An in situ phosphatizing coating on 2024 T3 aluminum coupons

Toxic chemicals, such as chrome, are commonly used in the application of conversion coatings to various metal surfaces. In situ phosphatizing coatings (ISPCs) are an innovative approach for eliminating the requirement of a conversion coating which ends the need of toxic materials used in a multi-step coating practice. An ISPC is formulated by predispersing an in situ phosphatizing reagent (ISPR) into a paint system. In this study, an ISPR, an arylphosphonic acid, is used in a polyester–melamine paint to react in situ with the metal surface and to provide the acidic catalyst needed, while thermally curing the paint. A second polyester–melamine paint system is used as the control that uses the standard catalyst para-toluenesulfonic acid (p-TSA) to catalyze the cross-linking reaction in the paint. These two paint systems are applied to bare 2024 T3 Al panels and to chromated 2024 T3 Al panels. The coated panels are treated in a corroding media for 2,400 h and monitored periodically using electrochemical impedance spectroscopy (EIS). Results of EIS data and the corresponding electrical equivalent circuit (EEC) show that the ISPC applied to both the chromated and untreated Al panels provide superior corrosion protection. At low frequency (0.01 Hz), the panels coated with the ISPC show 10 000 times more resistance than both the chromated and bare Al panels coated with the control polyester–melamine paint. The corresponding EEC shows that the panels with the control paint applied have double the amount of electrical components (resistors and constant phase elements). A physical interpretation is suggested for the EEC. The paint adhesion to the Al surface and the corrosion behavior are tested by salt-water immersion and salt fog. After the panels are exposed to the salt solution, a pressure tape is applied to test the adhesion. The results show that the ISPC applied on the chromated Al adheres the best. The simultaneous reaction of the ISPR catalyzing the curing of the paint and forming the metal–phosphate layer is the reason for the superior paint performance.     

In-situ phosphatizing coatings II: A high-solids polyester baking enamel

A single step in-situ phosphatizing coating (ISPC) can be formulated by pre-dispersing an optimal amount of in-situ phosphatizing reagents (ISPRs) into the paint system. The technique of ISPC is applied to a high-solids polyester-malemine baking enamel using a designed “ISPR-2.” The in-can stability of ISPC is verified using rheological measurements. The coating properties and protective performance of the ISPC are compared to those of the multi-step coating of control sample (MCCS). The immersion tests in a 3% NaCl solution and salt spray testings show a significant improvement in paint disbondment from the “X” scribe for ISPC. The observed coating performance enhancement of ISPC over MCCS is confirmed from the multi-functionality of ISPRs. Phosphate chemistry proceeds via an acid-base type of interaction, P-O⁻- Mⁿ⁺, and polymer chemistry generates a covalent P-O-C linkage with the polymer network. Presented at 24th International Waterborne, High-Solids, and Powder Coatings Symposium, February 5–7, 1997, New Orleans, LA. Dept. of Chemistry and Biochemistry, DeKalb, IL 60115-2862.     

In-situ phosphatizing coatings III: A water-reducible alkyd baking enamel

We report the successful formulation of stable and compatible in-situ phosphatizing coatings (ISPCs) for a waterborne alkyd-amino baking enamel applied on bare cold-rolled steel (CRS), iron phosphated Bonderite 1000 (BD), and iron phosphated plus Parcolene 60 chromated (BD+P60) coupons. The enhanced coating adhesion of water-based ISPCs is confirmed by the cathodic delamination measurements. After 100 hr of salt spray (fog) test, the corrosion resistance performance (measured by the corrosion disbondment across the “X” scribe, d in mm) of the water-based ISPC on CRS panel (d=4.0−7.0 mm) outperformed that of the control alkyd paint on B-1000 (d=26 mm) and also on BD+P60 (d=14 mm) coupons. The superior coating performance of water-based ISPCs is believed to result from the in-situ metal surface phosphatization as detected by the reflectance FTIR technique. Department of Chemistry and Biochemistry, DeKalb, IL 60115-2862.     

