The effect of benzimidazole and zinc acetylacetonate mixture on cathodic disbonding of epoxy coated mild steel

Electrochemical behavior of mild steel in the presence of zinc acetylacetonate (Zn(acac)₂) and benzimidazole (BIMIDA) was evaluated by electrochemical impedance spectroscopy (EIS) in 3.5% NaCl solution and compared to zinc phosphate (ZP) pigment and zinc potassium chromate (ZPC) pigment extracts. Results showed superior performance of Zn(acac)₂ and BIMIDA mixture (ZBM) compared to ZP pigment, while it introduced inferior inhibitive action compared to ZPC pigment. The epoxy coatings were formulated with ZBM as anticorrosive additive, ZP and ZPC pigments. The disbonding rate of coated steel follows the order: Blank > ZP > ZBM > ZPC. EIS results showed a complex film could be formed at the hole area for the coatings formulated with ZP, ZBM and ZPC. It is concluded that the stronger the complex film on the surface, the lesser the cathodic disbonding rate would be.     

Anticorrosive behaviour of alkyd paints formulated with ion-exchange pigments

Hexavalent chromium compounds (chromates) have been widely used as inhibitive pigments in the formulation of anticorrosive paints. However, their high toxicity and carcinogenic effects are forcing the development of effective chromate-free organic coatings. One such alternative, which is very attractive from a scientific point of view, is the use of ion-exchangeable pigments (IEPs).

The few studies conducted with this type of pigment are not conclusive about their anticorrosive efficiency and controversy surrounds their functioning mechanisms, interchange capacity and anticorrosive performance.

In the present research, which focuses on the anticorrosive protection of this type of pigment, alkyd paint coatings formulated with vanadate-hydrotalcite (HT/V) (anionic) and calcium/silica (Ca/Si) (cationic) IEPs have been applied on low carbon steel specimens. A traditional zinc chromate pigment has also been used for comparative purposes.

The effect of these non-toxic pigments on the protective properties of coatings has been tested by means of natural and accelerated corrosion tests (humidity, salt spray and Kesternich, 0.2 l SO₂) and electrochemical impedance spectroscopy (EIS).

None of the IEPs equalled the anticorrosive behaviour of the zinc chromate in the different tests. The anionic pigment (HT/V) seems to present good behaviour in chloride environments (salt spray, NaCl solutions, etc.) while the cationic pigment (Ca/Si) performs well in the humidity condensation and SO₂ tests.     

Characterization of active pigments in damage of organic coatings on steel by means of electrochemical impedance spectroscopy

Active anticorrosive pigments are solid additives for primers which can give further protection for areas with coating damage in addition to their barrier effect. These pigments are expected to prevent corrosion of metal substrate in coating damage by build-up of permanently passive conditions at the metal surface (electrochemical protection) and/or by build-up of solid compounds which plug the coating damage (chemical protection). Electrochemical Impedance Spectroscopy (EIS) was applied to characterize the corrosion protection behaviour of alkyd primers containing different pigments. Impedance spectra were recorded in the frequency range 50 mHz f 50 kHz at the open-circuit potential as a function of the type of pigment and the exposure time in different corrosive media. In general, two different parts can be distinguished in the impedance diagrams. The higher frequency part is related to the insulating properties of the primer and the lower frequency part can be attributed to electrochemical processes taking place within the coating defects. The parameters derived from EIS results show that the low frequency data can be used for characterization of the protective properties of anticorrosive pigments in the presence of defects in organic coatings.     

Inhibitor properties of “green” pigments for paints

Zinc chromate is one of the anticorrosive pigments most frequently used in the formulation of primers. However, its environmental aggressiveness and toxicity severely restrict its use, and different green alternatives have been proposed in order to replace zinc chromate. In the last decade, the behaviour of zinc phosphate as anticorrosive pigment has been intensively researched. During this time, various modifications have been made to this family of pigments to improve its properties, and a “second generation” of phosphate pigments, incorporating elements such as molybdenum, aluminium, or iron, has been produced. In this paper, the inhibitive properties of zinc phosphate and three second-generation phosphates have been investigated, using zinc chromate pigment as a reference. Pigment extract solutions, at different values of pH, have been used as corrosive media. Carbon steel samples were immersed in such solutions and their corrosion rates were measured using electrochemical techniques. The data obtained suggest that zinc chromate provides the highest percentage of inhibition in neutral and basic solutions, but phosphate-based pigments showed better results in acid solutions. Given this performance advantage, together with their less harmful environmental impact, these phosphate-based pigments can be proposed as realistic alternatives to chromates in the formulation of protective paints for use in acidic conditions.     

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.     

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.     

