Chloride-containing Solutions Research Articles

Synergistic corrosion inhibition effects of the non-hazardous cerium nitrate and tannic acid polyphenolic molecules on the surface of mild-steel in chloride-containing solution: Detailed surface and electrochemical explorations

The generation of novel inhibitive molecules that can compete with harmful conventional chromium ones has remained a serious challenge in corrosion engineering. The present study aims to develop a newfangled natural compound to hinder the aggressive consequences of steel corrosion. To this end, the synergistic effects of the eco-friendly cerium nitrate on the corrosion retardation ability of the tannic acid (TAA) were examined for the metal specimens subjected to the saline (NaCl containing) solution. The adsorption of the TAA molecules and Ce:TAA complex on the metal substrate was evaluated by FTIR analysis. The surface properties of the samples were analyzed via SEM, UV–Vis spectroscopy, GIXRD, AFM, contact angle, and the Raman spectroscopy techniques. The effectiveness of the Ce:TAA mixture on the mild steel (MS) corrosion mitigation was examined through the EIS and polarization techniques. The results showed that the minimum corrosion current density (icorr = 0.54 μA/cm2) and the maximum total resistance (Rt ~ 22 Kohm.cm2) were observed for the samples immersed in the solution containing the Ce:TAA mixture (with the 1:1 mass ratio). The complex formation between the TAA molecules and Fe/Ce cations was proved the surface studies. The contact angle of the steel samples immersed in the saline solution containing Ce:TAA mixtures increased at least threefold. The inhibition efficiencies of the independent Ce and TAA inhibitors in the saline solution was measured around 74–92% and − 16-64%, respectively, while their optimum composition showed more than 86% efficiency all over the immersion time.

(Invited) Passivity and Pitting Corrosion Behavior of Additive Manufactured 17-4PH Stainless Steel

Conventionaly manufactured, i.e. wrought, 17-4PH martensitic stainless steel (MSS) is widely used in a large variety of applications, going from biomedical ustensils to large turbine blades. Recently, it appeared as a good candidate for additive manufacturing processes, e.g. laser beam melting (LBM), which is certainly the most common and developed process at this time. The specific microstructures generated by LBM have been well discussed in the literature for many types of materials. Nevertheless, these peculiarities can also affect the durability of the LBM-manufactured parts and specifically their corrosion behavior.The main goal of this work was to propose a detailed study of the pitting corrosion behavior of a 17-4PH MSS manufactured by LBM. In this framework, LBM parts were built from 17-4PH MSS powder, using optimized machine parameters. Samples of a commercial counterpart (CM –MSS) machined from a wrought cylindrical bar were studied as references. The pitting corrosion behavior of both MSSs was studied in chloride-containing solutions by combining linear potentiokinetic polarization associated with the determination of pitting potentials, and a statistical analysis of the current transients observed during potentiostatic experiments for metastable pitting. Significant differences were observed between the LBM and CM MSSs. They were explained considering the passive film composition, structure and morphology evaluated by combining transmission electron microscopy (TEM), scanning TEM (STEM) using the high-angle annular dark field (HAADF) mode, and Energy dispersive X-ray Spectroscopy (EDS) analyses. Results were related to the specific microstructure of the LBM samples as compared to that of the CM MSS, both microstructures being characterized by TEM, STEM and EDS.

Effect of temperature on the electrochemical pitting corrosion behavior of 316L stainless steel in chloride-containing MDEA solution

