Maleic acid grafted low density polyethylene for thermally sprayable anticorrosive coatings

Low density polyethylene (LDPE) coatings are being used in an ever growing range of applications. However, non-polar characteristics of LDPE make its adhesion poor to metal substrate and so become less suitable for anticorrosive coating application. An anticorrosive coating can therefore be developed if LDPE is modified with requisite polar groups. In the present work, a polar group has been introduced in polyethylene matrix by grafting maleic acid. Grafted LDPE was characterized by chemical method, Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermo-gravimetric analysis (TGA), melt flow index (MFI), particle size analysis and hot stage optical microscopy. The presence of carbonyl peak of high intensity, high acid value and low melt flow index value confirmed grafting of maleic acid on LDPE. Change in crystallization behaviour of LDPE has been noticed after grafting. Grafted LDPE was applied on grit blasted mild steel surface by flame spray technique and adhesion study showed improved adhesion of grafted LDPE than LDPE. The coated panels were evaluated for resistance to corrosion in salt spray, humidity cabinet and seawater. The corrosion resistance of modified LDPE was also studied by AC Impedance technique. Grafted LDPE showed satisfactory corrosion resistance. Grafted LDPE was pigmented with red iron oxide and pigmented composition has shown improved resistance to corrosion in laboratory 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.     

Studies on anticorrosive properties of thermally sprayable EVA and EVAl coating

Application of polymeric coatings is one of the methods for protection of mild steel against corrosion. In the present work, blends of different grades of ethylene vinyl acetate (EVA) with varying vinyl acetate (VAc) content viz. 18%, 28%, 40% and hydrolyzed EVA i.e., ethylene vinyl alcohol (EVAl) with low density polyethylene (PE) have been used as binder for development of anticorrosive coating. The blend compositions were characterized using differential scanning calorimetry (DSC), thermo gravimetric analysis (TGA) and melt flow index (MFI) techniques for determination of melting point, degradation temperature and flow behavior respectively. The blend compositions were applied on grit blasted mild steel specimens by flame spray technique and the coated specimens were evaluated for their resistance to corrosion in salt spray, humidity and seawater. EVA/PE based compositions showed superior resistance to corrosion compared to EVAl/PE based compositions in all exposure conditions after 8 weeks. The corrosion resistance of blend compositions was also studied by electrochemical impedance spectroscopy (EIS) technique. The results indicate that EVA/PE coatings have better resistance to corrosion than EVAl/PE coatings.     

Studies on fly ash based geopolymeric material for coating on mild steel by paint brush technique

The present work focuses on the study of five different compositions of fly ash based geopolymeric material with varying silicate: alkali ratio as coating material on mild steel plates. Coated mild steel plates were tested for adhesion strength, heat resistance, fire resistance, water absorption and corrosion resistance characteristics. Mineralogy, morphology and vibrations of various functional groups present in the developed coating material compositions were evaluated by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and Fourier transform infra-red spectral studies (FTIR) respectively. The developed coating material possesses promising fire resistance, heat resistance, corrosion resistance characteristics and mechanical properties.     

Corrosion and Fire Protective Behavior of Advanced Phosphatic Geopolymeric Coating on Mild Steel Substrate

The research objectives of this study were to investigate and compare corrosion and fire protective properties of conventional and advanced phosphatic geopolymeric coating on mild steel substrate using spray coating technique For these studies two composition were developed using conventional geopolymerisation route by adding alkali activator solution to fly ash and six compositions were developed using advanced geopolymerisation process in which water was added to solid precursor powder obtained by together co-ginding of raw materials for a period of 8 h. Coated plates were tested for adhesion strength, water resistance, fire protection and corrosion resistance. Results indicated that coating developed from two passes with thickness 100 ± 15 μm showed better adhesion as compared to single pass and also proved to be promising corrosion protective coating material for mild steel substrate under sea water conditions. The developed material is able to withstand flame for more than 45 min and also no cracks were observed in coating by direct heating on liquefied petroleum gas flame. Thus developed phosphatic geopolymeric material is well suited for protecting the mild steel structures from fire and corrosion.     

