Observations on the testing of Mg-rich Primers for Totally Chromate – free Corrosion Protection of Aerospace Alloys Gordon Bierwagen*‡, Roger Brown§, Dante Battocchi‡ and Scott Hayes§ *
[email protected] Department of Coatings & Polymeric Materials North Dakota State University, 1735 NDSU Research Park Drive Fargo, ND 58102 ‡
b
AKZO Nobel Aerospace Coatings 1 East Water Street, Waukegan, Illinois 60085
Abstract: 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 + 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 B117 test results of full chromate primer systems.
Introduction: I. Introduction A. The need for Chromate replacement in Aircraft Coatings
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Why was the Mg-rich Primer technology developed? The initial and primary reason for its development was to provide a chromate-free corrosion protection system for aerospace Al alloys. The present use of chromates as pigments in the primers currently used from corrosion protection1 (largely SrCrO4 pigments2) as well as the chromates used in the Al alloy pretreatment for painting is the major environmental hazard of aircraft production, maintenance and repair.3 Lest we forget, chromates are among the most severe toxic and carcinogenic hazards that mankind has produced and introduced into the natural environment. It has long been acknowledged that the only allowable reason for their use is when no other scientifically verifiable replacement can be found in a safety related function. The total replacement of chromates has been identified as one of the major targets of DOD environmental R&D programs for almost 20 years. The handling and disposal of chromates in paint application and paint removal waste as a HAZMAT is further one of the major environmental costs of the DOD. Full details of the Chromate hazards of present aerospace coatings systems are detailed at the DOD Strategic Environmental Research and Development Program (SERDP) website at /www.serdp.org/ (e.g., SERDP Fact Sheet 1119: Critical Factors for the Transition from Chromate to Chromate-Free Corrosion Protection ). Chromate replacement in aircraft coatings is such a very technical problem for two major reasons. The first is the unique material properties of the high strength Al alloys involved in aircraft4, and the second the uniqueness of chromates as corrosion inhibiting materials for these alloys.5,6 Aircraft alloys are specially designed alloys that impart high strength and light weight to aircraft, but are often susceptible to corrosion, especially the two most commonly used Al alloys AA 2024 T-3 and AA 7075 T-6.7, 8, 9 These are phase separated alloys that are in themselves highly complex metal-in-metal composites, but tend to have weakness towards local galvanic corrosion because of this structure. Matte Surface Presently a flexible Polyurethane/polyol or polyester
Presently an epoxy-polyamide with Sr Chromate Presently Alodine 1200 with Chromate Al 2024 T3
Topcoat
Primer
Pretreatment
Substrate
Figure 1. Schematic of Current Aerospace Coating System Chromate pigments have a set of unique material properties, among the most important of which are a low, but significant, water solubility, the ability to act as both cathodic and anodic inhibitors, and a very complex oxidation/reduction chemistry. Details of these properties and their importance are discussed from the point of view of a pigment scientist in reference 5, and from the point of view of corrosion science in reference 6. For further details on the unique, difficult to replace, corrosion control properties of chromates, one 22
should see also the work of Frankel and McCreery.10 The richness of properties detailed in these and many related studies1 indicate that it is very difficult to replace, the present robust system based on chromate pigments and chromate pretreatments for Al. As NDSU became involved in the study of aircraft coatings, initially in the testing mode, it became apparent that multiple methods of testing were going to be needed to understand all of the nuances of performance and interactions that were taking place in the very complex aircraft coating systems. A schematic of the system is given in Fig. 1, and shows that one is considering a multi-layer coating system, primer & topcoat, that also includes a pretreatment layer at the primer/Al-alloy substrate interface. Many candidate systems have been examined for Cr-replacement in aircraft coatings. For replacing Chromate-based pretreatments, these have included sol-gel pre-treatment systems, cold-cathode plasma-polymerized pretreatment layers as well as the presently used chromate based pre-treatment baths. Many new pigments and composite pigmentary structures have been studied to replace the SrCrO4 pigments now in use. Many other types of systems have also been examined as Cr replacements in coatings or pretreatments. Some coatings are chrome free, but require a chromate pretreatment to provide even marginal replacement for present systems. Some Cr-free pretreatment systems have been developed, but they do not function satisfactorily without the use of primers based on Chromate pigments. No total aircraft coating system (pretreatment, primer and topcoat) system currently available provides the extended corrosion lifetimes of the presently used systems without chromates in the primer, pretreatment or both. Some authors have gone so far as to describe their candidate materials for Cr replacement “SuperPrimer,”11 but alas, this material also provides insufficient corrosion protection by itself without chromates of some sort present. Thus, there has existed a severe need for coatings that provide the excellent corrosion protection that chromate in pretreatment and primer provides. A true replacement system has not yet been found, as all of the widely touted systems for Cr replacement seem to give marginal corrosion protection when examined carefully in full qualification test and outdoor exposure. II. Alternates Previously Considered for Chromates Almost everything including the veritable “kitchen sink” has been tried for chromate replacement in coatings systems. (See www.corrdefense.org/ReferenceLibrary.aspx and www.serdp.org/ websites for further details as to the many studies on different methods and materials for chromate replacement that have been funded by the US DOD, DOE and EPA,) Also pertinent is an interesting analysis by Sinko5 of all of the organic and inorganic inhibitors examined for Cr replacement. Kendig and Buchcheit6 give a review of the many failed studies attempts at true chromate replacement in protecting aerospace alloys. Frankel and co-workers have done an extensive study of why chromates succeed so well at the corrosion protection of Al alloys, and have concluded that they function uniquely as anodic and cathodic inhibitors at very low concentrations in electrolyte solutions, especially those with Cl- ions that cause so many problems for Al substrates. So, before MgRP technology described below, many chromate replacement materials have been studied, but none have been chosen. That is to say, no Cr-free coatings system with no Cr in pretreatment, primer or topcoat has succeeded in passing all of the extensive qualification and field tests of developed for testing and qualifying earlier and present generation of chromate coatings. The ones that have been chosen temporarily have been withdrawn, as occurred with some Cr-free coatings used with the F-15. III.
