Cathodic disbonding of an unpigmented epoxy coating on mild steel under semi- and full-immersion conditions

Electrochemical impedance spectroscopy as a tool to measure cathodic disbondment on coated steel surfaces: Capabilities and limitations

“…The Na and Cl elements were not detected at sites 'c', 'd' and 'e' which are located outside the halo, this indicates that no NaCl solution reached these surface areas, and therefore the observation and measurement of the areas covered by the 'halo' can be a means of estimating coating disbondment areas. This is in agreement with previous studies [31,32] where the surface area defined by the radius to the outer edge of the halo minus the original defect area was considered to be the disbonded area. The growth of the circular halo area (Fig.…”

An investigation of cathodic oxygen reduction beneath an intact organic coating on mild steel and its relevance to cathodic disbonding

“…Nevertheless, the complex mechanism of cathodic disbonding of organic coatings has not been fully understood. Cathodic disbonding of coatings with an artificial defect was reported by us in a previous paper [11]. This identified the dominant rate-controlling process as transport of cations along the coating/metal interface.…”

“…Unpigmented phenalkamine-cured epoxy was applied with a steel rod by the draw-down method using adhesive tape to act as a gauge that controlled the wet-film thickness, as before [11]. The coating was cured at ambient temperature in a dust free environment for at least 2 weeks before testing.…”

“…To do this, a coated panel without a defect was coupled with a bare mild steel anode so that the coated sample acted as cathode, but without direct access for the solution to the coating/metal interface such as is present in the presence of defects. The coupled bare metal acts similarly to the bare metal exposed at the defect in cathodic disbonding tests (such as [11]) and drives the cathodic reaction underneath the paint but with no possibility of ions reaching the interface by short circuit routes at a defect. Electrochemical impedance spectroscopy (EIS) was applied at regular time intervals to assess the properties of the intact coating and in particular to provide a coating resistance value to correct the results of polarisation experiments for iR drop (the potential difference across the coating).…”

A model for cathodic blister growth in coating degradation using mesomechanics approach

“…It is, therefore, essential to understand the physical and metallurgical phenomenon of blistering from both scientific and engineering point of view. One of the most severe forms of blistering is known as cathodic blistering [14][15][16], which takes place when a metallic substrate with coating defects is exposed to saline environment, such as salt spray or immersion in salt solution [17][18][19][20][21].…”