The effect of chloride ions on the corroded surface layer of 00Cr22Ni5Mo3N duplex stainless steel under cavitation

The effects of Cl⁻ on the corroded surface layer of 00Cr22Ni5Mo3N duplex stainless steel under cavitation in chloride solutions were investigated using nanoindentation in conjunction with XRD and XPS. The results demonstrate that Cl⁻ had a strong effect on the nano-mechanical properties of the corroded surface layer under cavitation, and there was a threshold Cl⁻ concentration. Furthermore, a close relationship between the nano-mechanical properties and the cavitation corrosion resistance of 00Cr22Ni5Mo3N duplex stainless steel was observed. The degradation of the nano-mechanical properties of the corroded surface layer was accelerated by the synergistic effect between cavitation erosion and corrosion. A key factor was the adsorption of Cl⁻, which caused a preferential dissolution of the ferrous oxides in the passive film layer on the corroded surface layer. Cavitation further promoted the preferential dissolution of the ferrous oxides in the passive film layer. Simultaneously, cavitation accelerated the erosion of the ferrite in the corroded surface layer, resulting in the degradation of the nano-mechanical properties of the corroded surface layer on 00Cr22Ni5Mo3N duplex stainless steel under cavitation.     

Dependence of critical pitting temperature on the concentration of sulphate ion in chloride-containing solutions

Effects of varying concentration of sulphate (SO₄²⁻) ion on the pitting behavior of 316SS have been investigated using potentiostatic critical pitting temperature (CPT) measurements, potentiostatic current transient technique and scanning electron microscopy in NaCl solution containing 0.5% Cl⁻ ions. The results demonstrated that when the concentration of SO₄²⁻ ion is less than 0.42%, the CPT is surprisingly lower than that without SO₄²⁻ ion, showing an accelerating effect of the SO₄²⁻ ion on pit initiation, which is different from the traditional concept. As the concentration of SO₄²⁻ ion increases beyond 0.42%, the CPT is higher than that without SO₄²⁻ ion, displaying an inhibiting effect of the SO₄²⁻ ion on pit initiation. Based on the above results, a qualitative model is proposed to explain the inhibiting and accelerating effect of SO₄²⁻ ion on the pit initiation using the mechanism of ions-competitive adsorption between SO₄²⁻ and Cl⁻ ions. The electric charges calculated in the process of pitting corrosion indicated that the pit morphology and its dimension are dependent on the content of SO₄²⁻ ion in chloride-containing solutions. The higher the concentration of SO₄²⁻ ion, the larger the dimension of the pit, reflecting an accelerating effect on pit growth.     

Metastable and stable pitting events at zinc passive layer in alkaline solutions

The electrochemical behavior of Zn in 0.5 M NaOH solutions containing various concentrations (0.01–0.1 M) of ClO₃ ^? or ClO₄ ^? anions was studied with potentiodynamic anodic polarization and chronoamperometry techniques. Microstructural and topographical characterization of the pitted surfaces was carried out by ex situ scanning electron microscopy and atomic force microscopy examinations. Addition of either ClO₃ ^? or ClO₄ ^? stimulated general corrosion and ruptured the passive layer (stable pitting), with ClO₃ ^? being more aggressive than ClO₄ ^?. Metastable pitting events appear as current oscillations (spikes) at potentials close to the pitting potential when Cl^? ions are produced by cathodic reduction of ClO₃ ^? and ClO₄ ^? before passive layer growth. Current–time measurements are performed at fixed potential after production of Cl^? ions and show that the rate of metastable pitting and the intensity of current spikes increase with the potential and the concentration of aggressive anions. Concepts of thin film growth are applied to the passive layer formation in order to explain those results. Metastable events are related to the presence of defects in the passive layer because their frequency and intensity are enhanced in conditions that favor defect formation and roughening in growing films, while stable pitting typically occurs at regions of high metal disorder.     