Mg-rich Primer Technology
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A. System Description and Past Technical Studies In the 2000 time frame, the design hypothesis of the Mg-rich primer was conceived and then developed into a proven aircraft coating system. The design hypothesis was developed by reasoning by analogy to the formulation of Zn-rich primer coatings for the protection of steel. The testing of this hypothesis became feasible when it was realized that particulate Mg powder was available. Subsequent experiments rapidly proved that ; which allowed active metal sacrificial protection of Al and its alloys. The original work at NDSU had as its motivation protecting of commonly used aircraft Al alloys while simultaneously eliminating the use of chromate-based pretreatments and chromate pigments. Aircraft Al alloys, whose high strength is based on phase separated intermetallic compounds within the bulk alloy, have proved notoriously resistant to efforts to develop corrosion protective (pretreatment + coating) systems that do not contain any Cr., a metal whose compounds are notorious for their toxicity and carcinogenicity.12 Further, aircraft painting or refinishing/repair sites that utilize chromate -based pretreatments and coatings generate large amounts of costly hazardous waste.13 The primary goal of this Mg-rich technology was the development of a new type of primer for Al alloys and a resultant coating system that is suitable for objects whose structural components are made up of Al 2024 T-3 or other corrosion prone aluminum alloys. The system needed to be easy to apply and repair, be compatible with present aircraft topcoats14, and eliminate all use of chromate pretreatments and chromate pigments altogether if used as part the total coating system by providing cathodic protection to the alloy. In addition, cyanide and other toxic substances are also used in most methods for chromate pretreatments. The secondary goal in this study has been to chooses or develop coating matrix polymers appropriate for use with Mg and its oxidation products with an environmentally acceptable solvent formulation, so that VOC regulations were met. The development of the MgRP design hypothesis and the proof of concept work were first discussed the 2003 Roon Award Paper.15 We will paraphrase much of this paper below, but recast the major results in a form consistent with all of the later studies for our laboratories. The design characteristics of active-rich primer coatings that guided the design of Mg-rich primers are the following:16,17 1. The coating binder matrices are either organic or inorganic in nature (see ref. 16 for further discussion). 2. They are pigmented with particulate active metal, in either spherical or flake form. The metal M1 pigment should be more negative in the Galvanic series than the metal M2 substrate to be protected by the primer. See Ch. 13 and 14 of reference 18 for further details. 3. The Pigment Volume Concentration (PVC) of the M1 pigment in the coating should equal or exceed the critical PVC (CPVC) in order for the coating to properly provide sacrificial/cathodic protection to the underlying M2 substrate. [For the most up-to-date detailed discussion of the CPVC one should examine ref. 19] Under these conditions, the M1 particles are all in mutual contact as well as in electrical contact with the M2 substrate. 4. The mode of protection by these coatings is sacrificial as long as the M1 is electrically connected to the steel as the M1 is more anodic (reactive) than M2 (major constituent of steel) in the electrochemical series. Then the M1 oxides formed in the sacrificial oxidation sometimes fill damaged areas and also sometimes passivate the M2 surface by their basic nature. There is some evidence that the electrical connectivity of the M1 particles carries over from the PVC = CPVC (circa 60-70% by
44
volume) to PVC = Volume Percolation Threshold20 for Zn (~30% by volume for spherical particles), so some sacrificial protection occurs over this range even while the M1 is being consumed by sacrificial oxidation. The percolation threshold for flake pigments may be different, usually lower, than spherical pigments depending on particle alignment.21 5. The organic or inorganic matrix of the coating must be stable under the basic environment created by the M1 oxide, hydroxide, etc, formed from the oxidation of M1 in the presence of electrolyte. It must also adhere well to the M2 and be stable in a corroding environment. 6. These primer coatings must be top-coated to function properly and have a long field lifetime. When used properly, these primers provide almost as much protection to steel as a layer of the pure M1, such as galvanizing. With a topcoat, they provide both barrier and damage (sacrificial/cathodic) protection to steel substrates, and most of the oxidation of M1 goes to the protection of M2. Work in this lab and many others22 has shown that satisfactory corrosion protection has not been available for Al 2024 T-3 without the use of chromates. Many alternate options for protecting this alloy have been considered by this lab and others, including plasma polymer layers23 and conducting polymers24, 25,26 It should be noted here that much of the older airfleet such as the KC-135 was built with a pure Al cladding layer over the Al 2024 T-3 because of the sensitivity of the underlying alloy to corrosion. The classing is a relatively soft material and provides no structural support to the system. As these aircraft have aged and been repainted several times, the cladding layer has been almost worn off due to the abrasiveness of the paint stripping processes. In itself, the cladding layer is an important component to the total aircraft skin corrosion protection due to its much lower corrosion rate vs. the underlying alloy. Thus, as the aircraft age, their corrosivity increases. Because of the availability of particulate Mg appropriate for use as a pigment in coatings,18 it was decided to examine the possibility of designing Mg-rich coatings that would protect Al 2024 T-3 in a manner analogous to Zn-rich primers protecting iron alloys (steel). There were two confounding features of considering Mg for cathodic protection of Al versus Zn for cathodic protection of Fe. The first was that particulate Mg can be a fire hazard, but this concern was alleviated by the manner in which Mg pigment was delivered by Eckarta. This particulate Mg has a thin oxide layer that stabilizes it against further oxidation. Eckart GmBH, ECKA™ metallic magnesium powder produced from p-magnesium 99.95 % to (Deutsches Institut für Normung) DIN 17800 part-7 standards with Mg content@ 96% and MgO (magnesium oxide) content @ 4%. The second concern was that the oxidation products of Mg, MgO and its various hydroxides in hydrated form, would create such basic conditions that Al would undergo basic corrosionb as is indicated in its Pourbaix diagram.18 Fe is mostly passive under basic conditions, so this is not a valid consideration for Zn over steel. The natural Mg oxidation products do not yield a pH high enough to corrode and dissolve Al, so this concern was also alleviated. The relative corrosion protection capacity for cathodic protection of an Mg-rich system vs. a Zn-rich system may be calculated as follows: Assume 60% by volume of coating in each case; Area =A a
Eckart GmBH, Kaiserstrasse 30, Furth D-90763, Germany The primer binder was a two component epoxy-polyamide based on Epon®1001CX and Ancamide® 2353 mixed at stoichiometric ratios
b
55
Assume 3mil coating = 75 um thicknness = τ ((Capacity/unit area)/ (Capacity/unit area)) (Mg/Zn) = (moles Mg/area)/ (moles Zn/area) Where the density, ρ, and AtWt of the metals are ρZn = 7.14, AtWtZn = 65.38; ρmg = 1.74, AtWt mg = 24.32 Moles Mg/unit area = mass/Equil Wt = ρMg *τ*unit area/ (24.32/2) = 1.74*τ*A/ (24.32/2) = (moles Mg/ area)/ (moles Zn/ area) = (ρMg*τ*A/AtWtMg/2)/ (PZn*T*A/AtWtZn/2) = (ρMg*AtWZn)/ (ρZn*AtWtMg) Capacity Mg/Capacity Zn = (1.7*65.38)/ (7.14*24.32) = 111.146/173.645 = 0.64 Relative Capacity Mg-rich coatings vs. Zn at equal PVC’s and Thicknesses = 0.64 Mg-rich coatings should be applied at ~ 1.5 times the film thicknesses of Zn-rich for equal electrochemical equivalents of protection if total charge yielded by the primer film is the appropriate measure of capacity. B. Recent Results in Verification of Corrosion Protection of Al Alloys by Mg-rich Primer Technology We have published a considerable number of refereed articles (currently 18 peer reviewed journal articles published or accepted for publication) on the characterization of MgRP technology in the laboratory and demonstrated by numerous objective and subjective evaluations that the MgRP technology. If electronically published presentations made at technical meetings are also counted (for example, a SciFinder Scholar™ search through Chemical Abstracts Services), there are 27 accessible publications on this technology, and three patents. Appendix C contains all of this extended set of references. The original paper15 provided mainly visual observation results from exposure testing and EDAX/XRD analysis of the oxidation products of the Mg pigments with some initial OCP data. The subsequent papers extended the simple OCP measurements to include potentiodynamic scans,27,28 galvanic coupling experiments,29 scanning vibrating electrode technique (SVET) measurements,30scanning electrochemical microscopy (SCECM),31 further exposure measurements with electrochemical impedance spectroscopy (EIS) and electrochemical noise methods (ENM).32,33 In addition, we have been several publications that discuss scanning probe methods for studying MgRP systems,34 multiple analytical methods29,35,36 and general methods describing the behavior of these unique coatings.37,38 There are a considerable number of unpublished results involving testing of the MgRP system in almost every type of exposure environment except for a complete aircraft test.39 According to information provided to us by the DOD, there are up to 100 doors, port-hole covers, and other small parts on the exterior of aircraft coated with the MgRP system that are performing in a more than satisfactory manner in use. There are also may panels on outdoor exposure at varyng test sites including Daytona Beach, FL, and in all cases, the MgRP systems performed in an excellent manner. C. Further Laboratory Testing 1. Simulated Aircraft Structures testing Simulated Aircraft Structures (SAS boxes), a construct developed at WPAFB for testing of corrosion protection emulating an entire aircraftc, were subjected to accelerated c
SAS is the acronym for Simulated Aircraft Structure. When an airman goes through Aircraft Structural Maintenance technical school for training they build one of these over the course of the training. Many of the lab personnel at WPAFB had to make one in their training. As 66
weathering for 3000 hours and characterized by Electrochemical Impedance Spectroscopy (EIS) and visual evaluation. Based on drawings provided by AFRL, the side with the rivets was identified as the AA2024 T3 and the one with the machine screws the AA 7075 T6. The surfaces are generally in good condition (Figure 1) and the rows of fasteners are relatively undamaged in both sides. Looking at the salt deposits/corrosion-oxidation products on the various rows, it appears that one kind of the fasteners is more reactive than others. This was concluded after looking at the salt deposit, even if the coating is not visibly degraded. Sealed fasteners are still in good conditions with limited bubbles (Figure 2).