Here, the effect of temperature on the electrochemical corrosion of 316L stainless steel (SS) in methyl diethanolamine (MDEA) solution with/without 1.0 wt% NaCl in the presence/absence of CO2 was investigated using potentiostatic polarization, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS). The electrochemical measurements showed that although the MDEA solution was highly basic, both chloride and temperature played greater roles in the pitting corrosion of 316L SS, similar to plain NaCl solution. The critical pitting temperature (CPT) of 316L SS in MDEA solution with 1.0 wt% NaCl decreased from 67.2 °C to 59.6 °C, and the breakdown potential underwent a negative shift of approximately 400 mV, and the EIS Bode impedance decreased. Furthermore, the breakdown potential shifted negatively with increasing temperature when the temperature was lower than CPT in the MDEA solution containing Cl−; however, the breakdown potential decreased slowly, and its temperature dependence was unclear when the temperature was higher than the CPT. In addition, the passive film resistance of 316L SS in all MDEA solutions decreased as the temperature increased. Particularly for the MDEA solution containing Cl−, the passive film resistance decreased by one order of magnitude when the temperature increased from 50 °C to 60 °C. Although the presence of CO2 in the MDEA solution decreased the passive film resistance, it seemed to reduce the individual corrosion contribution of Cl−. The pitting corrosion process of 316L SS in MDEA solution containing chloride ions was discussed by combining these results with classical pitting mechanisms of stainless steel.

Cathodic and Anodic Stress Corrosion Cracking of a New High-Strength CrNiMnMoN Austenitic Stainless Steel

A new high-nitrogen austenitic stainless steel with excellent mechanical properties was tested for its resistance to stress corrosion cracking. The new conventional produced hybrid CrNiMnMoN stainless steel combines the excellent mechanical properties of CrMnN stainless steels with the good corrosion properties of CrNiMo stainless steels. Possible applications of such a high-strength material are wires in maritime environments. In principle, the material can come into direct contact with high chloride solutions as well as low pH containing media. The resistance against chloride-induced stress corrosion cracking was determined by slow strain rate tests and constant load tests in different chloride-containing solutions at elevated temperatures. Resistance to hydrogen-induced stress corrosion cracking was investigated by precharging and ongoing in-situ hydrogen charging in both slow strain rate test and constant load test. The hydrogen charging was carried out by cathodic charging in 3.5 wt.% NaCl solution with addition of 1 g/L thiourea as corrosion inhibitor and recombination inhibitor to ensure hydrogen absorption with negligible corrosive attack. Slow strain rate tests only lead to hydrogen induced stress corrosion cracking by in-situ charging, which leads to total hydrogen contents of more than 10 wt.-ppm and not by precharging alone. Excellent resistance to chloride-induced stress corrosion cracking in 43 wt.% CaCl2 at 120 °C and in 5 wt.% NaCl buffered pH 3.5 solution at 80 °C is obtained for the investigated austenitic stainless steel.

Synergistic mild steel corrosion mitigation in sodium chloride-containing solution utilizing various mixtures of phytic acid molecules and Zn2+ ions

In the present research, the synergism corrosion inhibition effects between the phytic acid (PA) molecules and zinc cations (Zn (II)) were investigated in 3.5 wt% NaCl solution through electrochemical measurements as well as surface (in micro/atomic scales) characterization methods. The efficiency and mechanism of inhibition were evaluated by the EIS and polarization techniques. The chelation between the PA and Zn (II) ions was studied by UV–vis spectroscopy. FT-IR, GIXRD, and FE-SEM/EDS analyses were conducted to identify the composition and structure of the precipitated film over the substrates. The hydrophobic/hydrophilic properties of the surface were assessed by the static contact angle (CA) measurements. The EIS studies proved that the PA-Zn (II) mixture acted as an efficient hybrid in the corrosion inhibition of the steel sample. The polarization plots indicated that the deposition of the PA-metal complexes led to the mixed-type corrosion inhibition mechanism. According to the electrochemical methods, the 250PA:750Zn sample resulted in the highest efficiency (95%) after 2 h. The FT-IR and EDS analyses verified the chelation and adsorption of the PA and Zn (II). The presence of the precipitated compounds on the sample was proved by FE-SEM images and GIXRD analysis.

