ICMCTF2005 Session H4: Novel Approaches to Nonchromate Corrosion Protection

Wednesday, May 4, 2005 1:30 PM in Room Royal Palm 4-6

Wednesday Afternoon

Start	Invited?	Item
1:30 PM	Invited	H4-1 Pigment Grade Corrosion Inhibitors: a Progress Review on their Chemistry and Mechanism J. Sinko (Wayne Pigment Corporation) As functional constituents of organic coatings, Pigment Grade Corrosion Inhibitors are designed to operate under atmospheric corrosion conditions. The extent of service life of high-performance (thin) organic coatings is directly determined by corrosion inhibitor pigment constituents. A brief review of fundamental aspects of the contemporary chemistry and specific properties of corrosion inhibitor pigments is presented. Generally accepted concepts are discussed on organic coatings' degradation mechanism in atmospheric corrosion conditions. A qualitative model is presented on the "inhibitor reservoir" function of pigmented organic coatings. In this context, pigment grade corrosion inhibitors' "modus operendi" in atmospheric corrosion conditions, is discussed. Demanded by environmental concerns and restricted by inherent limits of traditional inorganic chemistry, recent progress realized in corrosion inhibitor pigment synthesis, is reviewed.
2:10 PM	Invited	H4-3 Modifying the Corrosion Behavior of Active Metals by Conjugated Polymer Coatings D.E. Tallman, J. He, K. Levine, G.P. Bierwagen (North Dakota State University) Our group is exploring conjugated polymers (CPs) for corrosion control of aluminum alloys, motivated by the desire to find suitable replacements for the chromate-based coatings currently used for corrosion control of these alloys. Several unique properties of CPs distinguish them from traditional organic coatings used for corrosion control of metals. The doped (partially oxidized) form of the polymer is electronically conductive and also redox active, so interesting and potentially beneficial interactions of the polymer with the metal substrate are anticipated. One factor that limits the application of CPs as corrosion control coatings is the difficulty in casting such polymers as films or coatings. Since most common conjugated polymers (e.g., polypyrrole or polythiophene) are insoluble in environmentally friendly solvents such as water or alcohol, processibility is a key issue. In this presentation, we will first discuss several important issues surrounding the use of CPs for corrosion control. Then we will describe an approach using electron transfer mediation for the direct electrodeposition of polypyrrole films onto Al alloy. The influence of these films on the corrosion behavior of the alloy is being assessed by various scanning probe techniques, including the scanning vibrating electrode, scanning electrochemical microscopy and the scanning Kelvin probe. Results from these studies will be presented.
2:50 PM		H4-5 Non-Chromated Coating Systems for Corrosion Protection of Aircraft Aluminum Alloys N.N. Voevodin (University of Dayton Research Institute); V.N. Balbyshev, A.N. Khramov (Universal Technology Corporation); J. Johnson, R.A. Mantz (Air Force Research Laboratory) The Air Force requires the development of an environmentally compliant chromate-free aircraft coating system that meets or exceeds current corrosion protection capabilities. The current corrosion inhibition mechanism for high-strength aluminum alloys relies heavily on the use of Cr(VI) compounds which are incorporated into both the surface pretreatment and the primer. These corrosion inhibitor systems are very effective, however, Cr(VI) is a known carcinogen that is expected to be eliminated from use in the near future. To address this problem, a number of non-chromated pretreatments and primers have been independently developed over the past several years. Previous testing of non-chromate technologies has focused on either replacement of the chromate conversion coating (CCC) or the MIL-PRF-23377 chromated epoxy primer with non-chrome substitutes. Several chrome free pretreatments such as PreKote (Pantheon Chemical Corp), Boegel/AC-130 (AC Technology, Inc.), and AFRL's Self-assembled Nanophase (SNAP) coating have been developed. Test results suggest that SNAP, Boegel, and PreKote are possible effective replacements for the CCC. Complete coating systems were tested utilizing these non-chromated surface treatments and a standard chromated primer exhibiting corrosion protection equivalent to the current fully chromated system. However, these pretreatments have not been tested with the currently available chromate-free primers to evaluate the corrosion resistance. This research compares the corrosion resistance of fully chromate-free systems using UMR-Deft and PRC DeSoto EWDY048 primers. Corrosion resistance was evaluated by ASTM B117 Salt Spray, Electrochemical Impedance Spectroscopy (EIS) and ASTM D2803 Filiform corrosion resistance test. Using these results a relative performance ranking was developed. Pneumatic Adhesion Tensile testing Instruments (PATTI) measurements and impact flexibility testing were also utilized to characterize these coating systems.
3:10 PM		H4-6 Organo-Silicate Coatings with Phosphonate Functionalities for Corrosion Protection of Magnesium Alloys A.N. Khramov, V.N. Balbyshev (Universal Technology Corporation); L.S. Kasten (University of Dayton Research Institute); R.A. Mantz (Air Force Research Laboratory) New and environmentally adequate hybrid organic-inorganic protective coatings with phosphonate functionalities have been developed to improve low corrosion resistance and poor adhesion properties of magnesium alloys. The coatings have been processed via a sol-gel route by hydrolysis and condensation of alkoxy-silane precursors such as tetraethoxy-silane (TEOS) and diethylphosphonatoethyltriethoxy-silane (PHS). The effect of the organic/inorganic ratio and the processing conditions on the corrosion properties of the coatings has been investigated. The chemical structure of the materials has been characterized using infrared spectroscopy (FTIR), X-ray Photoelectron Spectroscopy (XPS), and Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS). The corrosion protection performance of the coatings has been examined by the group of electrochemical techniques including potentiodynamic polarization and electrochemical impedance spectroscopy. Based on the comparison of the corrosion properties of the developed hybrid coatings with both chromated surface treatments and pure silica films, the effectiveness of these coating materials for corrosion protection of magnesium alloys is discussed.
3:30 PM		H4-7 Optimization of Electrolytic Plasma Process (EPP) for Coating Mg Alloys for Corrosion Protection Y. Ma, X. Nie, D.O. Northwood, H. Hu (University of Windsor, Canada) Abstract Electrolytic plasma processing (EPP) technology has successfully been used for depositing ceramic coatings on magnesium alloys for corrosion protection. In this study, a Design of Experiment (DOE) technique, the Taguchi method, has been used in an effort to optimize the electrolytic plasma process (EPP) for corrosion protection of magnesium alloys. The experimental design that was used employed four factors (treatment time, current density, and concentration of KOH and Na₂SiO₃ or NaAlO₂), and three levels of each factor. Potentiodynamic polarization measurements were conducted to determine the corrosion resistance of the coated samples. Scanning Electron Microscopy and Energy Dispersive X-ray analysis were used to study surface morphology, and the thickness and chemical composition of the coatings. A microhardness tester was used to determine the hardness of coatings. Analysis of the experimental results has identified the contributing effects of each of the four experimental factors to the corrosion resistance and coating properties. Thus, the optimized process parameters have been defined.