In-situ phosphatizing coatings I: An air-dried lacquer system

The formulation of in-situ phosphatizing coatings (ISPCs) was successfully performed for lacquer systems using a commercial nitrocellulose lacquer and an optimum amount of in-situ phosphatizing reagents (ISPRs). The in-situ phosphatizing lacquer (ISPL) system is stable, and shows no change in surface appearance and drying speed as compared to the unmodified lacquer (UML). The ISPLs are applied on pine, poplar, and red oak wood boards, and on cold-rolled steel, aluminum, and laminated brass panels. Immersion tests in a 3% NaCl solution showed a remarkable enhancement in paint disbonding resistance for the paint film of ISPL on wood and metals compared to that of the UML sample. The paint film protective performance of ISPLs is further evidenced by the lattice pattern tape testings, and by the cathodic delamination and electrochemical impedance spectroscopy. Presented at 24th International Waterborne, High-Solids and Powder Coatings Symposium, February 5–7, 1997, new Orleans, LA. Dept. of Chemistry and Biochemistry, DeKalb, IL 60115-2862.     

Molecular design of in situ phosphatizing coatings (ISPCs) for aerospace primers

A novel chrome-free surface pretreatment and primer combined in one-step application for aircraft coating is described. First, a high-solids solvent-borne non-chromate epoxy primer (referred to as CD112) is developed. The formulation of CD112 system is based on epoxy/polyamide chemistry, Adheron’s proprietary anti-corrosive pigments, and a tightly packed passivating film made of fillers with different geometric shapes. The protective performance of CD112 has been tested at three independent laboratories and shown to pass a 3000 h salt spray resistance, compatible to its chromate counterpart, on both 2024-T3 Clad/Alodine 1000 and 7075-T6 Clad/Alodine 1000 aluminum alloys.

Second, a chrome-free acrylic emulsion for surface pretreatment of aluminum alloys is formulated, comprising an 60 nm particle size of acrylic resins, metal-chelating reagents, organofunctional silanes, and non-toxic anti-corrosive pigments. An 1 μm dry film is processed on 2024-T3 Bare Al panel (referred to as 2024-T3 Bare/AFP) and then coated with MIL-PRF-23377 Type I approved chromate-based primer. The electrochemical impedance spectroscopy (EIS) data indicate that 2024-T3 Bare/AFP show about 100 times more resistance than 2024-T3 Bare/Alodine 1200.

Third, two in situ phosphatizing reagents (ISPRs) were selected to formulate the in situ phosphatizing coating (ISPC) aerospace primers of MIL-PRF-23377 class N, and to promote the formation of a metal-phosphate layer at the molecular level. The ISPC technique combines a chrome-free surface pre-treatment and primer into a single-step application. The EIS data demonstrate that the ISPC CD112 primer on untreated 2024-T3 Al coupons shows 10–100 times more resistance than the control CD112 primer on 2024-T3 Bare/Alodine 1200. The chemistry of the simultaneous reaction of ISPRs catalyzing the curing of the paint film and forming the metal-phosphate layer at the interface will be illustrated.     

Occupational exposure to airborne isocyanates during brush/roller application of 2-pack polyurethane paints in a tropical climate

Shipboard and laboratory trials were conducted to determine airborne occupational exposure to isocyanates by brush/roller application of 2-pack polyurethane paints. Airborne concentrations in the breathing zones of the operators were found to be <0.1 μg/m³ during the paint application to a vessel deck, in a tropical climate, in the open air. Similarly, brush/roller application of the paints in an enclosed space generated airborne isocyanate concentrations <3 μg/m³. The dust generated during light sanding of the polyurethane paint, 24 h after curing, did not show detectable levels of isocyanates.     

Über einige wesentliche Unterschiede zwischen der Aufbringung von konventionellen Anstrichen und der Elektrotauchlackierung,insbesondere hinsichtlich der Vorbehandlung der Werkstücke

A Few Major Differences Between Coating with Conventional Paints and Electrical Dip Coating Especially with Respect to Pretreatment of the Article to be Coated The basic difference between conventional coatings and paints for electrical dip coating is that in the latter case a high voltage is applied during coating of the metallic surface. Consequently, a low and uniform resistance of the metal is required, which can be achieved by thorough cleaning for removal of the surface impurities and by coating of the surface with a thin layer of fine-sized phosphate or chromate. Paints for electrical dip coating are more susceptible to defects of the surface and various qualities of steel than the conventional paints. The problems in the single layer white painting by the electrical dip process and in the pigmentation process are discussed. The advantages of electrical dip coating over conventional coatings, which have led to a greater use of the former technique, are discussed. Best use of this process can be made by optimizing the steps, such as surface cleaning, washings before and after phosphatizing, passivation, drying, and by a suitable choice of the paint.     

