Volume 35, Issue 2

Anticorrosive coatings are commonly used to protect metal structures from corrosion and thus assure constancy of the metal profile area, and consequently the mechanical stability of the metal structure. Due to environmental factors, corrosion of metal structures is inevitable and is considered during the design process; however, it is very difficult to predict the corrosion rate a priori , and the designer usually relies on empirical data to make an assessment. In an attempt to address this issue, various types of sensors that monitor the state of metallic coatings have been developed. In this study, the abilities of two systems, one based on electrochemical impedance and one using electrical resistance, developed by the authors to allow remote real-time monitoring of bridges are described. A laboratory study is presented in which three different sensor coating configurations were evaluated in three simulated environments: a salt spray chamber, a humid chamber, and an industrial chamber. The corrosion rates were monitored over a 9-month study period. Periodic measurements were made of the sensor output signals, and visual inspections (close-up photographs) were made to compare the visual and monitored response of the sensors. The sensitivity of the sensors is described, and the advantages and disadvantages concerning their deployment for field operations are discussed.

Considering interacted damage accumulations induced by corrosion, cyclic fatigue, and stress corrosion cracking, a phenomenological corrosion fatigue (CF) life evaluation formula has been proposed. A concept of nominal CF limit has been introduced, which indicates whether cyclic damage accumulation is active or not. It is found that cyclic fatigue damage accumulation enhanced by corrosion is the dominative damage under relatively high stress amplitudes (compared to the nominal limit), whereas, under low stress amplitudes, corrosion damage accumulation would become the dominative one. Stress amplitudes below the nominal fatigue limit would lead to CF too due to corrosion damage accumulation, which can finally make the effective amplitude larger than nominal limit. Once the parameters included in formula have been determined by uniaxial tests, CF life under any complicated stress state could be estimated in a unified way.

Polyaniline (PANI) and its composites with multiwalled carbon nanotubes (MWCNTs) were synthesized by chemical oxidative polymerization. High-resolution transmission electron microscopy (HR-TEM), thermogravimetric analysis (TGA), and Raman spectroscopy were used to characterize the investigated compounds. The synthesized composite is formulated as pigments in alkyd resin with different pigment-binder (P/B) ratios and investigated as anticorrosive coatings on carbon steel in 1 m HCl using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The protection mechanism of PANI occurred through the barrier and passivation effect on the carbon steel surface. The encapsulation and dispersion of MWCNTs into the PANI matrix promoted the anticorrosive efficiency of the alkyd coating.

3-Formyl chromone (3FC) derivatives, viz. 5-methoxy-3FC (5-Me-3FC), 6-hydroxy-3FC (6-OH-3FC), and 7-hydroxy-3FC (7-OH-3FC), were studied for the inhibition of mild steel corrosion in 1 m H 2 SO 4 at different temperatures and concentrations. The inhibition was studied using mass loss method, polarization technique, electrochemical impedance spectroscopy (EIS), scanning electron microscopy, and quantum chemical calculations. The results from mass loss, potentiodynamic polarization, and EIS showed that inhibition efficiency (IE) increased with gradual increments in concentration of 3FC derivatives. The polarization study revealed that these compounds act as mixed-type inhibitors and Langmuir adsorption isotherm is fitted well for adsorption behavior. The order of IE provided by all the three compounds is 7-OH-3FC≈6-OH-3FC>5-Me-3FC and lies in the range of 85%–95%. A proposed inhibition mechanism has been further described, including the support from all the experimental and theoretical techniques.

The use of Tectona grandis leaf extract as a green corrosion inhibitor for stainless steel 304 (SS304) in 2 m hydrochloric acid was investigated using electrochemical techniques. Potentiodynamic polarization studies with different inhibitor concentrations showed that the inhibitor is of mixed type, which works by affecting both cathodic and anodic reactions. Adsorption analysis using the potentiodynamic polarization and electrochemical impedance spectroscopy runs result in standard free energy of adsorption values between −20 kJ mol −1 and −40 kJ mol −1 , indicating a comprehensive adsorption, which is a mixture of both physisorption and chemisorptions processes. Fourier transform infrared spectroscopy studies show the appearance of new peaks and shift in peak positions at some locations with the use of an inhibitor, which indicates the interaction between the inhibitor molecules and metal surface. Contact angle analysis indicates the formation of hydrophobic film on the metal surface.