Inhibition of corrosion of mild steel in acid media by N′-benzylidene-3-(quinolin-4-ylthio)propanohydrazide

In the present investigation a new corrosion inhibitor, N′-(3,4-dihydroxybenzylidene)-3-{[8-(trifluoromethyl)quinolin-4-yl]thio}propanohydrazide(DHBTPH) was synthesized, characterized and tested as a corrosion inhibitor for mild steel in HCl (1 M, 2 M) and H₂SO₄ (0·5 M, 1 M) solutions using weight-loss method, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization methods. The corrosion inhibition efficiency measured by all the above three techniques were in good agreement with each other. The results showed that DHBTPH is a very good inhibitor for mild steel in acidic media. The inhibition efficiency in different acid media was found to be in the decreasing order 0·5 M H₂SO₄ > 1 M HCl > 1 M H₂SO₄ > 2 M HCl. The inhibition efficiency increases with increasing inhibitor concentration and with increasing temperature. It acts as an anodic inhibitor. Thermodynamic and activation parameters are discussed. Adsorption of DHBTPH was found to follow the Langmuir’s adsorption isotherm. Chemisorption mechanism is proposed. The mild steel samples were also analysed by scanning electron microscopy (SEM).     

Effect of Cl<Superscript>−</Superscript>on the corrosive wear of AISI 321 stainless steel in H<Subscript>2</Subscript>SO<Subscript>4</Subscript> solution

The effect of Cl⁻ on the corrosive wear behaviour of AISI 321 stainless steel in H₂SO₄ solution was studied via the corrosive wear rate, the load bearing capacity of passive film and the relationship between pitting and corrosive wear. There is a critical load at natural potential, below which the corrosive wear rate is slightly lowered by Cl⁻, while above which is increased. At natural potential there are more pits at low load than that at a higher one in the wear tracks and the pits are also deeper. The load bearing capacity is lowered by Cl⁻ at passive region and then the corrosive wear rate increased.     

Corrosion and stress corrosion cracking behavior of 316L austenitic stainless steel in high H2S–CO2–Cl− environment

In oil and gas production environments, H₂S and Cl^? can coordinate to cause pitting or stress corrosion cracking (SCC) of stainless steels. There has been limited work conducted on corrosion and SCC of autenitic stainless steels in high H₂S–CO₂–Cl^? environments. In this paper, by four-point bending test method and scanning electron microscopy analysis, SCC of 316L steel was investigated under high H₂S–CO₂ pressures with 150,000 ppm Cl^? at 60 °C. The effect of high H₂S–CO₂ pressure was discussed. The results indicated that the higher H₂S–CO₂ pressure can accelerate anodic dissolution process, deteriorate passive films, and aggravate SCC sensitivity. Using cyclic potentiodynamic polarization measurements, the corrosion behavior of 316L steel was studied in high H₂S–CO₂–Cl^? environments. The effect of pH on pitting corrosion was discussed. Lower pH can promote both cathodic and anodic actions on 316L steel and facilitate passive film breakdown.     

The effect of Nb and heat treatment on the corrosion behavior of ferritic stainless steel in acid environments

The corrosion properties of ferritic stainless steel with admixtures of 0.5, 1.0, and 3.0 wt.% Nb are studied in 0.1M H₂SO₄ and 0.3M HCl solutions. The results obtained by the impedance and mass-loss methods demonstrate that the procedure of alloying with niobium and diffusion treatment positively affect the corrosion resistance of steel in these solutions. Published in Fizyko-Khimichna Mekhanika Materialiv, Vol. 44, No. 4, pp. 89–94, July–August, 2008.     

Naturally Occurring Organic Substances as Corrosion Inhibitors for mild Steel in Acid Medium: Concentration and temperature effects

Potentiodynamic cathodic and anodic polarization technique was used to study the effect of some common amino acids concentration on the corrosion inhibition of mild steel in H₂SO₄. A value of 1.0 × 10^?4 M represents a critical concentration, for the aliphatic amino acids, above which the corrosion rate increases. The increase of the sulphur-containing amino acids concentration largely decreases the corrosion rate. A mono-layer adsorption of the amino acid molecules on the metal surface was proposed with the adsorption behaviour following the Temkin isotherm at 30°C. The effect of temperature on the corrosion inhibition of amino acids was also studied over the temperature range 25 to 60°C. Values of the apparent activation energy in the range of 42 - 49 kJ mol^?1 were estimated for the steel corrosion in the inhibited acid solutions.     

