Anticorrosive polyurethane paints with nano- and microsized phosphates

Two types of phosphate fillers (nanosized aluminum phosphate and microsized aluminum–zinc phosphate) were tested as anticorrosive fillers in 2 K solvent-borne polyurethane paints based on commercial acrylic resin with OH groups and an isophorone diisocyanate-type hardener. Three coating compositions containing commercial fillers (mica/quartz, TiO₂, wollastonite, talc) and also mentioned nanosized aluminum phosphate or microsized aluminum–zinc phosphate were prepared using a pearl-mill as well as a laboratory dissolver, applied onto a steel substrate and cured at room temperature for 14 days. An influence of the type and content of a phosphate filler on properties of polyurethane paints and coatings has been investigated. Incorporation of nanosized aluminum phosphate into coating compositions increases their viscosity while cured paints exhibit reduced adhesion to steel substrates. The results of corrosion tests in a salts spray chamber as well as immersion in an aqueous NaCl solution indicated that the paint system with 9.8 wt.% of applied nanofiller had similar protective properties to a polyurethane coat containing a higher dose (i.e. 15.6 wt.%) of commercial microsized aluminum–zinc phosphate.     

Electrochemical study of protective behavior of organic coating pigmented with zinc aluminum polyphosphate as a modified zinc phosphate at different pigment volume concentrations

Electrochemical impedance spectroscopy was employed to evaluate protective performance of the solvent-borne epoxy coatings pigmented with zinc aluminum polyphosphate as a representative of phosphate-based anticorrosion compounds at different Lambda values. Furthermore, the effective ratio of the pigment volume concentration (PVC) to the critical pigment volume concentration (CPVC) was determined. To compare the function of zinc aluminum polyphosphate and zinc phosphate incorporated into coatings, electrochemical noise method as well as electrochemical impedance spectroscopy was taken into consideration. The trend and magnitude of charge transfer, coating and noise resistances plus the amplitude of the current noise fluctuation indicated superiority of the modified pigment. In order to provide an insight into the mechanism by which anticorrosion pigments improve protective behavior of coating, performance of bare metals exposed to pigment extracts was assessed through taking advantage of electrochemical impedance spectroscopy and electrochemical noise method as well.     

Development of heat-resistant anticorrosion urethane siloxane paints

Three two-layer heat-resistant and anticorrosion paints have been formulated from urethane siloxane binder and traditional anticorrosion pigments such as micaceous iron oxide (MIO), zinc phosphate (ZP), and aluminum oxide. These pigments were used as the dominant components of different undercoats or topcoats. Heat-resistant pigments such as silicon nitride and glass-spheres were used in the composition of the topcoats. Thermogravimetric analysis of paints shows that the paint with ZP as dominant component of the undercoat have the highest heat-resistance and stability in inert gas and oxygen. The paint with a combination of MIO and ZP has the best hardness as well as the best protective and anticorrosion properties based on the electrochemical impedance spectroscopy. A maximum synergic effect of the properties of pigments seems to appear in this paint. Surface morphology of paints was studied by means of scanning electron microscopy. Heated at different temperatures and for several hours, paint containing MIO as the dominant component in the undercoat exhibits the best mechanical and adhesion properties.     

Effects of particle sizes and shapes of zinc metal on the properties of anticorrosive coatings

The paper deals with a study of the zinc particle sizes and shape effects on the anticorrosive coating properties. As a binder the epoxyester resin is used. The zinc particle size and shape effects are discussed from the mechanical coating properties, film permeabilities to water vapor and above all the pigment anticorrosion protection efficiency points of view. The connection between the spherical particle sizes and the coating anticorrosive efficiency was found. The smaller particle sizes mean better anticorrosive coating properties. The lamellar zinc particles exhibit the highest anticorrosion efficiency at a concentration around 20 vol.%.     

