pH-Triggered Release of NaNO₂ Corrosion Inhibitors from Novel Colophony Microcapsules in Simulated Concrete Pore Solution

Abstract

Herein, pH-sensitive microcapsules containing NaNO 2 corrosion inhibitors for protection of steel reinforced concrete were synthesized via water-in-oil-in-water (W/O/W) double emulsion using colophony as the wall material. The average microcapsule size was 79.07 μm in diameter and exhibited a high encapsulation efficiency of 83.2%. Study of the release of corrosion inhibitors from microcapsules in deionized water (DI water, pH 6.8), carbonate/bicarbonate buffer solution (CBS, pH 9.1), and simulated concrete pore solution (SCPS, pH 12.6) demonstrates that the microcapsules are sensitive to pH and display higher release in alkaline media. This is the first study of colophony as an encapsulating agent for corrosion inhibitors. Furthermore, the alkaline pH-triggered release shows the suitability of its use in reinforced concrete systems. A wide thermal stability range was also found for the colophony microcapsules up to 100 °C. These high pH environments (CBS and SCPS) present pH values above the pK a of colophony (7.2), thus triggering enhanced inhibitor release by the ionization and deprotonation of colophony shell. The higher release in CBS and SCPS is demonstrated by the increases of the corrosion inhibitor diffusion coefficient by an order of magnitude from 3.30 × 10 −17 m 2 /s in DI water up to 1.66 × 10 −16 m 2 /s for SCPS. The release performance indicates that the proposed approach can be used to encapsulate a variety of inhibitors for the protection of steel reinforcements. After immersion in different pH solutions, the corrosion potentials of a carbon steel substrate with microcapsules containing nitrite were more noble than when immersed without microcapsules and the corrosion current densities showed comparable values to free corrosion inhibitors. The formation of a passive ferric oxide layer was confirmed by electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy.

Corrosion Inhibition Mechanism of Steel Reinforcements in Mortar Using Soluble Phosphates: A Critical Review

“…The formation of iron phosphate compounds, Fe 3 (PO 4 ) 2 and FePO 4 [103,104], see Equations ( 4) and ( 5), is thermodynamically favored over the formation of iron chloride compounds, FeCl 2 and FeCl 3 [105], see Equations ( 6) and (7), therefore leading to the formation of a stable phosphate barrier layer that can inhibit the chloride attack. Consequently, hindering the iron acid hydrolysis reaction [106], see Equations ( 8) and (9).…”

“…The corrosion of these steel reinforcements is considered to be the greatest threat to the integrity of these structures and their service life [3,4]. Various solutions have been implemented to deter corrosion, such as corrosion inhibitors and many others [6][7][8][9][10].…”

Effect of the Thermomechanical Treatment on the Corrosion of UNSM Processed Inconel 718: An Electrochemical Study

“…x is an integration variable, the value of which is between 0 and ∞, and ω is the angular frequency [31]. From the imaginary component, the real component can be calculated with Equation ( 1), and vice versa with Equation (2).…”

Design of Nanostructured Protective Coatings with a Sensing Function

“…To overcome these issues, micro- or nanoparticles encapsulating or bearing inhibitors were embedded in coatings. − For instance, the inhibitor 2-mercaptobenzothiazole was adsorbed on CeO 2 nanoparticles followed by the adsorption of poly­(acrylic acid) . Epoxy coatings containing the nanoparticles provided a coating resistance more than 8000 times larger than pure epoxy coatings.…”