Corrosion performance of Al–Al_2O_3 cold sprayed coatings on mild carbon steel pipe under thermal insulation

This paper focused on the corrosion resistance of cold spray Al–Al_2O_3composite coatings used on carbon steel pipe surfaces under thermal insulation. Al–Al_2O_3coatings were produced on the carbon steel pipe surface by cold spray(CS) technology. Experimental apparatus was built to test the corrosion resistance of coatings beneath mineral wool insulation under isothermal, thermal cycling and wet/dry conditions. The results showed that when α-Al_2O_3 was added in spraying powder, the coating could obtain higher hardness and a denser microstructure. From corrosionunder-insulation(CUI) tests, Al–Al_2O_3CS coatings were proven to be efficient in protecting carbon steel pipe from CUI mainly owning to lamellar microstructures of coatings. There was no evidence to show that α-Al_2O_3 might bring any negative effect on corrosion resistance. Al–Al_2O_3CS coatings were sensitive to the chloride ion concentration. When these coatings were exposed to higher concentrations of NaC l, the coating's exhibited faster degradation.     

Laser and furnace pyrolyzed organosilazane-based glass/ZrO2 composite coating system—A comparison

The laser pyrolysis of a ceramic coating system composed of an organosilazane (Durazane 1800) with monoclinic ZrO₂ and glass particles as fillers was investigated. The samples were produced by spray coating on pre-treated stainless steel substrates and subsequently pyrolyzed by Nd:YV0₄ laser radiation (λ =1064 nm). The interaction of laser radiation with the polysilazane-based glass/ZrO₂ coating system led to formation of semi-crystalline dense coatings with a thickness up to 20 μm in a short time.Laser pyrolyzed ceramic coatings were characterized and compared with furnace pyrolyzed coatings. The microstructure of the coatings was investigated by scanning electron microscopy (SEM). Additionally the corrosion resistance and mechanical properties, such as hardness, adhesive strength and the tribological behaviour have been investigated. Ceramic coatings generated by laser pyrolysis showing promising mechanical properties, a super-hydrophobic surface as well as a high corrosion resistance.     

Novel polymer-derived ceramic environmental barrier coating system for carbon steel in oxidizing environments

Polymer-derived ceramic environmental barrier coatings (EBCs) in combination with active fillers are highly attractive due to their facile processing and applicability at elevated temperatures. In this study, several kinds of active and passive fillers were added to polymer-derived ceramics and then coated onto carbon steel, using cheap and simple lacquer methods (such as dip or spray coating). The resultant coating, investigated by Thermal Gravimetric Analysis (TGA), Scanning Electron Microscopy with X-ray microanalysis (SEM/EDS), X-ray Diffraction (XRD), adhesion tests and oxidation tests, showed that it acted as an excellent film to withstand thermal cycling, and prevented carbon steel from being oxidized at elevated temperatures. The low-cost and effective coating method described in this paper can be used widely to protect carbon steel used at high temperatures (e.g. steel boiler tubes in waste-to-energy plants).     

Synthesis of 3-glycidoxypropyltrimethoxysilane modified hydrotalcite bearing molybdate as corrosion inhibitor for waterborne epoxy coating

Zinc aluminum hydrotalcite intercalated with molybdate (HTM) and modified by 3-glycidoxypropyltrimethoxysilane (HTM-GS) was prepared and incorporated into a waterborne epoxy coating. The synthesized HTM-GS was characterized by FTIR, XRD, SEM, and TEM. The inhibitive action of HTM-GS on carbon steel was evaluated using electrochemical measurement and SEM/EDX analysis. The corrosion protection of the waterborne epoxy coating containing HTM-GS was evaluated and compared to that of the pure waterborne epoxy coating and the waterborne epoxy coating containing HTM by salt spray test and adhesion measurement. It was shown that the molybdate was intercalated in the hydrotalcite structure and the molybdate contents in HTM and HTM-GS were 16.0 and 13.2 wt%, respectively. The polarization curves obtained on the carbon steel electrode showed that HTM and HTM-GS are anodic corrosion inhibitors, and their inhibition efficiencies at concentration of 3 g/l were 92.0 and 94.7%, respectively. Additionally, HTM and HTM-GS at concentration of 0.5 wt% improved corrosion resistance and adhesion of waterborne epoxy coatings. Surface modification by 3-glycidoxypropyltrimethoxysilane ameliorated the dispersion of HTM in epoxy matrix and the effect of HTM on protection properties of waterborne epoxy coating.     

