Showing papers on "Salt spray test published in 2017"

Investigating the effect of SiO2-graphene oxide hybrid as inorganic nanofiller on corrosion protection properties of epoxy coatings

Abstract: In this research, tetraethyl orthosilicate (TEOS) is used as organosilane to decorate the surface of graphene oxide (GO) nanosheets by SiO2 nanospheres via a facile method. Results of X-ray diffraction analysis, Raman spectroscopy, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, and atomic force microscopy reveal that SiO2 nanospheres have covered the surface of GO sheets through covalent bonding and SiO2-GO nanohybrids are successfully synthesized. Further, the effect of incorporating 0.1 wt% GO nanosheets and/or SiO2-GO nanohybrids on properties of epoxy coatings is investigated. The results show that the pull-off adhesion strength of epoxy coatings to mild steel substrates and the water contact angle on coatings significantly increase via adding SiO2-GO nanohybrids. The potentiodynamic polarization test, electrochemical impedance spectroscopy (EIS) and salt spray test results demonstrate that corrosion protection performance of epoxy coatings remarkably enhances by embedding well-distributed SiO2-GO nanohybrids compared to GO nanosheets.

RGO modified ZnAl-LDH as epoxy nanostructure filler: A novel synthetic approach to anticorrosive waterborne coating

Abstract: The reduced graphene oxide‑zinc‑aluminum layered double hydroxides (rGO-ZnAl-LDH) micro-nano fillers were prepared via a one-step process, then modified by 3-aminopropyl triethoxysilane and incorporated into a waterborne epoxy (EP) matrix to produce M-rGO-ZnAl-LDH/EP composite coating. The effects of the M-rGO-ZnAl-LDH hybrid on the corrosion resistance of the coating were studied by adjusting the ratio of GO: ZnAl-LDH and also the adding amount of M-rGO-ZnAl-LDH hybrid. The anticorrosive nature of the M-rGO-ZnAl-LDH/EP composite coating had been investigated by potentiodynamic polarization curves, electrochemical impedance spectroscopy (EIS) and salt spray test. The results indicated that the corrosion resistance of the coating was improved remarkably when the ratio of GO: ZnAl-LDH was 2:1 and the adding amount was 0.5 wt% into EP. The corrosion current density ( i corr ) was only 0.0733 μA/cm 2 and the coating resistance ( R c ) was up to 2.77E4 Ω cm 2 for M-rGO-ZnAl-LDH/EP (2:1–0.5 wt%), while the i corr for pure EP was 0.469 μA/cm 2 and the R c for pure EP was 2.10E3 Ω cm 2 , which suggested that the M-rGO-ZnAl-LDH micro-nano fillers had a higher anticorrosion properties relative to the waterborne epoxy resins.

Influence of silica nanoparticles on corrosion resistance of sol-gel based coatings on mild steel

Abstract: For this study, unfunctionalised and functionalised nanoparticles of silica (SiO2) were incorporated into a sol-gel based matrix in an effort to provide more effective corrosion protection on a mild steel substrate Tests such as atomic force microscopy (AFM) and white light interferometry (WLI) were carried out to characterise coating microstructure and properties Corrosion protection and coating durability was investigated using different methods which included electrochemical impedance spectroscopy (EIS) and accelerated salt spray testing to simulate a marine environment Electrochemical test results as well as results after exposure in the neutral salt spray test indicated that the addition of silica nanoparticles led to an improvement in corrosion resistance of the coating matrix The most effective performance was observed when the nanoparticles were functionalised Nanoparticle functionalisation helped to avoid agglomeration during incorporation leading to a more uniform nanoparticle distribution within the coating formulation and an improvement of the coating's ability to protect against corrosion

Surface modification of nickel-aluminum bronze alloy with gradient Ni-Cu solid solution coating via thermal diffusion

