Transmission Line Modeling of EIS Data for a Mg-Rich Primer on AA 2024-T3

Abstract

Mg-rich primers ͑MRPs͒ provide cathodic and barrier-type protection to aluminum substrates similar to that provided by zinc-rich primers ͑ZRPs͒ for steel. The former protection is driven by the more active Mg particles compared to the Al substrate, and the latter by the insulation of the substrate from the environment by Mg-containing products. A transmission line model was used to interpret ZRP electrochemical impedance spectroscopy ͑EIS͒ data that account for the contact impedance between zinc particles, the impedance associated with zinc dissolution, and the electrolyte resistance. Experiments were conducted for the evolution of the electrochemical behavior of an MRP on AA 2024-T3 under immersion in diluted Harrison's solution. The transmission line model was applicable to the MRP data. Comparison between the parameters of a ZRP and those for the MRP indicated that the loss of cathodic protection for an MRP was related to the interfacial resistance of the particles.Coatings containing chromate-based pigments have represented the prototype for the protection of aircraft structures made of aluminum alloys. 1,2 Pigments based on zinc chromate, zinc tetroxy chromate, and strontium chromate have been used to inhibit the corrosion of AA 2024-T3 structures by the U.S. Air Force. 3 The solubility of the chromate can result in its leaching from the polymeric binder, with environmental implications arising due to the toxic nature of chromates. 4,5 Federal regulations have been introduced by the U.S. government to curtail the use of chromate-based pigments, 6 and as such, there is ongoing research into alternatives to the chromatebased pigments. Alternative inhibitors that have been proposed include vanadates, phosphates, molybdates, borates, and silicates. 1,7-9 Commercial, nonchromate inhibitor pigments have been shown to be much less effective in corrosion protection as compared to the industrial standard of SrCrO 4 . 9 There has been recent progress in the application of an AlCo-Ce metallic coating that can provide cathodic protection as its open-circuit ͑OC͒ potential is as much as 750 mV lower than that of AA 2024-T3 depending on the Al-Co-Ce alloy. 10,11 The Co 2+ and Ce 3+ ions can be released from this metallic coating and provide additional inhibition of the AA 2024-T3 corrosion. There has also been recent progress in the development of a Mg-rich primer ͑MRP͒, and its applicability for the protection of aluminum structures has been demonstrated by Bierwagen and co-workers. 12-16 The application of MRPs does not require a chromate pretreatment, representing a Cr-free system.MRPs provide cathodic protection driven by the more active Mg particles compared to the Al substrate and also a barrier-type protection due to the insulation of the substrate from the environment by products of Mg hydroxide and hydroxy carbonate species that fill pores and voids. 13,17,18 The characterization of MRPs on Al substrates has been performed using OC potential evolution, potentiodynamic polarization, electrochemical impedance spect...

Synthesis, structural and electrochemical properties of sodium nickel phosphate for energy storage devices

“…The sample synthesized at 300°C showed a fused semicircle with no conspicuous difference in the low and high-frequency region and a straight line is observed in the low-frequency region. The intercept on the real axis (electrolyte solution ohmic resistance; R s ) 31 and the diameter of the semicircle (charge transfer nonohmic resistance; R ct ) 32 are about 5 Ω and 2 Ω, respectively.…”

Characteristics and corrosion behavior of nickel‐phosphorus coatings deposited by a simplified bath

“…The curves (log f vs. log |Z|) show that the impedance modulus values are two orders of magnitude greater than the magnesium alloy substrate, suggesting their significant corrosion protection in 3.5% NaCl solution. When frequency is below 100 Hz (log f < 2), the impedance (log |Z|) for the four Ni‐P coatings obviously keep increasing and that for the magnesium alloy is nearly a constant (about 2.5), which can be assigned to the increase in the barrier property of the coatings . The first relaxation process of the coatings have a value very close to 90° (Fig.…”

The effect of lithium loadings on anode to the voltage drop during charge and discharge of Li-ion capacitors

“…6(a) shows the equivalent circuit model which can be used to describe various physical and electrochemical processes inside LICs. In the model: L represents the wire inductance of leads and wires; R S represents the ohmic resistances including contacts, separator paper, and electrolyte solution [35,36]; R SEI and C SEI represent the solid electrolyte interface (SEI) layer [37,38] which, in this case, is on the surface of the Li-metal powder on the carbon anode and commonly found on carbon anodes; R ct is the charge transfer resistance, a non-ohmic resistance related to the exchange current density, while C dl is the double layer of charge formed at the electrolyte/electrode boundary [39,40]. Lastly Z Wo represents the finite state Warburg element which describes diffusion of ions with a reflecting boundary [37,41e44].…”