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.

Reparation and Performance Testing of Free Radical Photocurable Passivation Film Modified by Titanate Coupling Agent for Hot-plated Aluminum-zinc Steel Plate

To study the effect of free radical photocurable passivation film modified by titanate coupling agent for hot-plated aluminum-zinc plate,trimethylpropane triacrylate(TMPTA)and 2-phenoxyethyl acrylate were used as active diluents,a mixture of modified epoxy acrylate and modified polyester acrylate in a certain proportion was used as an oligomer,2-methyl-1-[4-(methylothyl)benzene]-2-morpholine acetone(907)was used as a free radical photoinitiator,isopropyl thioxanthone(ITX)was used as sensitizer,and bis(dioctyl phosphate acyl)titanate ethyltitanate acrylamide chelate(FD-812)was used as corrosion inhibitor modifier.After UV-curing,the passivation film was characterized by neutral salt spray test,electrochemical testing and other methods.The general performance of the passivation film may meet the requirements of downstream users of hot aluminum-zinc steel plate.The neutral salt spray test,electrochemical testing and microscopic surface morphology analysis of passivation film are in agreement.The introduction of titanate components may effectively promote the photocuring of free radicals.There have been few reports on the titanate coupling which is added to UV-curing coating formula.The titanate coupling agent contains acrylamide groups and terminal amine groups,acrylamide group has oligomer and crosslinking monomer,the terminal tertiary amine groups can provide hydrogen protons,reduce oxygen polymerization,and a phosphating film is formed on the surface of the metal substrate to improve the adhesion and corrosion resistance of the coating.

UV-LED Curing Cationic Passivation Film for the Surface of Hot-Dip Aluminum-Zinc Coated Steel Plate

The surface treatment technology of hot aluminum-zinc steel plate and UV curing technology may be effectively combined in the present research. According to different light curing mechanisms, different formulations from UV curing surface treatment agents can be applied to the surface treatment of hot aluminum-zinc steel plate, mainly including 3-ethyl-3-benzoxy-methyl oxacyclobutane (TCM 104) and 3,4-epoxy-cyclohexylformic acid -3',4'-epoxy-cyclohexyl methyl ester (UVR 6110) as active diluents, high molecular weight polyfunctional oxacyclobutane as oligomer, triaryl sulfonium salt as a cationic photoinitiator, and an anthracene compound as a sensitizer. 385 nm LED lamp used as a radiation resource, the effects of the proportion of active diluent, the type and amount of photoinitiator, the amount of sensitizer, the curing temperature, and the amount of nano-SiO2 on the photocuring rate were investigated by photoper-scanning differential calorimetry (Photo-DSC). The experimental results show that the system has the fastest photocuring rate under the conditions of 8:2 ratio of TCM 104 to UVR 6110, 2.5% photoinitiator, 0.6% sensitizer, 0.2% nano-SiO2 additive, and 80˚C curing temperature. Based on addition of the appropriate number of various additives, the cationic photocuring surface treatment solution was prepared and further coated on the hot-dip galvalume steel plates. After curing, the passivation films were characterized by neutral salt spray test (NSST), Fourier transform infrared spectroscopy (FT-IR), electrochemical testing and other methods. The results show that the formulations could be cured at an energy of 150 mJ/cm2, and the overall performance of the passivation film could meet with the requirements of the downstream users.

Formation of passivation film during pyrrhotite bioleached by pure L. ferriphilum and mixed culture of L. ferriphilum and A. caldus

Bioleaching and electrochemical experiments were conducted to evaluate pyrrhotite dissolution in the presence of pure L.ferriphilum and mixed culture of L. ferriphilum and A. caldus. The results indicate that the pyrrhotite oxidation behavior is the preferential dissolution of iron accompanied with the massive formation of sulfur in the presence of L. ferriphilum, which significantly hinders the leaching efficiency. Comparatively, the leaching rate of pyrrhotite distinctly increases by 68% in the mixed culture of L. ferriphilum and A. caldus at the 3rd day. But, the accumulated ferric ions and high p H value produced by bioleaching process can give rise to the rapid formation of jarosite, which is the primary passivation film blocking continuous iron extraction during bioleaching by the mixed culture. The addition of A. caldus during leaching by L. ferriphilum can accelerate the oxidation rate of pyrrhotite, but not change the electrochemical oxidation mechanisms of pyrrhotite. XRD and SEM/EDS analyses as well as electrochemical study confirm the above conclusions.

