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.     

Calcium tripolyphosphate: An anticorrosive pigment for paint

The objective of this work was to evaluate the performance of calcium tripolyphosphate in anticorrosive paints. Its anticorrosive properties were studied in pigment suspensions and in solventborne paints with 10% and 30% of the pigment by volume and a pigment volume concentration/critical pigment volume concentration (PVC/CPVC) equal to 0.8. The behavior of paints formulated with epoxy and alkyd resins was assessed by accelerated (salt spray cabinet and humidity chamber) and electrochemical tests (corrosion potential, ionic resistance, and polarization resistance). Calcium tripolyphosphate was proven to inhibit steel corrosion when incorporated in a paint film. Good protection was achieved employing only 10% by volume of the pigment, instead of 30%, as was suggested in the case of phosphates. The anticorrosion protection afforded by alkyd paints was impaired when the pigment content was increased. Epoxy paints seemed to be less sensitive to the pigment content. Centro de Investigación y Desarrollo en Tecnología de Pinturas (CIC-CONICET), Calle 52 e/121 y 122. (1900) La Plata. Argentina. Fax: 54.221.427. 1537. email: cidepint@ba.net     

Zinc hypophosphite: a suitable additive for anticorrosive paints to promote pigments synergism

In this investigation, the synergism promoted by zinc hypophosphite in an anticorrosive pigment mixture is reported. This paper describes the anticorrosive behavior of a commercial pigment mixture containing zinc hypophosphite, reduced levels of zinc phosphate, and zinc oxide. The anticorrosive performance of the pigment mixture was assessed by electrochemical techniques (corrosion potential and linear polarization measurements) employing pigment suspensions. The behavior of each separate component of the mixture was also studied in the same way. The nature of the protective layer was investigated by scanning electron microscopy (SEM). In a second stage, the anticorrosive properties of the pigment were assessed by incorporating it into alkyd and epoxy paints that were evaluated by accelerated (salt spray and humidity tests) and electrochemical measurements. Experimental results showed that improved anticorrosion protection is achieved in paints with reduced zinc phosphate contents as a consequence of the synergistic interaction between zinc hypophosphite and the other components of the pigment mixture.     

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.     

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.     

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.     

Evaluation of eco-friendly anticorrosive pigments for paints in service conditions

The performance of different replacements for chromates was studied. The anticorrosive properties of seven phosphate-based pigments, a calcium-exchange silica and a ferrite were assessed by electrochemical techniques and formulating solvent-borne paints with epoxy and alkyd resins. Paints contained 30% by volume of anticorrosive pigment, with respect to the total pigment content.     

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.     

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.     

Eco-friendly zero VOC anticorrosive paints for steel protection

With the growth of the green movement, it is important to prepare environmentally friendly anticorrosive paints to save lot of money, which are lost each year because of corrosion. High molecular weight organic corrosion inhibitor (safe adduct), barrier anticorrosive pigment (safe) and convertible anticorrosive pigment (toxic) are protective elements in paint formulations. Emulsification of the prepared adduct was the way to be applicable in water-borne paints, using mixture of emulsifiers. Surface tension measurements using ring method technique and thermal stability test could characterize the prepared emulsion systems. It was interesting to study the performance of the protective elements in water paint formulations based on short oil water thinned alkyd. Physical and mechanical properties of dry paint films, corrosion tests of the coated steel, water up-take% of the prepared paints, weight loss of steel under paint films after immersion in artificial sea water and corrosion inhibition efficiency of the protective elements were determined. Comparative studies of the protective elements in water-borne paints have been done according to performance, economic feasibility and environmental safety. It was found that zinc chromate as carcinogenic anticorrosive pigment could be replaced by 0.09% of the prepared water-borne corrosion inhibitor (MTDT adduct), 20% micaceous iron oxide (MIO) or their blend. Superior corrosion inhibition efficiency of steel was obtained in case of using MTDT/MIO blend. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

The effect of the PVC/CPVC ratio on the corrosion resistance properties of organic coatings

The effect of the ratio of the pigment volume concentration (PVC) to the critical pigment volume concentration (CPVC), denoted hereafter by Λ, on the corrosion resistance properties of paint films has been investigated by a.c. impedance and potential-time measurements. Painted mild steel electrodes were studied during exposure to 3% NaCl solution for up to 90 days. Paints based on alkyd, epoxy and chlorinated rubber/chlorinated paraffin (CR/CP) were prepared containing zinc phosphate as inhibitive pigment. The paints were prepared at Λ values 0.48, 0.51, 0.55, 0.58, 0.61, 0.64 and 0.67. It is concluded that, for all systems, corrosion resistance can be affected greatly by the PVC/CPVC ratio and each system has its own optimum Λ value. The optimum percentage of inhibitive pigment in the above systems has also been evaluated.     

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.     