Anticorrosive properties of the epoxy–cardanol resin based paints

An epoxy–cardanol resin was developed using epichlorohydrin, bisphenol-A and cardanol. On evaluation it was found that epoxy–cardanol resin exhibits better properties as compared to epoxy resin in terms of increase in tensile strength, elongation, bond with steel and lowering of water vapour transmission of the film. The improvement in these properties indicated that the paints based on modified resin would be more durable than the epoxy based paints. Accordingly, paints were formulated using the developed resin and their performance were compared with their counterparts made with unmodified epoxy resin. Zinc powder, zinc phosphate, micaceous iron oxide and synthetic iron oxide were used as pigments along with fillers, additives and an aromatic polyamine adduct hardener. For both types of paints similar doses of pigments and additives were used. Physico-mechanical properties, chemical resistance and corrosion protection efficiency of the formulated paints were determined. It was found that the anticorrosive properties of epoxy–cardanol resin based paints are superior to that of the paints formulated with the unmodified epoxy resin. Micaceous iron oxide based paints in epoxy–cardanol resin showed the best performance followed by zinc phosphate based paints. It is concluded that the developed resin is a better binder media for the formulation of paints.     

The impact of pigment volume concentration on the protective performance of polyurethane coating with second generation of phosphate based anticorrosion pigment

In this study the effect of conventional zinc phosphate and zinc aluminum phosphate, which represents second generation of phosphate based anticorrosion pigments, on the performance of a polyurethane coating was studied. While zinc phosphate modification was proved to be effective on the corrosion resistance, EIS data facilitated the determination of the optimum pigment volume concentration in which the coating offered the most efficient protection. The superiority of zinc aluminum polyphosphate was attributed to the release of more inhibiting species, leading to the formation of a protective layer at the coating/substrate interface. In addition to the assessment of the impact of pigment content on the resistance of polyurethane primer to cathodic disbonding, the dependency of adhesion strength on the pigment type was also studied using pull-off test.     

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.     

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。     

Anticorrosion efficiency of ZnxMgyAl2O4 core–shell spinels in organic coatings

Anticorrosion pigments were synthesized by reaction of metal aluminum lamellar particles whose surface is oxidized to Al₂O₃ during the first stage and by subsequent reaction with ZnO and/or MgO at 800–1150 °C producing a thin spinel layer that is chemically bonded to the metal core of the pigment particles. Core–shell spinels were synthesized: MgAl₂O₄/Al; Mg_0.8Zn_0.2Al₂O₄/Al; Mg_0.6Zn_0.4Al₂O₄/Al; Mg_0.4Zn_0.6Al₂O₄/Al; Mg_0.2Zn_0.8Al₂O₄/Al; and ZnAl₂O₄/Al. The prepared pigments were characterized by means of X-ray diffraction analysis and scanning electron microscopy. The synthesized anticorrosion pigments were used to prepare epoxy coatings that were tested upon application for their physical–mechanical properties, anticorrosion properties and resistance against a chemical environment. All of the synthesized pigments exhibit good anticorrosion efficiency in epoxy coatings. Compared to lamellar kaolin and metal core of aluminum without coverage, the protective function of the synthesized pigments in coatings is demonstrably better.     

Effect of surface treatment of pigment particles with polypyrrole and polyaniline phosphate on their corrosion inhibiting properties in organic coatings

The effect of pigment particle surface treatment with conductive polymers on the corrosion inhibiting properties of organic paints was investigated. Mixed oxides possessing the spinel and perovskite structures were synthesised for the study. Natural graphite and pigments based on ferric oxide and silicate were studied. Coating materials based on a water-based epoxy resin were prepared for the investigation of the corrosion protection properties of the pigments, the surfaces of which had been provided with a conductive polymer layer. Laboratory corrosion tests were applied to the paint films. A commercial corrosion protection pigment, based on modified zinc phosphate, served as the corrosion protection efficiency standard. Polyaniline phosphate was found preferable to polypyrrole as the modifying agent of the pigment surface regarding the pigment's corrosion inhibiting efficiency. Surface treatment with the conductive polymers is also beneficial to the mechanical properties of the paint.     

Anticorrosive coatings containing modified phosphates

The aim of this paper was to prepare and to compare anticorrosion efficiency of various types of pigments based on phosphates. Their exact composition was defined by X-ray diffraction analysis and their structure by scanning electron microscopy (SEM). Commercially available zinc phosphate was used as a standard. Pigments were prepared in three different ways and they were dispersed in the solution of epoxy medium-molecular resin. Paints were formulated with 10% PVC (pigment volume concentration). Anticorrosion efficiency of coatings was tested by three direct cyclic corrosion tests. These pigments seem to be a good alternative for corrosion protection. AlPO₄/Al(PO₃)₃, prepared according to process No. 1, showed very good results in all prepared pigments.     

