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The current study investigates the influence of immersion time (7, 14, 21, and 28 days) on the corrosion behaviour of American Petroleum Institute (API) X70 and X80 steel grades in freely aerated simulated concrete pore solution (pH ~ 12 to 13.8) utilizing electrochemical techniques such as electrochemical impedance spectroscopy, linear polarization, and cyclic polarization. The electrochemical results suggest that the corrosion resistance of X70 line pipe steel increases as immersion time increases (from 7 to 28 days) due to the formation of a stable protective oxide layer on the surface. In the case of X80 line pipe steel, however, the corrosion resistance increases as immersion time increases from 7 to 14 days due to the preferential dissolution of bainite as a result of its higher activity, which initiates the formation of passive film. Furthermore, after 21 days of immersion of X80 line pipe steel in simulated pore solution, a considerable decline in corrosion resistance was observed, which indicates de-passivation, as a result of an increase in oxide film thickness and subsequent spalling off. Intriguingly, as compared to X80 line pipe steel, X70 line pipe steel has a greater potential for producing a stable protective oxide layer without the appearance of minor cracks after a 28-day immersion period, thereby preventing further corrosion and enhancing corrosion resistance. [ABSTRACT FROM AUTHOR]

A systematic study is performed on the development of hot-dip galvanized coatings on a Mn-containing high-strength steel sheet by varying the dew point (− 50, − 10, and + 10 °C) during inter-critical annealing of the steel strip at 800 °C. It also studies the effect of dew point on the corrosion behavior of the coatings in freely aerated 3.5 wt% NaCl solution. The reducing gas atmosphere consists of 95% N2 and 5% H2, where inter-critical annealing is carried out. Surface oxidation of the steel has a strong effect on the development of sound coating. A defect-free adherent galvanized coating is obtained on the annealed steel surface at a fixed dew point of + 10 °C, and it is attributed to the fine and continuous compact Fe-Al crystals compared to galvanized coatings produced at other dew points as well as the highest atomically dense (0002) basal plane. This also leads to the lowest corrosion rate (~ 0.164 mm y−1, where mm and y stand for millimeter and year, respectively) of the galvanized coating produced at a dew point of + 10 °C when compared with galvanized coatings produced at dew points of − 50 °C (~ 0.279 mm y−1) and − 10 °C (~ 0.259 mm y−1). The lowest corrosion rate of the galvanized specimen developed at + 10 °C dew point can be attributed to the uniform and defect-free coating surface, together with the dominance of the more atomically dense (0002) basal plane. [ABSTRACT FROM AUTHOR]

This work aims at understanding the formation of a beneficial thin continuous aluminum (Al)-rich interfacial layer with uniform distribution of fine equiaxed Fe-Al crystals formed at the substrate/coating interface during the initial stages of interfacial reactions as well as hindrance of Fe dissolution in Zn layer as soon as copper (Cu) pre-coated high-strength steel substrate is immersed into the molten zinc (Zn) bath containing 0.2 wt.% Al. Pre-coated Cu does not allow the immediate interaction and interdiffusion of Fe and Zn because of the positive heat of mixing between Fe and Cu. As the Cu dissolves in liquid Zn, counter-diffusion of Al and Zn toward the steel interface allows Fe to react with Al and Zn forming the thin Fe-Al inhibition layer with finer equiaxed grains. Moreover, dissolved Cu in the Zn layer would also prevent Fe diffusion in Zn in the time span during dipping, which is beneficial. Atom probe tomography (APT) analysis at the substrate/coating interface location reveals the presence of 56.22 ± 1.36 at.% Al, 35.01 ± 1.31 at.% Fe, 6.33 ± 0.66 at.% Zn, and 0.032 ± 0.01 at.% Cu, similar to the intermetallic compound of Fe2Al(5-x)Znx, as well Cu in the Zn layer supporting the above reasoning. [ABSTRACT FROM AUTHOR]

The present study deals with the effect of isothermal holding time (10, 20, and 30 s) at a fixed annealing temperature of 500 °C on the formation of various Fe-Zn intermetallic phases during galvannealing treatment of a galvanized (GI) interstitial-free steel, and its correlation with the friction behavior determined by scratch test and electrochemical behavior in a freely aerated 3.5 wt. % NaCl solution. Pure Zn coating in GI specimen transforms to the various Fe-Zn intermetallic phases consisting of overlay zeta (ζ) phase with elongated rod type morphology, compact delta (δ) phase as well as a very thin layer of gamma (Γ) phase at the coating–substrate interface during isothermal annealing treatment of the GI sheet. The ζ phase has been noticed to get consumed by the more compact δ phase and increase in thickness of the thin Γ phase layer at the coating–substrate interface as iron content in the coating increases with an increase in galvannealing holding time. The galvannealed (GA) coating prepared at a galvanneal time of 30 s has the lowest coefficient of friction (COF ~ 0.26) as compared to 20 s (COF ~ 0.31) and 10 s (COF ~ 0.36), and the lowest corrosion rate (CR ~ 0.184 mm/y) as compared to 20 s (CR ~ 0.214 mm/y) and 10 s (CR ~ 0.227 mm/y). The dominance of compact and crater-free coating surface morphology along with the lowest zeta to delta (ζ/δ) phase fraction results in the lowest COF as well as the lowest corrosion rate of the GA coating prepared at a galvanneal time of 30 s. [ABSTRACT FROM AUTHOR]