Corrosion reaction of iron exposed to the open atmosphere in the Antarctic

Within a cooperative program for the elaboration of a Latin American Map of Atmospheric Corrosion, weathering steel and mild steel samples were exposed to the Antarctic atmosphere and the corrosion products analyzed by ICEMS, XPS and XRD. Superparamagnetic -FeOOH was the main corrosion product after 24 h of exposure. Cl^– ions are found on the surface of the corroded samples by XPS.     

Phase transition and pitting corrosion behaviour for Mo—implanted aluminium

Molybdenum ions are implanted into aluminium with high ion flux and high dose at elevated temperatures of 200℃, 400℃ and 500℃. Due to the high temperature and high flux of vacancies and interstitial atoms, the atom diffusion and chemical effects are enhanced during the ion implantation. The effects increase with increasing ion flux and dose, so that new phase formation and phase transition emerge noticeably. X-ray diffraction analysis shows that when the aluminium is implanted with Mo ions at a low ion flux (25μA/cm²), the Al₅Mo alloy is formed. The atomic ratio of Mo/Al of the Al₅Mo phase is close to 20%. When the aluminium is implanted with Mo ions at a high ion flux (50μA/cm²), the phase transition from Al₅Mo to Al₁₂Mo appears, and the latter is dominant, which is determined to be the final phase. The ratio of Mo/Al in Al₁₂Mo is 7.7%. Rutherford backscattering spectroscopy indicates also that the Mo/Al atom ratio is ～7% to ～8% in Mo-implanted aluminium. The atomic ratios of the constituents in Al₅Mo and Al₁₂Mo are of stoichiometric composition for these alloys. The thicknesses of the Al₁₂Mo alloy layers for Mo-implanted Al with ion doses of 3×10¹⁷/cm² and 1×10¹⁸/cm² are 550nm and 2000nm, respectively. The pitting corrosion potential V_p increases obviously. It is clear that due to the formation of Al₁₂Mo alloy layer, the pitting corrosion resistance is enhanced.     

Analysis of EIS characteristics of CO2 corrosion of well tube steels with corrosion scales

The electrochemical impedance spectroscopy (EIS) was used to study the characteristics of CO₂ corrosion of N80 and 4Cr steels with corrosion scales. The results indicated that CO₂ corrosion scale on tube steel could prevent the rate of mass transfer remarkably, corrosion rate was controlled by ions diffusion in corrosion scale, which led to finite length diffusion impedance occurred in electrochemical impedance spectra. Additionally, pitting of N80 steel could lead to additional capacitive reactance in impedance spectrum. The ion diffusion coefficient in corrosion scale and porosity of corrosion scale could be calculated by Warburg impedance coefficient, the results shown that the value of H⁺ diffusion coefficient in N80 and 4Cr corrosion scale is (3.46 and 1.76) × 10⁻¹⁰ m² s⁻¹, respectively. The protective ability of 4Cr corrosion scale was better than that of N80 corrosion scale.     

Anomalous concentration dependence of the coordination behavior of Cl− ion to Ln3+ ion (Ln3+ = rare‐earth ion) in anhydrous LnCl3 alcohol solutions

Raman spectroscopic measurements were carried out for the anhydrous LnCl₃·20ROH·XLiCl solutions (Ln³⁺ = La³⁺− Lu³⁺, X = 0–3; ROH = MeOH, EtOH, n‐PrOH) in the liquid state. The salt concentration (X) dependence of the wavenumber for the Ln–Cl stretching Raman band (ν_Ln–Cl) is examined in conjunction with the formation of chloro‐rare‐earth complexes. We have obtained very intriguing results including the fact that the chloro complexations of the middle rare‐earth ions (e.g. gadolinium, holmium ions, etc.) in the MeOH and EtOH solutions show peculiar behavior with regard to the salt concentration dependence: the ν_Ln–Cl wavenumber increases with the increasing chloride concentration. However, the ν_Ln–Cl wavenumbers of the light and heavy rare‐earth (e.g. lanthanum, lutetium, etc.) salt solutions show normal behavior; i.e. ν_Ln–Cl decreases with the increasing chloride concentration. On the other hand, in the n‐PrOH solutions, the ν_Ln–Cl frequency in the solutions of all the rare‐earth elements exhibits a normal behavior. We now present a possible mechanism for this anomalous concentration dependence of coordination of Cl⁻ ions to Ln³⁺ ions in anhydrous LnCl₃ alcohol solutions. Copyright © 2007 John Wiley & Sons, Ltd.     