Corrosion electrochemical behavior of epoxy anticorrosive paints based on zinc molybdenum phosphate and zinc oxide

Electrochemical impedance spectroscopy (EIS) was applied as a principal tool to describe the efficiency of anticorrosive epoxy paints (primers) based on zinc molybdenum phosphate (ZMP) pigment. Steel-coated samples were exposed to a 0.5 M NaCl solution. During the study the corrosion potential (E_oc) and R_p values also were monitored every 24 h. It is discussed the incorporation of micronized ZnO (1 μm) pigment to the base mixture and its positive, reinforcement effect on the protective properties of ZMP primer. The explanation is related to the izoelectric point (IEP) of ZnO particles (pH < 9), which determines their positive surface charge and electrostatic attraction with the molybdate anion. In this case the charge of the formed double layer capacitor is very high. Moreover, the mentioned attraction inhibits and saves ZnO particles from their rapid dissolution to hydroxide.     

The effects of zinc aluminum phosphate (ZPA) and zinc aluminum polyphosphate (ZAPP) mixtures on corrosion inhibition performance of epoxy/polyamide coating

The epoxy/polyamide coating was loaded with different pigment mixtures of the zinc phosphate (ZP), zinc aluminum phosphate (ZPA) and zinc aluminum polyphosphate (ZAPP) pigments. The electrochemical impedance spectroscopy (EIS) and salt spray test were used to investigate corrosion inhibition performance of the coatings. The adhesion strengths of the coatings were measured by a pull-off test. Results revealed lower coating pull-off strength loss when the ZPA and ZAPP pigments were used. A significant decrease in number of blisters together with low pull-off strength loss and best corrosion inhibition properties were observed when the mixture of 80:20 of ZAPP:ZPA was used.     

Mechanisms of non-toxic anticorrosive pigments in organic waterborne coatings

Investigations have been carried out concerning the mechanism of the behaviour of non-toxic anticorrosive pigments belonging to the group of phosphates, ferrites and ion exchange pigments in waterborne systems. The mechanism controlling the protective effectiveness of organic coatings is complex and results from simultaneous activity of various agents, from among which the kind of the corrosion inhibitor and the structure of the coating are of fundamental importance. The effect of pigments on the protective properties of coatings was tested by means of electrochemical impedance spectroscopy (EIS), scanning vibrating electrode technique (SVET) as well as the salt spray and Prohesion tests. For the investigation of the structure of coatings the porosymetric method and modulated-force thermomechanical analysis (mf TMA) were applied. The results of these investigations have shown that calcium zinc phosphate and zinc ferrite are the most effective. These pigments take part in the passivation of steel, which has been proved by the results of electrochemical investigations and by the presence of the passive layers as has been found out by X-ray diffraction (XRD), energy dispersive X-ray analysis (EDXA) and scanning electron microscopy (SEM). Calcium zinc phosphate and zinc ferrite affect the structure of the coatings, increasing the glass transition temperature (Tg) of the coatings. Zinc phosphate and calcium-exchanged silica do not act in compliance with electrochemical mechanism neither do they improve the barrier properties of the binder.     

Modification of zinc powder to improve the corrosion resistance of weldable primers

This paper reports the modification of zinc powder to improve the corrosion resistance of weldable primers. These primers are thin zinc rich organic coatings applied by roll coating at the steel manufacturer. The automotive industry uses them to protect areas in the car body that become inaccessible after joining processes. In this work, with the objective of increasing the corrosion resistance of these systems, the zinc particles were chemically treated or simply replaced by powder of 55AlZn alloy. The rest of the formulation remained intact. The performance of the commercial and modified formulations was compared by SEM, SVET and EIS. The best results were obtained when the zinc powder was replaced by powder of the aluminium zinc alloy.     

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.     

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.     

Electrochemical assessing corrosion inhibiting effects of zinc aluminum polyphosphate (ZAPP) as a modified zinc phosphate pigment

Undesirable anti-corrosion performance of zinc phosphate pigment, the classical chromate replacement, has led researchers to take modification into account. Polyphosphate-based anti-corrosion pigments as a result of modification of zinc orthophosphate have been found to function much more efficiently. This study aimed to evaluate performance of steel samples immersed in 3.5% NaCl aqueous solution-containing zinc aluminum polyphosphate (ZAPP) pigment extract compared to those involving conventional zinc phosphate (ZP) pigment extract and also no pigment (blank) using electrochemical tests such as electrochemical impedance spectroscopy (EIS) and linear polarization (LP) as well as surface analysis. Impedance spectra and polarization curves revealed two different trends, showing the superiority of ZAPP pigment. Based on the results of scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX), presence of a precipitated layer on the surface was confirmed when steel sample was immersed into the solution-containing ZAPP.     

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.     

