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ABSTRACT Background data are presented that support a concept for galvanic and ion exchange release of cathodic (oxygen reduction) corrosion inhibitors from conducting polyaniline (PANI). Such inherently conducting polymers can be potentially formulated into protective coatings for Cu-rich aluminum alloys. The results show that both reduction and ion exchange trigger the release of a species from the conducting polymer that inhibits oxygen reduction on the Cu-rich cathodic phases in the aluminum alloy. These results form the basis for a ?smart? corrosion- resistant coating concept. BACKGROUND The ongoing demand for the replacement of chromate by more environmentally benign corrosion inhibitors, particularly for corrosion-protective coatings used in the aerospace industry, has led to a better understanding of the mechanism by which hexavalent chromium inhibits corrosion. These results have been widely reported in the literature, a detailed review of which remains beyond the scope of this paper. However, inhibition of the oxygen reduction reaction (ORR) occurring on the Cu-rich intermetallics by hexavalent chromium (or chromate) represents an important result from this body of knowledge (Figure 1).1-2 We have recently reported an electrochemical test method3 based on earlier work by Ilevbare and Scully4 to quantify the effectiveness of ORR inhibitors for slowing the reaction on Cu cathodes. The method entails the observation of the cathodic current at Cu rotating disk electrode (RDE) biased at ?0.7 V vs saturated calomel electrode (SCE) in a 5% sodium chloride (NaCl) electrolyte. Suppression of this current by the addition of an inhibitor serves as a fi gure of merit for the ability of the inhibitor to stop the ORR. A recent concept for galvanically and environmentally controlled release of inhibitors has been proposed, and it involves the release of ORR inhibitors by an inherently conducting polymer (ICP), as triggered by the galvanic reduction of the polymer and an ion exchange in the presence of a coating defect and a corrosive electrolyte (Figure 2).5 This novel use of ICPs has been considered in light of concerns about the validity of generalizing Deberry?s anodic protection model6 for application to base metals in chloride environments. Rather, ICPs may actively protect metals from corrosion via ion exchange and reductive release of corrosion inhibitors.7-10 The use of ICPs for the controlled release of ionic compounds has been considered for some time for biomedical applications11 with work more recently reported by Pernault and Reynolds.12 In this paper we explore the possibility of the exchange of ORR anions into conducting polymers for subsequent release by reduction and ion exchange. The anions considered have appeared in the patent
- Materials > Metals & Mining (1.00)
- Water & Waste Management > Water Management > Water & Sanitation Products (0.79)
- Materials > Chemicals > Specialty Chemicals (0.79)
ABSTRACT The requirement for a high degree of integration while maintaining reliability of microelectronic devices places high demands on packaging and coating components for protecting microelectronic circuitry. This is particularly the case for microelectronic circuitry experiencing high-bias voltage. Moist or wet conditions can rapidly degrade conductor elements. While organic coatings used for microelectronic applications must provide a barrier against transport of corrodents to biased substrates, this is not the primary role that these coatings play in protecting substrates against corrosion. Corrosion protection provided by organic passivation layers lies mainly in their ability to adhere to the substrate, thereby inhibiting corrosion reactions. The authors have used a novel in situ acoustic microscopic approach to evaluate the degradation of biased aluminum metallization coated with polyimide and exposed to deionized water. The ability of acoustic microscopy to detect the early stages of degradation in situ and under electrical bias makes this method a valuable test for characterizing the environmental degradation of microelectronic devices. The authors report here the preliminary results of their work. EXPERIMENTAL The test device consisted of an evaporated 0.6 µm (6000 Å) Al metallization that formed a triple-track, meander pattern on an insulating 0.2 µm (2000 Å) film of silicon oxide sputter-deposited on a 3-in. diameter silicon wafer. The metallization was placed on the substrate using a photolithographic process following oxygen plasma cleaning. The metallized wafer was coated with 1 to 1.5 µm of polyimide. A 12-µm diameter pinhole defect was photolithographed over each
