Vinod Upadhyay

Preliminary investigation of the impact of polymer composition on electrochemical properties of coatings as determined by electrochemical impedance spectroscopy

The influence of structural and systematic compositional variations in glycidyl carbamate (GC) functional polymers on the electrochemical properties of their coatings was studied. There are few reports which focus on the correlation of structural and compositional variations in polymer films with their electrochemical barrier properties, diffusion properties with regards to water and aqueous electrolytes, and corrosion performance. To begin to fill this knowledge gap, two sets of GC functional polymers were studied. The polymer compositions were designed to vary the extent of polar hydrophilic groups, non-polar hydrophobic groups, and reactive epoxy groups in the final coatings. Impedance responses of the coatings were found to be closely related to the structural and compositional variations of these GC polymer films. In addition, single frequency EIS experiments were used in an attempt to understand the water uptake behavior of these polymer films using NaCl solution and ionic liquid under immersed condition. The resulting transport property data of the films was correlated to their polymer structure and composition. Moreover, a novel attempt at ranking the stability of coating using capacitance measurement during a cyclic wetting–drying condition was also attempted. The information obtained from this work can potentially be used to optimize the polymer for the specific performance properties needed in the protective coating applications, saving significant time and effort in the research and development stage.

Characterizing the Relaxation of the Open-Circuit Potential during an AC-DC-AC Accelerated Test

Abstract The non-conventional accelerated alternating current-direct current-alternating current (AC-DC-AC) testing method for organic coatings induces degradation by promoting cathodic reactions a...

Hydrogen Evolution and Early Blistering from Magnesium-Rich Primers on AA2024-T3

Early blistering was observed on topcoated magnesium-rich primers (MgRPs) over AA2024-T3 substrate under constant immersion or constant salt spray tests. Hydrogen evolution and the cause of early b...

The Use of AC-DC-AC Methods in Assessing Corrosion Resistance Performance of Coating Systems for Magnesium Alloys

The potential utility of AC-DC-AC electrochemical methods in comparative measures of corrosion-resisting coating system performance for magnesium alloys under consideration for the USAMP “Magnesium Front End Research and Development” project was previously shown in this forum [1]. Additional studies of this approach using statistically-designed experiments have been conducted with focus on alloy types, pretreatment, topcoat material and topcoat thickness as the variables. Additionally, sample coupons made for these designed experiments were also subjected to a typical automotive cyclic corrosion test cycle (SAE J2334) as well as ASTM B117 for comparison of relative performance. Results of these studies are presented along with advantages and limitations of the proposed methodology.

Characterization of Coatings on Steel Self-Piercing Rivets for Use with Magnesium Alloys

Incorporation of magnesium alloys in self-pierce rivet (SPR) joints poses several unique challenges among which are the creation of spurious galvanic cells and aggravated corrosion of adjacent magnesium when coated steel rivets are employed. This work firstly reviews efforts on development of coatings to steel fasteners for the diminution of galvanic corrosion when used with magnesium alloys. Secondly, approaches, based on several electrochemical methods, for the measurement of the galvanic-limiting effect of a number of commercially-available coatings to hardened 10B37 steel self-piercing rivets inserted into alloy couples incorporating several grades of magnesium are reported. Electrochemical impedance spectroscopy (EIS), zero-resistance ammeter (ZRA), corrosion potential and potential-mapping visualization methods (e.g. scanning vibrating electrode technique — SVET) are illustrated for the several rivet coatings considered.