Effects of cathodic electrodeposition parameters of cerium oxide film on the corrosion resistance of the 2024 Al alloy

Cerium oxide thin films obtained by cathodic electrodeposition on 2024 aluminium alloy have been studied. The coatings, obtained with electrochemical deposition, offer an effective corrosion protection and require a lower deposition time when compared to chemical conversion coatings. The coatings were obtained at room temperature by deposition from CeCl₃/H₂O₂ aqueous solutions and the influence of several parameters (CeCl₃ concentration, H₂O₂ concentration, deposition time, current intensity) on the corrosion resistance was studied. The composition, morphology and microstructure of the films have been characterized by SEM, XPS and AFM. The corrosion resistance was investigated through potentiodynamic tests in 3% NaCl solution.     

An XPS study of passive films on Nickel and alloy 600 in acids

Compositions of surface films formed on nickel and Alloy 600 in I M HCI, 0.5 M H₂SO₄ and I/3 M H₃PO₁ solutions were investigated as a function of polarization potential. The main constituent of surface films formed on Ni in 0.5 M H₂SO₄ or 1/3 M H₃PO₄ solution was hydrated nickel oxyhydroxide, in which the ratio of O₂ to OH⁻ increased when passivation occurred. The surface films formed on Ni and Alloy 600 at lower potentials in 0.5 M H₂SO₄ solution contain S² ions other than SOP_4²⁻ ions, whereas S²⁻ ions were not incorporated in the passive film. Passivation of Alloy 600 took place by the formation of hydrated chromium oxyhydroxide. Pitting led to no substantial change in the average composition of the film.     

Cerium‐based thermal conversion treatments on silicon carbide reinforced 2009 aluminum alloy composites

The conversion coatings on SiC_p/2009 aluminum (Al) composites and 2009 Al alloy were obtained by immersing the samples into the cerium (Ce)‐based solutions with varying the chemical concentration (CeCl₃·7H₂O, NaCl), solution pH/temperature, immersing time, and drying temperature. The corrosion inhibition mechanism and kinetics were studied by using the electrochemical techniques and surface analyses. Potentiodynamic polarization tests showed that coatings improved corrosion resistance as compared to untreated samples and environmental factors played important role in the formation of conversion layer. Scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS), and X‐ray photoelectron spectroscopy (XPS) analysis revealed that relatively high inhibition efficiency for composite with 25 vol% SiC_p was due to the existence of rather high surface area of cathodic intermetallics/SiC_p, which support to deposit Ce oxides/hydroxides on the entire surface.     

Effect of gelatin additions on the corrosion resistance of cerium based conversion coatings spray deposited on Al 2024-T3

The corrosion resistance of cerium based conversion coatings on Al 2024-T3 was improved by the addition of a water soluble gelatin to the coating solution. Auger electron spectroscopy depth profiling showed that coatings deposited from solutions containing 800-3200 ppm gelatin were ~ 400 nm thick, while coatings deposited from solutions with 0-200 ppm gelatin were ~ 850 nm thick. The thinner coatings exhibited reduced surface cracking and spalling. Open circuit potential measurements during deposition showed that adding gelatin to the coating solution resulted in a more negative and stable potential with increasing gelatin concentrations. Visually, increasing gelatin concentrations promoted the formation of stable bubbles that covered panel surfaces, which limited transport of cerium species to the surface and decreased the deposition rate. X-ray diffraction analysis revealed that only coatings deposited from solutions containing 400-3200 ppm gelatin could be converted to CePO₄H₂O during post-treatment, potentially improving the corrosion resistance compared to coatings deposited from solutions without gelatin.     

Characteristics of copper oxide films deposited by PBII&D

Copper oxide films were deposited by plasma based ion implantation and deposition using a copper antenna as rf sputtering ion source. A gas mixture of Ar + O₂ was used as working gas. During the process, copper that was sputtered from the rf antenna reacted with oxygen and was deposited on a silicon substrate. The composition and the chemical state of the deposited films were analyzed by XPS. The structure of the films was detected by XRD. It is observed that Cu₂O film has been prepared on the Si substrate. It is found that the microstructure of the deposited film is amorphous for the applied voltage of − 5 kV. The surface layer of the deposited films is CuO. This is because the surface layer absorbs the oxygen from ambient air after the treated sample was removed from the vacuum chamber. An appropriate applied voltage, 2 kV under the present conditions, brings the lowest resistance. It is also seen that the maximum absorbance of the deposited films moves to a lower wavelength with increased applied voltage.     