Electrophoretic deposition of biomimetic zinc substituted hydroxyapatite coatings with chitosan and carbon nanotubes on titanium

In this study, a biomimetic method was used to prepare hydroxyapatite (HAP) and zinc substituted HAP (ZnHAP) nanoparticles, in which silk fibroin was used as template. The morphology of HAP is rod-like, while ZnHAP changes to wrinkled sheets. HAP and ZnHAP nanoparticles were used to coat titanium by EPD with additional chitosan and multiwalled carbon nanotubes. Phase composition, morphology and structure were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared and Raman spectroscopy. The results showed that the composite coatings containing HAP and ZnHAP had homogeneous morphology and good apatite formation ability. The ZnHAP composite coating possessed class 5B adhesive strength using tape test. Furthermore, the ZnHAP composite coating had better corrosion resistance compared to the HAP composite coatings.     

Adhesion and adhesion degradation of a pressure sensitive tape on carbon steel

Corrosion protection of carbon steels by organic coatings is dependent on a good adhesion between coating and substrate. In this work the blister test method was used to study the adhesion of a pressure sensitive tape applied on carbon steel. Deionized water was used to pressurize a blister formed by the tape covering a through-hole in the steel substrate. Values of adhesion strength as measured by the strain energy release rate were determined for two different blister pressurization rates or water injection rates. The adhesion strength was higher for the larger injection rate, which is expected for pressure sensitive tape. These values were probably overestimates of the true adhesion strength owing to plastic yielding of the membrane. Resistance to adhesion degradation near coating defects or macroscopic scribes was characterized using a height regulating scanning Kelvin probe on samples exposed to sodium chloride solution or a salt spray environment. Although the tape exhibited good barrier properties to water and ions, cathodic delamination was observed near the scribe after salt spray exposure. Wet/dry cycles were more aggressive than continuous salt spray exposure, since during continuous exposure corrosion products are washed away. It was observed that the oxide layer grows to a larger extent during wet/dry cycles; therefore, acceleration of the delamination process is probably associated with a “wedge effect” of the oxide on the interface.     

Polyester-based powder coatings with montmorillonite nanoparticles applied on carbon steel

In nanotechnology and nanoscience the development of hybrid (organic-inorganic) nanocompounds has attracted particular attention due to the significant improvement in the properties and the wide diversity of applications compared to conventional composites. In this study, formulations of commercial powder coatings were investigated with 2 and 4% (w/w) of montmorillonite (MMT) in the polyester resin matrix. The coatings were applied by electrostatic spraying on AISI 1008 carbon steel panels. The samples were characterized by TGA, DSC, XRD and TEM. The corrosion performance was evaluated using the salt spray test. Transmission electron microscopy revealed the presence of MMT in the coatings in the exfoliated form. The formulations with MMT presented better performance in terms of the corrosion protection properties.     

跨海大桥钢结构防腐涂料设计方案

介绍了跨海大桥钢结构防护涂层(包括防锈底漆、中间漆和面漆)的选择标准、原则以及主桥钢箱梁热喷涂防腐蚀涂层体系和热喷涂锌、铝涂层钢铁防护标准.通过实例说明了跨海大桥钢箱梁防腐涂料体系设计方案及其涂装注意事项.论述了钢丝主缆涂装工艺及钢质护栏内、外表面防腐涂装方案.     