Adsorption of Organosilanes and Formation of Organo silicon Self-Assembled Nanolayerson the Aluminum Surface.Influence of Surface Nanolayerson Corrosion and Electrochemical Behavior of the Metal

Adsorption of vinyl triethoxysilane and γ-aminopropyltriethoxysilane on the surface of aluminiumfrom aqueous solutions was studied by quartz nanobalance technique. Adsorption isotherms were obtained. It was shown that during adsorption silanes displace adsorbed water from the surface. To interpret the adsorption data, we used the well-known approaches of adsorption data: Langmuir, BET, Flory-Higgins, Langmuir multicenter,Temkin,Frumkinand Freundlichadsorption isotherms. The surface orientation of adsorbed molecules was determined. The silanes adsorption heats were calculated by different ways. It was shown that silanes are chemisorbed on the aluminium surface. By means of quartz nanobalance, atomic force microscopy, scanning electron microscope, Fourier transform IR spectroscopy it has been shown that an uniform, selfassembled, anti-corrosionvinylsiloxanenanolayer is formed on the aluminium surface during adsorption of vinyl silane from aqueous solution. This layer covalently bonded to the hydroxylsurface groups of the metal. The thickness of the surface nanolayer can be controlled by changing the deposition conditions. The effect of the vinylsiloxanenanolayer on the dissolution of aluminium in chloride-containing solutions has been studied. It was established that an ordered vinylsiloxanenanolayer, up to five molecular layers thickness, effectively inhibits the uniform and localized aluminium corrosion. It was shown that after 10 days of corrosion tests vinylsiloxanenanolayer is preserved on the aluminium surface, indicating its resistance to water and corrosive components.vinylsiloxane Keywords: Aluminium; Adsorption; Alkoxysilane;Organosilicon Self-Assembled Nanolayers; Heterogeneous Processes; Corrosion; Electrode Reactions; Corrosion Test

Investigating the flow induced corrosion of copper in chloride-containing solution at the atomistic scale

Metal aqueous corrosion is a common electrochemical phenomenon. Nonetheless, the metal corrosion simulations at the atomistic scale have not been well-established yet. In this study, several copper corrosion cases in aqueous solution with chloride ions are studied with molecular dynamics, especially the flow induced corrosion is studied for the first time to the best of our knowledge. The copper corrosion in two kinds of solutions, which are HCl and chloride ions solutions, are simulated with pre-developed reactive force field (ReaxFF) method. Here, particles diffusion, bonding among elements, and charge evolution are analyzed to understand the mechanisms of the cases. It is found that the electrolyte flowing and initial Cu surface can accelerate the corrosion process, illustrated by higher mean-squared displacement (MSD) and Cu average charge. Moreover, the initial rough surface has different effects for different electrolyte concentrations. This work may provide important references for fundamental understanding the mechanisms of copper corrosion in chloride-containing solutions at nanosized scale.

Effect of tantalum film on corrosion behaviour of AA6061 aluminium alloy in hydrochloric acid- and chloride-containing solutions

ABSTRACT The present work is concerned with the corrosion resistance of AA6061 aluminium alloys with tantalum films in hydrochloric acid- and chloride-containing solutions. The tantalum films were produced by magnetron sputtering at different sputtering times (50 and 120 min). The films’ morphologies were observed by metallographic microscope and scanning electron microscope with energy dispersion spectrum. It is shown in this paper that with longer sputtering time, the film’s thickness increased, but it became less dense. The corrosion behaviour was characterised by potentiodynamic polarisation, scanning electrochemical microscopy analysis and an immersion experiment. These investigations revealed that the corrosion resistance of AA6061 aluminium alloy in chloride ions medium and hydrochloric acid was significantly improved after deposition of a tantalum film. Specifically, samples deposited for 50 min exhibited the best corrosion resistance in hydrochloric acid, while samples deposited for 120 min showed best corrosion resistance in sodium chloride solution.

Effect of Phosphate-Based Inhibitor on Corrosion Kinetics and Mechanism for Formation of Passive Film onto the Steel Rebar in Chloride-Containing Pore Solution.

