Study on the passive film formed on 2205 stainless steel in acetic acid by AAS and XPS

The properties of the passive film formed on 2205 stainless steel in acetic acid at high temperature that contained chloride ions were studied by atomic absorption spectrometry （AAS）, X-ray photoelectron spectroscopy （XPS）, and electrochemical polarization measurements. AAS results show that molybdenum is enriched on the surface as the passive film is dissolved. This enrichment decreases the corrosion resistance because it hinders chloride adsorption and Fe ion dissolution, and acts as a local pH buffer because it consumes protons. The dissolution ratio of Fe/Cr is approximately 10 during the active dissolution of the passive film. XPS results indicate that when the potential is in the passivation region, Cr comprises about 50% of the metal cations in the near-surface region of the passive film and is the main metal constituent in this region. When the polarization potential is much greater than the transpassivation potential, the Mo content accounts for approximately 45% of the metal cations in the nearurface region; Fe and Ni have no obvious influence on the formation, dissolution, or puncture of the passive film.

Effect of microstructure and passive film on corrosion resistance of 2507 super duplex stainless steel prepared by different cooling methods in simulated marine environment

The effect of microstructure and passive film on the corrosion resistance of 2507 super duplex stainless steel(SDSS)in simulated marine environment was investigated by electrochemical measurements,periodic wet–dry cyclic corrosion test,scanning Kelvin probe force microscopy,atomic force microscopy,and X-ray photoelectron spectrometry.The results show that the occupation ratio ofγphase increases with the decrease in cooling rate,whereas the content ofαphase reduces gradually.In addition,theσprecipitated phase only emerges in the annealed steel.The pitting sensitivity and corrosion rate of 2507 SDSS reduce first and then increase as the cooling rate decreases.Theσprecipitated phase drastically reduces the protective ability of the passive film and facilitates micro-galvanic corrosion of the annealed steel.For various microstructures,the pits are preferentially distributed within theσandγphases.The corrosion resistance of 2507 SDSS prepared by different cooling methods is closely related to the microstructure and structure(stability and homogeneity)of the passive film.Normalized steel shows an optimal corrosion resistance,followed by the quenched and annealed steels.

XPS analysis of passive film formed on the G3 nickel-base alloy tubing under corrosive conditions

In the present study, the passive film formed on the G3 nickel-base alloy tubing under corrosive conditions including H2S ,CO2 ,and Cl-at 130 ℃ and 205 ℃ is studied with X-ray photoelectron spectroscopy（XPS）. The results reveal that the passive film formed at 205℃ consists of Cr, Ni, Fe, S and O elements and is over 470 nm in thickness. The passive film can be divided into three layers, the outer-layer is composed of NiS2 and Cr2 S3 , the intermediate-layer of Cr（OH） 3, Ni （OH） 2, NiS2, Cr2 $3 and a small quantity of NiO and Cr2 O3, and the inner-layer of NiO, Cr2 O3, and alloy elements. Due to the invasion of S2 - into the passive film and the decrease of the content of chromium oxide in the film, the corrosion resistance of the G3 alloy in the sour environment at 205 ℃ is weakened.

STUDIES OF LOW-CONCENTRATION CHROMATE PASSIVE FILM FOR ZINC-BASED ALLOY COATED STEEL WIRES

The corrosion resistance of a low concentration chromate passive film for zinc based alloy coated steel wires was assessed by salt spray and electrochemical corrosion tests. XPS and AES analyses showed that the composition of such chromate passive film was S 5 5, Na 3 4, C 11 8, Ti 7 9, O 41 6, Cr 13 7, Zn 16 0.

Electronic Properties of Passive Films Formed on G3 and G30 Nickel-based Alloys in Bicarbonate/Carbonate Buffer Solution

The electronic properties of passive films formed on G3 and G30 alloys in bicarbonate/carbonate buffer solution were comparatively studied by electrochemical impedance spectra（EIS） and Mott-Schottky analysis, the chemical composition of the passive film formed on G3 alloy was detected by X-ray photoelectron spectroscopy （XPS）. The results show that passive film on G3 alloy had better protection than that on G30 alloy. The transfer resistance, film resistance and diffusion resistance of the passive films on both alloys increased with increasing formation potential, prolonging formation time, increasing pH value, decreasing formation temperature, and decreasing chloride and sulphide ions concentration. Mott-Schottky plot reveals that the passive films on the two alloys show a p-n semi-conductive character. XPS analysis indicates that the passive film on G3 alloy was composed of an inner Cr oxide and an outer Fe, Mo/Ni oxides.

