Corrosion and its protection are one of the major challenges that are faced by the industries. To overcome this, new coatings with characteristic properties which are environmentally friendly are introduced. A cost-effective and most reliable way of corrosion protection is via barrier coatings, in which water-based epoxy coatings showed significant corrosion resistance. Although the epoxy coating creates a barrier between the metal and the corroding ions, there is a chance of leakage due to mechanical rupture and the formation of micropores during the curing time of the epoxy. This leads to the incorporation of inhibitors into the epoxy coatings which in turn increase the corrosion resistance. This review discusses the different types of inhibitors that are incorporated into the epoxy coating to prevent corrosion. The use of Nano/micro containers for the encapsulation of the inhibitors leads to the discovery of self-healing smart coatings. Such water-based epoxy smart coatings are also discussed.
The adsorption of pectin and corrosion inhibition of dual-phase AISI1040 steel with ferrite–martensite and ferrite–bainite structure in 0.5 M sulphuric acid (H2SO4) solution have been investigated using the weightloss method. This work investigates the adsorption mechanism and quantum chemical calculations of pectin. For a specific set of parameters such as immersion time and concentration of inhibitor, the maximum inhibition efficiency of 83.36% is observed. The inhibition efficiency increased with pectin concentration and decreased with immersion time at 30 ℃. The results from the statistical analysis show that the concentration of inhibitor is having the highest influence with a 43.87% contribution on the inhibition efficiency. The adsorption study revealed that the Langmuir adsorption isotherm gave the best-fit results out of all the isotherms studied. Theoretical studies based on density functional theory supported experimental observations. From the results, it was also observed that lower weight loss and better inhibition efficiency are achieved in the case of ferrite–bainite when compared to the ferrite–martensite structure. Surface characterization confirmed corrosion and inhibition on the surface of the metal as the surface became uneven when exposed to a corrosive medium and smooth when immersed in the inhibited solution.
EN18 steel and copper are used as materials for oil and gas industries for chemical storage, which come in contact with the sulfuric acid medium during the pickling process. In such instances cleaning of impurities and oxide layer removal, leads to excessive corrosion. Thus, the improvement in the microstructure through annealing treatment and its effect on the corrosion behavior of EN18 steel and copper are studied by immersing in 0.5 M H2SO4 for as-bought and 0.5, 0.25, 0.1 M H2SO4 medium solutions after annealing treatment. The metal specimens were heated to 900 °C for EN18 steel and 600 °C for copper and then both were furnace cooled and the change in the microstructure of annealed and as-received metal specimens was analyzed using Scanning Electron microscopy (SEM). The Electrochemical Impedance Spectroscopy (EIS) and Potentiodynamic polarization (PDP) measurement showed that there is a decrease in the corrosion rate for both metals after annealing treatment. The effect of corrosion rate at the temperature range of 30-50 °C was analyzed and activation parameters were described using Arrhenius and transition state theories. Suitable corrosion mechanisms for both steel and copper in the H2SO4 medium have been discussed.
Dual-phase steels provide an excellent combination of strength and ductility, as well as improved energy absorption and anti-corrosion protection properties. This research aims at evaluating the microstructure and corrosion behaviour of EN8 steel under different heat treatment temperatures in 0.5 M sulphuric acid solution (H2SO4) using the EIS, potentiodynamic polarization, and gravimetric method (weight-loss method). Austenitizing is performed at 973 K, 1023 K, 1063 K, and 1173 K for 2 h followed by quenching in water to form a ferrite–martensite (F–M) dual-phase structure. From the results, it is seen that the corrosion rate increased with different heat treatment conditions depending on the change in the phase when immersed in 0.5 M H2SO4 at the temperature of 303 K, 313 K, 323 K, and 333 K. This work investigates the energy of activation, enthalpy, and entropy of activation. For dual-phase steel containing ferrite and martensite, the corrosion behaviour depends on the amount of martensite and ferrite. As the austenitization temperature increases from 1023 to 1173 K, the amount of martensite increases. This is reflected in the increase of micro galvanic corrosion cells in the region between the ferrite and martensite phases, which acts as active corrosion centres. The normalized specimen showed greater corrosion resistance compared to the water-quenched specimen at 1173 K. This is due to the presence of lower carbon content for normalized dual-phase steel containing ferrite–pearlite phase than the ferrite–martensite phase present in specimen austenitized at 1173 K. Surface characterization and XRD confirmed the corrosion behaviour of the specimens under investigation.
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