In the present work, zinc (Zn) coating was developed on an interstitial-free (IF) steel from Zn sulfate bath using direct current (DC) and pulse current (PC) electrodeposition techniques at different current densities of 10, 30, and 60 mA/cm2. The x-ray diffraction (XRD) analysis of the coatings reveals that the higher atomically dense (0002) crystal plane of the pure Zn in the PC deposits is pronounced as compared to the DC deposits. The scanning electron microscopic (SEM) study displays finer and compact morphology of the PC deposits as compared to the DC deposits. The electrodeposits change from coarser to finer morphology with an increase in current density in both the electrodeposition techniques. All the PC deposits show a higher water contact angle (WCA) as compared to the DC deposits at each applied current density. The finer and compact coating morphology, higher WCA values with the dominance of a higher atomically dense (0002) crystal plane as well as the higher fraction of simonkolleite phase lead to the higher corrosion resistance of the PC deposits than the DC deposits. [ABSTRACT FROM AUTHOR]

Corrosion and anodic performance of newly developed composite sacrificial anodes based on high phosphorus pig iron, Al, and Zn with the stoichiometry xP-yAl and xP-y(Al0.75Zn0.25) (x = 1.5, 3.5, and 8.0 wt% P and y = 2.5, 5.0, and 10.0 wt%) in 3.5% NaCl and artificial seawater are studied. The incorporation of Zn in the xP-y(Al0.75Zn0.25) anodes decreases the potential below the potential required for the protection of steel during cathodic protection (− 0.778 V vs saturated calomel electrode). However, the xP-yAl anodes without the presence of Zn are unable to reach protection potential due to passivity. The preferential dissolution of Zn leads to destabilization of the passive layer (ϒ-Al2O3), and this attributes to greater active potential and better anodic performance of the xP-y(Al0.75Zn0.25) anodes. Hence, the presence of Zn is necessary for the xP-y(Al0.75Zn0.25) composites to become effective sacrificial anodes. [ABSTRACT FROM AUTHOR]

In this study, a systematic investigation on the effect of both aging temperature (250 °C and 330 °C) and time (chosen based on aging curves) on the distribution and volume fraction of the Mg17Al12 precipitates and subsequently on the corrosion behavior of the AZ80 magnesium alloy was carried out by conducting both immersion and dynamic polarization test in a freely aerated 3.5% NaCl solution. The analysis of corrosion products using Raman spectroscopy and X-ray diffraction and investigation of corrosion morphologies using scanning electron microscopy suggested galvanic corrosion of the anodic α-Mg matrix in contact with the cathodic Mg17Al12 precipitates. The higher corrosion resistance of the alloy aged at lower temperature (250 °C) was attributed to the higher number density of the Mg17Al12 precipitates than that at higher temperature (330 °C). In the peak aged condition, the average number densities of precipitates (1/µm2) were measured to be ~ 0.74 and ~ 0.32 and average corrosion rates (mm/y) were measured to be ~ 3.0 and ~ 5.0 at the aging temperatures of 250 °C and 330 °C, respectively. At a particular aging temperature, the corrosion resistance increased to a maximum at peak-aged condition followed by a decline in the over-aged condition and further increase with prolong aging, which was correlated with the number density, size and distribution of the Mg17Al12 precipitates. [ABSTRACT FROM AUTHOR]

Mg17Al12 eutectic phase strongly affects the mechanical and corrosion properties of AZ80 magnesium alloy. In this study, the dissolution kinetics of Mg17Al12 phase was evaluated at 420°C. The dissolution was found to follow the Johnson–Mehl–Avrami–Kolmogorov (JMAK) model with time exponent (n) of ~ 0.61, suggesting a decrease in the rate of dissolution of Mg17Al12 with time due to enrichment of aluminum in the matrix adjacent to precipitates. The effect of dissolution of Mg17Al12 phase on the corrosion behavior of the alloy was investigated by dynamic polarization measurements in NaCl solution. Analysis of the morphology of the corrosion surface by scanning electron microscopy and investigation of the corrosion products by x-ray diffraction analysis and Raman spectroscopy suggested an increase in the corrosion resistance of the alloy with a decrease in the Mg17Al12 phase fraction. This was attributed to the loss of effectiveness of microgalvanic cells formed between the precipitate and matrix. [ABSTRACT FROM AUTHOR]

The total synthesis of Ardisinone E [ 15, 1-(2,4,6-trihydroxy phenyl)-11-(2-hydroxyphenyl)-undecan-1-one], a natural diarylundecanone, isolated from Ardisia arborescens, was accomplished along with 16 new diarylundecanone analogs ( 18a- p), by modified Wittig reaction. The structures of the compounds were confirmed by H, C and mass spectral data. Compound 15 showed potent cytotoxic activity with an ED of 4.19 µg/mL in brine shrimp lethality assay model. Compounds 18c, 18e, 18j, 18k, 18l, and 18m exhibited strong anti-oxidant activity with IC values of 18.75, 12.28, 18.35, 11.04, 12.05, and 11.32 µg/mL, respectively, in NBT free radical assay. Compounds 18e, 18k, and 18m also showed significant 5-lipoxyganase enzyme inhibitory potential with IC values of 12.8, 15.23, and 15.23 µg/mL, respectively. [ABSTRACT FROM AUTHOR]