Nickel-free sealing technology for anodic oxidation film of aluminum alloy at room temperature

Different additives were added into the potassium fluorozirconate solution to prepare different nickelfree sealing reagents,with which the anodic oxidation film of aluminum alloy was sealed at room temperature.The phosphor chromic acid weight loss method was used to evaluate the sealing effects.Using electron scanning microscopy(SEM),the surface and cross-sectional micromorphologies of the anodic oxidation films sealed by different fluorozirconate sealants were observed.The position and state of zirconium element distribution in the film hole were investigated by the further quantitative and distribution analysis of Zr element.This study provides an experimental evidence for the theoretical studies of fluorozirconate-sealed anodic oxidation films.It is shown that the fluorozirconate has good sealing effects and has a wide prospect for sealing the aluminum alloy samples.Its products were highly corrosion resistant,and were filled in the openings of the micropores in the oxide film.

Fabrication and characterization of anodic oxide films on a Ti-10V-2Fe-3Al titanium alloy

Anodic oxide films of the titanium alloy Ti-10V-2Fe-3Al in ammonium tartrate electrolyte without hydrofluoric acid or fluoride were fabricated. The morphology, components, and microstructure of the films were characterized by scanning electron microscopy （SEM）, X-ray photoelectron spectroscopy （XPS）, X-ray diffraction （XRD）, and Raman spectroscopy. The results showed that the films were thick, uniform, and nontransparent. Such films exhibited sedimentary morphology, with a thickness of about 3 μm, and the pore diameters of the deposits ranged from several hundred nanometers to 1.5 μm. The films were mainly titanium dioxide. Some coke-like deposits, which may contain or be changed by OH, NH, C-C, C-O, and C=O groups, were doped in the films. The films were mainly amorphous with a small amount of anatase and rutile phase.

Morphology and growth of porous anodic oxide films on Ti-10V-2Fe-3Al in neutral tartrate solution

Porous anodic oxide films were fabricated galvanostatically on titanium alloy Ti-10V-2Fe-3Al in ammonium tartrate solution with different anodizing time.Scanning electron microscopy(SEM) and field emission scanning electron microscopy(FE-SEM) were used to investigate the morphology evolution of the anodic oxide film.It is shown that above the breakdown voltage,oxygen is generated with the occurrence of drums morphology.These drums grow and extrude,which yields the compression stress.Subsequently,microcracks are generated.With continuous anodizing,porous oxides form at the microcracks.Those oxides grow and connect to each other,finally replace the microcrack morphology.The depth profile of the anodic oxide film formed at 1 800 s was examined by Auger electron spectroscopy(AES).It is found that the film is divided into three layers according to the molar fractions of elements.The outer layer is incorporated by carbon,which may come from electrolyte solution.The thickness of the outer layer is approximately 0.2-0.3 μm.The molar fractions of elements in the intermediate layer are extraordinarily stable,while those in the inner layer vary significantly with sputtering depth.The thicknesses of the intermediate layer and the inner layer are 2 μm and 1.0-1.5 μm,respectively.Moreover,the growth mechanism of porous anodic oxide films in neutral tartrate solution was proposed.

EIS Characterization of Sealed Anodic Oxide Films on Titanium Alloy Ti-10V-2Fe-3Al

Anodic oxide films grown on titanium alloy Ti-10V-2Fe-3Al in the solution of sodium tartrate, then sealed in boiling deionised water and calcium acetate solution were observed by using field emission scanning electron microscopy （FE-SEM）, and were chemically analysed by using energy dispersive spectroscopy （EDS）. Corrosion behaviour was investigated in a 3.5% sodium chloride solution, using electrochemical impedance spectroscopy （EIS）. The morphology of the anodic oxide films was dependent on the sealing processes. The surface sealed in calcium acetate solution presented a more homogeneous and smooth structure compared with that sealed in boiling deionised water. The corrosion resistance of the oxide films sealed in calcium acetate solution was better than that sealed in boiling deionised water.

WO_3 Anodic Oxide Film——I.Electrochromism and Auto-bleaching mechanism

Electrochromic and auto-bleaching processes at the WO2 anodic film in 0. 5 mol/L H2SO4 solution were investigated by cyclic voltammetry, a. c. impedance technique and photocurrent spectrometry. The colouration mechanism consists of hydrogen adsorption on the WO2 surface and the transport of H atoms in the WO, lattice. The bleaching process involves at least two steps: transport of interstitial H atoms and hydrogen desorption on the W surface, resulting in interstitial H+ ions; then extration of the H+ ions driven by the external electric field. The auto-bleaching arises from the hydroxylation due to both partial interstitial H atoms and a little of water contained in the film.

Formation and Morphology of Anodic Oxide Films of Ti

The morphology and structure of the oxide films of Ti in H3PO4 were investigated by galvanos tatic anodization, SEM and XRD. The oxide film grew from some pores in the grooves to layered microdomains as increasing anodizing voltage. The crystallinity of the oxide films decreased with the increase of the concentration of the electrolyte. The model has been proposed for the growth of the oxide films by two steps, i.e. by uniform thickening and by local deposition.