Low-nickel stainless steel passive film in simulated concrete pore solution: A SIMS study

Low-nickel and AISI 304 austenitic stainless steel (SS) passive films were studied using secondary ion mass spectrometry (SIMS). An alkaline Ca(OH)₂ saturated test solution containing different chloride additions was used at room temperature. The passive film formed consists mainly of an inner chromium-rich oxide layer and an outer iron-rich oxide layer. The chemistry of the passive film depends strongly on the chloride content in the alkaline solution. Under these exposure conditions nickel was detected in the outer part of the oxide, whereas chloride ions were not found in the passive film for either the low-nickel or AISI 304 SS alloys.     

Kinetics of decomposition of the solid electrolyte RbCu4Cl3I2

The processes of electrochemical decomposition of the solid electrolyte RbCu₄Cl₃I₂ at the vitreous carbon electrode and chemical decomposition of RbCu₄Cl₃I₂ by iodine has been investigated. The anodic decomposition of the electrolyte occurs in two steps. At first, the oxidizing electrode reaction of Cu⁺ ions up to Cu²⁺ ions takes place at potentials higher than 0.57 V and onto the electrode surface the layer of decomposition products is formed, including the compound of divalent copper RbCuCl₃. Then the oxidizing reaction of I ions occurs at potentials higher than approximately 0.67 V with deposition of the iodine layer onto the electrode surface. The deposition rate of the layers of decomposition products is controlled by instantaneous nucleation and two-dimensional growth of the deposit. It was shown that slow diffusion of the iodine in the reaction product layer is a limiting step in the chemical interaction of iodine with RbCu₄Cl₃I₂. For the compressed RbCu₄Cl₃I₂ sample investigated, iodine diffusion coefficient was calculated to be 6.2×10⁻⁷ cm² s⁻¹. Iodine loss from the glassy carbon surface is about 1.1×10⁻⁴ g cm⁻² s⁻¹ at the thickness of the RbCu₄Cl₃I₂ sample is equal to 2 mm.     

Analysis of the composition of the passive film on iron under pitting conditions in 0.05 M NaOH/NaCl using Raman microscopy in situ with anodic polarisation and MCR‐ALS

The composition of the surface film formed on pure iron was investigated in a solution of 0.05 M NaOH and 0.05 M NaCl. Raman spectra of the film were recorded in situ during anodic polarisation over the passive region after addition of the NaCl to the electrolyte, under conditions of preresonance enhancement using excitation at 636.4 nm. Multivariate curve resolution with alternating least squares analysis was applied to the spectra to measure the relative amounts of different iron oxide and oxyhydroxides in the film at different potentials. The water content was also determined in this way from Raman spectra recorded using excitation at 514.5 nm. It was found that the composition of the film and the amount of incorporated water were influenced by the applied anodic potential. The results show that stable pitting can occur when the composition changes from the primary constituents β‐FeOOH and Green Complex (a hydrated, amorphous magnetite) with smaller amounts of γ‐Fe₂O₃ and γ‐FeOOH, to δ‐FeOOH and Green Complex, simultaneously with a reduction in water content. These changes result in conditions that favour the rate of localised breakdown of the film by Cl⁻ ions over the rate of repassivation by water in the passive film. Copyright © 2011 John Wiley & Sons, Ltd.     

