Corrosion Resistance Of Films Research Articles

Effect of Al Content in the Mg-Based Alloys on the Composition and Corrosion Resistance of Composite Hydroxide Films Formed by Steam Coating.

Mg alloys are expected to be used in fields of the transportation industry because of their lightweight property, however, they show low corrosion resistance. To improve the corrosion resistance, preparation of the protective film on Mg alloys is essential. In this study, composite hydroxide films were prepared on three types of Mg alloys with different aluminum contents—that is, AZ31, AZ61, and AZ91D—by steam coating to investigate the relationship between the Mg-Al layered double hydroxide (LDH) content in the film and the Al content in the Mg alloys. Scanning electron microscopy (SEM) observation demonstrated that films were formed densely on all Mg alloy surfaces. X-ray diffraction (XRD) analyses revealed that all films prepared on AZ61 and AZ91D were composed of Mg(OH)2, AlOOH, and Mg-Al LDH, while the film containing Mg(OH)2 and Mg-Al LDH were formed only on AZ31. The Mg-Al LDH content in the film prepared on AZ61 was relatively higher than those prepared on AZ31 and AZ91D. The content of AlOOH in the film increased with an increase in the Al content in the Mg alloys. The film thickness changed depending on the treatment time and type of Mg alloy. Polarization curve measurements in 5 mass% NaCl solution demonstrated that the film prepared on the AZ61 showed complete passive behavior within the potential range of −1.0 to −0.64 V. In addition, immersion tests in 5 mass% NaCl aqueous solution for 480 h demonstrated that the film on the AZ61 had superior durability against 5 mass% NaCl aqueous solution. These results indicated that the film on the AZ61 had the most superior corrosion resistance among all samples. The results obtained in this study suggest that the LDH content in the film could be related to the corrosion resistance of the film.

Effects of pore parameters on performance of anodic film on 2024 aluminum alloy

Anodic films on aluminum alloys are prepared in sulphuric/phosphoric acid electrolyte. The relationship between the pore parameters and the mechanical properties and corrosion resistance of the film is studied. With increased film porosity, the film microhardness decreases and the bonding strength increases, while for the same film porosity, larger pores decrease microhardness but increase bonding strength. As sulfuric acid concentration increases, the number of dissolved pores increases while the interpore distance and the pore roundness decrease. All these changes would promote cracking of the anodic film after heating. With changed pore parameters, the crack density increases more quickly than the crack width. After 4800 h immersion in NaCl solution, for films with porosity of 24.3% and 28.2% the barrier layer resistance decreased slowly, but for films with porosity higher than 30%, the barrier layer resistance decreased much faster. The porous layer resistance of the films shows similar variations as the barrier layer resistance. The lower film porosity, better film continuity and more regular pore structure could improve the corrosion resistance of anodic films. From the view of corrosion protection, it is suggested that the porosity of anodic films should be controlled below 30%.

The electrochemical properties of alloy 690 in simulated pressurized water reactor primary water: Effect of temperature

By anodic potentiostatic polarization and electrochemical impedance spectroscopy (EIS) measurements, the effect of temperature (200 °C, 250 °C, and 300 °C) on the electrochemical behavior of Alloy 690 was investigated in oxygenated borate buffer solution containing H3BO3 (2000 ppm B) + LiOH (2 ppm Li). The steady state passive current density was independent of the film formation potential at each temperature, indicating that the passive film is n-type in electronic character based on the predictions of the Point Defect Model (PDM). The passive current density increased and the absolute value of impedance decreased with increasing temperature, indicating a corresponding decrease in corrosion resistance. A mixed potential model (MPM), containing the PDM for describing the anodic passive dissolution of the alloy and the generalized Butler–Volmer equation for the cathodic oxygen reduction reaction was optimized on the experimental EIS data in order to extract model parameters, including kinetic parameters for the generation and annihilation of point defects in the barrier layer of the passive film. Metal (Cr,Ni,Fe) interstitials, which were found to have a higher concentration than oxygen vacancies, dominate the point defect structure of the barrier layer of the passive film at each temperature, thereby accounting for the n-type behavior of the passive film. With increasing temperature, the film thickness and defect density also increased, resulting in the decreased corrosion resistance of film. This indicates that the defect density of passive film plays a more important role on corrosion behavior of alloy than the film thickness.