Macroscopic Studies on the Properties of the Anodic Oxide Films on Titanium

The effect of fluoride ions on the formation and dissolution behaviour of anodic oxide films on Ti has been investigated in acidic fluoride media (pH=1) using impedance and galvanostatic techniques. A5 the fluoride ion concentration and temperature increase the rate of oxide film formation decreases while the dissolution process increases. oxide film formed at high tem-perature and formation voltage was found to contain more defect sites in the film than that formed at a lower one. Activation energies are calculated during the oxide film formation and dissolution and found to be 20.76 and 28.72 kJ/mol, respectively. Formation rate and reciprocal capacitance data are reported as a function of polarizing current density. Values are recorded for the electrolytic parameters A and B. Potentiostatic curves are derived from the galvanostatic results.

Effect of citric acid on microstructure and electrochemical characteristics of high voltage anodized alumina film formed on etched Al Foils

Aluminum capacitor foils with a tunnel etch structure were reacted with boiling water and then anodized at 530 V in boric acid solution or boric acid＋citric acid mixed solution.The microstructure and crystallinity of the resulting anodized film were examined by TEM and XRD.The special capacitance,resistance and withstanding voltage of the film were explored with electrochemical impedance spectroscopy（EIS）,LCR meter and small-current charging.The results show that the high voltage anodized oxide film consists of an inner layer with high crystallinity and an outer layer with low crystallinity.However,the crystallinity of the film formed in boric acid＋citric acid mixed solution is higher than that of the film formed in only boric acid solution,leading to an increase in film＇s field strength and special capacitance.Meanwhile,there are more defects from phase transformation in the out layer of the film formed in boric acid＋citric acid mixed solution than in that of film formed in only boric acid solution,leading to a decrease in film＇s resistance and withstanding voltage.

Microstructure and abrasive wear behaviour of anodizing composite films containing Si C nanoparticles on Ti6Al4V alloy

Anodized composite films containing Si C nanoparticles were synthesized on Ti6Al4 V alloy by anodic oxidation procedure in C4O6H4Na2 electrolyte. Scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS) and X-ray photoelectron spectroscopy(XPS) were employed to characterize the morphology and composition of the films fabricated in the electrolytes with and without addition of Si C nanoparticles. Results show that Si C particles can be successfully incorporated into the oxide film during the anodizing process and preferentially concentrate within internal cavities and micro-cracks. The ball-on-disk sliding tests indicate that Si C-containing oxide films register much lower wear rate than the oxide films without Si C under dry sliding condition. Si C particles are likely to melt and then are oxidized by frictional heat during sliding tests. Potentiodynamic polarization behavior reveals that the anodized alloy with Si C nanoparticles results in a reduction in passive current density to about 1.54×10-8 A/cm2, which is more than two times lower than that of the Ti O2 film(3.73×10-8 A/cm2). The synthesized composite film has good anti-wear and anti-corrosion properties and the growth mechanism of nanocomposite film is also discussed.

Influences of pulse frequency on formation and properties of composite anodic oxide films on Ti-10V-2Fe-3Al alloy

A thick composite anodic oxide film was fabricated in an environmentally friendly malic acid electrolyte containing Poly Tetra Fluoro Ethylene(PTFE)nanoparticles on Ti-10V-2Fe-3Al alloys.The influence of pulse frequency on the morphology,microstructure and composition of composite anodic oxide films containing PTFE nanoparticles was investigated using Field Emission Scanning Electron Microscopy(FE-SEM)equipped with Energy Dispersive Spectroscopy(EDS),Atomic Force Microscopy(AFM)and Raman spectroscopy.The tribological properties in terms of the friction coefficient,wear loss and morphology of worn surfaces were measured by ball-ondisc tests.The electrochemical property was evaluated by potentiodynamic polarization.The results indicated that the titanium dioxide of composite anodic oxide films transformed from anatase to rutile with the change of pulse frequency,which could result from the electrochemical dynamic equilibrium.The combination of PTFE nanoparticles and malic acid electrolyte molecules can influence the energy fluctuation of electrochemical equilibrium and formation of composite anodic oxide films.Moreover,composite anodic oxide films fabricated under the condition of 1.0–2.0 Hz exhibited the best wear resistance and corrosion property.The schematic diagram of the film formation and PTFE nanoparticles spreading process under different frequencies was elucidated.