The effect of MIO pigments on corrosion resistance and adhesion of synthetic rubber-based primer

In this research, the corrosion resistance and adhesion property of a synthetic rubber-based primer reinforced with different ratios of micaceous iron oxide (MIO) pigments were studied. Coatings were applied on carbon steel panels and also on steel pipes of 219.1 mm outer diameter. Scanning electron microscopy (SEM) was used to investigate the dispersion of MIO particles in the rubbery matrix. The anticorrosion performance of the coatings was studied, using electrochemical impedance spectroscopy (EIS) and salt spray tests. In addition, the adhesion of primers to carbon steel substrates was evaluated by pull-off test. In order to investigate the effect of MIO particles on the flexibility of the pigmented primers, a cupping test was conducted. The adhesion of cold-applied tape to the formulated primers was assessed by peel adhesion test using hanging mass method. The results indicated that adding 5, 10, and 15 wt% of MIO pigments into the primer improved corrosion resistance of the coatings. An increase in the MIO loading up to 10 wt%, improved the adhesion of the primer to both steel substrate and cold-applied tape.     

Designing of corrosion resistant epoxy coatings embedded with polypyrrole/SiO2 composite

Polypyrrole/SiO₂ composite was synthesized by chemical oxidative polymerization of pyrrole using FeCl₃. The synthesized polymer composite was loaded in epoxy resin to develop coatings for mild steel substrates using powder coating technique. SEM and TEM images reveal homogenous dispersion of SiO₂ particles in polypyrrole matrix. TGA analysis confirms good thermal stability of the polymer composite. Tafel polarization and electrochemical impedance spectroscopy (EIS) results exhibit remarkably high corrosion protection efficiency of epoxy coatings with polymer composite in 3.5% NaCl solution. Corrosion studies of coatings with an artificial defect reveal the passivation of defect by the polymer composite present in the epoxy coatings. Salt spray test results revealed superior corrosion resistance offered by the polymer composite.     

Ferrochromium slag as a protective coating material against oxidation for caster rolls

In this study, ferrochromium (FeCr) slag, which is available as an industrial waste, is proposed as a protective surface coating material particularly for protection of continuous casting rolls against oxidation. FeCr slag was successfully deposited with atmospheric plasma spray (APS) method. Before the coating process, FeCr slag powder prepared in the particle size range of 5‐38 μm, was investigated using conventional characterization methods (XRD, SEM, TGA etc.). Thermal Barrier Coating (TBC) system was used as a basis for deposition processes. Accordingly, NiCoCrAlY (Amdry, ?45 + 5 μm) was firstly deposited as metallic bond coat layer onto the surface of AISI 420 substrate, and then FeCr slag layer was deposited as the top coating layer. After the deposition of FeCr slag powder, the resulting coating layer was found to have low porosity with a homogeneous microstructure. The deposited FeCr slag coatings were subjected to isothermal oxidation tests at different temperatures and test durations for determination of their oxidation behavior and upper operating temperature limits. The results obtained from this study indicate that FeCr slag can be considered as an alternative protective coating material for caster rolls which are subjected to high temperatures up to 800°C.     

Corrosion resistance performance of cerium doped silica sol–gel coatings on 304L stainless steel

The aim of this work is the synthesis and investigation of silane based organic–inorganic hybrid coatings, which can be used to improve the corrosion performance of steel structures subjected to a marine environment. The silane based sol–gel coatings were prepared by dip coating 304L stainless steel in a solution of organically modified silica sol made through hydrolysis and condensation of 3-glycidoxypropyl-trimethoxysilane (GPTMS) as precursor and bisphenol A (BPA) as a cross-linking agent in an acid catalyzed condition. The influence of the addition of cerium and the use of bisphenol A as a cross-linking agent on the microscopic features and morphology as well as on the corrosion resistance of the coatings were examined using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), neutral salt spray tests, potentiodynamic polarization and electrochemical impedance techniques. Results show that cerium modified nano-hybrid coatings exhibit a superior corrosion inhibition performance to that displayed by silica hybrid coatings. Additionally, data showed that the bisphenol A as a cross-linking agent has a significant effect on the morphology and corrosion resistance of the cerium doped silica coating. Omitting the use of bisphenol A causes the creation of defects/cracks in the coating, thereby promoting diffusion of the aggressive electrolyte toward the substrate and decreasing the corrosion resistance of the coating.     

