Chromate Primer Research Articles

Primers based on tara and quebracho tannins for poorly prepared steel surfaces

Steel panels must be protected during storage and transportation because they can corrode. This protection used to be afforded by chromate primers, but nowadays tannin-based primers are being studied. These primers are not only used as protection but also as adhesion promoter if the steel surface was not well prepared (presence of oxides or low roughness).The objective of this work was to prepare lanthanum “tannate”, employing tara and quebracho tannins. The “tannates” were incorporated in primers formulation and applied on steel SAE 1010 panels (previously exposed to the humidity chamber or with 6 μm of roughness depth). These primed panels were exposed to humidity chamber where corrosion and blistering degrees were evaluated. Adhesion test were done. Electrochemical assays such as ionic resistance and corrosion potential measurements were carried out.Results showed that the adhesion and the barrier properties of the primers were good. Besides, on low roughness steel, the primers diminished the corrosion current.Results were compared with traditional zinc tetroxychromate primer.

Characterization of Cr (VI) – Containing solid phase particles in dry dust deposition in Daejeon, South Korea

Solid phase speciation of chromium in dry dust deposition and road paint was determined using transmission electron microscopy (TEM) and X-ray absorption spectroscopy (XAS). Spherical black carbon aggregates in dry dust deposition contained discrete nano-sized lead chromate (PbCrO4) and zinc chromate (ZnCrO4), which likely originated from yellow traffic paint and zinc chromate primer (corrosion resistant pigment), respectively based on their main applications. Road marking paint samples from auto roads included lead chromate particles whose size, shape, composition and crystal structure were similar to those in dry dust deposition. A slight difference was found at the particle boundary. Namely, lead chromate in traffic paint was encapsulated by silica-bearing matrix, while discrete lead chromate in the black carbon of dry deposition was rarely enclosed within silica-bearing matrix. The Cr K edge X-ray absorption near edge structure (XANES) spectrum for dry deposition showed the characteristic pre-edge resonance peak similar to the spectra for the Cr(VI) standard and road paint, but the lower intensity. The amount of Cr(VI) accounted for approximately 45% of the total Cr in the dust sample. The solid phase speciation of Cr observed using TEM and their valence states determined using XANES were consistent with the chemical speciation determined using the sequential extraction. The contribution of this study is that XANES was applied to identify Cr valance states in urban dust deposition and zinc chromate was found as a Cr(VI) phase in dry dust deposition using TEM. These study results provide novel data on Cr speciation and Cr(VI)-containing mineral phases in dry dust deposition and their potential sources. Based on the wide use of lead and zinc chromate, atmospheric contamination with these solid phase speciation of Cr(VI) is expected in other cities in the world.

Characterization of inhibitor storage and release from commercial primers

Abstract Commercial primers are applied on aluminum alloys that are used in aerospace applications to prevent corrosion attack from aggressive environments. These primers contain inhibitors that help combat corrosion. During field operations, these primers store and release inhibitors to protect the underlying alloy. The goal of this study is to characterize storage and release behaviors of these commercial primers to better understand the rate and mechanism by which inhibitors are released. Three commercial primers were investigated in this study; 1) Akzo Nobel 10P20-13 High Solid Primer that contains strontium chromate (SrCrO 4 ), 2) Deft 02GN084 (Pr-based), and 3) Hentzen 16708TEP (BaSO 4 -based). The primers were coated on a Teflon tape, then stripped off and broken to small pieces. Pieces of the primer coating were immersed into solutions of different Cl − concentration, temperature, time, and pH. The solutions were then filtered and characterized by inductively coupled plasma mass spectroscopy (ICP-MS) to analyze the solution chemistry. Results showed that SrCrO 4 primer release behavior follows power law kinetics. Solubility limits played an important role in dictating the release kinetics of the chromate primer when accumulation of Cr ion occurs.The effect of pH and temperature can alter this solubility limit. Chloride seems to promote release of chromate because of greater ionic strength. The Pr-rich primer released a large amount of Ca 2+ upon exposure and release kinetics were not time-dependent thereafter. The Ba-rich primer did not release soluble constituents to any significant extent.