Abstract: The surface modification of nickel-aluminum bronze (NAB) alloy was developed by thermal diffusion of Ni coating and the alloy matrix. A multilayer coating was designed with the gradient outer layer of the Ni-Cu solid solution and the inner layer of the Ni-Al-Cu intermetallic layer. The evolution of the multilayer was a diffusion controlled model. The enhanced corrosion resistance of the Ni-Cu layer could be found in the salt spray test, which exhibited uniform corrosion behavior compared with severe selective phase corrosion of the NAB alloy. Besides the gradient distribution of the components, it was also attributed to the formation of protective film, which mainly consisted of Ni(OH) 2 and Cu 2 O. It has been confirmed by electrochemical impedance spectroscopy (EIS) test and X-ray photoelectron spectroscopy (XPS) results.

Novel anodic oxide film with self-sealing layer showing excellent corrosion resistance

Abstract: In the present work, the novel anodic oxide film (AOF) with self-sealing layer was successfully fabricated on 2024Al alloys by using an improved anodic oxidation method. The presence of the self-sealing layer on the porous layer of AOF was verified by Field emission scanning electron micro scope. Confocal laser scanning microscope (CLSM) and X-ray photoelectron spectroscopy (XPS) were used to evaluate the morphology and the corrosion products of the AOF after salt spray test. The microhardness test showed that the self-sealing AOFs still displayed high hardness even after salt spray test. Electrochemical test and salt spray test results illustrated the excellent corrosion performance of the novel structured self-sealing anodic oxide film (SAOF) compared with common porous AOFs. The narrow diameter makes it difficult for chlorine ions ingress into the pores of SAOFs. The self-sealing layer played an important role in protecting the SAOF from corrosion.

Anticorrosive yet conductive Hf/Si3N4 multilayer coatings on AZ91D magnesium alloy by magnetron sputtering

Abstract: Hafnium monolayer and Hf/Si3N4 multilayer coatings were deposited on AZ91D magnesium alloys via magnetron sputtering. The microstructure, conductivity and corrosion behaviors of these coatings were investigated. It was found that the columnar growth of the Hf sublayer was suppressed in the Hf/Si3N4 multilayer coating. This multilayered structure resulted in the relief of residual stress and the decrease in porosity. These changes in microstructure inhibited the permeation of corrosion media into the substrate and decreased the diffusion rates of corrosion products. The Hf/Si3N4 multilayer coatings with 10 bilayers showed the best anticorrosion performance revealed by the lowest corrosion current density of 2.798 μA/cm2 in electrochemical system and the smallest corrosion area of 0.22% after 48 h salt spray test, respectively. Additionally, the introduction of Si3N4 sublayer has little impact on the conductivity of the multilayer coating due to the shadowing effect during the deposition.

Influences of crystallographic texture and nanostructural features on corrosion properties of electrogalvanized and chromate conversion coatings

Abstract: Galvanized coatings are widely used in industry, but the influences of microstructure on corrosion behaviors have rarely been studied in these coatings. The present investigation aims to systematically analyze crystallographic texture and nanostructural features of galvanized coatings as well as their chromate conversion layers, and examines the relationship between their structures and corrosion properties. Three groups of electrogalvanized coatings fabricated with different types of plating additives are studied, using a series of complementary characterization techniques. The corrosion behaviors of the deposits are then analyzed with the potentiodynamic polarization technique and salt spray test, in light of their structural characteristics. The study reveals that the additives critically influence the microstructure of both the galvanized coatings and chromate layer. The corrosion resistance of the coatings can be enhanced by suppressing the {100} crystallographic planes of zinc and minimizing defects along the zinc/substrate interface, and by promoting formation of an amorphous-oxide layer in the chromate film.