Surface-fragmenting, self-polishing, tin-free antifouling coatings

Surface-fragmenting types of self-polishing tinfree resins were characterized by IR and NMR and demonstrated the successful synthesis of cupric carboxylate. According to the IR,¹H-NMR and¹³C-NMR measurements, it is clear that the unsaturated double bonds present in the resins changed into other new bonds after drying in a manner similar to alkyd resins. These resins were used as binders to prepare antifouling paints. Scanning electron microscopy (SEM), rotary tests, raft tests, and ship tests were used to investigate the self-polishing phenomena and the antifouling ability of this type of antifouling paint. The SEM photographs obtained from the paint surfaces demonstrate self-polishing phenomena. From the rotary tests, the polishing rates of paints were measured as 10μ ∼ 5.7 μ/month. The results from the raft tests show that all of the paints exhibit excellent antifouling ability and are about 80 ∼ 90% as effective as the conventional tin-containing antifouling paints. Dept. of Chemical Engineering, Tainan, Taiwan, R.O.C. #26 Yen Hai 3rd Rd., Kaohsiung, Taiwan, R.O.C.     

Service life prediction of organic coatings: electrochemical impedance spectroscopy vs actual service life

Electrochemical impedance spectroscopy (EIS) is used to derive an expression for predicting the service life of organic coating in a C4-type environment (industrial and costal areas with moderate salinity) as defined in ISO 12944 standard for paints and varnishes—corrosion protection of steel structures by protective paint systems. Three coating systems with a record of 2, 5, and 10 years of durability were selected for the study. The selection was also based on proven composition and dry film thickness (DFT) of the coatings as per ISO 12944. Electrochemical impedance measurements of the paint-coated panels were carried out by exposing the coated mild steel panels without scribe in different corrosive environments such as immersion in NaCl solution, neutral salt spray, etc. Neutral salt spray exposure was found to be the most severe corrosive environment among all the three coating systems. In most of the cases, EIS gave early indication of coating failure when compared to visual defects such as blistering and over-film corrosion.     

Effect of moisture‐ingress on adhesion energy in a metal oxide‐polymer system

This work quantifies the damage caused by moisture in a metal coating system under extreme weathering conditions, using Variable Radius Roll Adhesion Test (VaRRAT). Interfacial toughness (adhesion energy) between the metal oxide and the polymer in painted steel panels, studied by using VaRRAT, is observed to fall with increasing temperature and time of exposure to moisture. Possible cause for irreversible loss in adhesion energy in the paint system is attributed to the sorption of free water at the metal oxide–polymer interface. Different failure responses were observed in two different paint–metal systems. Adsorption or diffusion in the Henry's mode is rate controlling in green paints as indicated by the low activation energy of 12 kJ mol^?1. The white samples showed a high activation energy of 30 kJ mol^?1, indicating a mixed process of diffusion as well as chemical to be rate determining. Different paint/binder ratios are responsible for the different responses of these samples. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Fabrication and characterization of in-situ duplex plasma-treated nanocrystalline Ti/AlTiN coatings

