Showing papers on "Salt spray test published in 2016"

Preparation of polyaniline/graphene composites with excellent anti-corrosion properties and their application in waterborne polyurethane anticorrosive coatings

Abstract: Polyaniline, a novel conductive polymer, has been widely used as an anti-corrosive filler. In order to further improve the anti-corrosion performance, polyaniline/graphene (PANI/RGO) composites were prepared by in situ polymerization. And PANI/RGO composite anti-corrosion coatings were also prepared using PANI/RGO as anti-corrosive filler and waterborne polyurethane (WPU) as matrix. The anti-corrosion properties were proven by potentiodynamic polarization curves (Tafel polarization curves), electrochemical impedance spectroscopy and salt spray test analysis of the WPU anti-corrosive coatings. The results showed that the obtained composite coatings reinforced by 0.75 wt% of PANI/RGO composites possessed superior anti-corrosive performance when the graphene content of the filler was 4 wt%.

A comparative study on the corrosion behaviour of Al, Ti, Zr and Hf metallic coatings deposited on AZ91D magnesium alloys

Abstract: This paper focuses on the deposition of anti-corrosion, conductive coatings for Mg alloys used in electronics and aerospace industries. Metallic Al, Ti, Zr and Hf coatings were fabricated on an AZ91D Mg alloy surface via magnetron sputtering. Electrochemical system and salt spray tests were performed to investigate the corrosion resistance and the mechanism of corrosion failure of coated samples. The Hf-coated Mg alloy exhibited an extremely low corrosion current density of 0.825 μA/cm2 and a high protective efficiency of 99.49% during the electrochemical test. More importantly, the Hf coating provided superior protection for the Mg alloy against corrosion during the 24 h salt spray test. However, the Al-, Ti- and Zr-coated alloys exhibit poor performances in the above measurements. The low difference in potentials, the excellent corrosion resistance and the good adhesion to the substrate are considered probable causes for the anti-corrosion performance of the Hf coating.

Corrosion behaviour of TiB2 reinforced aluminium based in situ metal matrix composites

Abstract: Summary This paper focuses on corrosion characteristics of cast and forged aluminium 6061 based composites reinforced with TiB 2 particles. Composites were synthesised by in situ technique using potassium hexafluorotitanate salt (K 2 TiF 6 ) and potassium tetrafluroborate (KBF 4 ) halide salts by stir casting route at a temperature of 850 °C. Cast aluminium alloy and its in situ composites were subjected to open die drop forging at a temperature of 500 °C. Both cast and forged alloy 6061 and in situ composites were then subjected to microstructure studies, salt spray test. Salt spray test was conducted as per ASTM B117 standard test procedure using 5% sodium chloride test solution. Result reveals that, forged alloy and its in situ composites exhibited improved corrosion resistance compared to cast ones.

Preparation of microcapsules containing multi-functional reactive isocyanate-terminated-polyurethane-prepolymer as healing agent, part II: corrosion performance and mechanical properties of a self healing coating

Abstract: The preparation of microcapsules made of a polyurethane (PU) shell, and multi-functional isophorone diisocyanate based polyurethane prepolymer core as healing agent (BIH) was reported in the first part of this work. The preparation of epoxy coatings loaded with PU-based microcapsules, the self-healing ability of these coatings, the resistance of self-healed coatings against corrosive media and the mechanical strength of these healed coatings are described in the present communication. For comparison, a similar coating system, loaded with microcapsules containing monomeric isophorone diisocyanate (IPDI) core as healing agent, was also prepared and subjected to the same evaluations. For reliable comparison of these two coating systems and to show that the nature of the healing agent was the sole determining factor on the recorded results, the same reactive core fraction, solvent content, shell material and shell wall thickness were considered for the prepared microcapsules. In addition, an equal weight percent of the added microcapsules was used for both systems. The salt spray test and electrochemical impedance spectroscopy (EIS) techniques were utilized to show the ability of these two systems to heal a cracked area artificially created in the coatings. The recorded results confirmed the superior ability of multi-functional high molecular weight isophorone diisocyanate based healing agents for the protection of damaged areas of coating against corrosive media. The ability of a healing agent to repair the coating material was also verified by comparing the tensile strength of the coatings before and after crack formation and the healing of the cracked area, respectively. The epoxy coating could regain up to 95% of its original tensile strength, when loaded with 10 wt% of microcapsules containing multi-functional isophorone diisocyanate based polyurethane prepolymer as healing agent.