Evaluation of Coated Al Alloy Using the Breakpoint Frequency Method

Electrochemical Impedance Spectroscopy (EIS) was used to study coated Al alloys during long-term exposure in 5wt% NaCl solution. The breakpoint frequency extracted from Bode plots allows the determination of the electrochemically active area of the sample. It shifts from low to high frequency with increasing exposure time due to the enlargement of the active area. The appearance of a high breakpoint frequency fh, usually in the range of 102 to 103Hz, occurred after a certain exposure time associated with a sharp drop of open circuit potential and low frequency impedance, and was accompanied by the visual initiation of corrosion under the coating. The incubation time before fh appears can be used as a criterion to evaluate the performance of chromate primer combined with different surface pretreatments. Optical profilometry analysis was conducted to determine the corroded area of coated sample after long-term exposure. The corroded area of one coating system was very close to, but that of another coating system was much higher than, the electrochemically active area estimated by the breakpoint frequency method, due to the different extent of attack. This indicates that the breakpoint frequency may be only valid for the determination of defect area during the initiation of attack, but probably not for the propagation to large regions of attack.

Painting rusted steel: The role of aluminum phosphosilicate

Surface preparation is a key factor for the adequate performance of a paint system. The aim of this investigation is to employ a wash-primer to accomplish the chemical conversion of rusted surface when current cleaning operations are difficult to carry out. The active component of the wash-primer was aluminum phosphosilicate whose electrochemical behavior and the composition of the generated protective layer, both, were studied by electrochemical techniques and scanning electron microscopy (SEM), respectively. Primed rusted steel panels were coated with an alkyd system to perform accelerated tests in the salt spray chamber and electrochemical impedance measurements (EIS). These tests were conducted in parallel with a chromate wash primer and the same alkyd system. Results showed that the wash-primer containing aluminum phosphosilicate could be used satisfactorily to paint rusted steel exhibiting a similar performance to the chromate primer.

Effect of chromate primer on corrosion fatigue in aluminum alloy 7075

The Center for Aircraft Structural Life Extension (CAStLE) at the United States Air Force (USAF) Academy has undertaken work to produce a standardized test method for determining the effect of a corrosion inhibitor containing chromate on small scale fatigue damage. CAStLE is specifically focusing their research on the effect of chromate primers on the pit-to-crack transition and crack growth under the USAF damage tolerant flaw size (1.5mm). Quantifying the chromate effect on the small damage scale is necessary to provide a baseline to compare the efficacy of new and safer coatings on fatigue life. To correctly account for these factors, bare and chromate primered test specimens of AA7075-T651 were produced with a center hole and a corrosion pit at the edge of the hole, and subsequently fatigued using representative environments and loading schemes until a thumbnail crack of approximately 1mm radius was produced. How chromate coatings effect fatigue crack growth is dependent on enough chromate leaching from a coating to reduce the fatigue crack growth rate (FCGR) in the time it takes to grow from a 300 μm pit to a 1mm fatigue crack. The current results suggest that the amount of chromate required to leach from the primer to affect FCGR may be highly dependent on the amount of chloride present.

Active metal-based corrosion protective coating systems for aircraft requiring no-chromate pretreatment