Landfill leachate and industrial effluent treatment using advanced evaporation technology

Evaporation is one of the most efficient methods for separation of dissolved solids and water. Using evaporation, high quality, recyclable or dischargeable water can be produced. An advanced evaporation technology for industrial effluent and landfill leachate treatment has been developed. Construction material of the evaporative heat transfer surface is the key difference to conventional systems: thin, corrosion resistant and elastic polymeric film is used instead of rigid metals. The cost of the polymeric surface is low, decreasing the high costs that are associated with conventional evaporators. Thus, evaporation is now a feasible alternative in a number of effluent treatment applications. The technology applies Mechanical Vapor Recompression (MVR) concept using electrical energy or Multi-Effect (ME) concept utilizing waste heat as energy source. In both concepts the evaporative surface areas are larger than in conventional systems. As a result of the large surface electrical energy consumption is low in the MVR-type evaporators, typically 8-12 kWh/m3 of recovered water; in ME-type evaporators the large area enables the utilization of low value waste heat in an efficient way.

Effect of bias on structure mechanical properties and corrosion resistance of TiNx films prepared by ion source assisted magnetron sputtering

Titanium nitride (TiNx) films were deposited on 304 stainless steel and silicon (100) wafers by ion source assisted magnetron sputtering. The effect of substrate bias voltage on the preparation and properties of TiNx films was investigated. The results show that as the substrate bias voltage increases from 0 V to −400 V, the deposition rate of TiNx film decreases significantly and the density increases, which can be attributed to the re-sputtering effect at high ion bombardment. The texture of TiNx films varies gradually from (111) to (200) with the increase of energy delivered into the growing film. The hardness of the film deposited under −200 V bias voltage reaches the maximum value, 12.9 GPa. Meanwhile, the toughness and corrosion resistance of the film reach a maximum at a bias voltage of −400 V. In conclusion, the density, hardness, toughness and corrosion resistance of TiNx films can be increased by changing the substrate bias voltage.

Effect of Synthesis Conditions on the Controlled Growth of MgAl–LDH Corrosion Resistance Film: Structure and Corrosion Resistance Properties

In this study, a series of MgAl–layered double hydroxide (LDH) thin films were synthesized by a single step hydrothermal process at different synthetic conditions on AA6082, and the combined effect of reaction temperatures and crystallization times on in situ growth MgAl–LDH structural geometry, growth rate, and more importantly on the corresponding corrosive resistance properties are briefly discussed. The synthesis of LDH was performed at reaction temperatures of 40, 60, 80, and 100 °C, while the treatment time was varied at 12, 18, and 24 h. The as-prepared synthetic coatings were characterized by scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR), while the corresponding corrosion protection efficiency of the developed coating was studied through potentiodynamic polarization studies and electrochemical impedance spectra. The findings demonstrated that extended crystallization time and reaction temperature impart a significant effect on the oriented growth of layered double hydroxide, the surface morphology, and on the film thickness, which had a remarkable influence on the LDH corrosion resistance ability. The LDH coated specimen developed at 100 °C for 18 h reaction time showed a more compact and dense structure compared to the traditional platelet structure obtained at 80 °C for 24 h crystallization time, and interestingly that compact structure exhibited the lowest corrosion current density, up to five orders of magnitude lower than that of bare AA6082.

Enhancement of the Epoxy Coating Corrosion/Cathodic Delamination Resistances on Steel by a Samarium Based Conversion Coating

Samarium (III) (Sm)-based conversion layer was developed on carbon steel for improvement of the epoxy coating adhesion properties, corrosion protection performance, and cathodic delamination resistance. The post-heating and pre-heating actions impact on the Sm (III) film properties was studied. The morphology and chemistry of the Sm (III) film were examined by scanning electron microscopy, atomic force microscopy, contact angle, and X-ray photoelectron spectroscopy. The outcomes from these analyses proved that both pre-heating and post-heating actions altered the morphology and chemistry of the Sm (III) film. The pull-off test indicated that Sm (III) film could enhance the adhesion between the epoxy/steel through increasing the surface roughness and enhancing the surface free energy. The improvement in adhesion strength led to a decrease in the cathodic delamination rate up to 78%. Although both pre-heating and post-heating actions improved the corrosion protection performance of the epoxy film, the pre-heating method had a much higher impact on the epoxy film corrosion resistance enhancement. An excellent corrosion protective performance was observed in the samples preheated at 65°C after 1000 h exposure to salt spray test.

