resistance. This has been attributed to the fact that the miscibility of the polythiophene derivative with the alkyd formulation is better than that of polyaniline. Furthermore, accelerated corrosion assays and electrochemical impedance spectroscopy measurements revealed that the corrosion resistance of the paint with polythiophene is several orders of magnitude higher than that with zinc phosphate. The polythiophene derivative has been found to induce the formation of a passivating and well-adhered layer between the coating and the surface, preventing the access of chloride anions and oxygen to the substrate.     

Effect of vanadium additive and phosphating time on anticorrosion,morphology and surface properties of ambient temperature zinc phosphate conversion coatings on mild steel

An attempt has been made to investigate the effect of phosphating time and vanadium additive on the anticorrosion and surface properties of ambient temperature zinc phosphate coatings. Zinc phosphate coatings with different phosphating times and vanadium concentrations were applied to low carbon steel samples. A potentiostatic polarization test in 3.5 wt% NaCl solution was carried out to investigate the electrochemical properties of coated samples. Field emission scanning electron microscopy, energy-dispersive spectroscopy, and atomic force microscopy were utilized to evaluate the microstructure, chemistry and roughness of coatings. Surface properties such as wettability, surface tension, and work of adhesion were measured. Results indicate that the sample which was immersed for 30 min in the phosphating bath exhibits the lowest corrosion current density, one tenth of bare steel, due to formation of a compact coating while having a low number of microcracks. Addition of 500 ppm vanadium to the coating in a secondary bath decreases the corrosion rate of zinc phosphate coating remarkably, by almost 80%. Microstructural results reveal that vanadium-rich precipitates are formed and enhance the coating coverage on the steel substrate. Vanadium addition increases the surface roughness, surface free energy, and work of adhesion of the phosphate coating.     

Corrosion aspects of alkyd paints modified with linseed and soy oils

The anticorrosive performance of medium-long (54-59%) alkyd paints modified with linseed and soy oils was compared by accelerated tests (Prohesion Cycle) and natural exposition in marine and industrial atmospheres. Differences on the protection mechanism of anticorrosive pigments due to substitution of linseed oil by soy oil were investigated by polarization curves and electrochemical impedance spectroscopy (EIS). Complementary tests such as water vapor and ions permeability in freestanding films were also performed. Results suggested that the type of oil influenced the barrier properties of the paint pigmented with zinc phosphate. The same tendency was verified by resistance values obtained from impedance diagrams. Polarization curves suggest that the action of the pigments in the alkyd paintings is practically the same for both oils. The substitution of linseed oil by soy oil did not impair the anticorrosive performance of alkyd paints and from the economic point of view this substitution could be very interesting.     

Sodium zinc phosphate as a corrosion inhibitive pigment

A sodium zinc phosphate pigment synthesized using a co-precipitation method and characterized by X-ray diffraction was investigated for its corrosion inhibition activity in comparison with the commercial zinc phosphate using EIS in a 3.5% NaCl solution. A mild steel surface analysis after exposure to the test solutions was conducted using scanning electron microscope-energy dispersive X-ray and infrared spectroscopies. The results indicate that the corrosion inhibitive performance of the synthesized pigment is higher than that of the commercial zinc phosphate. This can be the result of the synthesized pigment's relatively high solubility, which affects the precipitation of a phosphate layer onto the mild steel surface and the modification of the crystalline structure of the corrosion products in the presence of the inhibitive pigment. The salt spray and wet pull-off tensile strength results revealed an improved corrosion protection of the coatings formulated with SZP.     