ELECTRON ENERGY SPECTRUM ANALYSIS ON PASSIVE FILM OF Si-BEARING STAINLESS STEELS

The surface films on the Si-bearing stainless steels formed after soaking in the concentrated nitric acid for 216 h have been investigated by means of an electron energy spectrometer.It can he reached that Si builds up in the surface in the form of SiO_2.It plays a main part as a passivating element in the Si-bearing stainless steels in strong oxidizing medium,whereas Cr drops down to the second place.

Corrosion and passive film characteristics of 3D-printed NiTi shape memory alloys in artificial saliva

Electrochemical tests and surface analysis were applied to study the corrosion behavior and passive film characteristics of three-dimensional-printed NiTi shape memory alloys fabricated by laser-powder bed fusion(LPBF) in artificial saliva at 37.C. The passivity of L-PBF NiTi shows to be influenced by the process parameters and resulting morphological and physicochemical surface properties. The results show that the defects at the surface of L-PBF Ni Ti can promote the passivation rate in the early stages of exposure but a slowly formed passive film shows the best corrosion protection. The thickness of the passive film is positively correlated with its corrosion protective performance. The L-PBF NiTi alloy prepared at a linear energy density of 0.2 J·m^(-1) and volumetric energy density of 56 J·mm^(-3) shows the least defects and best corrosion protection. An outer Ti-rich and inner Ni-rich dense passive film could be also obtained showing higher corrosion resistance.

Effect of Cl^- on the Properties of the Passive Films Formed on 316L Stainless Steel in Acidic Solution

The corrosion behavior of 316L stainless steel （31 6L SS） has been investigated in solutions containing various concentrations of chloride ions by using potentiodynamic polarization, capacitance measurement and Mott- Schottky relationship analysis （M-S）. The result indicates that passive currents change slightly with the addition of chloride ions. The pitting potential （Epit） decreases linearly with Iog[CI-]. Correspondingly, the point defect diffusion coefficient （Do） of the passive film increases linearly with increasing Iog[CI-]. The results also indicate that the pitting corrosion of 316L SS follows the adsorption mechanism in NaCI solution.

Dissolution and repair of passive film on Cu-bearing 304L stainless steels immersed in H_2SO_4 solution

The antibacterial Cu-bearing 304 L stainless steel is a new kind of structural and functional integrated metal material. In this work, evolution behavior of passive film of different heat treated Cu-bearing 304 L stainless steel immersed in 0.5 M H2SO4 solution was investigated by using electrochemical measurements, atomic force microscopy（AFM） observation and X-ray photoelectron spectroscopy（XPS） analysis.The results show that the solution and aging treated samples have the similar polarization behaviors. The passive film impedance experiences an initial decrease within 7 days followed by a subsequent increase,while the defect density of passive film presents the opposite trend. Meanwhile, the evolution of surface morphology and the estimated thickness of the passive film confirm that it experiences initial dissolution and follow-up repair. Furthermore, the Cr^3＋ content in passive film undergoes sequential reduction to increase, however the variation tendency of Cu^2＋ content is just opposite, indicating that the content variation of Cr and Cu in passive film reflects the competitive process of film dissolution and repair. In addition, compared with solution treated samples, aged samples have a bigger icorrvalue and the rougher passive film. This indicates that the passive film of solution treated steel is more compact and stable.

Monitoring the Diffusion Layer During Passive Film Breakdown on Alloy 800 with Digital Holography

The effects of chloride and thiosulfate ions on localized corrosion of alloy 800 are investigated through dynamical observation of the change in phase image of the diffusion layer during passive film breakdown using digital holography. The results indicate that solution chemistry has a significant effect on film breakdown and diffusion layer. The phase distribution changes at different applied potentials show that in the process of film breakdown, dissolution of metal ions from pitting is not remarkable in chloride-only solution, whereas dissolution of metal ions is significantly high in thiosulfate and chloride solution. Thiosulfate has a combined effect with chloride ions in passive film degradation.