Influence of Mo on the Microstructure and Corrosion Behavior of Laser Cladding FeCoCrNi High-Entropy Alloy Coatings

FeCoCrNi and FeCoNiCrMo_0.2 high-entropy alloy powders were prepared by gas atomization. Two kinds of coatings were prepared on the surface of 304 stainless steel by laser cladding technology. The effect of Mo element on the microstructure of laser cladding FeCoCrNi coating and its corrosion behavior in 3.5 wt.% NaCl solution was investigated. Both FeCoCrNi and FeCoCrNiMo_0.2 powders exhibit a single-phase FCC structure. Due to the remelting and multiple heat treatments during the preparation of the laser cladding coating, a small amount of σ and μ phases appeared in the FeCoCrNiMo_0.2 coating. The microstructures of the two coatings from the bonding area to the top layer are planar, columnar and equiaxed grains, respectively. The addition of the Mo element causes the dendrite size in the middle region of the FeCoCrNiMo_0.2 coating increases significantly and exhibits obvious orientation characteristics. FeCoCrNiMo_0.2 coating has high corrosion potential (−0.01 V_SHE) and low current density (0.94 × 10⁻⁷ A/cm²) in 3.5 wt.% NaCl solution, showing excellent corrosion resistance. The passivation film formed on corroded the FeCoCrNiMo_0.2 coating contains high content of oxides of Cr and Mo. The addition of the Mo element enhances the compactness and pitting resistance of the passivation film.     

Effect of surface nanocrystallization induced by fast multiple rotation rolling on hardness and corrosion behavior of 316L stainless steel

A nanostructured layer was fabricated by using fast multiple rotation rolling (FMRR) on the surface of 316L stainless steel. The microstructure in the surface was characterized by transmission electron microscopy and X-ray diffraction. The effects of FMRR on the microhardness, surface roughness and corrosion behavior of the stainless steel were investigated by microhardness measurements, surface roughness measurements, potentiodynamic polarization curves and pitting corrosion tests. The surface morphologies of pitting corrosion specimens were characterized by scanning electron microscopy. The results show that FMRR can cause surface nanocrystallization with the grain size ranges from 6 to 24 nm in the top surface layer of the sample. The microhardness of FMRR specimen in the top surface layer remarkably increases from 190 to 530 HV. However, the surface roughness slightly rises after FMRR treatment. The potentiodynamic polarization curves and pitting corrosion tests indicated that the FMRR treated 316L stainless steel with a surface nanocrystallized layer reduced the corrosion resistance in a 3.5% NaCl solution and enhanced the pitting corrosion rate in a FeCl₃ solution. Possible reasons leading to the decrease in corrosion resistance were discussed.     

Potentiodynamic studies on corrosion of copper by chloride ions and its inhibition by inorganic and organic ions in aqueous buffer solution

Electrochemical oxidation of copper in aqueous phosphate buffer solution leads to the formation of passive films, which breakdown in the presence of aggressive chloride (Cl^?) ions. The addition of Cl^? ions in the medium causes shift in current and potential for both cathodic and anodic peaks. At low Cl^? ion concentrations, the corrosion current is greatly enhanced and continues to increase up to a certain concentration, after which it decreases. The effect of inorganic ions, chromate (CrO ₄ ^2? ) and tungstate (WO ₄ ^2? ), and organic ions, acetate (CH₃COO^?) and oxalate (C₂O ₄ ^2? ), on the formation and breakdown of passive films in aqueous buffer solution containing 0.10 M Cl^? ions have also been investigated. All of the ions inhibit corrosion of copper in the presence of aggressive Cl^? ions following the order of overall inhibition efficiency of CrO ₄ ^2? > C₂O ₄ ^2? > WO ₄ ^2? > CH₃COO^? under the experimental conditions.     

