B. Jabeera, S.M.A. Shibli and T.S. Anirudhan
Zinc ions, produced by the electrolytic dissolution of zinc metal rods, exhibited excellent inhibition efficiency, especially in combination with the synergistic additions of…
Abstract
Zinc ions, produced by the electrolytic dissolution of zinc metal rods, exhibited excellent inhibition efficiency, especially in combination with the synergistic additions of tungstate and nitrite ions. The optimum ratio of tungstate: nitrite: zinc was found to be 10:10:1 and the combination of tungstate: 100 ppm ‐ nitrite: 100 ppm ‐ zinc: 10 ppm (System A) gave the best results of all the systems studied. This system requires a much smaller concentration of tungstate and nitrite ions, as compared to the concentrations typically used and claimed to offer optimal inhibition efficiency. Long‐term open circuit potential measurements indicated that effective passivation occurred within 3 days of immersion. The passive layer thus formed on the metal surface retained its protective capability for several weeks, even after test coupons were transferred into a depleted inhibitor solution. The possible mechanism of the passivation is discussed.
Details
Keywords
Yan Li, Zhi Xin Ba, Yong Liang Li, Yan Ge and Xi Chang Zhu
This paper aims to investigate the inhibition effect of sodium silicate (SS), sodium alginate (SA) and sodium tungstate (ST) on the corrosion behavior of AZ91D magnesium alloy in…
Abstract
Purpose
This paper aims to investigate the inhibition effect of sodium silicate (SS), sodium alginate (SA) and sodium tungstate (ST) on the corrosion behavior of AZ91D magnesium alloy in 3.5 per cent NaCl solution through polarization curve test at room temperature, electrochemical impedance spectroscopy and weight loss measurement.
Design/methodology/approach
The influence of SA concentration on the inhibition efficiency of the corrosion inhibitor was mainly analyzed. The corrosion morphology and inhibition mechanism of the samples were also analyzed with scanning electron microscopy and energy-dispersive spectroscopy.
Findings
The results show that with the increase of SA concentration, the corrosion inhibition first increases and then decreases. When SA concentration is 0.03 mol/L, the inhibition efficiency is the highest, reaching 98 per cent. The adsorption film formed by SA and other deposition films produce a synergistic effect on the improvement of corrosion resistance of AZ91D magnesium alloy.
Originality/value
The adsorption film formed by SA with other deposition films produces a synergistic effect on the improvement of corrosion resistance of AZ91D magnesium alloy. With the increase of SA concentration, the corrosion inhibition first increases and then decreases. When the concentrations of SA, SS and ST are 0.03 mol/L, 0.015 mol/L and 0.02 mol/L, respectively, the inhibition efficiency of the inhibitor is the highest, reaching 98 per cent.
Details
Keywords
Yijiang Chen, Pei Zhang, Yong Zhou and Fuan Yan
The purpose of this work is to reveal the mechanism of WO42− on surface passivation for Q235 carbon steel in tungstate solution.
Abstract
Purpose
The purpose of this work is to reveal the mechanism of WO42− on surface passivation for Q235 carbon steel in tungstate solution.
Design/methodology/approach
In Na2WO4 solutions with the different concentrations of WO42−, the spontaneous passivation occurred on the surface of Q235 carbon steel when the concentration of WO42− was up to 0.13 mmol/L, which was attributed to the formations of the inner deposition film and the outer adsorption film on the Q235 surface under the action of WO42−.
Findings
The inner deposition film presented a two-layer microstructure: the inside layer was composed of Fe2O3 mainly, and the outside layer comprised Fe(OH)2•nH2O, Fe(OH)3•nH2O, FeWO4 and Fe2(WO4)3.
Originality/value
Both FeWO4 and Fe2(WO4)3 repaired the defects in the outside layer of the inner deposition film; however, the outer adsorption film played a more important role in the surface passivation than the inner deposition film did.
Ayomide Osundare, Daniel Toyin Oloruntoba and Patricia Popoola
The purpose of this paper is to develop technically efficient and economically effective sacrificial anodes that can be used for cathodic protection (CP) of pipelines in marine…
Abstract
Purpose
The purpose of this paper is to develop technically efficient and economically effective sacrificial anodes that can be used for cathodic protection (CP) of pipelines in marine environment and fill the knowledge gap in the use of carbon anodes for CP.
Design/methodology/approach
A sacrificial anode was produced via sand casting by adding varying weight-percent of coal and ferrosilicon to a constant weight-percent of grey cast iron. The hardness of the produced anodes was evaluated using a Rockwell hardness tester. The microstructure of the anodes was observed with scanning electron microscope/energy-dispersive spectroscopy (SEM/EDS). X-ray diffraction (XRD) was used to study the phases present. A potentiostat was used to assess the corrosion behaviour of the produced anodes and mild steel in 3.5 Wt.% NaCl solution.
Findings
The SEM results showed that some anodes had interdendritic graphite formation, while others had pronounced graphite flakes. The EDS analysis showed carbon and iron to be the prominent elements in the anode. Anodes Bc, B2 and B5 with a corrosion rate of two order of magnitudes were observed to have similar dendritic structures. Anode B4 is the most electronegative with an Ecorr of −670.274 mV Ag/AgCl and a corrosion rate of 0.052475 mmpy. The produced anodes can be used to protect mild steel in the same environment owing to their lower Ecorr values compared to that of mild steel −540.907 mV Ag/AgCl.
Originality/value
Alloying has been majorly used to improve the efficiency of sacrificial anodes and to alleviate its setbacks. However, development of more technically efficient and economically effective sacrificial anodes via production of composite has not been exhaustively considered. Hence, this research focuses on the development of a carbon based anode by adding natural occurring coal and ferrosilicon to grey cast iron. The corrosion behaviour of the produced anode was evaluated and compared to that of mild steel in marine environment.