Effects of W Addition on the Electrochemical Behaviour and Passive Film Properties of Fe-Based Amorphous Alloys in Acetic Acid Solution

The electrochemical behaviour and passive film properties of Fe-Cr-Mo-W-C-B-Y amorphous alloys in acetic acid solution were investigated. The potentiodynamic polarisation and Nyquist curves demonstrated that W addition signifi- cantly enhanced the corrosion resistance. Mott-Schottky plots and angle-resolved X-ray photoelectron spectra indicated that passive films with different W contents exhibited dipolar （p-n） semiconducting characteristics separated by fiat-band potentials. The outer and inner oxide layers of the passive films were modified by reducing the acceptor and donor densities. Moreover, W addition favoured the formation of a thicker and more stable passive film to inhibit the dissolution of alloy elements.

Electrochemical Behavior of Passive Films Formed on the Surface of Coarse-,Fine-and Ultra-fine-Grained AA1050 Based on a Modified PDM

Electrochemical impedance spectroscopy （EIS） and Mott-Schottky analysis were carried out to evaluate the electrochemical behavior of the passive films formed on the surface of coarse-grained （CG）, fine-grained （FG） and ultrafine-grained （UFG） 1050 A1 alloy （AA1050） samples in alkaline media （pH value of 8.0） based on a modification of point defect model （PDM）. The EIS results revealed that the polarization resistance increased from about 22.71-120.33 kΩ cm2 for UFG sample when compared to CG sample （annealed sample）. The semiconductor properties of the passive films formed on CG, FG and UFG AA1050 samples in the test solution were investigated by employing Mott-Schottky analysis in conjunction with PDM. The results indicated that donor densities were in the range of 2.19 × 1021-0.61 × 1021 cm-3 and decreased with grain refinement. Finally, all electrochemical tests showed that the electrochemical behavior of AA1050 alloy was improved by decreasing the grain size, mainly due to the formation of thicker and less defective oxide films.

Stability of passive film and antibacterial durability of Cu-bearing L605 alloy in simulated physiological solutions

In this work,the stability of passive film for long-time immersed Cu-bearing L605(L605-Cu) alloy in the phosphate buffer solution(PBS) was studied by potentiodynamic polarization and electrochemical impedance spectroscopy.The results showed that the impedance of passive film for L605-Cu alloy experienced an initial increase and subsequent stabilization with the increase in the immersion time.In addition,the plate count method was employed to assess the antibacterial durability of L605-Cu alloy against Escherichia coli after long-time immersion.The results indicated that the antibacterial rate of L605-Cu alloy presented a declining tendency with the immersion time prolonging.X-ray photoelectron spectroscopy(XPS) was used to analyze the change of the chemical composition in the passive film on L605-Cu alloy immersed in the PBS for different time.The results showed that Cu content and its compounds in the passive film gradually increased with the immersion time prolonging,hinting declined activity of Cu ions penetrating into the passive film,which resulted in a decrease in the antibacterial performance.

Effect of Chloride on Semiconducting Properties of Passive Films Formed on Supermartensitic Stainless Steel in NaHCO_3 Solution

The effects of chloride ion on the electrochemical behavior and the semiconducting properties of the passive film on supermartensitic stainless steel in 0.5 mol/L NaHCO_3 solution were investigated using potentiodynamic polarization, the potentiostatic current transients and Mott-Schottky analysis. The results indicated that chloride ion narrowed passivation region and improved pitting susceptibility. The steady state current densities were independent of film-formed potentials, which was in good agreement with the assumption of the point defect model （PDM）. The capacitance results showed the fact that the passive films had a multilayer character. The defect density decreased with increasing passive film formation potential. The chloride ion induced changes of the acceptor densities and donor densities of the passive films.

Corrosion Resistance and Semiconducting Properties of Passive Films Formed on 00Cr13Ni5Mo2 Supermartensitic Stainless Steel in Cl^- Environment

The semiconducting properties of passive films grown on 00Crl3Ni5Mo2 supermartensitic stainless steel were investigated in comparison with conventional 2Cr13 martensitic stainless steel. Cyclic vohammetry and electro- chemical impedance spectroscopy （EIS） were used for the studies. 00Crl3NiSMo2 steel exhibited a good corrosion resistance performance, attributing to its passive capability. The results of Mott-Schottky analysis demonstrated n- type semiconductors for the passive films with doping densities of about 1020- 1021 cm -3, and the thickness of space- charge layers was also calculated. The experimental results confirmed that Mo plays an important role in improving the corrosion resistance of 00Crl3Ni5Mo2 steel due to its impact on the doping density.