Plasma nitriding and plasma-assisted PVD duplex treatment was adopted to improve the load-bearing capacity, fatigue resistance and adhesion of the AlTiN coating. Ion etch-cleaning was applied for better adhesion before plasma nitriding. After plasma nitriding Ti interlayer was in-situ deposited by high power impulse magnetron sputtering (HIPIMS), followed by the AlTiN coating through in-situ deposition by advanced plasma-assisted arc (APA-Arc). The microstructure and properties of the duplex-treated coating were carefully characterized and analyzed. The results show that the thicknesses of the nitriding zone, the γ′-Fe₄N compound layer, the Ti interlayer and the AlTiN top layer with nanocrystalline microstructures are about 60 μm, 2–3 μm, 100 nm and 6.1 μm, respectively. The nitriding rate is about 30 μm/h and the AlTiN coating deposition rate reaches 6.1 μm/h. The interfacial adhesion of the Ti/AlTiN coating is well enhanced by ion etch-cleaning and a Ti interlayer, and the load-bearing capacity is also improved by duplex treatment. In addition, the instinct hardness of the Ti/AlTiN coating reaches 3368HV_0.05 while the wear rate coefficient of 5.394×10⁻⁸ mm⁻³/Nm is sufficiently low. The Ti/AlTiN coating, which possesses a high corrosion potential (E_corr=−104.6 mV) and a low corrosion current density (i_corr=4.769 μA/cm²), shows highly protective efficiency to the substrate.     

Study of the effect of mechanically treated CeO2 and SiO2 pigments on the corrosion protection of painted galvanized steel

The effectiveness of mechanically treated CeO₂ particles and SiO₂ particles as active fillers into an organic coating was investigated. For this purpose, different combinations of CeO₂ and SiO₂ particles were added to an epoxy-polyester polymeric matrix: mechanically treated CeO₂ particles, mechanically treated CeO₂/SiO₂ particles and mechanically treated SiO₂ powders (used for comparison). The particles were dispersed into the polymeric matrix and HDG steel panels were coated with the different paints. A strontium chromates containing paint was used as a reference to compare the performances of the other samples. The salt spray results proved the good performance of coatings containing combinations of ceria and silica especially where these had been mechanically treated in a co-milling operation. The paint containing only the mechanically treated SiO₂ particles showed a fairly good resistance in the salt spray chamber considering the scratched samples. The EIS measurements evidenced the good corrosion protection properties of the paints containing the different combinations of mechanically treated CeO₂ and SiO₂ particles. After about 1000 h of immersion in 0.1 M NaCl solution, the samples containing the mix of mechanically treated CeO₂/SiO₂ particles showed impedance values which were comparable with the chromate control sample. The cathodic polarization tests evidenced the low extent of detachment of the coating containing the mix of mechanically treated CeO₂/SiO₂ particles. The electrochemical characterization and neutral salt spray test results proved the effectiveness of the mechanical treated cerium (IV) oxides treated together with SiO₂ as active pigments to improve the corrosion protection of the substrate. The reasons for the synergistic effect of the milled (together or separately) SiO₂ and CeO₂ particles was not clear at all, but a few hypothesis were discussed.     

Characterization of a water-based paint for corrosion protection

Corrosion of steel rebars in reinforced concrete is one of the major problems in the construction industry. Carbonation reactions of concrete with carbon dioxide and, mainly, the chloride salts action are the main causes responsible for concrete degradation. Protective coatings help to improve the durability of concrete structures by acting as a physical barrier against the corrosion agents. Waterborne paints are usually used for concrete protection rather than solvent-based paints since they are less pollutant. The aim of this work is to investigate the influence of the pore size and porosity on the permeability of the paints films toward sodium chloride. Three characterization methods from membrane science were implemented to characterize paint coatings. The time-lag method was used to determine the permeability toward the sodium chloride and toward helium and argon, these for approximately 100% relative humidity. From the seven waterborne paints formulated, only one was found to be suitable for surface protection of reinforced concrete, since its permeability toward NaCl was smaller than 10⁻¹⁴ m² s⁻¹, the threshold value required by National Laboratory of Civil Engineering (LNEC) in Portugal. For the formulated paints, it was observed that the average pore size correlates well with the permeability toward sodium chloride. This is an important result since obtaining the permeability toward sodium chloride of corrosion protective paints is very time consuming, while the average pore size can be obtained in a much shorter time.     

