The Mechanism of Cathodic Disbonding of Hydroxy‐Terminated Polybutadiene on Steel from Acoustic Microscopy and Surface Energy Analysis

Abstract

rate of cathodic disbonding of an organic coating from steel. The approach has been (i) to characterize the rate and mode of attack by in situ acoustic microscopy, and (ii) to characterize the influence of electrochemical and environmental variables on the surface energy of steel.Since acoustic microscopy senses changes in mechanical properties of solid/solid interfaces, it provides a number of advantages for the study of corrosion-induced loss of adhesion for organic coatings on steel (4, 5). This report compares the results of the acoustic microscopic study of the cathodic disbonding of hydroxy-terminated polybutadiene from steel with the results of an analysis of the potential dependent surface energy of steel. ExperimentalPreparation of the coated steel.~A filtered (0.2 ~m) solution, containing four parts of hydroxy-terminated polybu-) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 128.255.6.125 Downloaded on 2015-06-07 to IP ABSTRACT Chemical deposition of PbS from aqueous solutions has been studied using a reaction of PbS(NO3)2 and CS(NHj)2 with excess NaOH. The growth rate was measured as a function of temperature and concentrations of NaOH and CS(NHj)2 using glass substrates. It is found that the incubation time depends on temperature and CS(NHj)2 concentration. Epitaxial growth of PbS on Ge(100) and InP(100) substrates is confirmed by means of the Laue back reflection x-ray and the electron channeling patterns. The best surface morphology is obtained on the epitaxial film grown on InP(100) substrate at 298 K with the concentrations of NaOH and CS(NHj)2 at 0.57 and 0.4 M/liter, respectively.

Study of the coating/substrate interface by scanning acoustic microscopy Cathodic disbonding of epoxy-polyamide lacquer from mild steel

“…From this, it can be shown that disbonded distance increases with root time, as reported by other workers.12,13 The observation of blisters beyond the continuous disbondment front has been described previously14 and studied in the acoustic microscope. 15,16 In that work, the formation of blisters beneath the coating was seen, but Nomarski interference microscopy suggested that the coating surface above the blisters showed a level proÐle. This suggested that some unusual form of damage was taking place with dissolution of coating material.…”

An overview of recent progresses in probing and understanding corrosion under disbonded coatings

“…Cathodic disbondment is a well-known phenomenon that frequently takes place at the coating and metal interface, causing the loss of adhesion between a coating layer and its metal substrate due to local chemical and physical changes [5][6][7][8][9][10]. The products of CP-induced oxygen reduction or hydrogen evolution reactions such as hydroxyl ions, hydrogen gas and short-lived superoxide intermediates could form at coating's defect sites, causing cathodic disbondment of coatings either through dissolving metal oxide layer, saponification of polymer coating or displacing the coating at metal/ coating interface [5][6][7][8][9][10]. Cathodic disbondment occurs preferably at locations where CP overprotection exists such as at the stray current 'pickup' points where the potential could be significantly more negative than other areas of the pipeline.…”

“…Figure 1 illustrates corrosion occurring within the crevice between the metal surface and the disbonded coating layer. The crevice provides easy lateral paths for corrosive species to reach the metal surface while simultaneously shielding cathodic protection currents from reaching the metal substrate, permitting the initiation and propagation of many types of corrosion [5][6][7][8][9][10][11] including pitting [12], microbiologically induced corrosion (MIC) [13,14] and stress corrosion cracking (SCC) [15,16]. Currently, CUDC remains as major failure mode, probably the worst-case scenario form of electrochemical corrosion, affecting the integrity of civil and industrial infrastructures such as buried and submerged pipelines [3].…”

Rust creep assessment—A comparison between a destructive method according to ISO 12944 and selected non-destructive methods

“…This method showed a very good correlation with the destructive standardised approach. Scanning Acoustic Microscopy (SAM) is another way of non-destructively evaluating coating defects and failures, such as adhesion loss [14,15], cathodic delamination and blisters [16][17][18][19][20][21][22][23][24][25][26]. 3D Profilometer can also characterise coating features in a non-destructive way, such as the topographic profile or the levelling of coatings [27,28], with multiple measurements around the failure area.…”