In the present study, different contents, i.e., 1–3% of 0.5 M ammonium phosphate mono basic (APMB), were used as corrosion inhibitor to reduce the corrosion of steel rebar. Electrochemical impedance spectroscopy (EIS) results showed that up to 24 h of exposure, polarization resistance (Rp) and passive/oxide film resistance (Ro) gradually decreased in simulated concrete pore (SCP) + 3.5 wt.% NaCl solution owing to the reduction in pH of the solution. The steel rebar exposed in 2% inhibitor containing SCP + 3.5 wt.% NaCl solution exhibited 90% inhibition efficiency after 1 h of exposure. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy confirmed the formation of thermodynamically very stable and sparingly soluble goethite (α-FeOOH), maghemite (γ-Fe2O3), and iron phosphate (FePO4) as passive/oxide film onto the steel rebar surface exposed to 2% inhibitor containing SCP + 3.5 wt.% NaCl solution.

Galvanic coupling effects on the corrosion behavior of the 6061 aluminum alloy used in research nuclear reactors

The 6061 alloy is used in different thermomechanical conditions in research nuclear reactors. Nuclear fuel plates are manufactured by the picture frame technique (PFT) and the 6061 alloy is used as cladding for the nuclear fuel “sandwiches”. After the PFT process, these nuclear plates are placed in a case made of 6061-T6 alloy. In this work, the galvanic effects of coupling the 6061 alloy in the T6 and PFT temper conditions were investigated in different chloride-containing solutions. The results showed that galvanic coupling was favored between the PFT and 6061-T6 alloy. A potential difference of about 50 mV was observed between the temper conditions. This was attributed to differences in β’’ phase density between the two conditions (T6 and PFT) which was indicated by microhardness results. The 6061 alloy in the PFT condition was cathodic in relation to the T6 one. Results from conventional electrochemical techniques were in agreement with the local measurements. Local electrochemical techniques such as the SVET, SECM and LEIS were useful in characterizing the electrochemical behavior of the galvanically coupled alloys.

Investigation of photo-induced corrosion of copper in aqueous solution based on point defect model

The corrosion behaviors of Cu in a chloride-containing borate buffer solution (pH 8.4) with and without visible light illumination were investigated in the present work. Visible light illumination was shown to induce distinct corrosion behaviors during different stages of exposure. In the early stage, visible light illumination facilitated the growth of a less defective Cu2O film which offered higher resistance to corrosion. Whereas in the longer-term visible light illumination was found to destabilize the Cu2O film and hence accelerated the Cu dissolution. The corrosion mechanisms corresponding to the corrosion behaviors during different stages of exposure were discussed based on the point defect model (PDM).

Estimating the synergistic corrosion inhibition potency of (2-(3,4-)-3,5,7-trihydroxy-4H-chromen-4-one) and trivalent-cerium ions on mild steel in NaCl solution

The low-inhibition potency and the toxic nature of most of the conventional organic molecules in corrosion inhibition of metals against the chloride-containing solution, has forced the researchers to develop eco-friendly compounds. In the present study, (2-(3,4-dihydroxyphenyl)-3,5,7-trihydroxy-4H-chromen-4-one), called Quercetin, was selected as green corrosion inhibiting molecules for the steel protection against NaCl solution. The Quercetin molecules' ability for reaction with Ce (III) ions, forming hybrid organic-inorganic compounds was studied. The type of interactions between the Quercetin molecules and trivalent-cerium ions was investigated via FT-IR and UV–Vis (in water solution) analyses. The corrosion inhibition potency of the mixture of Quercetin:Ce was examined using polarization and EIS methods. Electrochemical achievements reflected that the Quercetin:Ce complexes could retard mild steel corrosion by a high inhibition efficiency degree of 96% via mixed cathodic and anodic inhibition mechanisms. The inhibited and uninhibited metal samples' surface morphology and microstructure were explored by FE-SEM, GIXRD, and EDS/Mapping techniques. The high presence of Ce atom in the deposited film evidences sufficient Quercetin:Ce adsorption.

Alternative to Nitric Acid Passivation of 15-5 and 17-4PH Stainless Steel Using Electrochemical Techniques.

