纳米SiO2改性环氧涂层的防腐性能

用电化学阻抗谱法(EIS)研究纳米SiO2改性环氧涂层在3.5%NaCl(质量分数)水溶液中的腐蚀规律,结合电容法和重量法分析改性涂层的吸水行为.结果表明,添加纳米SiO2可明显改善涂层的防腐性能,添加质量分数为2%时防腐性能最好.H2O在不同PVC(pigment volume concentration)环氧涂层中传输的起始阶段满足Fick第二扩散定律.纳米SiO2虽可与环氧树脂发生物理化学键合,填充涂层孔隙,但超过临界添加量时纳米粒子团聚作用又使涂层缺陷增多,防腐性能降低.     

Effect of nanoparticles on the anticorrosion and mechanical properties of epoxy coating

Homogeneous epoxy coatings containing nanoparticles of SiO₂, Zn, Fe₂O₃ and halloysite clay were successfully synthesized on steel substrates by room-temperature curing of a fully mixed epoxy slurry diluted by acetone. The surface morphology and mechanical properties of these coatings were characterized by scanning electron microscopy and atomic force microscopy, respectively. The effect of incorporating various nanoparticles on the corrosion resistance of epoxy-coated steel was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy. The electrochemical monitoring of the coated steel over 28 days of immersion in both 0.3 wt.% and 3 wt.% NaCl solutions suggested the beneficial role of nanoparticles in significantly improving the corrosion resistance of the coated steel, with the Fe₂O₃ and halloysite clay nanoparticles being the best. The SiO₂ nanoparticles were found to significantly improve the microstructure of the coating matrix and thus enhanced both the anticorrosive performance and Young's modulus of the epoxy coating. In addition to enhancing the coating barrier performance, at least another mechanism was at work to account for the role of the nanoparticles in improving the anticorrosive performance of these epoxy coatings.     

Improving the corrosion performance of epoxy coatings by chemical modification with silane monomers

In this communication, commercial epoxy resins were chemically modified with various silane monomers under the catalysis of organotin compound, aiming to enhance the corrosion resistance of epoxy coatings on 2024-T3 aluminum substrates. Immersion studies conducted in 3.5 wt.% NaCl solution showed that the coating capacitance (C_c) decreases significantly after the silane modification, as measured by electrochemical impedance spectroscopy (EIS), indicating the higher resistance to water permeation. EIS measurements also indicated an enhancement in protectiveness of silane-modified epoxy coatings against substrate corrosion, which was characterized by higher charge transfer resistances (R_ct) and lower double layer capacitance (C_dl) at substrate/electrolyte interface. The adhesion of epoxy coatings was also found to improve after the modification with silane components. The best performance was observed for coating system modified by 3-glycidoxypropyltrimethoxy silane (GPTMS).     

Corrosion performance of epoxy coatings containing silane treated ZrO2 nanoparticles on mild steel in 3.5% NaCl solution

Clear epoxy coatings were modified by adding various levels of ZrO₂ nanoparticles. In order to achieve proper dispersion of nanoparticles in the epoxy-based coating and making possible chemical interactions between nanoparticles and polymeric coating, the surface of the nanoparticles was treated with amino propyl trimethoxy silane (APS). Corrosion performance of mild steel coated specimens was investigated employing EIS, electrochemical noise (ECN) techniques and salt spray test. Coatings with 2–3 wt% ZrO₂ nanoparticles possessed the best corrosion performance among the coating specimens. Possible chemical interactions between polymeric matrix and treated nanoparticles in nanocomposites cause high barrier properties and ionic resistances.     

Study on corrosive electrochemical behaviors of zinc‐rich and graphite‐filled epoxy coatings in 3.5 wt% NaCl solution

Environment behaviors and degradation mechanisms of two organic epoxy coatings coated on carbon steel sheets in 3.5 wt% NaCl neutral solution were studied by electrochemical impedance measurements and atomic force microscopy (AFM). The results showed that the coating resistance (R_p) of the graphite‐filled epoxy coating tested, which presents the film barrier performance, is higher than those of 6101 epoxy resin for initial seawater immersion, but the coating resistance of the zinc‐rich epoxy coating was lower than that of 6101 epoxy resin. After salt spray tests, zinc‐rich epoxy coating coated on the metal still has good anti‐corrosion performances due to the existence of protection effects called “electrochemical” and “chemical” protection. Those behaviors and degradation mechanisms of two coatings can be explained by a series of measured electrochemical impedance spectroscopy measurements, and two equivalent circuit models were proposed to explain the degradation processes of the two organic coatings.     