双向脉冲电镀纳米级镍镀层耐腐蚀性能研究

用直流电沉积法制备了普通光亮镍镀层,同时用双向脉冲电镀制备了纳米级镍镀层。用X射线衍射(XRD)、扫描电镜(SEM)等方法研究了镀层的晶粒尺寸、组织结构和表面形貌,通过孔隙率测定、盐雾试验、静态浸泡腐蚀失重试验和电化学方法等测试了镀层的耐蚀性能。结果表明,采用双向脉冲电流制备的纳米级镍镀层的耐蚀性明显优于普通直流镍镀层。     

Synergistic effect of silane modified nanocomposites for active corrosion protection

This work presents an effective anticorrosion behavior of a hydrophobic surface on stainless steel 304. The protective coating has been designed by dispersing nanocomposites (cloisite 15A, multiwalled carbon nanotubes and cerium chloride) which act as a corrosion inhibitor. The sol was prepared by using 3-glycidoxypropyltrimethoxysilane (GPTMS), octyltriethoxysilane (OTES) and zirconium (IV) butoxide as precursors. The corrosion resistance of coated stainless steel got improved when nanocomposites were homogeneously embedded in silica sol. The influence of nano-particles on the barrier coatings impedes corrosion. The coatings were analyzed by X-ray diffraction (XRD) to ensure the intercalation and distribution of nanocomposites in layered silicates. Fourier transform infrared spectroscopy (FTIR) was employed to characterize the nanocomposites modified silica sol. Scanning electron microscopy (SEM) was used to examine the morphology of the modified silane coating. The contact angle measurements ensured the hydrophobic behavior of the coatings. The corrosion behavior was investigated using Electrochemical Impedance Spectroscopy (EIS). This study has led to a better understanding of active anticorrosive coatings with embedded nanocomposites and the factors influencing the anticorrosion performance.     

Effect on temporary protection and adhesion promoter of silane nanofilms applied on electro-galvanized steel

In this paper, the effectiveness of γ-mercaptopropyltrimethoxysilane (MTMO) films as temporary corrosion protection and adhesion promoter on electro-galvanized steel was studied. The films were synthesized from hydrolyzed MTMO with ethanol or methanol, applied by immersion on electro-galvanized steel and cured under different conditions. The porosity of the coating was evaluated by cyclic voltammetry, the corrosion behavior by polarization curves and the protection degree by exposure in the humidity and prohesion chambers. The films were characterized by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). From the obtained experimental results, it was concluded that this protection is markedly affected by the coating curing conditions and the alcohol used in the hydrolysis. MTMO is a good temporary protector against electro-galvanized steel corrosion in high humidity environment but it is less effective in environments containing aggressive ions such as Cl⁻ and SO₄⁻².In a second stage, pretreated samples were coated with an alkyd anticorrosive paint and exposed to the salt spray chamber. Dry adhesion tests as well as SEM and EDS studies were also done in order to know the nature of the disbonding fails (adhesion or cohesion).     

海洋环境下GH907合金耐高温防腐蚀涂层技术研究

研究了一种在海洋环境下使用的新型低温固化耐高温防腐蚀涂料及其制备方法,确定了涂覆工艺,并对涂层进行了附着力、热震、盐雾、湿热及耐高温氧化等性能的测试。结果表明,制备出的涂层抗高温氧化性能高,耐盐雾腐蚀时间长,结合力优良,达到了在海洋环境下的防盐雾、防湿热、防霉菌及耐650℃高温氧化的要求。研究成果已应用于生产,产品质量稳定。     