Study on the deterioration process of a chromium-free conversion coating on AZ91D magnesium alloy in NaCl solution

The morphology of a chromium-free conversion coating for AZ91D magnesium alloy was observed with an Atomic Force Microscopy. The results showed the uniform conversion coating has a relatively smooth appearance with shallow valleys. The EDX results indicated that the compositions of the coating were mainly compounds of Mg, Al, Mn, P, Ca and O. The XRD result showed that the coating contained amorphous materials and a small quantity of crystalline compound. The pitting product of the coating in NaCl water solution mainly composed of Mg, Cl, Mn, P, Ca and O. The corrosion behavior of the samples in NaCl solution was also studied by electrochemical impedance spectroscopy (EIS), which was characterized by one capacitive loop and one inductive loop. Based upon study on both a mathematical model for Faradic admittance of coating in NaCl solution and EIS, it could be considered that the inductive loop was caused by the adsorption of Cl anion and the appearance of pitting corrosion. A degradation mechanism of the coating in NaCl solution is set forth: dissolution velocity of the Cl⁻ adsorption regions of the coating is higher than those non-adsorption regions, for Cl⁻ anions are selective adsorption at some regions of coating surface. When the adsorption regions of coating layer are penetrated by dissolution, the pitting comes into being. The degradation mechanism of conversion coating and the mathematical model are consistent with the EIS results, polarization measurement results and coating's corrosion test results.     

Terbium‐Doped Layered Yttrium Hydroxide Nanocone: Controlled Synthesis,Structure Variations,Phase Conversion to Oxide/Oxysulfate Nanocone and Their Luminescence Properties

It is demonstrated herein that a series of terbium ions (Tb³⁺)‐doped layered yttrium hydroxide (LYH:Tb) nanocones (NCs) intercalating dodecyl sulfate (C₁₂H₂₅SO₄, DS) anions can be successfully synthesized in large quantities through a facile hydrothermal strategy. The DS anions in the interlayer gallery of LYH:Tb NCs can be readily modified with various anions (such as NO₃ ⁻, Cl⁻, and CH₃COO⁻) through a convenient anion‐exchange procedure. The luminescent properties of LYH:Tb NCs are sensitively influenced by the dopant concentration and the interlayer anions. In particular, the original DS⁻‐intercalated form and the anion‐exchanged product can be topotactically converted into oxysulfates and oxides with original conical features through a calcination process at 750 °C for 2 h, respectively. Compared with Y₂O₃:Tb NCs, Y₂O₂SO₄:Tb NCs exhibit efficient luminescent properties due to the stronger deformation of the crystal field. More interestingly, the conical structures also exhibit superior luminescent properties over the lamellar objects, originating from the extreme curvature and perturbation of crystal field, which are promising candidates for potential applications in optical and display devices.     

Improvement of hot-dip zinc coating by enriching the inner layers with iron oxide

The performance of hot-dip galvanic coating formed on steel not only depends on the alloy composition of the superficial layer but also significantly, on the composition of the inner alloy layers at the coating/substrate interface. Further, the presence of barrier oxide layers, if any can also improve the performance of galvanic coating. In the present work, the effect of inner iron oxide barrier layer formed prior to hot-dip galvanization was investigated. A continuous and adherent iron oxide layer was formed on steel by anodic oxidation of the steel substrate. Although the wettability of oxide surface by liquid zinc was initially poor, the increase in dipping time and the transition of the oxide layer to unstable form due to the presence of Cl⁻ ion in the flux facilitated localized growth of Fe-Zn alloy phases. The inhibitive nature of the oxide layer was temporary, since the presence of Cl⁻ induces micro cracks on the oxide surface thereby facilitating better zinc diffusion. The modification of the substrate structure during galvanization was found to influence the galvanizing process significantly. The present study predicts scope for application of this process for protection of rusted steel specimens too.     