Effects of Samarium on the Properties of the Anodic Pb(II) Oxides Film Formed on Pb in Sulfuric Acid Solution

The effects of samarium on the properties of the anodic Pb(II) oxides films formed on lead at 0 9 V (vs. Hg/Hg 2SO 4) in 4 5 mol/L H 2SO 4 solution were studied using linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS) and scanning electron micrographs (SEM). The experimental results show that adding Sm to lead metal can inhibit the growth of the Pb(II) oxides film effectively, and reduce the resistance of the PbO oxides film obviously. The addition of Sm increases the porosity of the anodic film, which may cause the increase of the ionic conductance produced by the interstitial liquid among the PbO particles in the film and lead to the decrease of the resistance of the anodic film.

Effects of current density on the corrosion behaviour of anodized aluminum alloy in FeCl_3 solution

In the present study, 2024 aluminum alloy specimen was anodized in acetic acid and oxalic acid e- lectrolytes. Effects of the current density on the microstructure and corrosion resistance of anodic oxide film have been investigated. The steady voltage increases from 11 V to 71 V with the current density increase from 0. 5 A/din2 to 2. 5 A/din2. The SEM reveals that there are pits, cavities and irregular pores in the anodic film, and their size and morphologies change with the current density. The corrosion resistance of the film was evalua- ted by potentiodynamic polarization and electrochemical impedance in 0.1 mol/L FeC13 solution at room temper- ature. The results show that corrosion resistance of the anodic oxide film changes with the current density, and the anodic fihn formed at the current density of 1.0 A/dm2 has the best corrosion resistance. These observations indicate that anodic film formed at J -- 1.0 A/dm2can serve as a support material for the Cu micrometallic pat-

Effect of Sb on the properties of anodic Pb(Ⅱ) oxide film formed in alkaline solution

The composition and properties of the anodic films formed on Pb and Pb-3at.%Sb alloy at -0.10 V (vs. Hg/HgO) for 2.5 h in 0.1 mol.dm-3 NaOH solution (25℃) were investigated by cyclic voltammetry, linear sweep voltammetry, open circuit decay curve, photocurrent technique, X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was found that the anodic film formed oh Pb mainly consists of t-PbO, while that on Pb-3at.%Sb consists of o-PbO, t-PbO and a small amount of orthorhombic Sb2O3. The dominant component of the film anodically grown on Pb-3at.%Sb for less than 5 min is o-PbO, however, t-PbO is the major component of the anodic film formed for 1 h or longer. It is established that Sb suppresses the growth of t-PbO. The anodic film formed on Pb-3at.%Sb is less porous than that on Pb. The bandgap energies of t-PbO and o-PbO in the films were determined by photocurrent measurements to be 1.83-1.84 eV and 2.60 eV, respectively.

Crack Propagation in Pipelines Under Extreme Conditions of Near-Neutral PH SCC

Stress Corrosion Cracking(SCC)process through which cracks occur in a variety of susceptible materials is a result of a combination of residual or applied stresses and corrosion.In oil and gas field,buried pipeline steels are made of low-alloy steels with a ferritic-pearlitic structure,such as X70.In dilute solutions,these materials are prone to SCC failure.The Near-neutral simulated soil solution(NS4)solution is established to imitate SCC conditions and subsequently became the industry requirement for crack growth experiments in the majority of laboratories.The strainassisted active crack pathways are considered while modelling SCC growth as an oxide film rupture and anodic dissolution process.It’s been hypothesized that increasing the strain concentration can help with dissolution at the filmfree crack tip.This research focuses on estimating the SCC crack growth rate under various environmental conditions in oil and gas pipelines using finite element modelling.The simulation is carried out using the J-integral theory in the COMSOL Multiphysics program.Simulations are performed to model the crack growth rate(CGR)using slip anodic dissolution(film rupture)mechanism.The plastic strain gradient is required to compute the SCC CGR(da/dt).Because the plastic strain located at crack tip increases proportionally to the crack length as it propagates,the CGR increases as the stress intensity factor(SIF)increases.The crack growth rates increase when constant loads are applied and as the temperature rises,and elevating the cathodic potential has a minimal influence on the propagation rate of cracks but raises the material yield strength and imparts brittle behavior to it.

Printing on Anodized Aluminium Surface

Anodizing of aluminium is widely applied when a controllable morphology and properties of the surface are required. Anodic oxide films may be developed by appropriate selection of electrolyte and film-forming conditions for various applications in the fields of architecture, aerospace, electronics, packaging and printing. In the present study, the printability of aluminium with respect to anodizing conditions is discussed. In particular, AA1050 alloy specimens were anodized in either sulfuric acid or phosphoric acid at temperatures ranging from 10?C to 40?C, thereby affecting the porosity and anodic layer thickness. Both the porosity and oxide thickness increase with the temperature, whereas anodization in phosphoric acid produces thinner and more porous layer than that in sulfuric acid. After the anodization step, two different printing techniques were used (i.e. digital printing and screen printing). Printed specimens were characterized by means of colour parameters, microscopy, adhesion and light fastness test. Colour parameters and ink adhesion measurements indicate that both digital and screen printing techniques give a better print quality when the anodization step is conducted in the range of 20?C - 30?C.