Effects of pigmentation on siloxane–polyurethane coatings and their performance as fouling-release marine coatings

Siloxane–polyurethane paints were formulated and characterized for coating properties and performance as fouling-release (FR) marine coatings. Paints were formulated at 20 and 30 pigment volume concentrations with titanium dioxide, and aminopropyl-terminated poly(dimethylsiloxane) (APT-PDMS) loadings were varied from 0 to 30% based on binder mass. The coatings were characterized for water contact angle, surface energy (SE), gloss, and pseudobarnacle (PB) adhesion. The assessment of the FR performance compared with polyurethane (PU) and silicone standards through the use of laboratory biological assays was also performed. Biofilm retention and adhesion were conducted with the marine bacterium Cellulophaga lytica, and the microalgae diatom Navicula incerta. Live adult barnacle reattachment using Amphibalanus amphitrite was also performed. The pigmented coatings were found to have properties and FR performance similar to those prepared without pigment. However, a higher loading of PDMS was required, in some cases, to obtain the same properties as coatings prepared without pigment. These coatings rely on a self-stratification mechanism to bring the PDMS to the coating surface. The slight reduction in water contact angle (WCA) and increase in pseudobarnacle release force with pigmentation suggests that pigmentation slowed or interfered with the self-stratification mechanism. However, increasing the PDMS loading is an apparent method for overcoming this issue, allowing for coatings having similar properties as those of clear coatings and FR performance similar to those of silicone standard coatings.     

Coating performance of finishes on wood modified with an N-methylol compound

This study describes the effects of wood modification with modified 1,3-dimethylol-4,5-dihydroxyethyleneurea (mDMDHEU) on the coating performance of solvent- and water-borne finishes. Although the basic colour of wood was slightly changed due to the modification, modified and unmodified samples did not display any colour differences after coating with translucent stains. Blocking of coated wooden substrates (degree of adhesiveness) was dependant on the type of finish system and, in a few cases, on the wood substrate. For all wood substrates, both treated and untreated, solvent-borne alkyd finish penetrated into the surface layers of the wood cells, while water-borne acrylic finishes spread only on the wood surfaces. The solvent-borne alkyd finish dried much more slowly on wood substrates than did the water-borne acrylics. Modification with mDMDHEU did not affect the drying rates of the finishes tested. The wet adhesion depended on the finish systems tested and on the pre-treatment of the wooden substrate. With regard to the pre-treatment, wet adhesion of one water-borne and the solvent-borne finish systems was significantly enhanced through precedent modification with mDMDHEU. The other two water-borne finish systems showed a higher degree of wet adhesion. This study demonstrates that modification of the wood substrate with mDMDHEU is compatible with both water-borne and solvent-borne finish systems and improves their wet adhesion on the wood surface.     

无苯无毒低表面处理环氧厚浆涂料的研制

以丙酮、乙醇作为溶剂,以高效、无毒的改性磷酸盐为主要防锈颜料制备无苯无毒低表面处理环氧厚浆涂料,制成的涂料可以容忍钢材经简单或手工预处理后残存的锈斑、氧化皮及各种旧涂层,具有环保、高性能、施工方便的优点,特别适用于水工、桥梁等各类钢结构的覆涂维护,也适合各类新建钢结构工程,符合新型涂料的发展方向。     

Fabrication of ZnO–GO hybrid for enhancement of chemically bonded phosphate ceramic coatings corrosion protection performance on AISI304L stainless steel

In this paper, a solvothermal method is used to prepare nano-sized zinc oxide-graphene oxide (ZnO–GO) hybrid, and the ZnO–GO hybrid is characterized by X-ray diffraction analysis, Raman, Fourier transform infrared spectroscopy, and scanning electron microscopy. In addition, chemically bonded phosphate ceramics coatings with different content of ZnO–GO hybrid are prepared on the stainless steel through the sol-gel method. The corrosion performance of the coatings is evaluated by electrochemical properties and the analysis of the surface and cross morphology of the coating. Results indicate ZnO–GO hybrid significantly enhances the compactness and corrosive behavior of the coating because the overlapping structure of GO flake improves the barrier performance of the coating. Besides, ZnO nanoparticles on the surface of GO can react with aluminum dihydrogen phosphate binder, in that case the adhesion between GO and the coating is improved.     