三聚磷酸铝防锈颜料在涂料工业中的应用

本文阐述ＡＰＷ了防锈颜料的特性及其在各种溶剂型涂料、水溶性树脂涂料以及厚浆型防腐涂料等方面的应用情况，表明ＡＰＷ颜料比红丹、锌铬黄。磷酸锌等防锈颜料具有更优越的性能，是一种值得推广的新型无毒防锈颜料。     

Quantitative measurement of adhesion between polypropylene blends and paints by tensile mechanical testing

A tensile mechanical test suiable to measure the adhesion between brittle coatings and ductile substrates was applied to measure the adhesion of painted layers on polypropylene blends. The test involves the tensile deformation of the painted assembly, resulting in the periodic cracking of the brittle coating on the ductile substrate. The interfacial shear strength was determined by measuring the strength of the coating, the thickness of the coating, and the average width of paint fragment after the crack density reaches saturation. Apparent interfacial shear strength was obtained for different paints on the same kind of blend, which gave consistent results over the experimental strain rate range from 10^?4 to 10^?3 sec^?1. Interfacial delamination was studied by optical microscopy (OM) and transmission electron microscopy (TEM). The delamination was observed to mainly occur near the adhesion promoter and substrate interface.     

Green chemistry in situ phosphatizing coatings

The current organic coating on metals for aerospace applications involves a multi-step process and considerable energy, labor and control, and it generates toxic wastes such as chlorinated solvents, cyanide, cadmium, lead and carcinogenic chromates. The green chemistry technology of in situ phosphatizing coatings (ISPCs) developed in our laboratory is a one-step self-phosphating process, in which the deposition of metal phosphate layer on the substrate surface and the curing of polymer paint film take place independently, but simultaneously. The formation of a metal phosphate layer in situ will essentially eliminate the metal surface pre-treatment step of employing a phosphating line/bath. The use of chemical bonds linked to the paint polymers to seal the pores of metal phosphate in situ should enhance coating adhesion and suppress metal corrosion without a post-treatment of final rinses containing chromium (Cr⁶⁺). The successful applications of ISPCs in three types of commercial paints (solvent-borne high-solids, water-reducible and VOC-free latex) on bare and pre-treated cold-rolled steel and 2024 aluminum coupons is presented. The protective performance (coating adhesion and corrosion inhibition) of ISPCs is shown to be superior over that of the current multi-step coating practice.     

Investigation of the anticorrosion efficiency of ferrites Mg1−xZnxFe2O4 with different particle morphology and chemical composition in epoxy-ester resin-based coatings

Mixed metal oxides with the ferrospinel structure ZnFe₂O₄, Mg_0.2Zn_0.8Fe₂O₄ and MgFe₂O₄ were synthesised by the high-temperature solid-phase process. A series of pigments containing the metals Mg–Zn–Fe was prepared from 4 different starting iron oxides: viz. goethite (FeOOH), hematite (Fe₂O₃), magnetite (FeO·Fe₂O₃) and specularite (Fe₂O₃). The properties of the ferrites as pigments were examined in a solvent-based epoxy-ester resin-based coating material at a pigment volume concentration PVC_ferrite = 10%. The anticorrosion efficiency of the paints with the ferrites was examined by exposing panels coated with the paints to atmospheres with SO₂, NaCl, or condensed moisture. Furthermore, the physico-mechanical properties of paint films containing the pigments were evaluated by standardised tests. Ferrites prepared from the needle-shaped FeOOH or lamellar Fe₂O₃ emerged as pigments with the best anticorrosion properties. From the aspect of chemical composition, the paint films containing Mg_0.2Zn_0.8Fe₂O₄, i.e. combinations of the cations Mg–Zn, were assessed as the best.     

Reaction rate estimation of controlled-release antifouling paint binders: Rosin-based systems