Performance of zinc phosphate coatings obtained by cathodic electrochemical treatment in accelerated corrosion tests

The formation of zinc phosphate coating by cathodic electrochemical treatment and evaluation of its corrosion resistance is addressed. The corrosion behaviour of cathodically phosphated mild steel substrate in 3.5% sodium chloride solution exhibits the stability of these coatings, which lasts for a week's time with no red rust formation. Salt spray test convincingly proves the white rust formation in the scribed region on the painted substrates and in most part of the surface on unpainted surface. The protective ability of the zinc corrosion product formed on the surface of the coated steel is evidenced by the decrease in the loss in weight due to corrosion of the uncoated mild steel, when it is galvanically coupled with cathodically phosphated mild steel. Potentiodynamic polarization curves reveal that E_corr shifts towards higher cathodic values (in the range of −1000 to −1100 mV versus SCE) compared to that of uncoated mild steel and conventionally phosphated mild steel substrates. The i_corr value is also very high for these coatings. EIS studies reveal that zinc dissolution is the predominant reaction during the initial stages of immersion. Subsequently, the non-metallic nature of the coating is progressively increased due to the formation of zinc corrosion products, which in turn enables an increase in corrosion resistance with increase in immersion time. The zinc corrosion products formed may consist of zinc oxide and zinc hydroxychloride.     

Ethylene vinyl acetate and ethylene vinyl alcohol copolymer for thermal spray coating application

Ethylene vinyl acetate (EVA) copolymer with varying vinyl acetate (VAc) content, viz. 18%, 28% and 40% has been hydrolyzed using alcoholic NaOH solution. Fourier Transform Infrared Spectroscopy (FTIR) analyses of hydrolyzed polymer showed the presence of both OH group and acetate group indicating that the EVA has been partially hydrolyzed. Differential Scanning Calorimeter (DSC) and Thermo Gravimetric Analyzer (TGA) of EVA and hydrolyzed EVA showed large difference in melting and decomposition temperature, respectively. Hydrolyzed EVA showed higher tensile strength and elongation at break compared to corresponding EVA. Blends of different grades of EVA and ethylene vinyl alcohol (EVAl) with low density polyethylene (LDPE) were applied on grit blasted mild steel surface by flame spray technique. FTIR analysis of blends before and after coating showed no degradation during flame spray. Measurement of adhesion strength of these coating showed that adhesion strength increased on hydrolysis of EVA.     

The effect of cationic surfactants in acid cleaning solutions on protective performance and adhesion strength of the subsequent polyurethane coating

The subsequent effect of the use of monomeric cationic surfactants, dodecyltrimethylammonium bromide (DTAB) and its gemini counterpart, 12-4-12, in 1 M sulfamic acid cleaning solution on the corrosion resistance and adhesion strength of polyurethane coating on mild steel surface was studied by salt spray and pull off, respectively. The EIS (electrochemical impedance spectroscopy) was employed to evaluate the corrosion behavior of mild steel during the contact with sulfamic acid solutions. Inhibition performance of DTAB on mild steel at the initial period of immersion was somewhat higher than 12-4-12, while at prolonged immersion period 12-4-12 was more effective than DTAB. The higher protection and adhesion for the coating applied on the mild steel washed with DTAB solution was connected to more rapid adsorption for DTAB than 12-4-12 at short immersion period due to its small molecular weight which resulted in better mobility of DTAB molecules.     

不同腐蚀试验的电化学阻抗谱评价

采用电化学阻抗谱分析了环氧涂层的介质浸泡、ASTM-B117盐雾试验、PROHESION循环试验的性能变化。实验结果表明:介质浸泡更侧重考察涂层的屏蔽作用,对环氧-聚酰胺体系酸性电解质更容易导致涂层失效;而盐雾试验更容易导致涂层吸收水分,干湿交替增加了有机涂层吸水能力;划痕试验表明样板在ASTM-B117和PRO-HESION遵循不同的腐蚀机理。     

Studies on effect of nanoclay on the properties of thermally sprayable EVA and EVAI coatings