Increasingly stringent environmental regulations in different sectors of industry, especially the aeronautical sector, suggest the need for more investigations regarding the effect of environmentally friendly corrosion protective processes. Passivation is a finishing process that makes stainless steels more rust resistant, removing free iron from the steel surface resulting from machining operations. This results in the formation of a protective oxide layer that is less likely to react with the environment and cause corrosion. The most commonly used passivating agent is nitric acid. However, it is know that high levels of toxicity can be generated by using this agent. In this work, a study has been carried out into the electrochemical behavior of 15-5PH (precipitation hardening) and 17-4PH stainless steels passivated with (a) citric and (b) nitric acid solutions for 60 and 90 min at 49 °C, and subsequently exposed to an environment with chlorides. Two electrochemical techniques were used: electrochemical noise (EN) and potentiodynamic polarization curves (PPC) according to ASTM G199-09 and ASTM G5-13, respectively. The results obtained indicated that, for both types of steel, the passive layer formed in citric acid as passivating solution had very similar characteristics to that formed with nitric acid. Furthermore, after exposure to the chloride-containing solution and according with the localization index (LI) values obtained, the stainless steels passivated in citric acid showed a mixed type of corrosion, whereas the steels passivated in nitric acid showed localized corrosion. Overall, the results of the values derived show very low and similar corrosion rates for the stainless steels passivated with both citric and nitric acid solutions.

Cyclic Voltammetry as an Electroanalytical Tool for Analysing the Reaction Mechanisms of Copper in Chloride Solution Containing Different Azole Compounds

Background: Cyclic voltammetry is widely employed in electroanalytical studies because it provides fast information about the redox potentials of the electroactive species and the influence of the medium on the redox processes. Azole compounds have been found to be effective corrosion inhibitors for copper in chloride-containing solutions. The aim of this work was to investigate in detail the influence of the addition of various azole compounds on the oxidation mechanism of copper in chloride-containing solutions, using cyclic voltammetry. Methods: The influence of thirteen azole compounds, at three different concentrations on the electrochemical/ chemical reactions of pure copper immersed in 3 wt.% NaCl solution was studied using cyclic voltammetry at different scan rates. The change of the peak current and potential with the scan rate were investigated. The possible linearity was compared with the theoretically derived mechanism. The possible reaction mechanisms were discussed based on the linearity of these parameters (peak current and potential) with the scan rate compared to theoretically derived models. Results: Both the peak current and peak potential of the copper samples immersed in chloridecontaining solutions with additions of the majority of azole compounds showed linearity with the square root of the scan rate, suggesting that copper follows the Müller-Calandra passivation model. The same behavior was also found for copper in chloride-containing solutions without additions of azole compounds. A linear variation of the peak potential with the natural logarithm of the scan rate and linear variation of the peak potential with the square root of the scan rate was observed for the copper samples immersed in chloride-containing solutions with the addition of 10 mM of 2-mercapto-1- methylimidazole, imidazole, or 2-aminobenzimidazole. This suggests that copper follows irreversible redox reactions under a diffusion controlled process. No other linear relations of the peak current and peak potential with the scan rate were found. Conclusion: Copper oxidation in chloride-containing solutions is controlled by passivation (following the Müller-Calandra passivation model) upon the addition of the majority of the selected azoles. In the minority of cases, irreversible redox reactions that follow a diffusion-controlled process were identified. None of the systems followed an adsorption-controlled process. Moreover, none of the tested systems underwent reversible redox reactions that followed a diffusion controlled process.

Specific Features of the Formation of the Disperse Polymetallic System Fe–Al–Mo–W in Aqueous Solutions

The coreduction of Fe(III), MoO$$_{4}^{{2 - }}$$, and WO$$_{4}^{{2 - }}$$ ions in chloride-containing aqueous solutions in the presence of 2-hydroxypropane-1,2,3-tricarboxylic acid on disperse aluminum suspended in the solution was studied. It was shown that the coprecipitation of molybdenum, tungsten and elemental iron proceeds during the reduction process; it was estimated that the precipitation of molybdenum prevails over the precipitation of tungsten. It was found that the formation of the deposit takes place on the surface of the aluminum particles; the shape and size of the initial aluminum matrix are preserved. It was experimentally found that the presence of the tungstate ions is preferable for the formation of particles with a smoother surface; the corresponding metals in the form of Fe + Mo and Fe + W solid solutions are present in the synthesized polymetallic disperse samples as well as elemental iron and aluminum.