Preparation of super-hydrophobic and corrosion resistant colored films on chemically etched 304 stainless steel substrate

A colored super-hydrophobic surface on stainless steel substrate was achieved by means of chemical coloring on etched substrate combined with modification by fluorosilane. Effect of chemical etching with HCl and FeCl3, and of passivation treatment for the etched substrate by H2O2/HNO3 on coloring behavior, micro-structure, chemical composition, wettability, mechanical durability and corrosion resistance of the surface was studied using spectrophotometry, water contact angle measurements, SEM, XPS, micro-fretting tests, potentiodynamic polarization and corrosion morphology observation. Etching was found to slow coloring speed and make the end color shift to the anti-clockwise direction in CIE coordinate. An orange super-hydrophobic surface with water contact angle of 152.6° and sliding angel of 8.9° could be realized on the 20-min etched substrate via subsequent coloration and fluorosilane modification, which showed improved corrosion resistance and durability under fretting wear compared with ordinary colored film formed on non-etched substrate. In spite of leading to a slight decreasing of water contact angle, oxidation treatment by H2O2/HNO3 for the etched substrate before coloring could further improved corrosion resistance and fretting contact durability of the finally got colored surfaces with fluorosilane layers, and the enhancement effect brought by H2O2 was found to be more remarkable in comparison to HNO3.

Effect of Vapor Pressure During the Steam Coating Treatment on Structure and Corrosion Resistance of the Mg(OH)₂/Mg-Al LDH Composite Film Formed on Mg Alloy AZ61.

Corrosion resistant films with almost the same film thickness were prepared on the magnesium alloy AZ61 by steam coating at different vapor pressure and treatment times. The effect of the vapor pressure on the structures and the corrosion resistance of the films was investigated by using FE-SEM, SEM-EDX, GAXRD, and potentiodynamic polarization curve measurements in a 3.5 mass percentage NaCl aqueous solution. These studies clarified that the interlayers of Mg-Al Layered Double Hydroxide (LDHs) increased and its structure became non-uniform with an increase in the vapor pressure. The corrosion current density slightly increased with an increase in the vapor pressure during the treatment, but pitting corrosion occurred at both low and high vapor pressures. These results indicate that water molecules were pushed into an interlayer of Mg-Al LDHs by high vapor pressure. Consequently, the interlayer distance of Mg-Al LDH was widened and the cracks were generated in the anti-corrosive film. On the other hand, the Mg-Al LDH with an insufficiently large interlayer distance could not fill the cracks in the Mg(OH)2 crystallites and caused pitting corrosion when the vapor pressure was low.

Formation of Corrosion-Resistant Films on Al–Zn–Mg Alloy by Steam Coating Using Acidic Zn(NO<sub>3</sub>)<sub>2</sub> Aqueous Solutions

Formation of Corrosion-Resistant Films on Al–Zn–Mg Alloy by Steam Coating Using Acidic Zn(NO<sub>3</sub>)<sub>2</sub> Aqueous Solutions

Formation of corrosion-resistance films on Al–Zn–Mg alloy by steam coating using acidic Zn(NO<sub>3</sub>)<sub>2</sub> aqueous solutions

Corrosion resistant films were fabricated on Al–Zn–Mg alloy by steam coating using Zn(NO3)2 aqueous solution at different concentrations. XRD patterns and FT-IR spectra demonstrated that nitrate type Zn–Al layered double hydroxide (LDH) and ZnO films were formed on the Al–Zn–Mg alloys by steam coating at the temperatures of 373 to 433 and 473 K, respectively, using Zn(NO3)2 aqueous solution at 1000 mM. γ-AlO(OH) films were found to be prepared on the Al–Zn–Mg alloys by steam coating at 513 K using Zn(NO3)2 aqueous solutions at the concentrations of 1 to 100 mM. The corrosion resistance of the films was investigated by potentiodynamic polarization curve measurements. The polarization curve measurements revealed that the γ-AlO(OH) films prepared by steam coating at 513 K using 1 mM of Zn(NO3)2 aqueous solution was most effective to suppress pitting corrosion and anodic current density.