Optimization of corrosive properties of carbon fiber reinforced aluminum laminates due to integration of an elastomer interlayer

Abstract: Fiber-Metal-Laminates (FML) show superior dynamic mechanical properties combined with low densities. The mechanical performance of for example commercially available fiber-metal-laminate, glass laminate aluminum reinforced epoxy, can be improved by the substitution of glass fibers with carbon fibers. However, carbon fiber reinforced aluminum laminate introduces a mismatch of coefficients of thermal expansion and the possibility of galvanic corrosion. The fiber-metal-laminate is altered by the integration of an elastomer interlayer which is desired to solve both problems. The high electrical resistance is supposed to inhibit the corrosion. This study focuses on the effect of galvanic corrosion caused by neutral salt spray tests on fiber-metal-laminates, the influence of an elastomer interlayer and the quantification of the residual mechanical properties. The galvanic corrosion affects the interfaces of the laminates, therefore in this study edge shear tests and flexural tests were carried out to quantify the residual properties and thereby the corrosive damage. The elastomer interlayer was found to inhibit galvanic corrosion in the salt spray chamber, whereas the fiber-metal-laminate without interlayer showed corrosive damage. Furthermore, the mechanical properties of the fiber-metal-laminate with elastomer interlayer remained constant after the corrosion tests, whilst the fiber-metal-laminate’s properties decreased with corrosive loads.

Corrosion Resistance of Copper Coatings Deposited by Cold Spraying

Abstract: In the article, a study of corrosion resistance of copper and copper-based cermet (Cu+Al2O3 and Cu+SiC) coatings deposited onto aluminum alloy substrate using the low-pressure cold spraying method is presented. The samples were subjected to two different corrosion tests at room temperature: (1) Kesternich test and (2) a cyclic salt spray test. The selected tests were allowed to simulate service conditions typical for urban, industrial and marine environment. Examination of corroded samples included analysis changes on the coating surface and in the microstructure. The physicochemical tests were carried out using x-ray diffraction to define corrosion products. Moreover, microhardness and electrical conductivity measurements were conducted to estimate mechanical and physical properties of the coatings after corrosion tests. XRD analysis clearly showed that regardless of corrosion conditions, for all samples cuprite (Cu2O) was the main product. However, in the case of Cu+Al2O3 cermet coating, chlorine- and sulfate-containing phases such as Cu2Cl(OH)3 (paracetamite) and Cu3(SO4)(OH)4 (antlerite) were also recorded. This observation gives better understanding of the lowest microstructure changes observed for Cu+Al2O3 coating after the corrosion tests. This is also a justification for the lowest decrease in electrical conductivity registered after the corrosion tests for this coating.

Effect of anti-corrosive performance, roughness and chemical composition of pre-treatment layer on the overall performance of the paint system on cold-rolled steel

Abstract: Many fundamental researches about the effect of some basic properties of a pre-treatment layer, such as anti-corrosive performance, surface roughness and chemical composition on the overall performance of paint systems were investigated. Three kinds of pre-treatment layers: bare polyacrylic acid (PAA) layer, Mo based layer and Mo doped PAA layer were deposited on cold-rolled steel surfaces through immersing the steel samples in the corresponding solution. The electrochemical measurements results indicated that after been treated in PAA solution, the steels became vulnerable to corrosion and the Mo based layer and Mo doped PAA layer could improve the corrosion resistance of steel to a certain degree. The values of root-mean-square roughness of the bare steel, bare PAA layer, Mo based layer and Mo doped PAA layer were 15.0 nm, 11.3 nm, 13.0 nm and 59.1 nm, respectively. The corresponding values of arithmetic average roughness of the samples were 16.9 nm, 10.5 nm, 9.1 nm and 41.0 nm, respectively. The spectroscopy results indicated that the surface of the bare PAA and Mo doped PAA layer covered steels contained abundant COOH groups and the composition of Mo based layer covered steel surface was mainly oxides. According to the impact test and neutral salt spray test results, the corrosion mitigation performance, microstructure and chemical composition of the pre-treatment layer could all affect the overall performance of the paint system. All the results indicated that the anti-corrosive performance was not the only index, the microstructure and chemical composition also needed to be considered in the development of a new generation pre-treatment layer.