Corrosion behavior of AZ91 magnesium alloy in dilute NaCl solutions

The corrosion behavior of AZ91 magnesium alloy in dilute NaCl solutions was studied using electrochemical measurements, whereby a corrosion map in terms of electrode potential and chloride concentration [Cl⁻] was obtained. AZ91 alloy exhibited the corrosion and passivation zones in dilute NaCl solutions. The passivation zone became narrow with increasing [Cl⁻]. The values of open-circuit potential were in the passivation zone when the [Cl⁻] was less than 0.5 mol/L. XRD patterns showed the presence of the Mg(OH)₂, Mg₅(CO₃)₄(OH)₂·8H₂O and MgO phases in the corrosion product, whereas the latter two phases found in the passive film.     

Green approach to corrosion inhibition of mild steel in hydrochloric acid and sulphuric acid solutions by the extract of Murraya koenigii leaves

The inhibition of the corrosion of mild steel in hydrochloric acid and sulphuric acid solutions by the extract of Murraya koenigii leaves has been studied using weight loss, electrochemical impedance spectroscopy (EIS), linear polarization and potentiodynamic polarization techniques. Inhibition was found to increase with increasing concentration of the leaves extract. The effect of temperature, immersion time and acid concentration on the corrosion behavior of mild steel in 1 M HCl and 0.5 M H₂SO₄ with addition of extract was also studied. The inhibition was assumed to occur via adsorption of the inhibitor molecules on the metal surface. The adsorption of the extract on the mild steel surface obeys the Langmuir adsorption isotherm. The activation energy as well as other thermodynamic parameters (Q, ΔH^*, and ΔS^*) for the inhibition process was calculated. These thermodynamic parameters show strong interaction between inhibitor and mild steel surface. The results obtained show that the extract of the leaves of M. koenigii could serve as an effective inhibitor of the corrosion of mild steel in hydrochloric and sulphuric acid media.     

红壤土浸出液中SO42-对铜包钢耐蚀性能的影响研究

本文采用扫描电镜/能谱分析(SEM-EDS)、动电位极化、电化学阻抗谱技术研究了铜包钢接地材料受SO₄^2-浓度影响的腐蚀行为.研究结果表明在含有不同浓度的SO₄^2-的红壤土浸出液浸泡20 d,铜包钢都已出现点蚀现象.随着SO₄^2-浓度从0.05~0.2 mol/L逐渐增加,铜包钢腐蚀程度呈现先增后减弱的趋势,在0.05 mol/L的SO₄^2-浸出液中浸泡20天腐蚀最为严重,已腐蚀至内层钢.由于0.05 mol/L的SO₄^2-浸出液中腐蚀后的铜包钢表面已被较多的不导电的腐蚀产物覆盖,因此实验结果显示其阻抗值最大和腐蚀速率最慢.     

Analysis of Copper Pitting Failure in Drinking Water Distribution System

Electrochemical tests, as well as surface and chemical analysis were used to investigate the cause of pitting failure of copper tubing in a drinking water distribution system. The results show that localized pitting was the cause of failure and copper corrosion problems were observed under a green deposit. The pitting corrosion was associated with the Cl⁻ and SO₄ ²⁻ ions introduced by the water softening treatment. These ions promoted the corrosion and the influence of Cl⁻ ion was much greater than that of the SO₄ ²⁻ ion.     

Potentiodynamic Polarization Behavior and Pitting Corrosion Analysis of 2101 Duplex and 301 Austenitic Stainless Steel in Sulfuric Acid Concentrations

The corrosion behavior of 2101 duplex and 301 austenitic stainless steel in the presence of sulfate (SO₄ ^2?) anion concentrations was investigated through polarization techniques, weight loss and optical microscopy analysis. The corrosion rates of the steels were comparable after 3M H₂SO₄. Results confirm that the duplex steel displayed a higher resistance to pitting corrosion than the austenitic steel. Experimental observation shows that its pitting potential depends on the concentration of the SO₄ ^2? ions in the acid solution due to adsorption of anions at the metal-film interface. The duplex steel underwent stable pitting at relatively higher potentials and significantly higher corrosion current than the austenitic steel. The duplex steel exhibited lower corrosion potential values thus less likely to polarize in the acid solution. Solution concentration had a limited influence on the polarization behavior of the austenitic steel and hence its reaction to SO₄ ^2? ion penetration from analysis of the pitting potentials and observation of its narrower polarization scans compared to the duplex steel which showed wide scatter over the potential domain with changes in concentration.     

Estimation of the accuracy of measurements of the corrosion rate by the method of polarization resistance

The method of polarization resistance is extensively used for the determination of the rate of corrosion. At the same time, the accuracy of measurements of the corrosion rate performed with industrial corrosion meters is often not estimated. By using an indicator, we find the accuracy of the measurements of the corrosion rate for 20 steel placed in 1N H₂SO₄ and 0.01N Na₂SO₄ solutions and for 12Kh18N10T steel placed in 1N and 10N H₂SO₄ solutions.Kiev Polytechnic Institute, Kiev. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 31, No. 3. pp. 22–27, May–June, 1995.     