AA2024 T3 side
AA7075 T6 side
Figure 1: Lateral views of SAS 741 Sys I
far as instructions for their construction, one might be able to get the plans from someone at the training school in Pensacola. The problem is tech school is taught in blocks and one makes the pieces one by one then assembles them over the time at the training course. The SAS design used in these studies was made from taking an old one apart and duplicating the parts. The original was modified to fit the needs of the demonstration study.
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Figure 2: Locations of the sealed fasteners The side with the machine screws showed some blisters along the edges and near one of the screws, as shown in Figure 3. All the other screws locations do not show any degradation.
Figure 3: Details of the machine screw side The bottom side (FIG 4) present localized rusted spots on one location, the topcoat is lifted on the spots and some red rust is visible. The box was not opened to check the inside and the rest of the surface did not present any visible sign of degradation
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Figure 4: bottom side, entire view (left) and particular (right) SAS 741 SYS K
Figure 5: Lateral view of SAS system K Sys K presents the same patterns shown by the system I. As seen in the other system, one row of fastener appears to be more active of the others, but, again, the coating does not appear to be visibly degraded. The sealed fasteners on the 2024 (Fig 6) side present the same features seen on the system I.
Figure 6: 2024 T3 side of SYS K
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On the other side, where the machine screws were used to seal the structure, some blisters can be seen around the fasteners and the feature seems to be the same seen in the other system, Figure 7
Figure 7: 7075 T6 side of SYS K In Figure 8 the bottom side of the Sys K is shown and it can be noted that there is one spot of red rust as seen in the other system. The rest of the coating does not show sign of degradation.
Figure 8: Bottom side of Sys K 2. Electrochemical data EIS was performed on both of the sides of the SAS boxes and the experimental set u[p for these measurements are shown in Figure 9. This data is reported elsewhere.39 The open circuit potential (OCP) is measured to assess the presence of the cathodic protection on the side where the Mg rich coating is used. We did not know which side was coated with the Mgrich primer and therefore the OCP was measured on all the four sides. Data were acquired on 4 locations and the data are summarized in one plot, OCP vs. |Z|. This type of graph gives an immediate representation of the situation of the 4 sides that were tested with EIS.
10 10
Figure 9: EIS performed on two sides of the SAS boxes
Comparing the two sides, the AA 2024 T-3(B) side in both the boxes shows slightly better performances, being the OCP lower and the Z slightly higher. System I present one of the sides in almost starting condition and the other at the substrate level. System K presents same trends. 0.0
-0.2
KA IA
OCP (V)
-0.4
-0.6
KB
IB
-0.8
-1.0 0.0
2.0x10
5
4.0x10
5
5
6.0x10
|Z|@0.01 Hz
Figure 10: OCP vs |Z|at 0.01Hz plot 2. SEM data on exposed particles
In figure 10 it is represented a SEM micrographic image of a Mg rich primer exposed for 15 days in dilute Harrison’s solution. SEM is a very useful tool to understand the formation of corrosion products for this type of coating system.
11 11
A thick layer, at the CPVC of the system, was left in immersion with the objective to see where the products were formed and to better understand the mode of degradation. It can be noted that the majority of the oxides/hydroxides are formed on the surface and localized areas are present through the layer. This confirms our findings, published in Corrosion Science (ref) where the formation of a protective layer was observed on the surface of a nontopcoated primer.
Figure 11: SEM image of a cross section of a thick Mg rich primer layer on Al 2024 T3 exposed for 15 days in DHS. In figure 11 a topcoated system is represented before exposure and after 5090 hours. The system is slightly below the CPVC of the system.
12 12
a)
b)
Figure 12: SEM image of a cross section of Mg rich primer with topcoat on Al 2024 T3. a)unexposed, b) after 5090 hours After 5090h it can be noted that the topcoat lost some thickness and the Mg particulate ig generally degraded. Interesting feature is the shape of the remaining Mg, that is evidenced in figure 12. From the figure it is clear that the particle is no more compact but the particular shape might allow electronic contact. It is worth noticing that this method analyses a 3dimentional network using 2 dimensional pictures, and contact between particles is very probable in the depth of the sample. Fig 13 represents the EDAX analysis of the areas represented with squares in figure 12.
13 13
Figure 13: particular of one of the Mg particles and three areas studied with EDAX for chemical composition
1)
2)
Figure 14: EDEX analysis of the chemical composition of area #1 (left) and #2 (right)
14 14
Figure 15: EDEX analysis of the chemical composition of area #3 3. XPS data on pure Mg
The surface of the Mg granulate is composed by Oxygen, and Carbon
O1s
Mg 2p
Intensity (arb. units)
C1s
535
530
295 290 285 280
55
50
Binding Energy (eV)
Figure 16 Surface Composition of pure Mg granulate. Note: The Y scale for different elements is different
15 15
60 50
O C Mg
Atom%
40 30 20 10 0
0
20
40
60
80
100
120
140
Depth (nm)
Figure 17. Depth Profile of Composition from XPS IV.