Influence of the composition of zinc-ethyl silicate paints on electrochemical properties

The protection of steel by zinc-ethyl silicate primers is based on the general principle of cathodic protection by metallic zinc in contact with a ferrous substrate. The influence of the zinc content on the paint behaviour has been studied, but little attention has been paid to effects caused by the incorporation of additives, such as extender pigments, to the formulation.The aim of this paper is to study the influence of the whole composition of zinc-ethyl silicate paints on their electrochemical properties. A second purpose is to establish the nature of the anticorrosive action of these paints. Four commercial zinc-ethyl silicate paints were chosen for these investigations.It was found that the incorporation of extender pigments modified the behaviour of these paints. The anticorrosive action was due to the cathodic protection by zinc powder and the inhibition of the electrochemical reactions by corrosion products. The barrier effect, in the sense of ohmic resistance, provided by these paints was of lesser importance.     

Ceramic microspheres to improve anticorrosive performance of phosphate paints

Zinc phosphate and related compounds have been proposed as “green” replacements for traditional anticorrosive pigments such as zinc chromate and lead oxides. However, environmental concerns have risen in the last years because the disposal of these materials in the environment increased phosphate levels in water and produce eutrophication of water bodies. The present paper deals with the possible incorporation of ceramic microspheres in alkyd paints in order to diminish phosphate content. The results suggested that paints with low phosphate content can be successfully formulated with a suitable selection of the amount and type of microspheres.     

Corrosion inhibition of aluminum by organic coatings formulated with calcium exchange silica pigment

One of the first commercial ion-exchange anticorrosive pigments to be developed was Shieldex^® (Si/Ca). Its proposed corrosion protection mechanism, based on the retention of aggressive cations and the subsequent release of calcium cations, has created certain controversy. A number of studies have focused on the anticorrosive behavior of this pigment on carbon steel and galvanized steel to replace chromates (Cr⁶⁺) as inhibitor pigment, but none has considered its performance on aluminum or aluminum alloys. In this research, alkyd coatings have been formulated with Si/Ca pigment at different concentrations and applied on aluminum 1050 (Al 99.5%) specimens. These specimens have then been subjected to accelerated tests (condensing humidity, salt spray, and Kesternich) and natural weathering in atmospheres of different aggressivity. Corrosion performance has been also evaluated in the laboratory by electrochemical impedance spectroscopy. The study has also considered an organic coating with zinc chromate anticorrosive pigment for comparative purposes. The results obtained with organic coatings formulated with Si/Ca pigments confirm that they provide corrosion protection of the underlying aluminum substrate, even improving the behavior of the reference zinc chromate in some environmental conditions.     

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).     

Improvement of the anticorrosion properties of polypyrrole by zinc phosphate pigment incorporation

A commercial zinc phosphate pigment was incorporated into polypyrrole (PPy) matrix during its electrochemical synthesis in order to improve the corrosion protection of polypyrrole on AISI 1010 steel. PPy/zinc phosphate composite films were synthesised in sodium salicylate medium with high current efficiency and containing 10% by weight of zinc and 4% by weight of phosphate. The influence of stirring and concentration of the electrolyte on the degree of pigment incorporation were investigated, as well as polymerisation time and applied current density. The morphology of the films was determined by scanning electron microscopy (SEM) and the distribution of pigment in the polymeric matrix was carried out by X-ray photoelectron spectroscopy (XPS). The PPy and PPy/zinc phosphate films were submitted to salt spray corrosion test, weight loss test and to electrochemical measurements like corrosion potential with time. In all tests, the composite films showed an enhancement in its protective action in comparison with PPy films.     

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.     

High performance water-based paints with non-toxic anticorrosive pigments

Legal restrictions have impelled the replacement of solvent-borne resins and of toxic chromates and lead-bearing pigments in the elaboration of paints. Water-based anticorrosive paints have come a long way to improve their efficiency but their behaviour is said to be poorer than that of solvent-based paints. Nevertheless, recent advances in water-borne technologies have now resulted in improved resin systems that may be employed to produce heavy-duty coatings.

The objective of this paper is to formulate high performance water-borne paints pigmented with non-toxic phosphate inhibitors. The anticorrosive properties of the paints were evaluated by accelerated tests (salt spray and humidity cabinets) and electrochemical tests (electrochemical impedance spectroscopy, EIS). The anticorrosive properties of the pigments were also evaluated by electrochemical tests.

It was found that it is possible to formulate high performance anticorrosive paints by selecting adequate water-borne resins and ecological pigments.     

Effect of different polymers on the efficiency of water‐borne methyl amine adduct as corrosion inhibitor for surface coatings

Styrene/acrylic emulsion copolymer and water‐based short oil urethane alkyd resin were used as binders to prepare water‐based, environmentally friendly paints by using 0.5% emulsified methylamine adduct as corrosion inhibitor. The choice of the two above‐mentioned binders was based on the fact that styrene/acrylic emulsion copolymer is a nonconvertible binder, whereas short oil urethane alkyd resin is a convertible binder. The physical, chemical, mechanical, and corrosion properties of the paint films were evaluated and compared with a commercially known anticorrosive water‐based paint. It was found that the prepared paints have unique desirable properties such as the following: they do not contain anticorrosive pigments (which contain heavy metals in their main chemical structure); they are solvent‐free; and they can be produced to match any color. Corrosion tests on the films of the formulated paints revealed that the short oil urethane alkyd resin is superior to the styrene/acrylic copolymer. Moreover, the corrosion inhibition properties of the paint films prepared from both binders are comparable with the commercially available paints containing anticorrosive pigments. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 879–885, 2002