Effect of heat treatment on corrosion resistance and adhesion property in Zn-Mg-Zn multi-layer coated steel prepared by PVD process

Abstract: In this study, as the alternatives to the depletion of Zn resources, the Zn-Mg alloy was deposited on a steel substrate by a PVD process. Considering the difference of vapor pressure between Zn and Mg in vacuum condition, Zn, Mg and Zn were sequentially coated by PVD process to form a uniform coating layer, and a heat treatment was separately conducted at 200 °C under vacuum condition. As the heating time increased, the volume fraction of the intermetallic compound phases (Mg 2 Zn 11 and MgZn 2 ) gradually increased up to the heat-treated sample for 360 s. From the 0T-bending test, delamination of the coating layer was observed from heat-treated sample for 240 s which is composed of over 85% of the intermetallic compound phases. And from the salt spray test, it is confirmed that the red rust generation time was 624 h in heat-treated sample for 360 s which was composed entirely of Zn-Mg intermetallic compound phases.

Studies on Silicon Containing Nano-hybrid Epoxy Coatings for the Protection of Corrosion and Bio-Fouling on Mild Steel

Abstract: An epoxy nano-composite coating was developed using amine functionalized nZnO (in the amount of 2.5 %, 5.0 % and 7.5 wt %) as the dispersed phase and a commercially available epoxy resin as the matrix phase. The structural features of these materials were ascertained by FT-IR spectral studies. The anti-corrosive properties of the epoxy/nZnO hybrid coatings in comparison with a virgin coating were investigated by a salt spray test and electrochemical impedance spectroscopy technique. The surface morphology determined by SEM, indicates that nZnO particles were dispersed homogenously through the epoxy polymer matrix. The results showed improved antifouling and anticorrosive properties for epoxy-nZnO hybrid coatings.

Rust morphology characterization of silicone-based marine antifouling paints after salt spray test on scribed specimens

Abstract: A newly developed, silicone-based, marine antifouling coating, containing 0.56% immobilized Econea, was examined in terms of its anticorrosion performance. The novelty of the experimental formulation arises from the immobilization of the biocide which minimizes leaching and was accomplished via a newly developed functionalization method, based on reaction of the biocide with highly reactive isocyanate functionality. The painting system was applied on steel specimens, then scribed with a sharp cutter and examined for 12 weeks in cyclic salt spray exposure. Identification of the rust morphologies was done with XRD, Raman spectroscopy, SEM and EDS methods. The observed paint swelling during the experiment caused the formation of large, coarse rust agglomerates without adherence, which detached frequently causing reinitiation of the corrosion process. This procedure was revealed by the oxyhydroxide nature of the corrosion products. The basic corrosion morphology observed was a mixture of akaganeite and goethite. A commercial, silicone-based, foul-release coating served as a reference. The experimental formulation exhibited superior anticorrosion performance overall, since the reference system presented higher enlargement of the scribed areas, increased substrate material loss, a highly inhomogeneous corrosion layer with voids and smaller (stable) goethite amounts in the rust areas containing mainly akaganeite/goethite mixture.

Durability of self-healing ultra-high-strength reinforced micro-concrete under freeze–thaw or chloride attack

Abstract: The durability of an innovative self-healing micro-concrete in aggressive environments simulated by freeze–thaw cycles and salt spray test is studied. Tests are conducted on an ultra-high-strength reinforced micro-concrete that incorporates an autonomous self-healing mechanism based on the reaction of an epoxy compound enclosed within silica microcapsules and amine functionalised silica nanoparticles distributed within the cementitious matrix. The effect of aggressive environments is analysed in the self-healing micro-concrete and in a reference micro-concrete stored for 28 d in laboratory conditions after cracking, for crack widths of 150 and 300 μm. The results of capillary water absorption tests, complemented by electron microscopy analysis, confirm the enhanced durability of the autonomously self-healed material in both the freeze–thaw and the salt spray tests, as compared to the reference micro-concrete. In conclusion, the innovative self-healing mechanism is expected to increase the service life of ...