Performance of zinc molybdenum phosphate in anticorrosive paints by accelerated and electrochemical tests

This work studied the anticorrosive behaviour of micronized zinc molybdenum phosphate (zinc phosphate modified with zinc molybdate). It was proposed to evaluate its efficiency in solvent borne paints with 30 and 15% of the pigment by volume and a pigment volume concentration/critical pigment volume concentration ratio (PVC/CPVC) of 0.8. The behaviour of paints formulated with different binders such as epoxy, chlorinated rubber, vinyl and alkyd resins, was assessed by accelerated (salt spray cabinet and accelerated weathering) and electrochemical tests. Epoxy and chlorinated rubber paints showed the best anticorrosive performance. The inhibitive action of zinc molybdenum phosphate was confirmed. Good correlation was obtained between salt spray and electrochemical tests.     

Predictive power for life and residual life of the zinc rich primer coatings with electrical measurement

Zinc rich primers with lamellar and spherical shaped zinc pigments and their combinations were formulated. These zinc rich primers were used to measure the electrical conductance and subjected to the corrosion analysis for 3000 h. The lamellar shaped pigments at lower PVC were found to be better than spherical shaped pigments, whereas the typical combination of spherical and lamellar zinc was the best in providing corrosion protection. A set of equations were developed to predict the life and residual life for pigment of both shapes using PVC, conductance and corrosion resistance for 3000 h in salt spray as parameters. Finally the influence of zinc particle shape on the flow and orientation behavior was evaluated using rheological measurements.     

Solventborne paint systems on carbon steel and hot-dip galvanized steel for a wide range of atmospheric exposures

The paper analyzes the performance of solventborne paint systems applied on carbon steel and hot-dip galvanized steel in a wide range of atmospheric exposures. The study has involved paint systems exposure for 3.5 years in eight natural atmospheres. The atmospheric conditions cover from temperate rural climates to tropical severe marine and Antarctic coastal regions. The paint systems included several alkyds formulated with a variety of pigments (anticorrosive and barrier), epoxies, chlorinated rubber, and zinc-rich (ethyl silicate and epoxy). It has been concluded that in rural and urban atmospheres alkyd systems afford equivalent anticorrosive protection of steel to the epoxy/polyurethane system. The toxic red lead pigment may be replaced in long linseed-oil alkyd primer paints by non-toxic pigments, such as a mixture of micaceous iron oxides (MIO) and black iron oxides or zinc phosphate, without affecting the anticorrosive properties of the paint system. In aggressive atmospheres (industrial, marine), paint systems including zinc-rich primers or applied on galvanized steel must be used, especially in surface regions with coating faults (scribes).     

颜填料体积浓度对水性环氧导静电防腐蚀涂层性能的影响

考察了颜填料体积浓度（PVC）对水性环氧导静电防腐蚀涂料涂层导静电性能和防腐蚀性能的影响,运用X射线能谱（EDX）分析了导电填料的元素组成,采用电化学阻抗谱（EIS）、扫描电镜（SEM）等手段对不同颜填料体积浓度的涂层进行了性能测试及表征,根据不同颜填料体积浓度涂层的物理机械性能、盐水浸泡实验结果和电化学阻抗谱分析,确定该水性环氧导静电防腐蚀涂料的最佳颜填料体积浓度为35%。     

A method for preparation and application of micronized ferrite pigments in anticorrosive solvent-based paints

This work presents a method of preparing single-, double-, and triple-cation ferrite pigments by employing simple chemical techniques to study their corrosion protection properties. The prepared pigments were characterized using X-ray diffraction and scanning electron microscopy. All prepared ferrite pigments were evaluated using ASTM methods. Anticorrosive paint formulations were performed using different prepared pigment loadings. The physico-mechanical and corrosion properties of dry paint films were examined. The tests revealed that the prepared ferrite pigments show excellent anticorrosive behavior, and that the best among them in performance are zinc and zinc magnesium. Calcium, zinc–calcium, and zinc–magnesium–calcium ferrites show better performance in high pigment loadings, while magnesium ferrite pigments show good results only in low pigment loading.     

集装箱用水性聚氨酯外面漆的研制

以物理性能优异的水性聚氨酯树脂为主要成膜物质,并利用防腐性能优异的苯丙乳液对其进行共混改性,优选了无毒防锈颜料,制备出了一种综合性能优异的集装箱专用水性聚氨酯外面漆。结果表明:当丙烯酸树脂B的混入量为20%,以磷酸锌为防锈颜料,颜填料体积浓度(PVC)为25%时,外面漆的性能满足JH/T E01—2008集装箱涂料行业标准。并系统地考察了外面漆施工时易出现的流挂、针孔等漆膜弊病的影响因素及防治措施。