Comparison study on anticorrosion performances of the epoxy coatings with two different nano‐polyanilines for Q235 steel

Sulfuric acid doped nano‐polyaniline was prepared by direct mixed oxidation in two different systems. A novel approach for preparing polyaniline (PANI) in FeCl₂/H₂O₂ system was developed. The PANI possessed an excellent dispensability. Corrosion protection of epoxy coatings containing two kinds of polyaniline (PANI) on Q235 steel was studied by electrochemical impendance spectroscopy (EIS) technique and Tafel polarization test in 3.5 wt% sodium chloride (NaCl) aqueous solution. The results indicated that the epoxy coating containing PANI obtained in FeCl₂/H₂O₂ system had the best performance of the corrosion protection among three systems under investigation. The possible protective mechanism of PANI was discussed.     

Chromate replacement in coatings for corrosion protection of aerospace aluminium alloys

Mixed rare earth organophosphates have been investigated as potential corrosion inhibitors for AA2024‐T3 with the aim of replacing chromate‐based technologies. Cerium diphenyl phosphate (Ce(dpp)₃) and mischmetal diphenyl phosphate (Mm(dpp)₃) were added to epoxy coatings applied to AA2024‐T3 panels and they were effective in reducing the amount and rate of filiform corrosion in high humidity conditions. Ce(dpp)₃ was the most effective and characterisation of the coating formulations showed approximately a factor of 5 reduction in both the number of corrosion filaments initiated as well as the length of these. Mm(dpp)₃ appeared to reduce the corrosion growth rate by a factor of 2 although it was the more effective inhibitor in solution studies. Spectroscopic characterisation of the coatings indicated that the cerium based inhibitor may disrupt network formation in the epoxy thus resulting in a coating that absorbed more water and allowed greater solubilisation of the corrosion inhibiting compound.     

Corrosion Inhibition of 304 Stainless Steel by Nano-Sized Ti/Silicone Coatings in an Environment Containing NaCl and Water Vapor at 400–600°C

The corrosion behavior of 304 stainless steel (SS) and its corrosion inhibition by brushing nano-sized Ti/silicone coatings on its surface in an environment containing a solid NaCl deposit and water vapor at 400–600°C was studied. Results indicated that water vapor or NaCl, especially water vapor plus NaCl accelerated the corrosion of the steel markedly. The corrosion scales of the uncoated steel had a duplex structure at 400–500°C and internal oxidation occurred for the uncoated steel at 600°C in an environment containing NaCl and water vapor. The corrosion of the 304SS was inhibited efficiently by the coatings at 400–500°C, and the coated steel suffered corrosion to some extent and most of the coatings were destroyed at 600°C. X-ray diffraction (XRD) indicated that the corrosion products of the uncoated steel were mainly Fe₂O₃, Cr₂O₃, NiO or Na₂CrO₄, and the coatings consisted mainly of TiO₂ and SiO₂ after exposure at 400–500°C. The good corrosion resistance of the nano-sized Ti/silicon coatings was attributed to the formation of SiO₂, and TiO₂ that resulted from the decomposition of the organic components in the coating and fast oxidation of nano-Ti powder respectively during the experiments, TiO₂ mixed together with SiO₂ and formed a new coating on the steel surface that played an important role in the protection of the steel.     