Fabrication and corrosion property of conversion films on magnesium alloy from deep eutectic solvent

A facile anodic treatment for magnesium alloy was proposed in a choline chloride-ethylene glycol based deep eutectic solvent (DES). Conversion films with interconnected porous networks and jagged nanorod arrays can be formed, which depends on the applied anodic current density. Crystallographic orientation of the substrate is accordingly changed. The conversion films are mainly composed of MgCO3 which results from the interaction between the Mg alloy and the released species from the decomposition of DES. A higher anodic current density produces a better corrosion resistant conversion film. Superhydrophobic and slippery surfaces can be achieved on the as-prepared conversion films to further improve the corrosion resistance.

The Formation Mechanism and Corrosion Resistance of a Composite Phosphate Conversion Film on AM60 Alloy.

Magnesium alloy AM60 has high duc and toughness, which is expected to increase in demand for automotive applications. However, it is too active, and coatings have been extensively studied to prevent corrosion. In this work, a Ba-containing composite phosphate film has been prepared on the surface of AM60. The composition and formation mechanism of the film have been investigated using a scanning electronic microscope equipped with energy dispersive X-ray spectroscopy, Fourier transform infrared, X-ray photoelectron spectroscopy, and X-ray diffractometry tests. The corrosion resistance of the film has been measured by electrochemical and immersion tests. The results show that the deposition film has fully covered the substrate but there are some micro-cracks. The structure of the film is complex, and consists of MgHPO4·3H2O, MnHPO4·2.25H2O, BaHPO4·3H2O, BaMg2(PO4)2, Mg3(PO4)2·22H2O, Ca3(PO4)2·xH2O, and some amorphous phases. The composite phosphate film has better anticorrosion performance than the AM60 and can protect the bare alloy from corrosion for more than 12 h in 0.6 M NaCl.

Deposition, Characterization and Evaluation of Monolayer and Multilayer Ni, Ni–P and Ni–P–Nano ZnOp Coatings

Ni, Ni–P and Ni–P–ZnOp monolayer films along with multilayer coatings containing different arrangements of these layers were produced on steel substrates by electrodeposition and electroless deposition techniques. Co-deposition of ZnO nano-particles, as well as morphology, cross-section, microstructure and microhardness of coatings were investigated. Corrosion behaviors of monolayer coatings were studied by potentiodynamic polarization and electrochemical impedance spectroscopy techniques, and the results were compared to multilayer films. Results revealed that, Ni–P–1.5 vol% ZnOp monolayer film obtained from a bath with 4 g L−1 of these particles had the highest hardness between all samples. Further addition of nano-particles to the bath lead to the formation of discontinuous films. Most of the multilayer coatings with different arrangements exhibited higher corrosion resistance as compared to monolayer films. Corrosion current density of three-layer Ni–P–ZnOp/Ni/Ni–P coating, considered as the most corrosion resistant film, was about 538 times lower than monolayer Ni–P coating.

Electrochemical Evaluation of WD-40 Oil as Temporary Protection with Additions of Natural Compounds as Inhibitors in Cast Iron

Electrochemical techniques are a valuable instrument for the determination of the effectiveness of anti-corrosion temporary protections applied. The object of this research was to evaluate the WD-40 oil film with additions of organic inhibitor for protection against corrosion. Iron samples were selected to simulate the composition and morphology of historical artifacts and oil as temporary protection a common practice in conservation controls. Electrochemical evaluation showed the utmost protection was oil WD-40 with nicotine as an additive, caffeine also increases film corrosion resistance. Both compounds added as corrosion inhibitors showed a considerable anti-corrosive properties improvement.