Comparison of the efficiency of inorganic nonmetal pigments with zinc powder in anticorrosion paints

This paper deals with the study of properties of anticorrosion pigments of varying chemical composition in epoxyester paints. Two type lines of paints were prepared. The first line comprised an anticorrosion pigment with a PVC concentration of 10% while the other line comprised an anticorrosion pigment with a PVC concentration = CPVC. The following nontoxic anticorrosion pigments were observed: zinc phosphate, zinc phosphomolybdate, calcium hydrogen phosphate, zinc phosphate modified with an organic corrosion inhibitor, strontium–aluminum polyphosphosilicate, zinc–aluminum polyphosphate, calcium metaborate, calcium ferrite, calcium borosolicate, and strontium chromate. The epoxyester primers were observed for the effect of the type of pigment on the anticorrosion properties. Anticorrosion efficiency was derived from tests in a condenser chamber and in a salt spray cabinet as well as from a test of chemical resistance of pigmented coatings. The evaluation of anticorrosion efficiency of inorganic nonmetal pigments was carried out by means of comparison with anticorrosion efficiency of metal dust.     

Evaluation of anti-corrosive pigments by pigment extract studies, atmospheric exposure and electrochemical impedance spectroscopy

The inhibition efficiencies of zinc chromate, barium metaborate, calcium silicate, amino carboxylate, calcium barium phosphosilicate, aluminum triphosphate and a modified zinc phosphate on the corrosion of steel and zinc were determined by polarization experiments on pigment extracts. Zinc phosphate and zinc chromate were the best and were studied further to determine the effect of pH and chloride concentration on their inhibition of steel. Zinc chromate is adversely affected by high concentration of chloride ions, which effect seems to be less pronounced on zinc. A low pH, although increasing the solubility of zinc phosphate, does not increase its efficiency. The pigments were also incorporated into an epoxy-poly(amide) binder, applied to cold-rolled steel and galvanized steel, exposed at a marine exposure station and the degradation monitored by electrochemical impedance spectroscopy. There was a general correlation between the results of pigment extract studies and atmospheric exposure except in the case of phosphate pigments on cold rolled steel.     

钢结构带锈涂装用水性自干封闭涂料体系的制备

介绍了一种应用于带锈钢结构涂装的水性自干封闭涂料体系。重点阐述了水性自干封闭底漆及配套水性面漆的制备、施工工艺。探讨了分散剂、防锈颜料、颜基比以及成膜助剂与中和剂的选择对涂料体系性能的影响。该涂料体系性能达到或超过现有溶剂型醇酸涂料体系,满足企业安全生产的需求。     

低成本铁红水性防锈涂料的制备

介绍了以氧化铁红为体质防锈颜料、磷酸锌和氧化锌为化学防锈颜料、红云母为片状颜料,苯丙乳液为基料的水性防锈涂料的制备。对影响其性能的因素进行了分析,并与溶剂型防锈涂料进行了性能对比。     

Study of epoxy and alkyd coatings modified with emeraldine base form of polyaniline

In this work we examine the ability of the emeraldine base form of polyaniline to impart protection against corrosion when it is used as additive of commercial paints. For this purpose, three paints, which are used as primers in marine environments, were checked: two epoxy coatings that differ in the presence or absence of inorganic anticorrosive pigment (zinc) and one alkyd coating. In a first stage, the rheological, structural, thermal and mechanical properties of the three coatings were characterized using viscosity measurements, infrared spectroscopy, thermogravimetric analyses and stress–strain assays, respectively. Furthermore, we observed that the resulting properties were not altered by the addition of a low concentration of polyaniline (0.3%, w/w). Accelerated corrosion tests were performed to compare the degree of protection of both the modified and unmodified paints. The polyaniline did not affect to the protective properties of the epoxy without inorganic anticorrosive pigment nor the alkyd formulations. In opposition, the polyaniline added to the epoxy paint with inorganic anticorrosive pigment induced the formation of a zinc oxide layer, which promoted the corrosion attack.     