Electrodeposition of black chromium from environmentally electrolyte based on trivalent chromium salt

Thin films of black chromium have been prepared by electrodeposition technique on steel substrates. Deposition of 1 µm thickness is conducted in a solution of chromium trivalent salt and oxidizing agent fluorosilicic acid (H₂SiF₆) operated at a current density 350 mA cm^− 2 at 25 °C and 1 min. The influence of H₂SiF₆ concentrations on the trivalent chromium electrodeposition was studied by the potentiodynamic technique. The phase structure and surface morphology of the deposited films were examined by using X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The chemical composition of these thin films was determined by energy dispersive X-ray analysis (EDS) and X-ray photoelectron spectroscopy (XPS) analysis. The spectral reflectance in the visible light, for films coating was characterized. From the SEM analysis, it was found that the black chromium has nano lamellar morphology that leads to a strong dispersion level. The XRD results showed that chromium, chromium oxide and cobalt oxide are the main bulk chemical compounds in the films. However, from XPS analysis of these surfaces, it was possible to determine that the most external layers of the films are made of different kinds of chromium and cobalt compounds. The black chromium-cobalt alloy thin film has better optical properties to transform solar energy into thermal energy, and these properties remain practically constant even when heat treated to a high temperature, 400 °C for 24 h.     

Cerium(III) chloride and sodium octylthiopropionate as an effective inhibitor mixture for zinc corrosion in 0.5 M NaCl

It has been reported that cerium(III) chloride CeCl₃ and sodium octylthiopropionate C₈H₁₇S(CH₂)₂COONa (NaOTP) are effective inhibitors for zinc corrosion in 0.5 M NaCl. In this study, synergistic inhibition of zinc corrosion in an aerated 0.5 M NaCl solution by a mixture of these inhibitors was investigated by polarization measurements after immersion of a zinc electrode in the solution for many hours. The inhibition efficiency of 1×10⁻⁴ M CeCl₃ plus 1×10⁻⁵ M NaOTP mixture was high, 95.1% after both 3 and 120 h. X-ray photoelectron spectroscopy and electron-probe microanalysis for the inhibited electrode revealed that the zinc surface was covered with a protective film composed of an hydrated or hydroxylated Ce-rich oxide, a small amount of Zn(OH)₂ and a trace of Zn(OTP)₂ chelate. The inhibition effect of 1×10⁻⁵ M NaOTP in the NaCl solution for the zinc electrode previously treated in 1×10⁻³ M CeCl₃ for 30 min was also examined, indicating a higher inhibition efficiency, 96.3% after immersion of the electrode in the solution for 120 h.     

Enhanced corrosion resistance of magnesium and its alloys through the formation of cerium (and aluminium) oxide surface films

Cerium (and aluminium) oxide layers were formed on magnesium and its alloys (AZ91) by chemical surface treatment with or without subsequent annealing. The corrosion behaviour modifications provided by the formation of these surface films were studied by means of different electrochemical and surface analysis techniques. The electrochemical behaviour, studied in sodium sulphate (Na₂SO₄) solution, showed (i) a marked shift of the corrosion potential towards more positive values, (ii) a slight inhibition of the cathodic reaction and (iii) a significant decrease of the anodic dissolution current. X‐ray photoelectron spectroscopy (XPS) was used for the characterisation of the composition of the deposited films and of the changes in the film composition during the electrochemical corrosion tests. The components of some oxide films are cerium dioxide (CeO₂), aluminium oxide (Al₂O₃) and aluminium hydroxide (Al(OH)₃). Other metallic mixed oxide films were obtained as a function of the solution composition. Very little (or no) change in the oxide film composition during the cathodic and anodic polarization experiments was observed from XPS measurements. Chemical treatment provides thick and moderately adherent protective oxide films. Annealing under oxygen further improves the beneficial effect of the chemical treatment.     

Molybdenum disulfide coating deposited by hybrid treatment and its friction-reduction performance

To obtain the MoS₂ film, a hybrid method, ion plating plus low temperature ion sulfuration, is utilized. A layer of metal molybdenum with 2–3 μm thick was first deposited by the multi-arc ion plating, and then the layer of metal molybdenum was treated by the low temperature ion sulfuration to obtain the composite MoS₂ film. The friction and wear experiment results showed that the MoS₂ film possessed an excellent performance of friction-reduction. SEM equipped with EDAX was adopted to analyze the morphologies and compositions of surface and worn scar of the MoS₂ film. XPS was used to detect the valence states of the film surface, and a nano-tester was employed to measure the nano-hardness and nano-modulus of the films.     