Corrosion resistance of ceramic coatings sprayed on stainless steel substrates

Abstract: Ceramic thermal barrier coatings are being used in oil and gas industries, gas turbines and diesel engines. An atmospheric plasma spraying process is used to coat the ceramics on stainless steel grade 304 substrates. The salt spray (fog) test procedure was used to assess the corrosion resistance of ceramic-coated specimens. The coatings with ceria and without ceria on yttria-stabilised zirconia were compared for corrosion resistance. The commencement of red dust and the amount of weight loss of the coated specimens were related to time. The results indicated that the ceria mixed yttria-stabilised zirconia showed a better corrosion resistance.

Environment Friendly Nano Silicon Dioxide Accelerated Zinc Phosphate Coating on Mild Steel Using a Series of Surfactants as Additives

Abstract: Mild steel panels were subjected to zinc phosphate conversion coating accelerated by environment friendly nano silicon dioxide using a series of cationic surfactants as additives. Four cationic surfactants have been synthesized in the absence of solvent using triethylamine and four different long chain alkyl halides. From 1H NMR and 13C NMR spectra the chemical structures of the synthesized surfactants were confirmed. The nano silicon dioxide accelerator provided a highly porous phosphate coating ensuring good adhesion to the consecutive top coating. The incorporation of cationic surfactants as additives led to fine-grained coatings which enhanced adherence and excellent corrosion resistance property to the phosphate coating. The performance of the surfactants as a corrosion inhibitor increases with the increase in the hydrophobicity of the side-chain length. Accelerator and additive incorporation effectively reduced the extent of zinc dissolution during phosphating and exhibited the highest polarization resistance. The good dispersability of additives and increased hydrophobicity yielded coatings with improved protection against corrosion. The corrosion inhibition performance of the coated steel has been studied by Open Circuit Potential (OCP), Potentiodynamic Polarization Curve, Electrochemical Impedance Spectroscopy (EIS) and salt spray test.

Rust morphology characterization of polyurethane and acrylic-based marine antifouling paints after salt spray test on scribed specimens

Abstract: A newly developed, polyurethane-based, marine antifouling coating, containing 2% immobilized Econea, was examined in terms of its anticorrosion performance. The novelty of the experimental formulation arises from the immobilization of the biocide which minimizes leaching and was accomplished via a newly developed functionalization method, based on reaction of the biocide with highly reactive isocyanate functionality. The painting system was applied on steel specimens, then scribed with a sharp cutter and examined for 12 weeks in cyclic salt spray exposure. Identification of the rust morphologies was performed with XRD, Raman spectroscopy, SEM, and EDS methods. The absence of paint deformation during the experiment led to the formation of compact corrosion products, firmly adherent to the substrate, allowing transformation to more protective forms, such as oxides (hematite, maghemite, magnetite) and the least harmful of the oxyhydroxides (goethite, feroxyhyte), found in the mixture, ensuring sufficient corrosion protection. The unscratched part of the paint served as a barrier to corrosion product expansion beyond the scribed areas. An acrylic-based antifouling system was also examined for reasons of comparison. The experimental formulation exhibited superior anticorrosion performance overall, since the acrylic system presented extended material loss, blistering, checking, and extensive substrate rust coverage beneath the multilayer coat, implying unsatisfactory corrosion protection.

Offset Effect of Chromium on the Adverse Impact of Manganese in a Low-C Medium-Mn Steel with Reversed Austenite in the Neutral Salt Spray Condition

Abstract: This work used the neutral salt spray test to investigate the effects of microstructure and alloy elements on the corrosion process of medium manganese steel by analyzing the microstructure, corros...