Effects of Solution and Aging Treatments on Corrosion Resistance of As-cast 60NiTi Alloy

Abstract: 60NiTi alloy has become a competitive candidate for bearing applications due to its shape memory effect, superelasticity, high strength, hardness, excellent abrasion resistance and corrosion resistance, etc. However, the relationship between its corrosion resistance and heat treatment is not clearly understood. Therefore, we used OM, XRD, SEM and EDS to study the evolution of microstructure in as-cast, solution-treated and aged 60NiTi alloy. Besides, the potentiodynamic polarization and salt spray test were used to compare corrosion resistance of 60NiTi alloy and 316 stainless steel and to study the effect of microstructures on corrosion resistance of 60NiTi alloy. The results show that the corrosion resistance of as-cast 60NiTi alloy is comparable to that of 316 stainless steel, but the corrosion resistance of solution-treated and aged 60NiTi alloys is much superior. The significantly reduced Ni3Ti phase after the solution and aging treatments is responsible for the remarkable improvement in the corrosion resistance of as-cast 60NiTi alloy.

Corrosion resistance of tin coatings deposited by cold spraying

Abstract: This article presents a study of corrosion resistance of tin and tin-based composite (Sn + Al2O3 and Sn + SiC) coatings deposited onto aluminium alloy substrates using the low-pressure cold spraying method. The samples were subjected to three different corrosion tests at a room temperature: (i) Kesternich test, (ii) a cyclic salt spray test and (iii) anodic polarisation test. The selected tests allowed extreme environment simulation typical for wide range of urban, industrial and marine service conditions. Evaluation of corrosion was carried out by analysing changes on the coating surface as well as in the microstructure. Additionally, the physicochemical tests were carried out using X-ray diffraction. XRD analysis clearly showed that abhurite Sn21O6Cl16(OH)14 is the main corrosion product established after the polarisation measurements. Despite extreme corrosive conditions used in experiments all tin coatings showed minor corrosion changes which implies that abhurite serves as a buffer between the metal ...

An investigation into different nickel and nickel–phosphorus stacked thin coatings for the corrosion protection of electrical contacts

Abstract: This paper presents an investigation on the corrosion performance of Ni/Au (NA), Ni–P/Ni/Au (PNA), Ni–P/Au (PA), Ni/Ni–P/Au (NPA) and Ni–P/Ni/Ni–P/Au (PNPA) coating stacks for electrical contact application. These five stack arrangements were exposed to sodium chloride neutral salt spray test (NSS) and mixed flowing gas test (MFG). Post-corrosion analyses were carried by X-ray diffraction, focused ion beam microscopy, scanning electron microscopy, energy dispersive spectroscopy, spectrophotometry and pits counting to evaluate the performance of each stack. Pitting behavior due to the MFG was explained through a proposed dominant pit concept. Results showed that multi-layer stacks, such as PNA, NPA, and PNPA, displayed worse corrosion resistance than single-layered stacks (NA, PA). The pitting in multi-layer stacks was attributed to the introduction of Ni and Ni–P interfaces that has accelerated the corrosion due to galvanic coupling. Removing these interfaces proved effective for corrosion prevention against NSS and MFG environments. Corrosion that occurred in the nickel layer grew horizontally while in the Ni–P penetrated vertically. This was attributed to the arrangement of Ni and Ni–P within a stack. The tunneling corrosion through the Ni–P layer became more pronounced as the Ni–P thickness was reduced, possibly due to an increase in the film porosity.

Conducting poly(o-anisidine) nanofibre dispersed epoxy-siloxane composite coatings: synthesis, characterization and corrosion protective performance

Abstract: Conducting polymers (CPs) exhibited a promising ability of corrosion inhibition and find application in the formulation of new generation smart anti-corrosive coating materials. CPs not only act as an active barrier for corrosive ions but also provide protection to the metal substrate through the redox mechanism. In view of this, the present article reports the synthesis, structural, physico-chemical, physico-mechanical characterization and corrosion protective performance of tartaric acid (TA) and functionalized protonic acid-dodecyl benzenesulphonic acid (DBSA) doped poly(o-anisidine) nanoparticles (TA–DBSA-POA) and these nanoparticles dispersed epoxy-siloxane (ES) nanocomposite coatings (TA–DBSA-POA–ES) on carbon steel (CS). The structure, size and morphology of TA–DBSA-POA nanoparticles and those of coatings were investigated by FT-IR, XRD, TEM and SEM analysis. The conductivity of TA–DBSA-POA nanoparticles (2.09 S cm−1), and TA–DBSA-POA–ES nanocomposites (5.02 × 10−3 S cm−1) as well as their thermal stability were investigated with the help of the four-probe method and the TGA technique. The physico-mechanical properties of these coatings were evaluated using standard laboratory methods. To the best of our knowledge, the corrosion protective performance of these coatings was investigated for the first time in our laboratory, using the salt spray test (SST), potentiodynamic polarization (PDP), and electron impedance spectroscopy (EIS) techniques at varying concentrations of NaCl viz. 3.5 wt%, 5.0 wt% and 7.0 wt% NaCl. SEM-EDAX and Raman studies revealed the presence of a passive ferric oxide layer. These studies revealed that nanocomposite coatings show far superior thermal stability, physico-mechanical and corrosion protective performance than plain ES and other such CP reinforced epoxy coating systems.