Electrochemical Hydrogen Charging on Corrosion Behavior of Ti-6Al-4V Alloy in Artificial Seawater

This study employs advanced electrochemical and surface characterization techniques to investigate the impact of electrochemical hydrogen charging on the corrosion behavior and surface film of the Ti-6Al-4V alloy.The findings revealed the formation ofγ-TiH andδ-TiH_(2) hydrides in the alloy after hydrogen charging.Prolonging hydrogen charging resulted in more significant degradation of the alloy microstructure,leading to deteriorated protectiveness of the surface film.This trend was further confirmed by the electrochemical measurements,which showed that the corrosion resistance of the alloy progressively worsened as the hydrogen charging time was increased.Consequently,this work provides valuable insights into the mechanisms underlying the corrosion of Ti-6Al-4V alloy under hydrogen charging conditions.

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.

Electrochemical study on semiconductive properties of the passive film on rebar in concrete

The electrochemical behavior of metallic passive film on rebar in concrete is characterized by its semiconductive nature. The charge distribution at the interface between a semiconductor and an electrolyte is often determined by measuring the capacitance of the space-charge layer （Csc） as a function of the electrode potential （E）. When the space charge-layer serves as the depletion layer, the relation of Csc^-2 vs E resembles a Mott-Schottky plot （M-S plot）. The semiconductive properties of the passive film on rebar in concrete were analyzed with M-S plots to study the effect of chloride ions and mineral admixtures on rebar passive films. Some rebar electrodes were immersed in simulated concrete pore solutions, while others were embedded in concrete with/without mineral admixtures. In saturated Ca（OH）, solutions, the relation of Csc^-2-E of rebar electrodes shows linear MottSchottky relationship indicating that the passive film on rebar is a highly disordered n-type semiconductor, with donor density （ND） in the order of 10^26m^-3. After adding chloride ions （Cl wt%〈0.2%） in system solutions, the M-S plot slopes significantly decreased and ND increased, suggesting that chloride ion will cause passive film corrosion and breakdown. The M-S plots of the passive film on rebar electrodes embedded in concrete were similar to those immersed in simulated system solution. However, ND of those in concrete with mineral admixtures tended to be a little smaller, indicating that introducing proper quantity admixtures into concrete could make the rebar passive film have a thicker space-charge layer and therefore a thicker passive film layer.

Passivation Mechanism of 316L Stainless Steel in Oxidizing Acid Solution

The compositions and the chemical valence states of elements of 316L stainless steel passive film formed in the oxidizing acid solution were studied by X-ray Photoelectron Spectroscopic (XPS) analysis. The electrochemical polarization curve was measured. The passivation process in the oxidizing acid solution was studied by AC impedance technology. The results indicated that the stable compounds layer was formed on the surface of the sample and the adsorption was the main step in the nitrite solution during passivation process. The catalysis passivation mechanism was put forward according to the experimental results. During passivation process, the water molecule was adsorbed on the surface of the sample at first in the oxidizing acid solution. The oxidizer in the solution played a role as catalyst. The oxide and hydroxide, which could be changed each other and finally formed stable passive film, were generated from adsorbing intermediate under the catalytic action. The mathematical models for predicting the steady polarization curve and the AC impedance spectra at certain conditions have been obtained. The passivation mechanism of 316L stainless steel in the oxidizing acid solution can be interpreted by the catalysis passivation mechanism.

The passivation mechanism of Fe in the acidic AlCl_3-EMIC ionic liquid

The passivation behavior of Fe in the acidic AlCl_3-1-ethyl-3-methyl-imidazolium chloride(AlCl_3-EMIC) ionic liquid was studied by linear sweep voltammetry and chonopotentiometry. Various approaches were used to characterize the composition and morphology of passive film formed on the Fe electrode, such as scanning electron microscopy(SEM), Raman spectra and X-ray Photoelectron Spectroscopy(XPS). The results showed that the critical passivation potential of Fe shifted to more negative when the molar ratio of AlCl_3:EMIC changing from 2 to 1.3.A film with a light yellow color was observed on the surface of the Fe electrode after passivation. The composition of the passive film was demonstrated to be FeCl_2. The passive film was composed of particulate FeCl_2 with average diameter of about 500 nm. The formation of FeCl_2 film was attributed to the variation of the electrolyte Lewis acidity from acidic to neutral at the interface during the dissolution process of Fe. The reason caused the variation of the electrolyte acidity was discussed.