High performance alkyd paints based on platy kaolin for corrosion protection of steel

Calcination of kaolin presents an easy route to obtain high performance and eco-friendly anticorrosive filler. The objective of the present work was to prepare a new ecologically friendly inorganic filler, based on thermal treatment of kaolin to be used as an anticorrosive. This work studied the corrosion protection of medium oil-modified alkyd paints based on thermally treated kaolin at different temperatures. Paints were formulated with different pigment volume concentrations (PVCs) and critical pigment volume concentrations (CPVCs). The prepared paints were formulated with increasing content of kaolin, with PVC ranging from 10 to 30%. The physical and chemical properties of kaolin were evaluated at different temperatures. Particle shapes of thermally treated kaolin were characterized using scanning electron microscopy. The physico-mechanical properties of dry films, water vapor transmission and their corrosion properties using accelerated laboratory corrosion test were tested. The thermal treatment of kaolin enhanced both the oil absorption and the alkalinity. This led to alkyd results in saponification and consequently passivation of the substrate. Good wetting with alkyd resin gave homogeneous films without defects which resisted water and oxygen permeation and protected steel against corrosion. The results revealed that thermally treated kaolin at 400°C was the best at protecting steel substrates for all PVCs.     

Long-term hydrophobicity and ice adhesion strength of latex paints containing silicone oil microcapsules

Waterborne anti-icing coatings were prepared by embedding silicone oil microcapsules in latex paints. The long-term hydrophobicity and ice adhesion strength of the coatings were examined with a QUV accelerated weathering tester and a pull-off adhesion tester. The effects of silicone oil content and pigment/binder (PB) ratio on the long-term hydrophobicity and the ice adhesion strength of the coatings were investigated. A higher silicone oil content and a PB ratio close to the critical pigment volume concentration favor long-term hydrophobicity of the coatings. An obvious decrease in ice adhesion strength was achieved for coatings with a PB ratio of 5.0 and a silicone oil content of 4.2%. For coatings with the same surface roughness, a higher water contact angle (WCA) led to lower ice adhesion strength. However, for coatings with different surface roughnesses, the ice adhesion strength was found to be dependent on surface roughness rather than on WCA.     

淋涂玻璃烤漆的研制

讨论了颜基比、基体树脂/交联剂配比、流平剂种类和添加比例、催化剂种类和添加比例,对涂料的流平性能、涂料在油墨上的重涂性能、涂膜附着力、漆墨层间附着力、涂料遮盖力、干燥速度、储存稳定性以及涂膜耐水性、耐溶剂性及硬度的影响。结果表明:选择有机硅类流平剂添加比例为0.04%0.05%,颜基比为0.8:1,氨基树脂/基体树脂配比为0.3:1,选择长碳链二酸类有机酸催化剂加入比例为0.8%1.0%,在淋涂工艺中于150℃条件下烘烤15min制备成的单组分溶剂性玻璃烤漆涂膜具有优良的遮盖力、耐水性、耐溶剂性、附着力、漆墨层间附着力及高硬度。同时涂料还具有适宜的重涂性能、优良的储存稳定性及较好的流平装饰效果。     

Water transportation through organic coatings: correlation between electrochemical impedance measurements, gravimetry, and water vapor permeability

A primary cause of coating failure is diffusion of water through organic coatings during which many corrosive species are transported to the metal-coating interface. However, water vapor permeability through the coating improves blister resistance to a certain extent. The present work describes the influence of chemical nature of the polymer on the above two properties. Attempts were also made to establish a correlation between these two properties for pigmented organic coating. Six paints were formulated and processed using six different types of binders at a constant pigment volume concentration (PVC) and specific gravity. Water ingress, water vapor permeability, and water absorption of these coatings were estimated using electrochemical impedance measurements (EIS), permeability cup method, and gravimetric method, respectively. There exists a good linear correlation between water uptake measured by EIS and water absorption measured by gravimetry. Similarly, a correlation was also noticed between water uptake by EIS and water vapor permeability. However, polyurethane type polymers did not fit into this linear correlation. Furthermore, influence of the resin chemistry on anticorrosive properties of these coatings was also studied using EIS and salt spray exposure test. Among all polymers under investigation, acrylic polyol-based polyurethane has shown the lowest water uptake, higher impedance, better salt spray resistance but higher water vapor transmission rate.