There has been much R&D effort expended to develop pretreatments and coatings that allow the replacement of toxic, carcinogenic, mutagenic, environmentally hazardous chromates used as pretreatments and pigments in aircraft coating systems. There have been many claims for chromate replacement in primer and pretreatment systems for aircraft, but no systems presently are in use that can function and meet specifications without some form of chromate used in the pretreatment and/or primer. The Mg-rich primer technology developed at North Dakota State University and now in final commercial development at AKZO Nobel Aerospace Coatings shows that finally aerospace Al alloys can be protected against corrosion. With simple cleaning only or a non-chromate pretreatment, the Mg-rich primer (MgRP) + aerospace topcoat provides an aircraft protection system that gives corrosion protection that equals or exceeds any system using chromate in any form. About 18 peer reviewed papers have been published and at least twice that many presentations at technical meetings describing this new aircraft primer technology. There are an extensive number of samples in outdoor exposure, and in exposure on small parts of aircraft like port-hole covers and doors, and the coating system has been in accelerated exposure cabinets of all sorts. In the first versions of the magnesium primer premature blistering was noted during immersion or B117 continuous salt spray testing which may be due to hydrogen generation from water contact at a particle. Efforts to control the level of activity of the magnesium have been successfully accomplished since the testing reported in this paper which controls this phenomenon. Current formulations meet and exceed the ASTM B117 test results of full chromate primer systems. Open circuit potential (OCP) measurements indicate an extended period of cathodic protection of the Al aircraft alloys such as AA 2024 T-3 and AA 7075 T-6. After this stage of protection, a combination of Mg oxide, hydroxide and carbonate compounds seem to give protection to the system, as we have seen corrosion protection given to samples for greater than 10,000 h of cyclic exposure for Mg-rich primers with good aerospace topcoats. Preliminary data are presented for other Mg alloys as pigments in metal-rich coating systems. All data indicate that the Mg-rich (or Mg-alloy pigment-rich) primer + aircraft topcoat system gives excellent corrosion protection by mechanisms entirely different from the modes of protection for aircraft alloys given by the toxic, carcinogenic chromate compounds now in use in all corrosion protection systems for aircraft. In most cases thus far examined, the protection, especially in cyclic exposure, exceeds the present chromate-based systems.

Active metal-based corrosion protective coating systems for aircraft requiring no-chromate pretreatment

There has been much R&D effort expended to develop pretreatments and coatings that allow the replacement of toxic, carcinogenic, mutagenic, environmentally hazardous chromates used as pretreatments and pigments in aircraft coating systems. There have been many claims for chromate replacement in primer and pretreatment systems for aircraft, but no systems presently are in use that can function and meet specifications without some form of chromate used in the pretreatment and/or primer. The Mg-rich primer technology developed at North Dakota State University and now in final commercial development at AKZO Nobel Aerospace Coatings shows that finally aerospace Al alloys can be protected against corrosion. With simple cleaning only or a non-chromate pretreatment, the Mg-rich primer (MgRP) + aerospace topcoat provides an aircraft protection system that give corrosion protection that equals or exceeds any system using chromate in any form. About 18 peer reviewed papers have been published and at least twice that many presentations at technical meetings describing this new aircraft primer technology. There are an extensive number of samples in outdoor exposure, and in exposure on small parts of aircraft like port-hole covers and doors, and the coating system has been in accelerated exposure cabinets of all sorts. In the first versions of the magnesium primer premature blistering was noted during immersion or B117 continuous salt spray testing which may be due to hydrogen generation from water contact at a particle. Efforts to control the level of activity of the magnesium have been successfully accomplished since the testing reported in this paper which controls this phenomenon. Current formulations meet and exceed the ASTM B117 test results of full chromate primer systems. Open circuit potential (OCP) measurements indicate an extended period of cathodic protection of the Al aircraft alloys such as AA 2024 T-3 and AA 7075 T-6. After this stage of protection, a combination of Mg oxide, hydroxide and carbonate compounds seem to give protection to the system, as we have seen corrosion protection given to samples for greater than 10,000 h of cyclic exposure for Mg-rich primers with good aerospace topcoats. Preliminary data are presented for other Mg alloys as pigments in metal-rich coating systems. All data indicates that the Mg-rich (or Mg-alloy pigment-rich) primer + aircraft topcoat system gives excellent corrosion protection by mechanisms entirely different from the modes of protection for aircraft alloys given by the toxic, carcinogenic chromate compounds now in use in all corrosion protection systems for aircraft. In most cases thus far examined, the protection, especially in cyclic exposure, exceeds the present chromate-based systems.

Application of embedded sensors in the thermal cycling of organic coatings

A standard Air Force polyurethane topcoat/epoxy chromate pigmented primer system was characterized using the thermal cycling method. This method is an accelerated test method for organic coatings that involves exposing the coating to alternating room temperature and elevated temperature cycles under constant immersion. Electrochemical properties were monitored using electrochemical impedance spectroscope for the total topcoat/primer system, the inner layer of primer, and the outer layer of the topcoat. The individual layers were monitored using platinum sensors embedded between the layers. Characterization of a system comprising of two layers of the epoxy chromate pigmented primer was also performed using EIS monitoring, and embedded sensors. The systems were cycled between room temperature, and set temperatures up to 80 °C. The barrier property of the topcoat and the bulk resistance of the primer were consistent with Arrehenius behavior. The results obtained were consistent with the intended design of the polyurethane topcoat and chromate primer with the former providing the significant barrier protection, whereas the primer providing the passivating chromate to the metal/coating interface. Analysis of the EIS data obtained from the sensor with an equivalent circuit decoupled the bulk primer properties from the metal/coating interface properties.