N80钢表面陶瓷涂层的制备及耐酸蚀性研究

采用热化学反应方法在N80钢基体表面制备了陶瓷涂层。通过X射线衍射仪(XRD)、扫描电子显微镜(SEM)、体视显微镜和划痕仪对涂层的物相结构、组织形貌和膜基界面结合力进行了研究,利用失重法在20%的质量分数盐酸溶液中测试了涂层的耐蚀性能。结果表明:在600℃固化温度下,以SiO2粉体和SiO2、Al2O3、MgO等两类不同骨料制得的陶瓷涂层中,前者无新相生成,涂层与基体界面结合力24 N;后者有新相MgAl2O4生成,且涂层比较致密,涂层与基体界面结合力约40 N。以水玻璃作粘结剂的复合氧化物陶瓷涂层的表面致密度、平整性均优于以磷酸氢铝作粘结剂的涂层。酸腐蚀测试表明,以水玻璃作粘结剂的复合氧化物陶瓷涂层的平均腐蚀速率约为基体的1/2左右。     

Studying the corrosion protection properties of an epoxy coating containing different mixtures of strontium aluminum polyphosphate (SAPP) and zinc aluminum phosphate (ZPA) pigments

Epoxy/polyamide coatings were loaded with different mixtures of strontium aluminum polyphosphate (SAPP) and zinc aluminum phosphate (ZPA) pigments. Moreover, a coating containing zinc phosphate (ZP) was prepared as a reference sample. The coatings were applied on St-37 steel substrates and then were exposed to 3.5 wt% NaCl solution up to 35 days. The corrosion inhibition properties of the pigments extracts were studied on bare steel samples by a potentiodynamic polarization technique after 24 h immersion. The morphological properties and corrosion resistance of the coatings were investigated by scanning electron microscope (SEM), optical microscope, electrochemical impedance spectroscopy (EIS) and salt spray tests.     

Effect of pigmentation on mechanical and anticorrosive properties of thermally sprayable EVA and EVAl coatings

To study the effect of pigmentation on mechanical and anticorrosive properties of thermally sprayable ethylene vinyl acetate (EVA)/polyethylene (PE) and ethylene vinyl alcohol (EVAl)/PE coatings, red iron oxide (RIO) and titanium dioxide (TiO₂) pigments at varying concentration (10, 20 and 30%) were mixed using internal mixer. Pigmented compositions were characterized for mechanical properties and water vapor transmission rate (WVTR). These compositions were applied on grit blasted mild steel surface by flame spray technique and coated specimens were evaluated for adhesion strength, abrasion resistance and resistance to corrosion by exposing them in different environments. The corrosion resistance of pigmented composition was also studied by electrochemical impedance spectroscopy (EIS) technique.     

Peel‐strength behavior of bilayer thermal‐sprayed polymer coatings

We prepared various bilayer polymer coatings of ethylene methacrylic acid (EMAA) copolymer and ionomer by the thermal‐spray process under a range of preheat temperatures (PTs) to investigate their ability to be repaired. The thermal properties, crystallinity, microstructure, and interface strength of the coatings were investigated with differential scanning calorimetry, X‐ray diffraction, scanning electron microscopy, and mechanical testing. Processing parameters influenced the final morphological structure of the coatings. The crystallinity of the coatings increased with a higher final temperature, whereas the coating density decreased. The decrease in density was attributed to the appearance of bubbles, 250 μm in size, formed in the coatings during the spray process. For the monolayer coating of polymer on a metal substrate, a higher PT produced a greater contact area of the coating to the substrate. The adhesion of EMAA ionomer to steel was always lower than that of EMAA copolymer to steel. This may have been largely due to the interfacial adhesion between the polymer and steel being dominated by strong secondary bond interactions. Experimental results also indicate that the peel strength between polymers was at least twofold stronger than that between the polymer and the steel substrate for PTs greater than 100°C. The mixed bilayer coating of ionomer on copolymer produced the highest peel strength. The interface between the plastic layers was clearly visible under the scanning electron microscope at lower PTs, becoming more diffuse with an increase in PT. On the basis of these observations, the adhesion mechanism between polymers was explained by the formation of welding points. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 214–226, 2003