Trazodone as an efficient corrosion inhibitor for carbon steel in acidic and neutral chloride-containing media: Facile synthesis, experimental and theoretical evaluations

Trazodone (TDO, 2-(3-(4-(3-chlorophenyl)piperazin-1-yl)propyl)-[1,2,4]triazolo-[4,3-a]pyridin-3(2H)-one) was synthesized via a facile strategy without using acid-removing agent of strong activity, and its structure was confirmed by nuclear magnetic resonance and Fourier transform infrared spectroscopy. The efficient corrosion inhibition of protonated and neutral TDO for 20# carbon steel (C-steel) in the respective acidic and neutral chloride-containing solutions was verified by gravimetric, electrochemical measurements and surface analyses. The inhibition efficiency of TDO for C-steel in 3.5% NaCl solution was moderately higher than that in 0.5 M HCl medium, reaching 93.1% at 298 K with 8 mM concentration. TDO simultaneously inhibited anodic and cathodic reactions with dominantly anodic effect, and prominently elevated interfacial polarization resistance for C-steel in both media. Morphology observations indicated that the appearance of C-steel was improved with reduced surface roughness due to TDO adsorption. The existence of cationic TDO caused by protonation was confirmed in the adsorption layer after immersion in acidic solution by X-ray photoelectron spectroscopy. Adsorption of TDO on C-steel surface in both solutions conformed to Langmuir isotherm. Quantum chemical calculations under dominant solvent model and molecular dynamics simulations were also performed, the outcomes of which were in good correlation with experimental results.

Synergistic Action of Sulfate and Chloride Anions on the Corrosion Behavior of AZ31B Magnesium Alloy

Magnesium and its alloys have a great potential for lightweight structure applications, because magnesium has lower density (~1.7 g.cm-3) compared to aluminum (2.7 g.cm-3) and iron (~7.9 g.cm-3). Magnesium alloys also exhibit high strength-to-weight ratios [1]. Their use enables the weight reduction of automotive and aerospace vehicles for more energy consumption efficient. However, magnesium alloys have a limitation for practical application, namely the high chemical activity, porous corrosion product and high corrosion rate. In addition, due to the rapid industrialization in some developing countries, air pollution (like PM2.5) has become a hot topic. Most of air pollutants contain ions like SO4 2-, NO3- and NH4+, which have high solubility [2]. The corrosion behavior of magnesium in chloride-containing environment is also worth studying because Cl- is the most common aggressive corrosion species. In contrast, sulfate ions in chloride-containing solutions can inhibit hydrogen evolution [3]. It is thus of great interest to understand the corrosion behavior of magnesium alloys in solution containing different anions, which provides a basis for designing the effective conversion coating process.In this study, the corrosion behavior of magnesium alloy AZ31B in sulfate and chloride solutions was investigated by using real-time imaging, hydrogen evolution test, electrochemical analysis, and cross-sectional TEM characterization. Through the results of the real-time imaging, the corrosion behavior of magnesium alloy AZ31B in the solution can be roughly divided into three stages. Firstly, the uniform corrosion proceeds with a large amount of hydrogen evolution. Secondly, the corrosion product gets thicker accompanied by the reduction in the amount of hydrogen evolution. Final stage only happens in the chloride containing solution. A hydrogen stream and dark corrosion products are produced [4]. Cross-sectional TEM was employed to characterize the sample, which was immersed for 25 min (the time when the dark corrosion product was produced). The results show that when the magnesium alloy AZ31B was treated in the chloride solution, the thickness of the corrosion product layer is about 80 ± 30 nm. Furthermore, the corrosion product layer formed in a sulfate-containing solution shows a uniform film thickness about 170 nm. This difference in thickness was further confirmed in the hydrogen evolution test. The hydrogen evolution test shows that the amount of hydrogen produced by the magnesium alloy AZ31B in the sulfate solution is about twice that in the chloride solution. This indicates that the corrosion product formed in the sulfate solution is about twice that in the chloride solution, implying that the corrosion product formed in the chloride ion environment is more protective. The EIS results also show the same trend. The total impedance of the corrosion product in the chloride ion immersion environment is much larger than that of the sulfate solution and the total impedance value increases as the chloride concentration is increased. As a result, chloride ions can effectively fill the weaker areas of the airform film during the early stages of corrosion. This localized corrosion phenomenon also causes the difference in film thickness.The third stage of corrosion was found to be absent when the magnesium alloy AZ31B was immersed in a chloride and sulfate mixture solution. The TEM results show that the corrosion product is more uniform than immersed in solution containing only chloride. Thus, it is proposed that sulfate ions serve as a physical barrier to hinder chlorine ions from attacking the magnesium substrate, which, in turn, results in a uniform corrosion product layer.