Anodic passivation of Pb-Ag-Nd anode in fluoride-containing H_2SO_4 solution

An attempt was made to build up a thick and compact oxide layer rapidly by pre-treating the Pb-Ag-Nd anode in fluoride-containing H2SO4 solution. The passivation reaction of Pb-Ag-Nd anode during pre-treatment process was investigated using cyclic voltammetry, linear scanning voltammetry, environmental scanning electron microscopy and X-ray diffraction analysis. The results show that Pb F2 and PbSO4 are formed near the potential of Pb/PbSO4 couple. The pre-treatment in fluoride-containing H2SO4 solution contributes to the formation of a thick, compact and adherent passive film. Furthermore, pre-treatment in fluoride-containing H2SO4 solution also facilitates the formation of PbO2 on the anodic layer, and the reason could be attributed to the formation of more PbF2 and PbSO4 during the pre-treatment which tend to transform to PbO2 during the following electrowinning process. In addition, the anodic layer on anode with pre-treatment in fluoride-containing H2SO4 solution is thick and compact, and its predominant composition is β-PbO2. In summary, the pre-treatment in fluoride-containing H2SO4 solution benefits the formation of a desirable protective layer in a short time.

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.

Characterization of Passive Film Formed on 304 SS in Simulated Alkaline Water Chemistries Containing Sulfur at 300℃

Passivity degradation of 304 stainless steel(SS) in simulated alkaline water chemistries at 300℃ was investigated using polarization curve, scanning electron microscope, time-of-flight secondary ion mass spectrometry(SIMS) and X-ray photoelectron spectroscopy(XPS). Experimental results indicated that 304,SS was selfpassive in the test solution and the thickness of passive film was about 500 nm. Hydroxide was enriched in the outer layer whereas oxide was enriched in the inner layer. Sulfur in thiosulfate could be reduced into lower valence of sulfur and enter the passive film so that the composition of passive film was modified by sulfur. Fe and Cr were enriched in the passive film whereas Ni was depleted in the passive film.

Characterization of Zinc Passive Film by Sonication in 7 M KOH Solution

The influence of 40 kHz ultrasound radiation on the passivation behavior of zinc in 7 M KOH is presented. The results of potentiodynamic and potentiostatic measurements combined with the current oscillation caused by the irradiation were examined to explain the mechanism and the sequence of formation of the oxide films during passivation. In this study, sonication was also used to investigate both effects of the passivation duration and passivation potential on the structure of the oxide layers; the adherence of the layers was found to depend strongly on both parameters. Scanning electron microscopy-energy dispersive X-ray （SEM-EDX） analysis of the zinc surface provided complementary information on the oxide layer composition and structure.

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.

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.

Effect of phosphoric acid concentration on conductivity of anodic passive film formed on surface of lead-indium alloy

The addition of phosphoric acid into sulfuric acid solution is mentioned to be helpful in the reduction of sulfation after deep discharge of lead-acid battery. The anodic behavior of Pb and Pb?In alloys was studied in pure phosphoric acid and sulfuric acid containing various concentrations of phosphoric. The electrochemical measurements were performed using potentiodynamic, potentiostatic and cyclic voltammetric techniques. The composition and morphology of passive layer formed on the surfaces of Pb and Pb?In alloys were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy analysis (EDX) and scanning electron microscopy (SEM). The potentiodynamic study shows that the passive current density increases with increasing the indium content in the alloy in the examined solutions. The addition of 0.1 mol/L H3PO4 into theelectrolyte is more effective to decrease the thickness of passive film on the surface of alloys containing higher indium content (10% and 15%). The XRD, EDX and SEM data reveal that the formation of PbSO4 and PbO on the surface decreases with increasing the indium level in the alloy and is completely prevented at higher indium content (15%) in mixed acid.

Dry passivation of austenitic SUS 301L stainless steel against pitting corrosion in marine atmospheric environment

Being an exclusive construction material for lightweight rail vehicles,protection from pitting corrosion in harsh marine atmospheric environment in high humidity and Cl-ion concentration is critical for austenitic SUS 301L stainless steel(SS),especially when it inevitably suff ers from mechanical damages during post disposals.Herein,an innovative dry passivation method for austenitic SUS 301L SS was established in a closed air atmosphere at low temperature and constant pressure.The process parameters were optimized,and the passivation mechanism was explained using polarization curve,electrochemical impedance spectroscopy(EIS),X-ray photoelectron spectroscopy(XPS),and contact angle measurement.The pitting corrosion susceptibility of the passive fi lm prepared in a closed air chamber under 1.0×10^(5) Pa at 80℃ for 80 min was evaluated in 3.5%NaCl solution and exhibited higher pitting potential and corrosion resistance,lower passivity-maintaining current density,and wettability when compared with conventional nitric acid treatment.Besides,dry passivation facilitated the repairing of the surface structural defect itself and the post-processing damage,similar to the accelerated aging of fi lm.The decrease in oxygen concentration and convection-diff usion strengthened the preferential chromium oxidation to form a compact chromium-rich passive fi lm to resist the aggression of Cl-ion.

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.