Influence of curing temperature, silica nanoparticles- and cerium on surface morphology and corrosion behaviour of hybrid silane coatings on mild steel

This work is aimed at developing and investigating silane based organic-inorganic hybrid coatings possessing unique properties, which can be used to improve the performance of steel structures subjected to marine corrosion. These silane based sol-gel coatings were prepared by dip coating planar samples of mild steel in solution of an organically modified silica sol made from hydrolysis and polycondensation of tetraethylorthosilicate (TEOS) and methyltriethoxysilane (MTES) in acid catalysis condition. Crack-free coatings were obtained on curing at 200 °C. On increasing the curing temperature to 400 °C, however, cracks developed in the plain organic-inorganic hybrid coatings. This observation was consistent with the visual observations where appearance of the coated specimen changed from colourless metallic to brownish grey on curing from 200 °C to 400 °C temperature. The coatings were further modified using SiO₂ nanoparticles and cerium. The effect of change in the - temperature as well as - composition on the microstructural properties of the coatings was determined using optical microscopy, scanning electron microscopy and atom force microscopy. Additionally, Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR/FTIR) was carried out to show the formation of the Si-O-Si structural backbone of the hybrid material with the organic CH₃ group incorporated into the silica network. The corrosion protection performance of these coatings was examined using potentiodynamic polarisation technique and electrochemical impedance spectroscopy in aerated 3.5 wt.% NaCl solution. The polarization curves and corrosion resistance as measured by the bode plots suggested that the plain hybrid coatings offer good protection against corrosion. However, the SiO₂ and cerium modified nano hybrid coatings exhibited superior performance to that displayed by plain hybrid coatings.     

Characterization of plasma electrolytic oxidation coatings formed on Mg–Li alloy in an alkaline silicate electrolyte containing silica sol

We investigate the influence of silica sol addition on the ceramic coatings of Mg–Li alloy by plasma electrolytic oxidation (PEO) in an alkaline silicate electrolyte. Scanning electron microscopy, X‐ray diffraction, X‐ray photoelectron spectroscopy, and energy dispersive spectroscopy are employed to characterize the microstructure and composition of the ceramic coatings. The anti‐corrosion behavior of the ceramic coatings is evaluated by potentiodynamic polarization measurements in conjunction with electrochemical impedance analysis. The ceramic coating formed in the electrolyte containing silica sol contains SiO₂ and Mg₂SiO₄ phase and has more uniform morphology and higher corrosion resistance than that formed in the electrolyte without addition of silica sol.     

纳米二氧化钛硅烷接枝密度对水性环氧涂层耐蚀性能的影响

目的研究水性环氧/硅烷化纳米TiO2复合防护涂层在3.5%NaCl溶液中的失效规律和防腐性能。方法采用3-氨丙基三乙氧基硅烷(APTES)化学接枝改性纳米TiO2颗粒,将硅烷改性纳米TiO2均匀分散在水性环氧涂料中,并把混合涂料涂覆在Q235钢试样上。采用傅里叶红外光谱仪(FTIR)和热重分析仪(TGA)测试纳米TiO2表面化学接枝改性情况,采用电化学工作站测试复合涂层的电化学性能,采用激光共聚焦显微镜观察复合膜层的表面形貌。结果使用质量分数10%APTES改性纳米TiO2,单齿螺旋结构占有的比例更高;使用质量分数20%APTES改性纳米TiO2,具有最高的接枝密度,为11.78 APTES/nm^2。电化学测试结果显示,环氧/TiO2复合涂层比纯环氧涂层具有更好的耐蚀性能,其中加入质量分数20%APTES改性纳米TiO2的环氧/TiO2复合涂层对基体的保护性能最好,其涂层电阻是纯环氧涂层的12倍,电荷转移电阻是纯环氧涂层的18倍。在相同的腐蚀条件下,单齿螺旋结构更容易被破坏。加入硅烷纳米TiO2颗粒后,可以显著减少涂层表面尖峰状突起和孔洞。结论纳米TiO2的APTES接枝分子密度,是水性环氧/硅烷化纳米TiO2复合防护涂层耐腐蚀性能提高的直接原因。     

Delamination of polymeric coatings on silidized iron

The delamination of polymeric coatings (pc) on iron and steel is a phenomena everybody knows e.g. from his rusting car. The damage caused by it costs the Western countries hundreds of millions Euro every year. Hence it is a very important task for the steel industry and also for scientists to improve the stability of the pc on iron and steel. The authors developed a new corrosion protection of iron by covering it with a thin layer of a‐SiO₂:Fe. An adhesion promoter sticks on top of it so that the pc adhers well. The delamination of the pc as function of the surface preparation (roughness, adhesion promoter) is described in this paper. The Scanning Kelvin Prove (SKP) is utilized to detect the delamination.     