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.     

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.     

Study of the anticorrosive efficiency of zincite and periclase-based core–shell pigments in organic coatings

The objective of this work was to identify the anticorrosive efficiency of synthesized, MeO/core pigments and of MeO pigments (MeO = ZnO, MgO) with varied morphology of particles. The synthesized MeO-type pigments displayed varied particle morphologies and the MeO/core core–shell pigments exhibited surface of particles made of zincite and periclase. These core–shell pigments have the properties of both the ZnO layer and of the core (wollastonite or graphite). Epoxy-ester based coatings containing the synthesized pigments were also formulated. To test the anticorrosion properties of the coatings, accelerated corrosion tests were carried out in the environment of condensed water, of NaCl mist, and of condensing water and SO₂. The synthesized core–shell pigments have good anticorrosion efficiency in an epoxy-ester coating.     

A study of diatomite and calcined kaoline properties in anticorrosion protective coatings

Comparison of properties of diatomite and kaoline in paints were studied in dependence on their volume concentration (PVC). Model paints were prepared containing increasing filler contents, PVC = 5% up to the critical volume concentration of the pigment (CPVC). The properties of the prepared coatings were tested by laboratory corrosion tests in both the neutral salt mist and the condensation moisture environments. The effect of diatomite and kaoline PVC on mechanical and anticorrosion protective properties of coats based on epoxide and epoxy–ester binders was studied. It was established that diatomite can be used as a filler in anticorrosion protective coatings.     

Anticorrosion efficiency of zinc-filled epoxy coatings containing conducting polymers and pigments

The dependence of the corrosion-inhibiting properties of zinc-filled organic coatings on the nature of the conducting polymers and conducting pigments added and on the pigment particles’ surface coating with conducting polymer layers were investigated. The following materials were selected to examine the corrosion-inhibiting properties of the conducting polymers: polyaniline phosphate (PANI), polypyrrole (PPy), natural graphite, and carbon nanotubes. Conducting pigment combinations for application in coating materials were formulated by applying pigment volume concentrations (PVC) of 0.3%, 0.5% and 1%, which were completed with Zn dust to obtain pigment volume concentrations/critical pigment volume concentrations (PVC/CPVC) = 0.64. Such conducting pigment/zinc dust combinations represented corrosion inhibitors to be used as ingredients in protective coatings. Solvent-based 2K epoxy resin based coating materials containing the corrosion inhibitors so formulated were prepared to examine their anticorrosion properties. The pigmented coatings were subjected to laboratory corrosion tests in simulated corrosion atmospheres and to standardized mechanical resistance tests. The protective coatings so obtained exhibited a higher efficiency than coating materials containing zinc dust alone. The coating material containing carbon nanotubes at PVC = 1% and the coating material containing graphite coated with polypyrrole (C/PPy) at PVC = 0.5% emerged as the best zinc-filled coating materials with respect to their corrosion-inhibiting efficiency. Treatment with the conducting polymers had a beneficial effect on the coating materials’ mechanical properties.     

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     

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.     

Improvement of anticorrosive performance of phosphate-based alkyd paints with suitable additives

The purpose of this investigation was focused on reducing the content of zinc phosphate in anticorrosive paints by means of the incorporation of low quantities of selected soluble corrosion inhibitors. The article describes the anticorrosive behavior of alkyd paints containing reduced levels of zinc phosphate, zinc oxide, and some soluble compounds used as additives (e.g., sodium polyphosphate, sodium phosphate, and sodium benzoate). Anticorrosive solventborne alkyd paints were formulated with a zinc phosphate content of 10% by volume (v/v) with respect to the total pigment concentration. In all cases, the PVC/CPVC (pigment volume concentration/critical pigment volume concentration) ratio was 0.8. Experimental paints, applied on sandblasted SAE 1010 panels, were evaluated by accelerated tests (salt spray cabinet) and electrochemical measurements (electrochemical impedance spectroscopy, EIS). The results show that the additions of small amounts of soluble corrosion inhibitors to low content zinc phosphate paint formulations enhance their performance in a very remarkable way. Perhaps, the most outstanding feature is that the employment of soluble additives allowed the reduction of the zinc phosphate content with concomitant savings.     

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.