Further Development Studies In MgRP Technology
A. Potential System Design Concerns from User Point of View The perceptions of a coating system as viewed by a university basic R&D laboratory (NDSU’s Coatings/Corrosion Research Center) and by a coatings company (ANAC) and the potential users of the coating (the DOD) may all be different. As discussed above, the proof of concept and extensive direct coating development activities had been achieved by NDSU and documented in many basic and applied research publications. But to ANAC, many design and performance issues remained to be treated before the user community would treat the system as a complete replacement for present chromate-based technology. The film roughness due to the particle size of the Mg pigments here-to-fore available was considered a problem, while NDSU had not considered this a concern. These issues have been resolved by ANAC dealing directly with the pigment manufacturer (ECKA Granules) in a manner unavailable to a university. Pigment grade materials satisfactory for commercial use have been developed, and surface textures of the primer formulations under study are now deemed satisfactory by ANAC and its potential customers. ANAC has developed safe handling methods for the Mg-rich primer and its manufacture based on its own work and a risk assessment performed by an outside company (details are available from ANAC care of one of the authors of this paper, Roger Brown). The primary safety concern identified by everyone involved is keeping the particulate Mg dry and out of contact with water in storage and production before it is incorporated into the solvent and polymer system of choice. As this is an organic solvent-based coating technology, the primary safety concerns are the dangers of solvent handling, the same concerns as the present technology. No new safety concerns exist for the user vis a vis the present solvent epoxy chromate system, and a lot fewer toxicity issues, or course, are present for the user in application and use. B. Examination of the Fully Formulated MgRP Technology for US DOD as User The coating system was taken by ANAC and a technology prototype MgR primer was developed with military aircraft as the target use. The test protocols used to evaluate this coating were those of the Mil-P23377. The additional data obtained by EIS, OCP and ENM measurements as well as local electrochemical measurements are detailed in the publications 16 16
of the NDSU laboratory.27,28,30, 35,36,37 There have been two tests in the MIL-P-23377 protocol that have proved somewhat problematical in the early generations of the MgRP technology. These are constant immersion and ASTM B117 Continuous Neutral Salt Spray, especially without a top-coat, but also sometimes with a top-coat. We hope we now have everyone involved understanding that a Mg-rich primer near or above the CPVC will somehow have water in contact with a Mg pigment particle if it is not topcoated, as it is designed to be used. Identifying something as a primer, as we have consistently done, implies that it is to be used with a topcoat. [Many of the MIL-P-23377 requirements go beyond primer specifications when used with Chromate pigments and are really for a single coat system for topcoat use on interiors, and have invalidly been applied to the MgRP technology. The Navy for some time has recommended that the MIL-P-23377 primer be used with a second coat on interior.] None-the-less, the early generation MGRP system shows some early blistering at 500 hrs in B117. This is most likely some random hydrogen generation when water gets into void next to a Mg pigment particle from constant immersion or the constant wetting at 37oC of the B117. This is show in Figures 18, 19 and 20 along with the resistance to this effect in the most current generation of the MgRP technology from the ANAC lab.
Previous generation MgRP over PreKote
Improved MgRP over PreKote
Figure 18. Improved MgRP formulation versus previous generation MgRP, 2000 hours ASTM B117 Neutral Salt Spray, 2024-T3 over non-chromate Pretreatment
17 17
Previous generation MgRP over PreKote
Improved MgRP over PreKote
Chromate Primer over CCC
Negative Control over PreKote
Figure 19. 2000 Hours ASTM Neutral Salt Spray: Topcoat: Aerodur 5000, Substrate: 2024-T3
Topcoated MgRP System
Topcoated Chromate System
Figure 20. Newest Generation MgRP formulation over PreKote versus chromate primer over CCC, 2000 hours ASTM B117 Neutral Salt Spray on 2024-T3 Exposure at various exterior test sites such as Key West, and beach exposure at Daytona Beach has shown the topcoated MgRP system to give excellent performance (> 3 years).. ? 18 18
We did not observe corrosion in the scribe area during this test This is shown clearly in the Figure 21, below. Competitive Fully Chromated System
Competitive Fully Chromated System
2100P003
2100P003
2000 hours B117, Aerodur 5000 topcoat, PreKote treated 2024-T3 Competitive Fully Chromated System
Competitive Fully Chromated System
2100P003
2100P003
2000 hours B117, Aerodur 5000 topcoat, PreKote treated 2024-T3, Stripped Panels Figure 21. Chromated and MgRP systems with no chromates: Coated and Stripped Systems At NDSU, the cyclic exposure of the ASTM D 5894-96 Test Protocol, see Figure 22, has been used to study the topcoated MgRP system, and we have seen no failures of any type below 4800 hours and have seen some systems exceed 10,000 hours (see Fig. 23)
19 19
Prohesion Exposure for Even Weeks (ASTM D 5894-96): fog/dry cycle • 1 hour fog @ 25ºC [0.05% NaCl & 0.35% (NH4)2SO4] • 1 hour dry @ 35ºC
QUV Exposure for Odd Weeks (ASTM D 5894-96): UV/condensation cycle • 4 hour UV-A light @ 60ºC • 4 hour condensation @ 50ºC
Certain Period of Time
Every Week Physical Property Measurements
• Gloss @ 20º, 60º, & 85º • Color • Contact Angle/Surface Energy Electrochemical Investigation
• Noise (ENM) • Impedance (EIS)
Topography & Roughness Analyses: Atom Force Microscopy (AFM)
Certain Period of Time
Spectroscopic Studies • Raman Spectroscopy/ Imaging • Photoacoustic Spectroscopy (PAS) • FT-IR Microscope Mapping Process continues until panels show significant difference in corrosion protection
Surface Appearance Assessment
Figure 22. Test Protocol Used at NDSU for Examining Aircraft & Vehicle Coatings
Figure 23. A, B, C and D - Prohesion™ (ASTM D5894-96) results for Al 2024 T-3 panels using NDSU Mg-Rich primer Hybrid N3300 at 50% PVC with topcoat at A) 0-hrs.; B) 1,200 hrs.; C) 3,000-hrs.; 4,800-hrs exposure. All other components of the military test protocols have been met including mechanical performance, solvent resistance, and chemical resistance.