RF sputtering of ZnO films in Ar and Ar–H2 gas mixtures: Role of H incorporation in developing transparent conductive coatings

Fundamental and applied investigation of ZnO has been recently experiencing a renaissance due to its prospective use in various technological domains and, in particular, as transparent conductive oxide (TCO). In this respect, the present work aims to study the structural and physical properties of ZnO thin films deposited by RF sputtering in pure Ar and Ar–H₂ plasmas, at various concentrations (0–50%). The plasma chemical species were followed in function of the different gas mixture settings by optical emission spectroscopy (OES). X-ray photoelectron spectroscopy (XPS) and ATR-FTIR (Attenuated Total Reflection Fourier-Transformed Infrared) spectroscopy were used to study the bulk and surface chemical composition of the films, X-ray Diffraction (XRD) analysis allowed lattice structure and grain size determination while samples morphology was checked with a scanning electron microscope (SEM). The films were also characterized for their electrical and optical properties.The introduction of hydrogen in the plasma phase strongly affected the structural, chemical and physical properties of the films. In particular a pronounced change in the film electrical behavior was observed which become conductive when H is added in the gas mixture ([H₂] > 6%). The film transparency was on the other hand maintained. By combining XPS, ATR-FTIR and OES data we could correlate the established conductivity and its variations with intentional hydrogen incorporation in the crystal structure in the form of hydroxide species.     

Effects of the substrate temperature on the deposition of thin SiOx films by atmospheric pressure microwave plasma torch (TIA)

The effect of surface temperature on the deposition of silicon oxide (SiO_x) films with a non-thermal microwave axial injection torch (TIA) was investigated in an open air reactor. Argon was used as plasma gas and hexamethyldisiloxane (Si₂O₂C₆H₁₈) as silicon precursor. The parametric study reported here focuses on the influence of the substrate temperature on the morphological and chemical properties of the films deposited in the interval [0 °C–130 °C]. A similar effect of low and high surface temperature on the deposition process and on the microstructure of the deposited films was highlighted. Macroscopically, particles were promptly produced in the gas phase and incorporated to the film, which generates high surface roughness. Microscopically, FTIR results have shown a high carbon contamination of the deposited films at low and high temperatures, resulting in understoichiometric SiO_x films. They have also demonstrated that an optimum growth window for smooth and particle free SiO_x was to keep the surface temperature between 30 and 60 °C. Simple reaction mechanisms for powder formation and continuous silicon oxide thin films growth are suggested for each temperature ranges.     

Self-healing mechanism of an organosiloxane polymer film containing sodium silicate and cerium(III) nitrate for corrosion of scratched zinc surface in 0.5 M NaCl

A highly protective and self-healing film of 1,2-bis(triethoxysilyl)ethane (C₂H₅O)₃Si(CH₂)₂Si(OC₂H₅)₃ polymer containing sodium silicate (water glass) Na₂Si₂O₅ and cerium(III) nitrate Ce(NO₃)₃ was prepared on a zinc electrode previously treated in a Ce(NO₃)₃ solution. The film was examined by polarization measurement of the electrode in an aerated 0.5 M NaCl solution after the electrode was scratched and immersed in the solution for 4-72 h. Self-healing mechanism of the film was investigated by X-ray photoelectron spectroscopy and electron-probe microanalysis for the coated electrode surface after scratched and immersed in the NaCl solution. A passive film composed of Zn(OH)₂, ZnSi₂O₅ and Ce³⁺-Si₂O₅²⁻ salt or complex was formed on the scratched surface and preferential deposition of Si₂O₅²⁻ compounds occurred at a defect of the passive film where Cl⁻ accumulated, resulting in suppression of pitting corrosion at the scratch.     

Thermal plasma CVD of PSZ and double layered TiN/PSZ coatings by injection of alkoxides solutions with H2O