Corrosion protection of aluminum alloy by epoxy coatings containing polyaniline modified graphene additives

In the study, polyaniline/reduced‐graphene oxide (PANI‐RGO) composites, fabricated by loading 2, 5, and 8wt% graphene oxide, was prepared by in‐situ emulsion polymerization and reduction. They are characterized by Fourier transform infrared spectroscopy, X‐ray diffraction, and scanning electron microscopy. Epoxy coatings adding PANI and PANI‐RGO composites were coated on the surface of AA5083 Al alloy. The anticorrosion performance of the coatings is measured by electrochemical impedance spectroscopy and potentiodynamic polarization curve in 3.5wt% NaCl solution. The results demonstrate that the epoxy/PANI‐RGO coating exhibits a better protection against AA5083 alloy corrosion compared with the epoxy/PANI coating. Enhancement of the passivation performance of PANI was obtained by the addition of RGO into epoxy/PANI coating system.     

High temperature corrosion of coatings and boiler steels below chlorine-containing salt deposits

High temperature corrosion tests were performed on low-alloy ferritic steel and austenitic stainless steel, five high velocity oxy-fuel (HVOF) coatings, a laser cladding, and a diffusion chromized steel. Test conditions simulated superheater conditions of biofuel-fired boiler. The samples were exposed to synthetic salt containing 40 wt% K₂SO₄, 40 wt% Na₂SO₄, 10 wt% KCl, and 10 wt% NaCl. Exposures were carried out in oxidizing and in reducing atmospheres. The test temperature was 550 °C and the test duration was 100 h. Corrosion was extremely severe in oxidizing conditions because of active oxidation. In reducing atmosphere corrosion was retarded due to depletion of chlorine in the scales by evaporation of metal chlorides, and formation of a layer rich in chromium, sodium, sulfur, and oxygen adjacent to the metal surface. The corrosion resistance of coatings was determined by composition and microstructure. Oxides at splat boundaries were attacked by chlorine, and chlorine was able to penetrate through the coatings along splat boundaries.     

Water permeability of organic/inorganic hybrid coatings prepared by sol-gel method: a comparison between gravimetric and capacitance measurements and evaluation of non-Fickian sorption models

Acrylic-TiO₂ coatings prepared from alkoxide precursors were deposited on mild steel. The coatings were transparent and continuous at thicknesses up to 200 μm. The water uptake characteristics were investigated by EIS measurements in 3 wt% NaCl solutions. The non-ideal diffusion is analysed considering a superposition of Case II swelling and Fickian sorption. The physical meaning of the coefficient (SC_c) that is linear in time is discussed. A comparison with the relaxation model of Berens and Hopfenberg notably shows that SC_c can numerically account for relaxation phenomena in the case when the rearrangements in the polymer structure are so slow that they exceed the measuring time. EIS results are compared with gravimetric measurements on free films. The influence of titania content on the water uptake properties (solubility, diffusion coefficient and long-term behaviour) of the hybrids has also been studied.     

Improving the protective properties of La‐conversion coating on α‐brass surface by the combined use of La2O3 nanoparticles incorporation and electrodeposition

The La₂O₃ nanoparticles incorporation and electrodeposition were used together to prepare the La‐conversion coatings on α‐brass surface in a basal solution containing rare earth salt. The results showed that both techniques can improve the protective properties of coatings. A ‘critical nano‐La₂O₃ content’ and a ‘critical deposition potential’ were observed, under which the conversion coatings had the highest protective properties. Increased electrodeposition time improve the quality of conversion coatings. The La‐conversion coatings could provide important protection against α‐brass corrosion for considerable immersion periods in 3.5 wt% sodium chloride solution because it ennobled the corrosion potential and decreased the anodic current.     