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V. Discussion of Results Many experiments at a local and global scale have shown that the Mg-rich primer technology give corrosion protection in an aircraft coating system the equals or exceeds the present chromate-based system. The use of Mg-rich primer technology has been unequivocally shown to be the only totally chromium metal-free corrosion control system that provides equivalent or better corrosion mitigation to the presently used chromate pretreatment + chromate pigmented primer technology. With no need for a pretreatment beyond good cleaning or a proven no-chromate pretreatment like Pre-Kote™ and Mg-rich primer cathodic protection of aerospace alloy + a standard aerospace PUR topcoat, a coating system is evolving that will give increased corrosion protection without the frightful ecological cost of chromate use now presently required. Open Circuit Potential 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 hours of cyclic exposure for Mg-rich primers with good aerospace topcoats. Further, the possibility of Mg pigments acting as active oxygen traps drastically reducing oxygen transport to the surface underneath an undamaged topcoat may also be occurring, and this is currently under investigation. All data indicates that the Mg-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 used 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.. The newest generation work by ANAC has yielded Magnesium reaction controlled formulations now in place which produce acceptable results in accelerated testing. Current ANAC developed formulation maintains the corrosion properties which were the basis of the initial interest in the technology. Current formulation in total non-chrome MgRP systems outperform chromate standards in all accelerated testing protocols. Smaller particle size provides uniform smooth primer coatings for topcoat. Physical properties of developed coating meet military specificaions such as MIL-PRF-23377. Product performance has been consistent between multiple lab, scale up, and production batches If an acceptance of the difference in protection modes between toxic chromate systems and the MgRP protection system is accepted and taken into consideration in the testing of the system, and direct or continuous immersion in an aqueous electrolyte, and thus H2 generation from the Mg pigment is avoided, all quantitative lab data and field testing indicate that the MgR system can be used to provide protection equivalent or better that now achieved. Even this issue is now moot as ANAC has modified the system so even this is not occurring The possibility in these primer films, that even when a given Mg particle is not electrically connected to other Mg pigments because of surface oxidation of the Mg particle, the Mg can still act as an O2 sequestrant when activiated by the presence of moisture acting as an extremely good O2 barrier may explain why these films inhibit corrosion even after no measurable cathode protection is shown. This is now under investigation. Other work ongoing is to define testing and correlation factors to accurately predict the service life of MgRP based coating systems on aircraft. While results are excellent on 2047, 7075, steel,
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and composite, many other alloys remain to be evaluated with the technology in the aerospace context.
Acknowledgements: The work in this paper was mainly supported by AFOSR through a series of Grant given to NDSU from 1996- 2007. Also, some of this work was supported by AFRL, Materials Laboratory at WRAFB under the title “Durable Hybrid Coatings” and support from the State of North Dakota Center for Surface Protection – Center of Excellence. Appendix C. Complete set of all Electronically Searchable Publications and Presentations on Mg-rich Primer Technology 1, Use of magnesium alloys as pigments in magnesium-rich primers for protecting aluminum alloys. Xu, H.; Battocchi, D.; Tallman, D. E.; Bierwagen, G. P.. Coatings and Polymeric Materials Department, North Dakota State University, Fargo, ND, USA. Corrosion (Houston, TX, United States) (2009), 65(5), 318-325. Publisher: NACE International, CODEN: CORRAK ISSN: 0010-9312. Journal written in English. AN 2009:558807 CAPLUS (Copyright (C) 2009 ACS 2,Transmission line modeling of EIS data for a Mg-rich primer on AA 2024-T3. Allahar, K. N.; Battocchi, D.; Bierwagen, G. P.; Tallman, D. E. Coatings and Polymeric Materials Department, North Dakota State University, Fargo, ND, USA. ECS Transactions (2008), 13(27), 61-76. Publisher: Electrochemical Society, CODEN: ECSTF8 ISSN: 1938-5862. Journal; Computer Optical Disk written in English. AN 2009:241647 CAPLUS (Copyright (C) 2009 ACS on SciFinder (R)) 3. Sol-gel coatings on metals for corrosion protection. Wang, Duhua; Bierwagen, Gordon. P.. Department of Coatings and Polymeric Materials, North Dakota State University, Fargo, ND, USA. Progress in Organic Coatings (2009), 64(4), 327-338. Publisher: Elsevier B.V., CODEN: POGCAT ISSN: 0300-9440. Journal written in English. AN 2009:227790 CAPLUS (Copyright (C) 2009 4. Assessment of the corrosion protection of aluminium substrates by a Mg-rich primer: EIS, SVET and SECM study. Simoes, Alda; Battocchi, Dante; Tallman, Dennis; Bierwagen, Gordon. ICEMS, Department of Chemical and Biological Engineering, IST, Technical University of Lisbon, Lisbon, Port. Progress in Organic Coatings (2008), 63(3), 260-266. Publisher: Elsevier B.V., CODEN: POGCAT ISSN: 0300-9440. Journal written in English. AN 2008:1137776 CAPLUS 5. Modeling of Electrochemical Impedance Data of a Magnesium-Rich Primer. Allahar, Kerry N.; Battocchi, Dante; Orazem, Mark E.; Bierwagen, Gordon P.; Tallman, Dennis E. Department of Coatings and Polymeric Materials, North Dakota State University, Fargo, ND, USA. Journal of the Electrochemical Society (2008), 155(10), E143-E149. Publisher: Electrochemical Society, CODEN: JESOAN ISSN: 00134651. Journal written in English. CAN 149:535871 AN 6. Studies of Electron Transfer at Aluminum Alloy Surfaces by Scanning Electrochemical Microscopy. Jensen, Mark B.; Guerard, Audrey; Tallman, Dennis E.; Bierwagen, Gordon P.. Department of Chemistry, Concordia College, Moorhead, MN, USA. Journal of the Electrochemical Society (2008), 155(7), C324C332. Publisher: Electrochemical Society, CODEN: JESOAN ISSN: 0013-4651. Journal written in English. CAN 149:233760 AN 2008:664638 7. The physical chemistry of organic coatings revisited-viewing coatings as a materials scientist. Bierwagen, Gordon. Department of Coatings & Polymeric Materials, Center for Surface Protection, North Dakota State University, Fargo, ND, USA. Journal of Coatings Technology and Research (2008), 5(2), 133-155. Publisher: Springer, CODEN: JCTRCP Journal; General Review written in English. CAN 150:308311 AN 2008:513906 CAPLUS (Copyright (C) 2009 ACS on SciFinder 8. The development of a two-component, magnesium-rich primer for controlling corrosion of a aluminum alloys. Li, Jun; He, Jie; Chisholm, Bret J.; Berry, Missy; Battocchi, Dante; Bierwagen, Gordon P.. Center for Nanoscale Science and Engineering, North Dakota State University, Fargo, ND, USA. Proceedings of