Coatings of partially Y₂O₃-stabilized ZrO₂ (PSZ) (Y > 2 at.%) and double layered TiN/PSZ films were deposited on Si wafers at 700 °C from zirconium tetra-buthoxide (ZTBO), yttrium tri-buthoxide (YTBO) and/or titanium tetra-ethoxide by chemical vapor deposition with H₂O in a thermal Ar/N₂/H₂ plasma. A small amount of H₂O was fed into the plasma to oxidize the ZTBO and YTBO to produce the PSZ coatings. Double layered TiN/PSZ film coatings were deposited without severe oxidation of under-layered TiN by controlling the feeding rate of H₂O. The product phases were identified by grazing incidence X-ray-diffractometry. The surfaces and cross-sections of the PSZ and double layered TiN/PSZ coatings were observed by scanning electron microscopy. An in-depth semi-quantitative analysis of the double layered TiN/PSZ films was performed by X-ray photoelectron spectroscopy, revealing the changes in the concentrations of Zr, Y, Ti, O, and N with depth. The effect of the Y content in mixed solutions of ZTBO and YTBO on the evolution of ZrO₂ is examined. It is proposed that the controlled feed rate of H₂O is effective in producing coatings of PSZ on TiN films without severe oxidation.     

Effect of cerium chloride on corrosion resistance and adhesion of chromate conversion coatings

The corrosion resistance, adhesion and morphology of the chromate conversion coating (CCCs) formed on AA6061 in a chromate conversion solution containing mainly potassium dichromate (K₂Cr₂O₇), chromic anhydride (CrO₃) and sodium fluoride (NaF), using cerium chloride (CeCl₃) as additive, were investigated by using potentiodynamic polarization curves, EIS, adhesion test and SEM. The corrosion resistance and adhesion of the CCCs are improved greatly by adding a small amount of CeCl₃ (from 20 to 40 mg/L), whereas the excessive CeCl₃ (60 mg/L) deteriorates these properties of the CCCs. The results of polarization curves are in good agreement with those of EIS. SEM photographs show that the precipitation of cerium hydroxide significantly affects the morphologies of CCCs.     

Synergistic inhibition of zinc corrosion in 0.5 M NaCl by combination of cerium(III) chloride and sodium silicate

The synergistic inhibition effects of cerium(III) chloride, CeCl₃ and sodium silicate, Na₂Si₂O₅ (water glass) on corrosion of zinc in an aerated 0.5 M NaCl solution at 30°C were examined by polarization measurements. Equimolar mixtures of these inhibitors were markedly effective, indicating that the inhibition efficiencies of the mixture at 1×10⁻⁴ of each inhibitor were 95.9 and 93.6 after immersion of a zinc electrode in the solution for 3 and 120 h, respectively. X-ray photoelectron spectra revealed that a protective layer composed of hydroxylated or hydrated cerium-rich oxide and small amounts of zinc hydroxide and silicate formed on the zinc surface. A high inhibition efficiency of 1×10⁻³ M Na₂Si₂O₅, 97.7% was obtained for corrosion of a zinc electrode which was previously treated in the NaCl solution of 1×10⁻³ M CeCl₃ at 30°C for 30 min.     

Formation of subsurface crevices in aluminum alloy 2024-T3 during deposition of cerium-based conversion coatings

The processing variables that contributed to the formation of subsurface crevices under cerium-based conversion coatings on AA 2024-T3 were investigated. Focused ion beam milling revealed the presence of subsurface crevices underneath a small fraction (∼ 10%) of coated areas, typically in areas with large cracks through the coatings. A solution of sodium chloride and H₂O₂ etched AA 2024-T3 and produced features similar to subsurface crevices, which confirmed that crevices formed during deposition due to the composition of the coating solution. Using sodium nitrate in place of sodium chloride resulted in no etching of the substrate. Thus, coatings free of subsurface crevices could be produced by using cerium nitrate instead of cerium chloride in the coating solution. Electrodeposited coatings, even those deposited from solutions containing chloride ions and H₂O₂, were also free of subsurface crevices. As a result, subsurface crevices are not inherent to cerium-based conversion coatings, but rather were formed due to certain process parameters, specifically the presence of chloride ions and hydrogen peroxide in the coating solution.     

The role of Ce ions in electrochemical corrosion of 304 SS in Ce(NO<Subscript>3</Subscript>)<Subscript>3</Subscript>.6H<Subscript>2</Subscript>O

Effects of temperature and potential on the electrochemical corrosion behavior of alloy AISI 304 (UNS S30400) Stainless steel were investigated in 3 wt.% cerium nitrate (Ce[NO₃]₃.6H₂O) solution. With an increase in electrolyte temperature from ambient temperature to 90°C, the corrosion potential of the alloy shifted towards the noble direction, and the resistance to polarization increased due to the formation of Ce-oxide on the electrode surface. The oxide films formed at the open circuit potential (OCP) and a passive potential of 0.4 V_SCE were examined by x-ray photoelectron spectroscopy (XPS). The oxide film formed at 50°C and a passive potentialof 0.4 V_SCE consists of mixed oxides of Ce and Cr, whereas that at OCP consists of only Cr oxide. The formation of Cr oxides on the electrode surface was primarily due to the nitrate (NO₃ ⁻) ions in Ce(NO₃)₃.6H₂O electrolyte.     