Durability of an off-optimum cured aluminium joint

The durability of an aluminium alloy joint, in which the adherends have been pre-treated with silane coupling agent and strontium chromate primer and bonded with the film adhesive FM-73, was examined for an off-optimum adhesive cure cycle. For bonded repairs a cure cycle of low temperature and longer duration (8 h at 80°C) for FM-73 is employed regularly to reduce thermal stresses. Double cantilever beam testing showed that the improved durability that results from primer application when the adhesive is cured at 120°C does not occur for the 80°C cure. Scanning electron microscopy and X-ray photoelectron spectroscopy of fracture surfaces and cross-sections cut from test specimens indicate differences in fracture paths and interfacial regions for the 120°C and 80°C cure specimens. Changes in the interphase region caused by the off-optimum cure cycle may contribute to an increased susceptibility of the adhesive joint to moisture and consequent bond degradation.

Effectiveness of Ion Vapor-Deposited Aluminum as a Primer for Epoxy and Urethane Topcoats

Environment-regulation-compliant replacement coatings for use in various aerospace programs were evaluated. Although coatings that employ chromate primers and conversion coatings work effectively, enacted and pending changes in government regulations make it imperative that alternative coating systems be developed and evaluated. An integral part of the present investigation involved the use of electrochemical impedance spectroscopy to screen candidate coating systems. Preliminary results indicated that ion vapor-deposited aluminum afforded protection to AA2219-T87 (UNS A92219) and type 4340 (UNS G43400) steel substrates at least as good as the protection afforded by more-conventional coating systems. Results from electrochemical impedance spectroscopy measurements provided reliable predictions on the performance of the various coating systems.

Cancer Mortality Among Workers Exposed to Zinc Chromate Paints

To evaluate the carcinogenicity of chromium compounds among user industries, the proportionate mortality experience of spray painters exposed to zinc chromate primer paints and electroplaters exposed to chromic acid in the aircraft maintenance industry was examined. Compared to the mortality patterns of U.S. white males, no excess of cancer was found in the 48 deaths among electroplaters. Analysis of the 202 deaths among spray painters revealed a significant excess of cancer, primarily of the respiratory tract. The relative increase of respiratory cancer showed a positive gradient with the length of estimated exposure time, and was confined to painters whose interval from first employment to death was at least 20 years. The findings consistent with occupational exposure to chromium compounds, previously shown to be carcinogenic in manufacturing processes, but the effect of other paint constituents, tobacco smoking, or methodologic limitations could not be discounted.

Damping in Friction-Grip Bolted Joints

The object of the work reported in this paper is to obtain a measure and an understanding of the damping in high-strength friction-grip bolted joints. Static tests to determine the coefficient of friction and cyclic tests to determine the amount of damping in symmetrical double-coverplated butt joints are described. Four plate surfaces were examined, i.e., galvanized, inorganic zinc silicate, urethane chromate primer, and mill scale. An energy loss relationship was found for each surface type. At the working load levels, the damping factors ranged from 5% to 12%, and the energy losses, after early variations, tended to stable values with increasing numbers of cycles. Suggestions on improvements to increase joint damping are given.

Primers for sprayed aluminium and zinc coatings on steel

Abstract Exposure trials of up to 8 years' duration have been conducted on priming paints for sprayed aluminium and sprayed Zinc exposed in the atmosphere.Most of the paints tested performed well and the chemical composition chosen for the primer is therefore not considered critical, although its physical characteristics may need adjusting for the somewhat rough and porous surface. One combination of paint and sprayed metal (zinc chromate primers on sprayed zinc in a marine atmosphere) led to degradation of the top-coat paint and this combination is not recommended. On the whole, thepainted metal-sprayed coatings exposed at both sites (industrial and marine atmospheres) are still in satisfactory condition and the tests are continuing. The formulations -of the experimental priming paints are given in full.