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the International Waterborne, High-Solids, and Powder Coatings Symposium (2007), 34th 115-130. Publisher: University of Southern Mississippi, Dep. of Polymer Science, CODEN: PIWCF4 Journal written in English. AN 2008:433201 CAPLUS (Copyright (C) 2009 ACS on SciFinder (R)) 9. Studies of electron transfer at aluminum alloy surfaces by scanning electrochemical microscopy. Jensen, M. B.; Bjordahl, T. J.; Tallman, D. E.; Bierwagen, G. P.. Department of Chemistry, Concordia College, Moorhead, MN, USA. ECS Transactions (2007), 3(31, Critical Factors in Localized Corrosion 5), 545-555. Publisher: Electrochemical Society, CODEN: ECSTF8 ISSN: 1938-5862. Journal; Computer Optical Disk written in English. CAN 149:430253 AN 2008:341950 CAPLUS (Copyright (C) 2009 ACS on SciFinder (R)) 10. A combinatorial/high-throughput workflow for the development of hybrid organic-inorganic coatings. Chisholm, Bret J.; Berry, Missy; Bahr, James; He, Jie; Li, Jun; Balbyshev, Seva; Wang, Duhua; Bierwagen, Gordon P.. The Center for Nanoscale Science and Engineering, Department of Coatings and Polymeric Materials, North Dakota State University, Fargo, ND, USA. ICE 2007, International Coatings Expo: CleanLean-Green: Innovative Solutions for the Global Coatings Community, Toronto, ON, Canada, Oct. 3-5, 2007 (2007), 69/1-69/42. Publisher: Federation of Societies for Coatings Technology, Blue Bell, Pa CODEN: 69KFKA Conference; Computer Optical Disk written in 11. The physical chemistry of organic coatings revisited-viewing coatings as a materials scientist. Bierwagen, Gordon. North Dakota State University, Fargo, ND, USA. ICE 2007, International Coatings Expo: Clean-Lean-Green: Innovative Solutions for the Global Coatings Community, Toronto, ON, Canada, Oct. 3-5, 2007 (2007), 54/1-54/37. Publisher: Federation of Societies for Coatings Technology, Blue Bell, Pa CODEN: 69KFKA Conference; Computer Optical Disk written in English. 12. Corrosion protection of aluminium substrates by a Mg-rich primer studied using electrochemical scanning techniques. Simoes, Alda M.; Battocchi, Dante; Tallman, Dennis E.; Bierwagen, Gordon P.. Technical University of Lisbon/ICEMS, Port. ICE 2007, International Coatings Expo: Clean-Lean-Green: Innovative Solutions for the Global Coatings Community, Toronto, ON, Canada, Oct. 3-5, 2007 (2007), 39/1-39/14. Publisher: Federation of Societies for Coatings Technology, Blue 13. Assessing the role of magnesium in magnesium rich coatings. DeRosa, Rebecca L.; Szabo, Istvan; Battocchi, Dante; Bierwagen, Gordon P.. Alfred University, Alfred, NY, USA. ICE 2007, International Coatings Expo: Clean-Lean-Green: Innovative Solutions for the Global Coatings Community, Toronto, ON, Canada, Oct. 3-5, 2007 (2007), 37/1-37/18. Publisher: Federation of Societies for Coatings Technology, Blue Bell, Pa CODEN: 69KFKA Conference; Computer Optical Disk written in English. AN 2007:1479912 CAPLUS (Copyright (C) 2009 ACS on SciFinder (R)) 14. Magnesium-rich primers for chromate-free protective systems on Al 2024 and Al 7075. Battocchi, D.; Bierwagen, G.; Stamness, A.; Tallman, D.; Simoes, A. North Dakota State University, USA. European Federation of Corrosion Publications (2007), 54(Innovative Pre-Treatment Techniques to Prevent Corrosion of Metallic Surfaces), 63-70. Publisher: Woodhead Publishing Ltd., CODEN: EFCPE4 ISSN: 1354-5116. Journal written in English. CAN 148:219340 AN 2007:1225909 CAPLUS (Copyright (C) 2009 ACS on SciFinder (R)) 15. SVET and SECM imaging of cathodic protection of aluminum by a Mg-rich coating. Simoes, A. M.; Battocchi, D.; Tallman, D. E.; Bierwagen, G. P.. ICEMS/Chemical Engineering Department, Instituto Superior Tecnico, Lisbon, Port. Corrosion Science (2007), 49(10), 3838-3849. Publisher: Elsevier Ltd., CODEN: CRRSAA ISSN: 0010-938X. Journal written in English. CAN 148:481641 AN 2007:1041288 CAPLUS (Copyright (C) 2009 ACS on SciFinder (R)) 16. Scanning probe studies of active coatings for corrosion control of Al alloys. He, Jie; Battocchi, Dante; Simoes, Alda M.; Tallman, Dennis E.; Bierwagen, Gordon P.. Departments of Chemistry and Molecular Biology, North Dakota State University, Fargo, ND, USA. ACS Symposium Series (2007), 962(New Developments in Coatings Technology), 8-23. Publisher: American Chemical Society, CODEN: ACSMC8 ISSN: 0097-6156. Journal written in English. CAN 149:154803 AN 2007:888483 CAPLUS (Copyright (C) 2009 ACS on SciFinder (R)) 17. The use of multiple electrochemical techniques to characterize Mg-rich primers for Al alloys.
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Bierwagen, Gordon; Battocchi, Dante; Simoes, Alda; Stamness, Anthony; Tallman, Dennis. Department of Coatings and Polymeric Materials, North Dakota State University, Fargo, ND, USA. Progress in Organic Coatings (2007), 59(3), 172-178. Publisher: Elsevier B.V., CODEN: POGCAT ISSN: 0300-9440. Journal written in English. CAN 148:587494 AN 2007:652202 CAPLUS (Copyright (C) 2009 ACS on SciFinder (R)) 18. The application of combinatorial/high throughput methods to the development of hybrid organicinorganic coatings for the protection of aluminum alloys. Chisholm, Bret J.; Berry, Missy; Bahr, James; He, Jie; Li, Jun; Battocchi, Dante; Bierwagen, Gordon P.. The Center for Nanoscale Science and Engineering, North Dakota State University, Fargo, ND, USA. Polymer Preprints (American Chemical Society, Division of Polymer Chemistry) (2007), 48(1), 143-144. Publisher: American Chemical Society, Division of Polymer Chemistry, CODEN: ACPPAY ISSN: 