Interactions of evaporated aluminum atoms with polyaniline films — effects of dopant anion and adsorbed oxygen

Aluminum was thermally deposited onto H₂SO₄-protonated, HClO₄-protonated and neutral emeraldine (EM) base films. The interfacial interactions of Al atoms with these EM films were studied in situ by X-ray photoelectron spectroscopy (XPS). The Al atoms interact preferentially with the dopant anions in the cases of the protonated EM films, and with the nitrogen atoms of the conjugated polymer backbone in the case of the neutral EM film. For the H₂SO₄-protonated EM film, interactions with Al resulted in the formation of aluminum sulfate species, whereas, for the HClO₄-protonated film, the reaction resulted in the decomposition of the perchlorate dopant and the formation of aluminum chloride species. For the neutral EM film, the incoming Al resulted in a decrease in the intrinsic oxidation state of the polymer. The migration of bulk-adsorbed oxygen to the surface in response to Al deposition was observed in all of the EM films, and the formation of aluminum oxides, such as Al₂O₃, suggests that the adsorbed oxygen plays an important role in the interface formation.     

Mechanical properties and corrosion resistance of nanocrystalline ZrNxOy coatings on AISI 304 stainless steel by ion plating

Transition metal oxynitrides have become emerging decorative coating materials due to their adjustable coloration and high hardness and corrosion resistance. This research studied the effect of oxygen content on the coloration, mechanical properties and corrosion resistance of ZrN_xO_y thin films deposited on AISI 304 stainless steel using hollow cathode discharge ion plating (HCD-IP). The Zr/N/O ratios of the ZrN_xO_y films were determined using X-ray photoelectron spectroscopy (XPS). The color of the ZrN_xO_y thin film changed from golden yellow to blue and then slate blue with increasing oxygen content. X-ray diffraction (XRD) patterns revealed that phase separation of ZrN and m-ZrO₂ occurred as the oxygen content reached 31.2 at.%. ZrN(O) (ZrN with dissolving oxygen) is dominant at oxygen content less than 18.1 at.%, while m-ZrO₂ phase was prevailed at oxygen content above 40.3 at.%. Phase separation lowered the hardness of the ZrN_xO_y films as the fraction of ZrO₂ was less than 40%. The residual stresses in ZrN phase was higher than that in ZrO₂, and the residual stress decreased for the specimen containing 30 to 37% ZrO₂. For the samples containing more than 44% ZrO₂, the average residual stress was close to that in ZrO₂ phase. The corrosion resistance was evaluated by salt spray test and potentiodynamic scan in two solutions: 0.5MH₂SO₄ + 0.05 M KSCN and 5% NaCl solutions. The results showed consistent trend in the two solutions. From the results of potentiodynamic scan, corrosion resistance increased as the packing density of the film increased, whereas the film thickness was not a crucial factor on corrosion current; moreover, the electrical conductivity of the film may be one of the significant factors in corrosion resistance. Results of salt spray tests suggested that the corrosion of ZrN_xO_y in NaCl may play an important role in corrosion resistance.     

A self-healing protective film prepared on zinc by treatment in a Ce(NO3)3 solution and modification with Ce(NO3)3

A self-healing protective film was prepared on a zinc electrode by treatment in 1 × 10⁻³ M Ce(NO₃)₃ at 30 °C for 30 min to form a thin layer of hydrated Ce₂O₃ and by modification with 114 μg/cm² of Ce(NO₃)₃ · 6H₂O. The film was dried at 30 °C under a dry atmosphere. After the electrode surface was scratched with a knife-edge crosswise and immersed in an aerated 0.5 M NaCl solution at 30 °C for many hours, polarization measurement of the electrode was carried out in the NaCl solution. The protective efficiency of the film was markedly high, 97.7% at the immersion time, t_i=24 h. Neither pit-like anodic dissolution feature nor pit was observed within the scratches at t_i=72 h. X-ray photoelectron spectroscopy and electron-probe microanalysis revealed that Ce³⁺ migrating into the scratches from the film was adsorbed on the hydrated or hydroxylated zinc surface to form a new layer of hydrated Ce₂O₃ within the scratches, resulting in the self-healing activity of the film for preventing zinc corrosion at the scratched surface.