Biofouling on ship hulls is prevented by the use of antifouling (A/F) paints. Typically, sea water soluble rosin or rosin-derivatives are used as the primary means of adjusting the polishing rate of the current chemically active self-polishing paint systems to a suitable value. Previous studies have shown that mathematical coating models based on a fundamental knowledge of the underlying mechanisms of A/F paints is a promising tool for accelerated product testing at different operational conditions of a sailing ship or a paint rotor. Such models can also be used for generation of ideas aiming at product optimisation and innovation (e.g. incorporation of natural active agents).This study seeks to attain scientifically founded knowledge of the reaction mechanisms and the rate of reaction with sea water of a Zn-carboxylate of a synthetic rosin compound. The kinetic expression attained can be used as input to mathematical models describing the behaviour of rosin-containing tin-free A/F paints. The experimental procedures developed can be easily implemented by marine paint companies for the screening of novel controlled-release binder materials for A/F paints.As a first step, it is demonstrated that the degradation of this Zn-containing rosin-derivative by sea water plays a key role in the polishing mechanism of paints formulated with such a resin. Then, the relevant literature available on the sea water behaviour of rosin and rosin-based binders is reviewed. Subsequently, two experimental procedures for the reaction rate estimation of the selected rosin-derived resin are presented; one is based on a gravimetric approach while the other uses flame atomic absorption spectroscopy (FAAS) to determine the total Zn²⁺ released by the resin. Both methods yield well-defined reaction conditions and sufficiently high accuracies. The latter is important because very low steady state reaction rates (about 0.70 ± 0.26 μg Zn²⁺ cm⁻² day⁻¹ at 25 °C and pH 8.2) are measured. Steady state reaction rates of Cu²⁺- and Mg²⁺-derivatives are also determined and discussed. The experimental procedures developed are used to investigate the influence of NaCl concentration (12–52 g/l), pH (7.8–8.5) and sea water temperature (10–35 °C) on the rate of reaction of the Zn-carboxylate. Within that range of sea water conditions, the following kinetic expression is found to describe the steady state Zn²⁺ release rate resulting from the reaction of the Zn-carboxylate with sea water:

where the natural logarithm of the pre-exponential factor, ln (A), is 18.0 ± 2.5 (the unit of A being the same as k₁), the activation energy, E_a, is 18.5 ± 6.0 kJ/mol and the reaction order with respect to the hydroxide ion concentration, a, is 0.86 ± 0.42. L_ZnR is the estimated solubility product of the ZnR resin which has a value of 3.1 × 10⁻¹² (mol/l)⁻³ (about 6 mg Zn²⁺/l in equilibrium). The low value of the activation energy is believed to result from the complex reaction mechanisms hypothesised rather than pointing at a certain diffusion control in the reaction rate experiments. The reverse reaction is found not to affect the hydrolysis rate within the pores of antifouling paints significantly. It is concluded, from the reaction mechanism proposed, that the observed partial exchange of Zn²⁺ for Cu²⁺ in the resin structure during paint dispersion and immersion results in a lower reaction rate compared to the pure ZnR. Cu-carboxylate has a reaction rate of about 5.8 ± 1.0 μg CuR cm⁻² day⁻¹ at 25 °C and pH 8.2. The presence of Mg and Na compounds (probably Mg- and Na-resinate) in the solid paint film has also been detected, and will influence the reaction rate by modifying the ZnR exposed surface area.     

A Novel Method to Fabricate Silicon Nanowire p–n Junctions by a Combination of Ion Implantation and in-situ Doping

We demonstrate a novel method to fabricate an axial p–n junction inside <111> oriented short vertical silicon nanowires grown by molecular beam epitaxy by combining ion implantation with in-situ doping. The lower halves of the nanowires were doped in-situ with boron (concentration ~10¹⁸ cm⁻³), while the upper halves were doubly implanted with phosphorus to yield a uniform concentration of 2 × 10¹⁹ cm⁻³. Electrical measurements of individually contacted nanowires showed excellent diode characteristics and ideality factors close to 2. We think that this value of ideality factors arises out of a high rate of carrier recombination through surface states in the native oxide covering the nanowires.     

Corrosion inhibition of steel in sodium chloride solution by undoped polyaniline epoxy blend coating

In this study an undoped polyaniline (PAni) was synthesized by chemical oxidative polymerization with ammonium persulfate as an oxidizing reagent. The synthesized PAni was used as a corrosion inhibitive pigment in an epoxy matrix. The corrosion protection performance of steel coated panels in 3.5% sodium chloride solution was evaluated via determination of open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS). It was found that after 300 days of immersing the resistance of coating was about 4 × 10⁵ Ω cm². The OCP was shifted to the noble region due to the passivation effect of PAni pigment. Besides, the phase angle (theta) at 10 kHz was stable around 87 ± 1° during immersion period. Results revealed that PAni pigmented paint showed acceptable protection against the corrosion of carbon steel in 3.5% sodium chloride solution.