The Performance of Alcan 65S-T6 Aluminum Alloy Embedded in Certain Woods Under Marine Conditions

Laboratory and marine exposure tests were carried out to assess the performance of Alcan 65S-T6 (6061-T6) aluminum alloy embedded in certain woods under marine exposure conditions. The tests also involved the assessment of several protective paint systems designed to protect the wood in the simulated hull sections used in the tests.The relative corrosivity to aluminum of the woods tested under ship hull conditions is: rock elm (least), mahogany and British Columbia fir (most). Only very slight corrosion occurs when the aluminum is coated with zinc chromate priming paint even in the most corrosive woods after extended immersion periods in sea water. Alcan 65S-T6 (6061-T6) has a corrosion resistance greatly superior to that of Alcan 24S-T3 & 4 (2024-T3 & 4) under the same marine exposure conditions. Anodizing increases the corrosion resistance of both alloys, particularly if this treatment is followed by a coat of zinc chromate primer. The use of wooden dowels to protect aluminum embedded in these woods is also beneficial. Among the variations in paint systems which were tested, the most complete paint system, comprised of sealer + barrier layer + copper antifouling paint provided maximum protection from corrosion. Where pitting occurred on 65S-T6 (6061-T6) embedded in sea water wetted wood, it has been shown that the rate of penetration falls off sharply with time. 6.4.2

Corrosion of Light Metals for Ship Construction and Effect of Surface Preparation

Apply of Aluminium and its alloy for marine use instead of steel has been found to increase corrosion resistance. After the alternating immersion or weathering test for a year, corrosion loss of aluminium alloy such as 2S, 52S, and 56S are 1/230 to 1/125 of that of mild steel and decrease of strength was not almost noticed. Though zinc chromate primer and phthalic resin paint finish are best coating, the method of surface preparation before painting is great importance. The electrolylic-polishing, anodic coating, chemical oxide coating are superior in anticorrosion to ordinary phosphate coating, but these methods can not be easily applied on the large plate or construction in view of the capacity of electric source or the equipment of heating. After the study of the corrosion test in salt solution, it has been developed to the new modified phosphate-alcohol method. It can be applied by either brushing or immersion and need not solution heating, and after the treatment, metal surface can be immediately painted without water rinse. This method can be almost equally on 2S, 61S, 52S and 56S and the paint film after this treatment adhere to metal surface and can endure long time against the weathering test.

フタル酸樹脂系舶用塗料の剥離に対する塗装上の若干の考察(日本航海学会第16回講演会)

We have recently come to use the phthalic alkyd resin paint in painting many ships. To test the adhesion of the paint on prime coats the auther studied on the experiments of painting on some prime coats and also of drying time of the primers. As the result, the marine zinc chromate primer is suitable for the paint and it is desirable that the drying time of the primer is one day to a week.

A STUDY OF PROVENTION FOR CONTACT CORROSION OF LIGHT METALS

When light metals contact with other metals, for instance steel, it eroded especially in the presence of electrolytic solution, such as NaCl.Aluminum alloy (52S) panels are worn with steel bands with or without various coating or insulating pastes, and submerged into a aqueous solution containing 5.85%NaCl, 0.3%H2O2.In untreated (direct contact and bare) panels, aluminum panels generals gas bubbles and considerably eroded, but steel band not so eroded. When insulating cloth tape (cloth painted with paste consists of polybutene, paraffine, boiled oil, gilsonite and zinc chromate etc.) Placed between aluminum alloy and steel, the corrosion rectrogressed. Steel band eroded and aluminum alloy not affected. After the submerge over 1 month, significant lowering in tensile strength of aluminum alloy not founded.When panels are coated with various coatings, (zinc chromate primer, wash-primer, vinyl resin primer) showed good resistance.Between insulating paste, polybutene-boiled oil-zinc chromate type showed best results, and in coatings, vinyl type primer was best and wash primer-zinc chromate primer (synthetic resin vehicle) was the second.It is interesting what then metals are contact directly, erosion occured at aluminum panel and produce white precipitate, aluminum hydroxide, and when metals are insulated by paste, erosion occured at steel and produce reddish ferric precipitate.