Formation of Anticorrosive Film for Suppressing Pitting Corrosion on Al-Mg-Si Alloy by Steam Coating

Al alloys offer excellent physical and mechanical properties, such as a low density, high specific strength, and good ductility. However, their low corrosion resistance has restricted their application in corrosive environments. There is a need, therefore, for a novel coating technology that is capable of improving the corrosion resistance of Al alloys. In the present study, we examined a steam-based method of forming a corrosion-resistant film on Al alloys. Al-Mg-Si alloy was used as the substrate. The cleaned substrates were set in an autoclave with ultrapure water as the steam source and processed using different temperatures and holding times, resulting in the formation of anticorrosive films on the alloy. FE-SEM images of the film surfaces showed that plate-like nanocrystals were densely formed over the entire surface. XRD patterns indicated that the film was composed mainly of AlOOH crystals. The potentiodynamic polarization curves revealed that the corrosion current density of the film-coated substrates significantly decreased, and that the pitting corrosion was completely suppressed, indicating that the corrosion resistance of the Al-Mg-Si alloy was improved by the film formed by means of steam coating.

Formation mechanism of Mg-Al layered double hydroxide-containing magnesium hydroxide films prepared on Ca-added flame-resistant magnesium alloy by steam coating

Corrosion resistant films were prepared on the Ca-added flame-resistant magnesium alloy AZCa612 by steam coating at different treatment time and temperature. The formation mechanism of the films was investigated by using the digital microscope, FE-SEM, XRD, FT-IR, XPS and the potentiodynamic polarization curve measurements in a 5mass% NaCl aqueous solution. XRD, FT-IR and XPS studies indicated that the film was composed mainly of Mg(OH)2 and carbonated-based Mg–Al LDHs. In addition, MgCO3 and AlO(OH) were also incorporated slightly in the film. The formation mechanism of the film on AZCa612 was proposed that amorphous Mg(OH)2 was initially formed by reaction of steam and MgO as a natural oxide film on the substrate. With an increase in the temperature and pressure, the amorphous Mg(OH)2 was crystallized, and further increase in temperature, pressure, and treatment time induced the formation of Mg-Al LDH and AlO(OH) in the film.

Research on corrosion resistance of metal films sputtered by rotating target and planar target

AbstractThe corrosion resistance of MoNb/AlNd/MoNb film during different sputter conditions was studied for G6 rotating target sputter equipment. The results show that with the increase of sputter power and the increase of the thickness, top MoNb tends to form coarse columnar crystals, and the corrosion resistance of the metal thin films, at first, increases and then decreases with the increase of sputter power and metal thickness. As the sputter temperature increases, top MoNb tends to form coarse grains while the corrosion resistance of the film is poor. The result also release that with the increase of the target speed, top MoNb film becomes loose so that it is difficult to play a protective role because of its poor corrosion resistance ability. Under the same conditions, the sputter of the planar target film is denser; as a result, the top MoNb layer can protect the inner AlNd layer from corrosion.

Effect of Electrolyte Concentration on the Structure and Corrosion Resistance of Anodic Films Formed on Magnesium through Plasma Electrolytic Oxidation

The thickness and corrosion resistance of films formed on AZ31 magnesium alloys through plasma electrolytic oxidation for the same amount of electricity supplied increased with decreasing electrolyte concentration irrespective of the current density. For all electrolytes of phosphate, silicate, and aluminate, the initial bending/breakdown voltage increased linearly with the logarithm of the decreasing electrolyte concentration and exhibited no dependence on the current density. The chemical composition of the films was independent of all electrolysis conditions such as electrolyte concentration, current density, and anodization time. This behavior is explained by a mechanism in which anion incorporation is governed by a chemical reaction/precipitation under plasma but not by the electric field, unlike the case for conventional anodizing of valve metals without sparking. The corrosion resistance of the films tended to increase as a function of the logarithm of the film thickness, irrespective of the electrolyte species and electrolysis conditions.

Evolution of corrosion resistance and passive film properties of Ni-Mo alloy coatings during exposure to 0.5 M NaCl solution

The corrosion properties of Ni-Mo alloy coatings with different molybdenum content (11–32wt%) were investigated in the course of exposure to 0.5M NaCl solution. Polarization resistance and impedance measurements showed that after contact with corrosive media, the formation of passive film on the coating surface, determines the corrosion resistance of Ni-Mo alloys. XPS analysis revealed that, the passive film growth was enhanced by the presence of higher amounts (26–28wt%) of Mo in the coating. It was found, that after exposure to corrosive solution, Mo oxides occurred at the passive film/metal interface, while Ni hydroxide dominated in the bulk of the passive film.