Effect of different structured TiO2 particle on anticorrosion properties of waterborne epoxy coatings

Abstract: Anticorrosion properties of waterborne epoxy coatings with three structured nano-particles of TiO2 were investigated and compared. The surface morphology and structure of TiO2 have been analysed by XRD, SEM and N2 adsorption–desorption. Corrosion performance of the nano-composite coating was investigated employing electrochemical impedance spectroscopy and salt spray test. Coatings with mesoporous TiO2 (meso-TiO2) possessed the best corrosion performance among the coating specimens. The EIS results show that the resistance value of coating with meso-TiO2 was above 5.4 × 108 Ω cm2 which was higher than the other nano-composite coatings. Possible strong interactions between polymeric matrix and meso-TiO2 caused high barrier properties.

Surface characterization and corrosion resistance of fluoferrite conversion coating on carbon steel

Abstract: Fluoferrite conversion coating has been studied for the corrosion protection of carbon steel by using the conversion solution mainly containing potassium fluoride, ammonium persulfate and other compositions. As a summary, this paper gave the detailed properties of the conversion coating prepared with hydrogen peroxide as the best composition. The morphology, composition and corrosion resistance of the coating were investigated by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), electron probe micro-analyzer (EPMA) and linear polarization, electrochemical impedance spectroscopy (EIS) and the salt spray test (SST). The results showed that the coating, mainly consisting of K 3 FeF 6 , exhibited good corrosion resistance (up to 72 h salt spray time) due to its close-packed particle structure and the great thickness (73 μm).

Ultra low water adhesive metal surface for enhanced corrosion protection

Abstract: A superhydrophobic surface with ultra low water adhesive force is fabricated on various metals for enhanced corrosion protection. The superhydrophobic surface is constructed by passivated zinc oxide (ZnO) and low surface energy poly(dimethylsiloxane) (PDMS). The process of wettability transformation and corrosion are evaluated by a salt spray test and electrochemical measurement. The superhydrophobic surface is separated layer-by-layer to reveal the function of each layer in corrosion protection. The surface adhesive force is applied as a novel metric for precisely determining the wettability state on the substrate surface. The results reveal that the ultra low water adhesive force of the superhydrophobic surface can effectively suppress water condensation on the metal surface which can suppress the transformation from the Cassie to Wenzel state. The superhydrophobic surface can effectively inhibit corrosion because of the synergistic effect of the triple layered protection system of air, PDMS and ZnO.

Electrochemical and long term corrosion behavior of Mn and Mo oxyanions sealed anodic oxide surface developed on aerospace aluminum alloy (AA2024)

Abstract: In the present investigation, an anodic oxide layer was developed on AA2024 specimens by sulfuric acid anodization process and subsequently sealed with chromate free Mn–Mo oxyanions (PMMO) by simple dip method. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy studies showed the presence of multiple oxidation states of Mn and Mo and the polymolybdate in the sealed anodic oxide layer respectively. Various electrochemical techniques were used to evaluate the corrosion performance of the developed coatings. Cyclic polarization test results showed a wide trans-passive potential region (> 2 V) for PMMO. Electrochemical noise measurement (ENM) results revealed pit growth of PMMO is highly controlled due to the presence of inhibitors in the sealed oxide layer. Scanning vibrating electrode technique (SVET) results revealed a minimal localized distribution of anodic and cathodic corrosion sites on PMMO compared to plain oxide layer (PO) and HTO after 168 h of immersion in 0.6 M NaCl solution. The results obtained from electrochemical impedance spectroscopy (EIS) showed one to two orders magnitude higher impedance (│Z│0.1 Hz) value for PMMO compared to PO and HTO. Neutral salt spray test result of PMMO after 1000 h showed comparable corrosion performance with conventional chromic acid anodized (CAA) specimen.

Influence of electroless plating on the deterioration of the corrosion resistance of MAO coated AZ31B magnesium alloy

Abstract: A composite bi-layer film is prepared on AZ31B Mg alloy for corrosion protection by means of micro arc oxidation (MAO) and electroless Ni–P plating. The electroless plating of Ni–P on MAO coated Mg alloy is accomplished based on a St-co-NIPAAm/Pd nanoparticles activator. The structure and corrosion protection are characterized by scanning electron microscopy (SEM), electron probe X-ray micro-analyzer, potentiodynamic polarization measurements in 3.5 wt% NaCl solution and salt spray tests. A compact and continuous bi-layer coating on Mg alloy substrate can be formed via MAO for 10 min and electroless plating coating for 40 min. However, our results show that the bi-layer coating exhibited a much worse corrosion resistance than that of the Mg alloy with a single MAO coating. After a systematical investigation in corrosion behaviors, a possible mechanism for the deterioration of corrosion resistance is proposed in this study.