Effect of Waveform and Heat Treatment Processes on the Performance of Electrodeposited Co-P Coating

Abstract: Cobalt-phosphorus (Co-P) alloy is a promising material for the replacement of traditional hard chromium alloy of high hardness. In this paper, the cobalt-phosphorus alloy layer with high phosphorus content was formed by electrodeposition in a cobalt sulfate solution system under direct current (DC), single pulse (SP) current and double pulse (DP) current, separately. Surface morphology, structure and properties of the deposited layer were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), Vickers microhardness and a neutral salt spray test, respectively. The results showed that the dense Co-P coatings could be obtained by DC, SP and DP with P content of 9.6, 8.9 and 9.1 wt %, respectively. After 30 min heat treatment at 400 °C, coatings deposited under DC, SP and DP currents transformed from an amorphous to a nanocrystalline state, while the grain size was 12–13 nm, 10–12 nm and 8–10 nm, respectively. Among all these conditions, the microhardness of coatings deposited under DP current was the highest, which was 1211 HV, while the microhardness of coatings deposited under DC current was the lowest but higher than that of hard chromium. The wear rate of Co-P coatings was 4 × 10−6–5 × 10−6 mm3/N m with Si3N4 ball as bearing material, which was lower than that of hard chromium. In coatings deposited under different currents with a thickness of ca. 40 μm, no visible corrosion area appeared after 1000 h of a neutral salt spray test. Coatings heated at 300 and 400 °C reached the corrosion grade 7 and grade 4–5, respectively after 1000 h of a neutral salt spray test, so the wear resistance of Co-P coatings was better than that of hard chromium.

Development of an advanced DC-polarisation/AC-impedance cyclic test to evaluate the corrosion of electrically-conductive coating/substrate systems

Abstract: In this work, an advanced (AC)DC/OCP/AC cyclic test regime has been developed (and validated experimentally) as a new tool for the evaluation of the corrosion behaviour of metallic substrates and/or electrically-conductive coatings. Incorporation of concurrent solution pH measurement with the advanced (AC)DC/OCP/AC technique developed in this work, qualifies this approach to be applied in different industrial applications, such as in aircraft, nuclear and biomedical sectors. It provides opportunities to evaluate objectively the detailed corrosion behaviour in shorter exposure times (as little as 1 day) compared to the widely-used and accepted (but highly subjective) salt spray test (SST) and to conventional (periodically repeated but laborious) electrochemical impedance spectroscopy (EIS) evaluation at open circuit potential (EOCP). The (AC)DC/OCP/AC cyclic test provides valuable information concerning the corrosion behaviour of uncoated Al 6082 alloy (repeat tests are performed, to eliminate test protocol variables and improve the robustness of the test). The three examples of prototype PVD Al-based nanostructured coatings (AlCr, AlCr(N) and AlCrTi), deposited on 17/4 PH steel, were then evaluated from a scientific perspective, to acquire a fundamental understanding of their performance and degradation with time. The results are shown in two main sets; i) electrochemical results obtained at EOCP and six repeated cycles of (AC)DC/OCP/AC cyclic testing and ii) solution pH results during continuous monitoring of the cyclic electrochemical test procedure. AlCrTi coating showed the best corrosion resistance after application of six successive DC/OCP cycles as a sacrificial protection for the substrate, followed by the AlCr(N) and AlCr coatings. However, the repassivation behaviour exhibited by the AlCr(N) coating after breakdown during extreme DC polarisation, may suggest an advantage to use this coating preferably in aerospace applications because of its strong ability to self-heal. This might be promising for future coating materials for corrosion protection where cadmium or hard chromium needs to be replaced. In addition, the structural and chemical composition of these samples was characterised using SEM and EDX analysis. Conventional open circuit potential (EOCP) and potentiodynamic polarisation scans were also employed, to determine the ‘as-received’ corrosion behaviour.