LiF-LiCl-B2O3系统非晶态快离子导体结构的研究

本文通过对¹¹B核磁共振(¹¹B-NMR)、红外光谱等实验方法,研究了LiF-LiCl-B₂O₃三元系统玻璃的结构和离子导电性,着重于F^-离子在玻璃网络中所起的作用,以及F^-,Cl^-和Li⁺离子对导电率的影响。LiF-LiCl-B₂O₃三元系统玻璃,随LiF含量的增加,B由三角体向四面体变化,从而F^-离子进入网络,使玻璃结构由[B₂O₃]三角体层状结构向三维空间延展,形成了含有[BO₃F]基团的三维空间网络,Cl^-离子以游离的离子存在于网络中,起着松散网络的作用,对提高电导率有利,而Li⁺离子作为传导离子,对电导率的贡献是主要的。本系统玻璃的电导率是随LiF,LiCl含量的增加而增大,在300℃时测得电导率σ=6.12×10^-4Ω^-1·cm^-1。 关键词：     

Effects of metal ion on the water structure studied by the Raman O?H stretching spectrum

Raman spectra in the O H stretching region of aqueous salt solutions were measured and compared, and the effects of metal ions on water structure deduced. The effects of alkali ions, alkaline ions or the first‐row transition metals on water structure were found to be similar. Differences of metal ionic effects on water structure exist among Na⁺, Mg²⁺ and Al³⁺, and between Ca²⁺ and Mn²⁺ and Al³⁺ and Fe³⁺. The factors that influence the metal ionic effects on the water structure are the ionic charge, the outmost electronic structure and ionic size, the ionic charge being the most important. With a five‐component Gaussian deconvolution of the Raman spectra of the aqueous solutions of NaCl, MgCl₂, AlCl₃ and FeCl₃ with concentrations of 0 to ∼1mol/l, the ionic effects were found to be similar on the bands at 3233, 3393, 3511 and 3628 cm⁻¹, but different on the band at 3051 cm⁻¹. With increasing polarization of the metal ion, the band at 3051 cm⁻¹, due to strong hydrogen bonding, increases. Copyright © 2009 John Wiley & Sons, Ltd.     

Influence of argon ion bombardment on the formation of intermetallic compounds in the nickel-aluminum system

The formation of Ni _x Al _y intermetallic compounds in two-layer (Ni/Al) structures (nickel films deposited on aluminum substrates in vacuum) under bombardment by Ar⁺ ions has been studied experimentally. The method based on Rutherford backscattering of He⁺ ions is used to demonstrate that argon ion bombardment causes the formation of intermetallic compounds in the near-surface layer. The thickness of the intermetallic layer formed in the near-surface region substantially exceeds the projective ion path. The composition and thickness of the intermetallic layer depend mainly on the implantation dose and the substrate temperature, rather than on the ion current density. In the intermetallic layer, the content of nickel increases with increasing temperature. It has been established that, in the absence of bombardment, intermetallic phases are not observed at temperatures lower than T = 400°C and that, in the presence of bombardment, the Ni₃Al intermetallic layer arises at a temperature of 320°C.     

Study of the composition and properties of protective layers formed by the ion-beam-assisted deposition of cadmium,zinc, and aluminum onto steel surfaces

Layers formed by the ion-beam-assisted deposition of cadmium, zinc, and aluminum onto the surface of carbon and stainless steels to protect aluminum and its alloys from corrosion in the case of their contact with steel parts are investigated. The protective layers are created via ion-beam-assisted deposition, in which metal deposition and mixing of the deposited layer with the substrate surface (this process is implemented by accelerated (U = 5 kV) ions of the same metal) occurs, respectively, from a neutral vapor fraction and the vacuum arc plasma of a pulsed electric-arc ion source. The morphology and composition of the generated surface layers are studied by means of scanning electron microscopy, electron-probe microanalysis, and Rutherford backscattering spectrometry. The layer composition is revealed to include atoms of the deposited metal, the substrate material, oxygen, and carbon. The layer thickness varies from ~50 to 80 nm, and the deposited metal content of the layers is ~(1.0–3.5) × 10¹⁷ atom/cm². Corrosion tests of the aluminum and its alloy in contact with the materials under study confirm the efficiency of the ion-beam modification of steel surfaces.