The formation and corrosion behavior of a zirconium-based conversion coating on the aluminum alloy AA6061

Abstract: To understand the mechanism of the coating formation, the formation process of a zirconium-based conversion coating on aluminum alloy 6061 has been studied by means of AFM in PeakForce Kelvin Probe Force Microscope (PF-KPFM) mode which could provide direct evidence for the existence of driving force for the film formation. In addition, various techniques including SEM, XPS, EIS, salt spray test, and scanning electrochemical microscope were used to investigate the surface state and corrosion behavior of the conversion film. The direct driving force for the coating formation is the Volta potential difference between the intermetallic particles and matrix. That difference produces an ocean of micro electrochemical cells in which the intermetallic particles act as cathodic sites for the film deposition. However, the precipitation of the layer is a self-limited process in which the driving force gradually decreases as the conversion layer covers the surface of the aluminum alloys. The anti-corrosion performance of the film is unfavorable compared to the conventional chromate conversion coatings due to the pitting corrosion that occurs when exposed to harsh environment containing chloride. Furthermore, the zirconium-based conversion coating possesses no self-healing ability leading to the continuous degradation of the film until it completely lose efficacy.

Synthesis and assessment of novel anticorrosive polyurethane coatings containing an amine-functionalized nanoclay additive prepared by the cathodic electrophoretic deposition method

Abstract: Cathodic electrophoretic deposition (CEPD) was utilized to cover a mild steel cathode in an aqueous solution consisting of a newly synthesized two-component one-pack waterborne polyurethane resin. The resin mixture was composed of a hydroxyl terminated polyurethane prepolymer and a blocked isocyanate cross-linker, both contain build-in tertiary amine groups to provide the condition for formation of quaternary ammonium centers under acidic pH. Thermal treatment of the electrodeposited components led to formation of crosslinked polyurethane coatings with high gel content (80%). The coating was also modified by incorporation of a clay additive. For this purpose, Cloisite 30B, a quaternary ammonium modified clay was surface modified with (3-aminopropyl)trimethoxysilane and co-electrodeposited with base polyurethane components under optimized condition. All of the prepared coatings showed promising physico-mechanical properties including very good adhesion to the mild steel surface, excellent flexibility, high impact resistance as well as high pendulum hardness. Evaluation of the corrosion inhibition properties of the coatings with and without co-electrodeposited clay nanoparticles by the Electrochemical Impedance Spectroscopy (EIS) method revealed good corrosion protection of neat polyurethane coatings when exposed to 3.5% NaCl solution for 7 days. EIS assessment on the nanocomposite coating containing 0.5 wt% of modified clay showed corrosion resistance up to 8 GΩ after 2 h immersion in NaCl 3.5%. The time needed for the failing of the coating resistance was extended to 17 days for this sample. Also, results of the salt spray test revealed a lower sign of corrosion on the mild steel plate coated with the nanocomposite sample during 17 day exposure to NaCl 5% fog.

Self‐healing silane coatings of cerium salt activated nanoparticles

Abstract: This work investigates the effect of cerium salt activated nanoparticles as nanoreservoirs on the self-healing properties of silane hybrid coatings deposited on electro-galvanized steel substrates. The substrates were pre-treated with 3–glycidoxypropyl-trimethoxysilane (GPTMS) and bisphenol A (BPA), modified with cerium ion-activated CeO2-ZrO2 and CeO2-SiO2 nanoparticles. The morphology of the coating before corrosion tests was examined using atomic force microscopy (AFM). The results indicate the formation of nanostructured surfaces with relatively uniform dispersion of nanoparticles in the silane coating containing CeO2-ZrO2 nanoparticles. The corrosion behavior of the sol-gel coatings was also investigated using salt spray tests, electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization tests. During the salt spray test, the samples are exposed 600 h (or 25 days), revealing the improved resistance of the coated substrate containing CeO2-ZrO2 nanoparticles. Incorporation of activated CeO2-ZrO2 nanoparticles reduces the cathodic and anodic current density by one order of magnitude and shifts the corrosion potential to more positive values compared with the coating containing CeO2-SiO2 nanoparticles. Also, the EIS test results revealed higher impedance for the coating containing activated CeO2-ZrO2 nanoparticles. Corrosion tests results suggest that the activated CeO2-ZrO2 nanoparticles are more effective as nano-structured cerium ion reservoirs and can provide prolonged release of the inhibitor ions.