0032-3934. Journal; Computer Optical Disk written in English. CAN 148:240946 AN 2007:334873 CAPLUS (Copyright (C) 2009 ACS on SciFinder (R)) 19. The application of combinatorial/high-throughput methods to the development of hybrid organicinorganic coatings for the protection of aluminum alloys (2024-T3). Chisholm, Bret J.; Berry, Missy; Bahr, James A.; He, Jie; Li, Jun; Battocchi, Dante; Bierwagen, Gordon. Center for Nanoscale Science and Engineering, North Dakota State University, Fargo, ND, USA. Abstracts of Papers, 233rd ACS National Meeting, Chicago, IL, United States, March 25-29, 2007 (2007), POLY-393. Publisher: American Chemical Society, Washington, D. C CODEN: 69JAUY Conference; Meeting Abstract; Computer Optical Disk written in English. AN 2007:298472 CAPLUS (Copyright (C) 2009 ACS on SciFinder (R)) 20. The development of a combinatorial/high-throughput workflow for hybrid organic-inorganic coating research. Chisholm, Bret J.; Berry, Missy; Bahr, James A.; He, Jie; Li, Jun; Bonitz, Verena; Bierwagen, Gordon. Center for Nanoscale Science and Engineering, North Dakota State University, Fargo, ND, USA. Abstracts of Papers, 233rd ACS National Meeting, Chicago, IL, United States, March 25-29, 2007 (2007), POLY-132. Publisher: American Chemical Society, Washington, D. C CODEN: 69JAUY Conference; Meeting Abstract; Computer Optical Disk written in English. AN 2007:298212 CAPLUS (Copyright (C) 2009 ACS on SciFinder (R)) 21. Comparison of testing solutions on the protection of Al-alloys using a Mg-rich primer. Battocchi, D.; Simoes, A. M.; Tallman, D. E.; Bierwagen, G. P.. Department of Coatings and Polymeric Materials, North Dakota State University, Fargo, ND, USA. Corrosion Science (2006), 48(8), 2226-2240. Publisher: Elsevier Ltd., CODEN: CRRSAA ISSN: 0010-938X. Journal written in English. CAN 146:233534 AN 2006:728799 CAPLUS (Copyright (C) 2009 ACS on SciFinder (R)) 22. Chromate-free corrosion protection of Al alloys by metal-rich coatings based on Mg pigments. Bierwagen, Gordon P.; Battocchi, Dante; Tallman, Dennis E. Department of Coatings & Polymeric Materials, North Dakota State University, Fargo, ND, USA. Abstracts, 38th Central Regional Meeting of the American Chemical Society, Frankenmuth, MI, United States, May 16-20 (2006), CRM-017. Publisher: American Chemical Society, Washington, D. C CODEN: 69ICV2 Conference; Meeting Abstract written in English. AN 2006:436080 CAPLUS (Copyright (C) 2009 ACS on SciFinder (R)) 23. SVET investigations of protection mechanism of Mg-rich primer on Al 2024. Battocchi, Dante; Bierwagen, Gordon P.; Tallman, Dennis E.; He, Jie. Polymers and Coatings Department, North Dakota State University, Fargo, ND, USA. Surface Engineering, Proceedings of the International Surface Engineering Congress, 3rd, Orlando, FL, United States, Aug. 2-4, 2004 (2005), Meeting Date 2004, 14-17. Publisher: ASM International, Materials Park, Ohio CODEN: 69IAXW Conference written in English. CAN 146:208032 AN 2006:372335 CAPLUS (Copyright (C) 2009 ACS on SciFinder (R)) 243 Electrochemical behaviour of a Mg-rich primer in the protection of Al alloys. Battocchi, D.; Simoes, A. M.; Tallman, D. E.; Bierwagen, G. P.. Department of Coatings and Polymeric Materials, NDSU, Fargo, ND, USA. Corrosion Science (2006), 48(5), 1292-1306. Publisher: Elsevier Ltd., CODEN: CRRSAA ISSN: 0010-938X. Journal written in English. CAN 145:219729 AN 2006:361939 CAPLUS (Copyright (C) 2009 ACS on SciFinder (R)) 25. New developments in Cr-free primers for aerospace alloys. Bierwagen, Gordon P.; Tallman, Dennis E.; Nanna, Michael; Battocchi, Dante; Stamness, Anthony; Gelling, Victoria Johnston. Department of Polymers and Coatings, North Dakota State University, Fargo, ND, USA. Abstracts of Papers, 228th ACS National Meeting, Philadelphia, PA, United States, August 22-26, 2004 (2004), POLY-238. Publisher:
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American Chemical Society, Washington, D. C CODEN: 69FTZ8 Conference; Meeting Abstract written in English. AN 2004:660700 CAPLUS (Copyright (C) 2009 ACS on SciFinder (R)) 26. New developments in Cr-free primers for aerospace alloys. Bierwagen, Gordon; Tallman, Dennis; Nanna, Michael; Battocchi, Dante; Stamness, Anthony; Gelling, Victoria Johnston. Corrosion/Coatings Research Center, Departments of Polymers & Coatings, North Dakota State University, Fargo, ND, USA. Polymer Preprints (American Chemical Society, Division of Polymer Chemistry) (2004), 45(2), 144-145. Publisher: American Chemical Society, Division of Polymer Chemistry, CODEN: ACPPAY ISSN: 0032-3934. Journal; General Review; Computer Optical Disk written in English. CAN 142:76201 AN 2004:653308 CAPLUS (Copyright (C) 2009 ACS on SciFinder (R)) 27. Mg-rich coatings: A new paradigm for Cr-free corrosion protection of Al aerospace alloys. Nanna, Michael E.; Bierwagen, Gordon P.. Dept. of Polymers & Coatings, North Dakota State University, Fargo, ND, USA. JCT Research (2004), 1(2), 69-80. Publisher: Federation of Societies for Coatings Technology, CODEN: JRCEB5 ISSN: 1547-0091. Journal written in English. CAN 141:191962 AN 2004:365773 CAPLUS (Copyright (C) 2009 ACS on SciFinder (R))
References: 1
R.L.Twite & G.P.Bierwagen, “Review of Alternatives to Chromate for Corrosion Protection of Aluminum Aerospace Alloys,” Prog. Org. Coatings, 33 (1998) 91-100 2 G. Buxbaum, Editor, Industrial Inorganic Pigments, 2nd Ed. “Anticorrosive Pigments,” Ch. 5, p191, WileyVCH, New York (1998) 3 G.P.Bierwagen, R.Twite, G.Chen, & D.E.Tallman, “AFM, SEM and Electrochemical Characterization of Al Alloys, Conversion Coatings, and Primers used for Aircraft,” Prog. Organic Coatings, 32(1997) 25-30 4 L.B.Reynolds, R.Twite, M.S.Donley, G.P.Bierwagen & M. Khobaib, “ Preliminary Evaluation of the Anticorrosive Properties of Aircraft Coatings by Electrochemical Methods,” Prog. Organic Coatings, 32 (1997) 31-34 5 John Sinko, “Challenges of chromate inhibitor pigments replacement in organic coatings,” Prog. Organic Coatings 42 (2001) 267–282 6 M.W. Kendig, and R.G. Buchheit, “Corrosion Inhibition of Aluminum and Aluminum Alloys by Soluble Chromates, Chromate Coatings, and Chromate-Free Coatings,” CORROSION 59 (2003) 379 7 .R. G. Buchheit, R. P. Grant, P. F. Hlava, B. McKenzie, and G. L. Zender, J.Electrochem. Soc., 144, 2621 ~1997!. 