Effect of intentional convection on the passivity of an Fe–6Cr surface in pH 4.5 Na2SO4 solution

The anodic oxidation behavior of Fe–6Cr during potentio-dynamic polarization in pH 4.5 Na2SO4 solution was investigated by electrochemical ellipso-microscopy. Active, passive, and trans-passive states of the Fe–6Cr surface showed heterogeneous oxidation behaviors depending on the substrate micro-structure, electrode potential and solution convection. Enhancement of mass-transport by solution injection in the latter half of the active state resulted in acceleration of passivation of the Fe–6Cr surface. The passivity-current density of the surface passivated by intentional convection was reduced to almost half of the current density of the surface that had been in the passive state in a stagnant solution, and the surface passivated by intentional convection showed better resistance against pitting in a chloride-containing solution. The improvement of passivity of the surface was attributed to the formation of a Cr-enriched passive film by a decrease in the thickness of the diffusion layer in the latter half of the active state.

Features of zinc passivation by sodium dodecylphosphontate in a neutral aqueous solution

The features of the adsorption and passivating effect of sodium dodecylphosphonate (C12PNa2) on zinc, as well as the effect of electrode potential and presence of a surface oxide on them were studied. The possibility of zinc adsorption passivation by C12PNa2 with formation of nanolayers that inhibit zinc corrosion in a chloride-containing neutral solution and in a humid atmosphere was shown. The adsorption properties of C12PNa2 are most pronounced on an oxide-free zinc surface. The composition of the layers formed by C12PNa2 depends on the initial state of the surface and determines their protective ability.

Controlling the corrosion behavior of Ti-Zr alloy by tuning the α/β phase volume fraction and morphology of β phase

Herein, the influence of relative ratio α and β phases and morphology of β phase on the corrosion behavior of Ti-Zr alloy is systematically studied. The fraction of α and β phases is controlled by carrying out heat treatment at elevated temperatures, followed by water quenching. The electrochemical characterization reveals that the corrosion resistance of Ti47Zr5Al3V (47Zr) alloy in a chloride-containing solution initially decreased with the decrease of α phase fraction, followed by a gradual increase. Moreover, the alloy surface passivation film became rougher with the decrease of α phase content. One should note that the β phase coarsening also decreased the corrosion resistance and increased the surface passivation film roughness of the 47Zr alloy by reducing nucleation sites for the passivation film. In general, the corrosion resistance of two-phase Ti alloy has been significantly affected by the relative content of α/β phases and morphology of β phase, which can be ascribed to the different concentration of nucleation sites for the passivation film and number of galvanic interactions between α and β phases. The detailed X-ray photoelectron spectroscopy (XPS) analysis has been carried out to assess the composition of the passivation film, revealing the presence of TiO2 and ZrO2 as well as a small amount of Al2O3 and V2O5. Despite the fact that the relative fraction of α and β phases and grain size are influenced by the heat treatment, the content of each element in the passivation film remained unchanged. This study provides an insight how the relative phase ratio of α to β and surface morphologies affect Ti corrosion behaviour in the simulated acidic ocean environment.