Influence of Cr on the Electronic Properties of Passive Film on B30 Alloy in NaOH Solution

The influence of Cr on the electronic properties of the passive film on B30 alloy in NaOH solution was studied via electrochemical impedance spectra（EIS）, potentiodynamic curve and Mott-Schottky plot. The Cr doped in the passive film on B30 alloy was detected by X-ray photoelectron spectroscopy（XPS）. XPS results show that Cr203 appeared on the passive film, which implied the enhanced anti-corrosion of B30 alloy. The passive film showed a p-type semi-conductive character. The acceptor density（NA） was in an order of magnitude of 1022 cm-3, and NA de- creased with the increment of Cr. EIS results show that the film resistance（Rf） increased with increasing the amount of Cr. The diffusion coefficient（D0） was calculated to be in a range of 10^-16---10^-17 cm-2/s on the basement of point defect modcl（PDM）.

Investigation of the passive behaviour of AZ31B alloy in alkaline solutions

In this work,the passivity of AZ31B alloy in NaOH solutions was studied by potentiodynamic polarization,electrochemical impedance spectroscopy(EIS)and Mott-Schottky analysis.Potentiodynamic polarization results indicated that decreasing NaOH concentration leads to decrease the corrosion rate of this alloy.EIS results showed that the reciprocal capacitance(1/C)of the passive film is directly proportional to its thickness which increases with decreasing NaOH concentration.Therefore,it is clear that dilute NaOH solutions offer better conditions for forming the passive films with higher protection behaviour,due to the growth of a much thicker and less defective films.The Mott-Schottky analysis revealed that the passive films displayed n-type semiconductive characteristics,where the oxygen vacancies and interstitials(over the cation vacancies)preponderated.Also,Mott-Schottky results showed that the donor densities evaluated from Mott-Schottky plots are in the range of 10^(20) cm^(−3) and decreased with decreasing NaOH concentration.

Investigation on Semi-conductive Properties of Hot Growth Film on 316L Austenitic Stainless Steel

The semi-conductive performances of hot growth film on 316L stainless steel were studied by means of electrochemical impedance spectroscopy（EIS） and Mott-Schottky analysis.The chemical compositions of the hot growth films were detected by X-ray photoelectron spectroscopy（XPS）.The results show that the transfer resistance and film resistance increase with increasing temperature to 400℃,then they decrease sharply with further continuously increasing temperature.Formation time plays an important role in determining the electron properties of the hot growth film,when formation time reaches to 1 d,the transfer resistance and film resistance reach to the maximum value.Hot growth film has better anticorrosion behaviour in bicarbonate/carbonate solution containing chloride ions or sulfide ions.Mott-Schottky analysis reveals that hot growth film has n-p type semi-conductive property.XPS results show that the hot growth film is mainly composed of the inner chromium oxide and the outer iron oxide.

Influence of reflow processing conditions on the uniformity of the chromium passivation film on tinplate

This study aims to systematically analyze the key parameters of the reflow process that influence the uniformity of the chromium passivation film coated on tinplate. The distribution characteristics of the chromium passivation film coated on the tinplate surface under different treatment conditions were systematically characterized using the scanning Kelvin probe technique, X-ray photoelectron spectroscopy, and X-ray diffraction. Results indicate that the use of flux reduces the porosity of tin coating, thereby favoring the uniform growth of the passivation film. Furthermore, an increase in the reflow power and quenching temperature facilitates the homogeneous distribution of the passivation film on the tinplate surface,particularly when treated with electrolytic cathodic sodium dichromate.

INFLUENCE OF MAGNETIC FIELD ON ACCURACY OF ECM BY CHANGING THE CONDUCTIVITY OF ANODE FILM

The change of conductivity, thickness and scanning electron microscopy （SEM） appearance of the anode film of CrWMn in 10% NaNO3 at different anode potential either with or without the magnetic field applied are investigated by testing film resistance, galvanostatic transient and using SEM to design magnetic circuit in magnetic assisted electrochemical machining （MAECM）. The experiments show that the anode film has semi-conducting property. Compared with the situation without magnetic field applied, the resistance of the film formed at 1 .SV （anode potential） increased and decreased at 4.0V while B=0.4T and the magnetic north pole points toward anode. The SEM photo demonstrates that the magnetic field will densify the film in the passivation area and quicken dissolution of the anode metal in over-passivation area. Based on the influence of magnetic field on electrochemical machining（ECM） due to the changes of the anode film conductivity behavior, the magnetic north pole should be designed to point towards the workpiece surface that has been machined. Process experiments agree with the results of test analysis.