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (0.89)
- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (0.88)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (0.88)
ABSTRACT The use of the higher harmonic content in the electrochemical current response to an applied 30 mHz sinusoidal potential for detecting the onset of pitting corrosion in Al 8090 and type 304 stainless steel has been evaluated. The level of higher frequencies relative to the fundamental in the AC current signal increases just when pitting initiates. However, the relative intensity of the higher frequency component decreases as the rate of pitting increases contrary the prediction of a simple model. This decrease with increasing pitting current is attributed to the increasing importance of the effect of IR drop. INTRODUCTION The higher harmonic content of electrochemical current responding to an applied sinusoidal potential has been used to evaluate the nonlinearity of electrochemical current vs voltage relationships in order to obtain Tafel coefficients needed for accurate evaluation of corrosion rates.1-5 McKubre has used the higher harmonic response to characterize cathodic protection.6 Liebert has suggested that the higher harmonics in the electrochemical current stimulated by an applied cyclic potential can predict pitting.7 Since conditions leading to pitting must be detected before commencement of rapid attack, the feasibility of using the higher harmonic content of an electrochemical current stimulated by a low-frequency potential was evaluated.
- Europe (0.29)
- North America > United States (0.28)
- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (0.87)
ABSTRACT The force of adhesion of an aqueous phase (pH 9.6 borate) to steel in the presence of a xylene solution of hydroxyterminated polybutadiene increases below the potential of zero charge (-550 mV vs Ag/AgCl). Incorporation of a high molecular weight quaternary ammonium cation in the xylene phase inhibits displacement of the organic phase at cathodic potentials. These results suggest that cathodic polarization of steel below the potential of zero charge can initiate cathodic disbonding. The disbonding will then irreversibly propagate by the alkaline attack of the cathodic electrolysis product on the organic film. INTRODUCTION Composite materials require good adhesion between the different phases, particularly in wet and corrosive environments. Indeed, Kane has stated that the role of the matrix/fiber interface is a key one in determining the environmental resistance.''1 Experience with adhesion of organic coatings on metals and in particular organic films on steel suggests that strong adhesive bonds, which may exist in the absence of a corrosive environment, can rapidly degrade as a result of the electrochemical reactions associated with corrosion. In the case of steel, the usual cathodic half of the corrosion reaction (reduction of oxygen to form hydroxide ion) degrades adhesion. This process,cathodic disbonding, has been associated with the buildup of hydroxide ion at the interface leading to hydrolysis of the organic polymer.2 Alkaline reduction/ dissolution of the oxide interphase3 has also been considered, but recent results4 have shown a Fe3O4 oxide to be stable for cathodic potentials negative of the potential where cathodic disbonding commences (typically 750 mV vs Ag/AgCl in neutral 0.5 M NaCl). Interfacial failures due to changes in surface energetics have also been suggested as a mode for cathodic disbonding.5 For example, cathodic generation of base at the surface of rough steel appears to catalyze the advancement of electrolyte contact.6 A number of excellent reviews of cathodic disbonding are available.7,8 Castle and Watts have provided a useful classification of proposed cathodic disbonding mechanisms.9 Although there is no doubt that alkaline attack of an organic coating causes irreversible damage to the coating/steel bond, the changes in surface energy resulting from cathodic polarization are hypothesized to contribute to the initiation of cathodic disbonding. Accordingly, the substrate must remain above the potential of zero charge (pzc) to ensure adhesion when the polymer of the coating has a negative zeta potential. The zeta potential differs from the galvanic potential in that the potential at the plane of shear for a solid liquid interface defines the zeta potential; hence, the zeta potential depends on the charge that is hydrodynamically affixed to (or absorbed at) the metallic surface. A three-phase wetting experiment was performed to characterize the role of potential in causing the aqueous displacement of an organic layer from steel.
- Research Report > Experimental Study (0.48)
- Research Report > New Finding (0.34)