Green approach to corrosion inhibition of mild steel in two acidic solutions by the extract of Punica granatum peel and main constituents

The effect of the extract of Punica granatum (PG) and their main constituents involve ellagic acid (EA) and tannic acid (TA), as mild steel corrosion inhibitor in 2 M HCl and 1 M H₂SO₄ solutions was investigated by weight loss measurements. The results obtained from the weight loss measurements show that the inhibition efficiency of TA even in high concentration is very low. Thus, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) investigations were used for different concentrations of PG and EA and best concentration of TA. Potentiodynamic polarization curves indicated that PG and EA behave as mixed-type inhibitors. EIS measurements show an increase of the transfer resistance with increasing inhibitor concentration. The temperature effect on the corrosion behavior of steel without and with the PG extract was studied. The inhibition action of the extract was discussed in view of Langmuir adsorption isotherm.     

Phosphonium iodine as nickel corrosion inhibitor in 1 M sulfuric acid medium

The inhibiting action of alkyltriphenylphosphonium iodine salt ((C₈H₁₇)Ph₃P⁺,I⁻) towards the corrosion behaviour of nickel in 1 M H₂SO₄ solution has been studied. This compound was found to retard both anodic and cathodic reactions of nickel corrosion. At constant temperature, the corrosion rate decreases with increasing inhibitor concentration. On the other hand, the increase in temperature leads to an increase in the corrosion rate. The activation energy, ΔE _a, were calculated. They were found 19.3 kJ mol⁻¹ and 71.1 kJ mol⁻¹, respectively for the uninhibited solution and in the presence of 10⁻³ M of phosphonium salt. The inhibitor adsorption was identified to occur according to Langmuir isotherm. The equilibrium constant, k, as well as the free energy of adsorption, Δ_ads G°, for inhibitor process were then calculated. Phosphonium iodine exhibited a singular behaviour for T ≥ 318 K where inhibitor desorption increases.     

The inhibition of mild steel corrosion in hydrochloric acid media by two Schiff base compounds

Schiff bases of 2-({-1-methyl-3-[(2-sulfanylphenyl)imino]butylidene}-amino)-1-benzenethiol and 2-({-1,2-diphenyl-2-[(2-sulfanylphenyl)imino]ethylidene}amino)-1-benzenthiol are investigated as corrosion inhibitors in acid solution. Polarization, electrochemical impedance spectroscopy, and weight loss measurements were performed on mild steel in 15% HCl with and without the inhibitors. A significant decrease in the corrosion rate of mild steel was observed in the presence of investigated inhibitors. Polarization curves indicate that both compounds are mixed inhibitors, affecting both cathodic and anodic corrosion currents. The adsorption of inhibitors on mild steel surface in 15% HCl was found to follow Langmuir adsorption isotherm. Thermodynamic adsorption parameters (K _ads, ∆G _ads) of studied Schiff bases were calculated using the Langmuir adsorption isotherm. Activation parameters of the corrosion process such as activation energies, E _a, activation enthalpies, ∆H*, and activation entropies, ∆S*, were calculated by the obtained corrosion currents at different temperatures.     

Structural characterization and electrochemical behaviour of Fe-Ni-Mo-B Amorphous alloys

A series of amorphous alloys obtained by the “melt-spinning” technique, with variable nickel and molybdenum contents, have been examined. Potentiodynamic anodic and cathodic polarization curves have been obtained for each of these amorphous alloys in various environments (1N HCl, 1N H₂S0₄, 3% NaCl, 1N NaOH).Their electrochemical properties were correlated with the amorphous structure and with their composition, characterized by means of X-ray diffraction and Mössbauer spectroscopy. Surface morphology has been observed by Scanning Electron Microscopy (SEM). The nickel content, in amorphous Fe-Ni_x-Mo₄-B₁₃ (balance iron) alloys enhanced the corrosion resistance in acid (IN H₂SO₄, 1N HCl), neutral (3% NaCl) and alkaline (1N NaOH) environments. The molybdenum content (from 4 to 8.5%) in the amorphous Fe-Ni₂₀-Mo_x-B₁₃ (balance iron) alloys increased the corrosion resistance only in alkaline solutions.In the various environments tested, the corrosion potentials tend to ennoble on increasing the nickel content. While the alloys are in the active state in acid and neutral environments, they are passive in alkaline environments. A correlation has been found between the short range order in the alloys of the Fe-Ni-Mo-B type, of similar chemical composition, and the electrochemical behaviour.     