Corrosion protection of 1008 carbon steel by hybrid coatings

Abstract

Potentiodynamic polarisation curves have been used to evaluate the corrosion performance of 1008 carbon steel coated with hybrid (inorganic-organic) and mixed oxide coating systems deposited by dip coating. Several coatings have been prepared by the sol-gel method, using metallic alkox ides, such as tetraethylorthosilicate, aluminium isopropoxide, and zirconium propoxide, and polymers like allyl methacrylate (AMA) and polymethylmethacrylate (PMMA), together with zirconium dioxide (ZrO₂) and silicon and aluminium oxides (SiO₃-Al₂O₃). The aqueous test solutions included hydrochloric acid (HCl), sodium chloride (NaCl), and sulphuric acid (H ₂SO₄) at various concentrations (0·1, 0·5, and 1M). Scanning electron microscopy was used to examine the coatings following testing. The results have shown that SiO₂-Al₂O₃ based coatings are not beneficial for corrosion protection in HCl, but are of value in the other aqueous media. In 1·0M HCl, the best protection was offered by a hybrid SiO₂-ZrO₂-poly(methylmethacrylate-allyl methacrylate) (P(MMA-AMA)) coating. In NaCl, the best results, were generally obtained with SiO₂-Al₂O₃ and SiO₂-ZrO₂-P(MMA-AMA) coatings. Similarly, in H₂SO₄, the best results were generally displayed by the SiO₂-Al₂O₃ and SiO₂-ZrO₂-P(MMA-AMA) coatings. The corrosion behaviour of the coatings is discussed in terms of the integrity and stability of the film.     

Comparison of corrosion behaviour of thermal sprayed and diffusion‐coated materials

In this paper, the corrosion behaviour of thermal sprayed and diffusion‐coated materials are compared. The result of the high temperature corrosion test shows that the layers with NiCr applied by atmospheric plasma spraying (APS) and high velocity oxy fuel flame spraying (HVOF) are more resistant than the layers with NiCrBSi and Cr₃C₂/ NiCr. Furthermore, the layer with NiCr on 15 Mo 3 is more resistant than that on 13 CrMo 44 as base material. The corrosion behaviour of Al, Cr, and Cr/Si diffusion‐coated materials on 13 CrMo 44‐ are better than those same diffusion coatings on 15 Mo 3‐surfaces. In particular, the Cr diffusion‐coated materials show the highest corrosion resistances in this work. Also, the diffusion‐coated materials have higher resistances than thermal sprayed materials in HCl‐H₂O‐O₂‐N₂‐atmosphere.     

Microstructural Characterization and Cyclic Hot Corrosion Behaviour of Sputtered Co�CAl Nanostructured Coatings on Superalloy

Nanostructured Co?CAl coatings on Superni-718 superalloy substrate were deposited by DC/RF magnetron sputtering in the present work. The microstructure and cyclic hot-corrosion behavior of nanostructured Co?CAl coatings on Superni-718 superalloy were investigated in molten salt of 40 wt% Na₂SO₄ + 60 wt% V₂O₅ at 900 °C. The results showed that a dense scale formed on the coated samples exposed to corrosive environment during thermal cycling. The spinel phases of CoCr₂O₄, CoAl₂O₄ and NiCr₂O₄ were found in the corroded scale of the coatings, resulting in an effective inhibition of O and S diffusion. The sputtered Co?CAl coatings exhibited high hot corrosion resistance due to the formation of ??-CoAl phases in the coating. The relevant corrosion mechanisms substantiating the role of coatings are discussed.     

Nano‐enamel: a new way to produce glass‐like protective coatings for metals

Nanoparticles and nanostructured films have gained an increasing interest for industrial application in the last years. Based on chemical nanotechnology glass‐like protective coatings thermally processed at comparatively lower temperatures around 500°C were developed for metal substrates by two different ways. Starting from polymeric sols (suspension consisting of branched macromolecules) containing multicomponent oxide of the SiO₂‐B₂O₃‐P₂O₅‐Na₂O system produced by hydrolysis and polycondensation of an alkoxide mixture under acidic condition, thin, hard, transparent, crack‐free and corrosion resistant coatings could be applied to aluminium and steel. Coatings from particulate sols (suspension consisting of solid particles) containing multicomponent oxide synthesized under basic condition by electrophoretic deposition (EPD) proved to be a promising method when very thick coatings are required. Both routes offer the potential of a new type of purely inorganic coatings for corrosion and abrasion protection.