8 G. O. Ilevbare, J. R. Scully, J. Yuan, and R. G. Kelly, Corrosion, 56, (2000)227 9 R. G. Buchheit, J. Electrochem. Soc., 142 (1995) 3994 10 William J. Clark, Jeremy D. Ramsey, Richard L. McCreery, and Gerald S. Frankel, “A Galvanic Corrosion Approach to Investigating Chromate Effects on Aluminum Alloy 2024-T3,” J Electrochem. Soc., 149 (2002) B179-B185, and other work by this group at Ohio State University 11 Wim J. van Ooij, Danqing Zhu, Vignesh Palanivel, Anna Lamar and Matthew Stacy, “The Potential of silanes for chromate replacement in metal finishing industries,” Silicon Chemistry, 3 ( 2006) 11-30 12 J. Janata, D.Baer, G.P.Bierwagen, H.Birnbaum, R. Buchheit, A. Davenport, H.Isaacs, F.Hedberg, M.Kendig,F.Mansfeld, B.Miller, A.Wieckowski, & J.Wilkes, “Issues Related to Chromium Replacement,” presented at 187th Meeting of The Electrochemical Society, May 21-26, 1995, Reno, Nevada 13 R.L.Twite, G.P.Bierwagen, “Review of Alternatives to Chromate for Corrosion Protection of Aluminum Aerospace Alloys,” Prog. Org. Coatings, 33 (1998) 91-100 14 Gordon P. Bierwagen and Dennis E. Tallman, “Choice and Measurement of Crucial Aerospace Coating System Properties,” Prog. Organic Coatings, 41 (2001) 201-217 15 M.E. Nanna, & G.P. Bierwagen, “Mg-Rich Coatings: A new Paradigm for Cr-Free Corrosion Protection of Al Aerospace Alloys,” JCT Research, 1 (2004) 69-81 16 C. Hare, “Corrosion Control of Steel by Organic Coatings,” Ch. 55 in Uhlig’s Corrosion Handbook, 2nd Edition. R. W. Review, Editor, John Wiley & Sons, New York (2000) pp.1023-1038 17 S. Felix, R. Barajas, J.M.Bastidas, M. Morcillo & S. Feliu, “Study of Protections Mechanism of Zinc-Rich paints by Electrochemical Impedance Spectroscopy,” in Electrochemical Impedance Spectroscopy, ASTM STP 1188, J.R.Scully, D.C.Silverman, & M. Kendig, eds., Amer. Soc. Testing and Materials (ASTM), Philadelphia, PA (1993) pp. 438-449 18 D. A. Jones, Principles and Prevention of Corrosion, 2nd Ed., Prentice–Hall, Upper Saddle River, NJ (1996)
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G.P.Bierwagen, R.S.Fishman, T. Storsved, & J. Johnson, “Recent Studies of Particle Packing in Organic Coatings,” Prog. Organic Coatings, 35 (1999) 1-10 20 S. Böhm, R.J. Holness, H.N. McMurray and D.A. Worsley, “Charge percolation and sacrificial protection in zinc-rich organic coatings,” Eurocorr 2000, Queen Mary and Westfield College, London, 10th-14th September 2000 21 Kalendová, A., Kuckačová, A., Macromol. Symp., 187 (2002) 377-386 22 Joseph H. Osborne, Kay Y. Blohowiak, S. Ray Taylor, Chad Hunter, Gordon P. Bierwagen, Brenden Carslon, Dan Bernard, and Michael S. Donley, “Testing and Evalation of Non-Chromated Coating Systems for Aerospace Applications,” Prog. Organic Coatings, 41 (2001) 217-225 23 H.K.Yasuda, C.M.Reddy, Q.S.Yu, J. Deffeyes, G.P.Bierwagen & L.He, “Effect of Scribing on Corrosion Test Results,” Corrosion, 57 (2001) 29-34 24 He, J., Johnston Gelling, V., Tallman, D.E., Bierwagen, G. P. and Wallace, G.G., “Conducting Polymers and Corrosion III: A Scanning Vibrating Electrode Study of Poly(3-Octyl Pyrrole) on Steel and Aluminum,” J. Electrochem. Soc., 147 (2000) 3667-3672 25 D.E.Tallman, Y. Pae, & G.P.Bierwagen, “Conducting Polymers and Corrosion 2: Polyaniline on Aluminum Alloys,” Corrosion, 56 (2000) 401-410 26 Dennis E. Tallman and Gordon P. Bierwagen, “Corrosion Protection Using Conducting Polymers,” Chapter 15 in Handbook of Conducting Polymers, Third Edition,: Conjugated Polymers-Processing and Applications, CRC Press (2006) pp. 15-1 to 15-53. 27
D. Battocchi, A. M. Simões, D. E. Tallman, G. P. Bierwagen, “Electrochemical behaviour of a Mg-rich primer in the protection of Al alloys,” Corrosion Science 48 (2006) 1292-1306 28 D. Battocchi, A.M. Simões, D.E. Tallman & G. P. Bierwagen, “Comparison of testing solutions on the protection of Al-alloys using a Mg-rich primer,” Corrosion Science 48 (2006) 2226-2240 29 D. Battocchi, G. Bierwagen, A. Stamness, A. Simoes, D. Tallman, “The Use of Multiple Electrochemical Techniques to Characterize Mg-rich Primers for Al Alloys,” Refereed Paper 06250 NACE Corrosion 2006 Conference, San Diego CA 30 A. M. Simões, D. Battocchi, D. E. Tallman and G. P. Bierwagen, “SVET and SECM examination of cathodic protection of aluminum using a Mg-rich coating,” Corrosion Science, 49 (2007) 3838-3849 31 Mark Jensen, Travis Bjordahl, Dennis E. Tallman, and Gordon Bierwagen, “Studies of Electron Transfer at Aluminum Alloy Surfaces by Scanning Electrochemical Microscopy,” , J. Electrochem. Soc., 155 (2008) C324-C332 also published in ECS Trans. 3, (31) 545 (2007) 32 Allahar, Kerry N.; Battocchi, Dante; Orazem, Mark E.; Bierwagen, Gordon P.; Tallman, Dennis E. “Modeling of Electrochemical Impedance Data of a Magnesium-Rich Primer,” J.Electrochem. Soc.,155 (2008) E143-E149. 33 Kerry.Allahar, Gordon Bierwagen Dante Battocchi and Dennis Tallman, “Transmission Line Modeling of Electrochemcial Impedance Spectroscopic Data of a Mg-rich Primer,” Submitted to Electrochmimica Acta, in review (2008) 34 Jie He, Dante Battocchi, Alda M. Simoes, Dennis E. Tallman and Gordon P. Bierwagen, “Scanning Probe Studies of Active Coatings for Corrosion Control of Al Alloys,” ACS Symposium Series 962 (New Developments in Coatings Technology), pp.8-23 (2007) Amer. Chem. Soc. 35 Gordon Bierwagen, Dante Battocchi, Alda Simões, Anthony Stamness and Dennis Tallman, “The Use of Multiple Electrochemical Techniques to Characterize Mg-rich Primers for Al Alloys,” Progress in Organic Coatings 59 (2007) 172-178 36 Simoes, Alda; Battocchi, Dante; Tallman, Dennis; Bierwagen, Gordon. “Assessment of the corrosion protection of aluminium substrates by a Mg-rich primer: EIS, SVET and SECM study,” Progress in Organic Coatings 63 (2008) 260-266. 37 D. Battocchi, G.Bierwagen, A. Stamness, D. Tallman, & A. Simões, “Magnesium-rich primers for chromatefree protective systems on Al 2024 and Al 7075,” ch. 5, pp.63-71 in Innovative Pre-treatment Techniques to Prevent Corrosion of Metallic Surfaces, L. Fedrizzi, H.Terryn & A. Simões, editors, Number 54 in European Federation of Corrosion Publications, Woodhead Publishing, Ltd., Cambridge, UK (2007) 38 Gordon Bierwagen, “The Physical Chemistry of Organic Coatings Revisited-Viewing Coatings as a Materials Scientist,” 2007 Matiello Lecture, J. Coatings Tech & Research 5 (2008) 133-155 39 Unpublished results of OSD testing coordinated by AFRL/MLB, Joel Johnson – Team Leader.
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