Specific features of the selective dissolution of 12Kh18N10T steel in ozonized sulfuric acid

We study the laws of corrosion-electrochemical behavior and selective dissolution of 12Kh18N10T steel in ozonized aqueous 20, 30, 40, and 70% sulfuric acid solutions. Ozone retards the corrosion rate of the steel only for acid concentrations lower than 40%. In ozonized 30 and 40% H₂SO₄ solutions, the dissolution of nickel and chromium in the course of corrosion of 12Kh18N10T steel becomes slower, but the amount of dissolved chromium is twice as great as that of nickel. We propose a hypothesis on the influence of ozone on the dissolution of components of the steel through the formation of OH⁻ ions, favoring the oxidation of iron and chromium to higher valences, which limits the anodic process. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 41, No. 5, pp. 69–73, September–October, 2005.     

The corrosion of tantalum in oxidizing sub- and supercritical aqueous solutions of HCl, H2SO4 and H3PO4

The corrosion of tantalum was investigated in sub- and supercritical oxidizing solutions of hydrochloric, sulfuric and phosphoric acid at temperatures between 360 and 500 °C. The corrosion rates in HCl and H₂SO₄ increased strongly above the critical temperature of water, which was attributed to a phase transformation from vitreous to crystalline Ta₂O₅. Corrosion rates in H₃PO₄ were low at all temperatures due to the formation of a top phosphate layer.     

Influence of Temperature on the Inhibiting Action of Benzazoles in Ozonized Sulfuric Acid

We showed that benzazoles are inhibitors of acid corrosion in ozonized solutions of 5% and 20% H₂SO₄. Benzazoles are oxidized under the action of ozone and decrease its concentration and influence on steel: benzotriazole does so more than benzimidazole. An increase in the of temperature of ozonized solutions of 5% and 20% H₂SO₄ to 60°C and 40°C, respectively, significantly lowers the inhibiting action of benzotriazole; the inhibiting action of benzimidazole drops with increase in temperature to 40°C and 20°C, respectively.     

Influence of substitution of phenyl group by naphthyl in a diphenylthiourea molecule on corrosion inhibition of cold-rolled steel in 0.5 M H2SO4

N,N′-Diphenylthiourea (DPTU) and N-naphthyl-N′-phenylthiourea (NPTU) synthesized in our laboratory, were tested as inhibitors for the corrosion of cold-rolled steel in 0.5 M H₂SO₄ by weight loss and electrochemical measurements. The studies clearly reveal that when we substitutes a phenyl group in N,N′-diphenylthiourea (DPTU) by naphthyl group to obtain N-naphthyl-N′-phenylthiourea (NPTU), the inhibition efficiency increases from 80 to 96% at 2 × 10⁻⁴ M. Polarization curves show that NPTU acts as mixed type inhibitor whereas DPTU predominates as cathodic inhibitor. Changes in impedance parameters (charge transfer resistance, R _t, and double layer capacitance, C _dl) were indicative of adsorption of DPTU and NPTU on the metal surface, leading to the formation of protective films. The degree of the surface coverage of the adsorbed inhibitors is determined by ac impedance technique, and it was found that the adsorption of these inhibitors on the cold-rolled steel surface obeys the Langmuir adsorption isotherm. The effect of the temperature on the corrosion behavior with addition of 10⁻⁴ M of DPTU and NPTU was studied in the temperature range 20–50 °C. Results show that the rate of corrosion of mild steel increased with increasing temperature both in the presence of inhibitors and in their absence. Activation energies in the presence and absence of DPTU and NPTU were obtained by measuring the temperature dependence of the corrosion current. The reactivity of these compounds was analyzed through theoretical calculations based on density functional theory to explain the different efficiency of these compounds as corrosion inhibitors.     

Behaviour of 316 Ti stainless steel in deuterium oxide with chloride

Since tritiated water contains deuterium oxide, we require a better understanding of stainless steel corrosion in tritiated water and thus we have compared the behaviour of 316 Ti stainless steel in ²H₂O and H₂O with and without chloride. This was done by anodic polarization curves, cyclic voltammetry and electrochemical impedance spectroscopy. The corrosion potential of 316 Ti stainless steel in deuterium oxide changes and is related to pH modification due to the dissociation constant of this aqueous medium which shows the importance of pH in passivity. Without chloride, the insulating properties of the passive oxide layer depending on the pH and passive potentials are enhanced with ²H₂O. With deuterium oxide containing chloride at near neutral pH, the repassive potential is lower than that obtained with H₂O, consequently localized corrosion in grain boundaries and pit propagation, which lead to crevice corrosion, are greater. The critical pitting potential is in transpassivity indicating that pitting is less likely to occur. Comparison with and without Cl^- for the passive potentials near the corrosion potential, shows that although chloride reduces the insulation provided by the passive oxide layer it is still greater than that obtained with H₂O. This revised version was published online in November 2006 with corrections to the Cover Date.