Dispersion of nanoclay (NC) in polymer blend system is governed by the sequence of addition of different ingredients. In the present work nanoclay was added in different sequences to blend composition such as ethylene vinyl acetate (EVA)/low density polyethylene (LDPE) and ethylene vinyl alcohol (EVAl)/LDPE in internal mixer to get nanocomposite. It was found that sequential addition of individual polymers and nanoclay influenced mechanical properties of resulting composites. Blending sequence of PE/NC/EVA and PE/NC/EVAl gave best mechanical properties. After optimization of addition sequence, concentration of nanoclay was varied from 1 to 8% by weight in the polymer blend. The resulting composites were evaluated in terms of their mechanical properties, dispersion characteristics (XRD), water vapor transmission rate (WVTR) and water absorption (Wa). Nanocomposite containing EVA/LDPE blend with 4% nanoclay showed optimum properties. The optimized composition was applied on grit blasted mild steel specimens by flame spray technique. The coated specimens were evaluated for adhesion strength, abrasion resistance and resistance to corrosion properties.     

预磷化电镀锌钢板粉末喷涂前处理工艺

对一种用于汽车和通讯行业的新型预磷化镀锌钢板的粉末喷涂前处理工艺进行了研究,通过晶相、膜质量及盐雾试验,对预磷化板的现有工艺进行了改进。酸洗工艺对预磷化板是不利的,酸洗工艺完全破坏了预磷化膜层。盐雾试验结果表明,预磷化镀锌钢板经过弱碱性脱脂剂清洗,经表调、磷化然后和粉末涂料结合,可以得到良好耐蚀性和附着力强的涂层。     

Evaluation of pre-treatment processes for HRS (hot rolled steel) in powder coating

Hot rolled steel (HRS) is used extensively in the automotive, agricultural and appliance industries. The corrosive response of HRS was investigated after it had been exposed to various surface treatments, prior to powder coating. The behaviour of three conversion coatings: zinc phosphate (ZnP), iron phosphate (FeP) and zirconium (Zr)-based nano-scaled, on HRS was studied. HRS is naturally covered with iron oxide scale and this was removed from the surface by mechanical and chemical processes, prior to the application of surface treatment and organic coatings. The following tests on differently treated panels were conducted to evaluate corrosion performance: adhesion tests such as, crosshatch, pull-off, and conical bending, SEM, XPS, salt spray and electro-chemical impedance studies were also performed. Good correlations were recorded showing that zinc phosphate conversion coating gave the best performance, and zirconium-based nano-structured conversion coating, was superior to that of iron phosphate conversion coatings on HRS.     

Corrosion stability of polyester coatings on steel pretreated with different iron–phosphate coatings

The influence of steel surface pretreatment with different types of iron–phosphate coatings on the corrosion stability and adhesion characteristics of polyester coatings on steel was investigated. The phosphate coating was chemically deposited either from the simple novel plating bath, or with the addition of NaNO₂, as an accelerator in the plating bath. The morphology of phosphate coatings was investigated using atomic force microscopy (AFM). The corrosion stability of polyester coatings on steel pretreated by iron–phosphate coatings was investigated by electrochemical impedance spectroscopy (EIS) in 3% NaCl solution, while “dry” and “wet” adhesion were measured by a direct pull-off standardized procedure. It was shown that greater values of pore resistance, R_p, and smaller values of coating capacitance of polyester coating, C_c, on steel pretreated with iron–phosphate coating were obtained, as compared to polyester coating on steel phosphated with accelerator, and on the bare steel. The surface roughness of phosphate coating deposited on steel from the bath without accelerator is favorable in forming stronger bonds with polyester coating. Namely, the dry and wet adhesion measurements are in accordance with EIS measurements in 3% NaCl solution, i.e. lower adhesion values were obtained for polyester coating on steel phosphated with accelerator and on the bare steel, while the iron–phosphate pretreatment from the novel bath enhanced the adhesion of polyester coating on steel.     

Polyaniline for corrosion prevention of mild steel coupled with copper

Polyaniline emeraldine base/epoxy resin (EB/ER) coating was investigated for corrosion protection of mild steel coupled with copper in 3.5% NaCl solution. EB/ER coating with 5-10 wt% EB had long-term corrosion resistance on both uncoupled steel and copper due to the passivation effect of EB on the metal surfaces. During the 150 immersion days, the impedance at 0.1 Hz for the coating increased in the first 1-40 days and subsequently remained constant above 10⁹ Ω cm², whereas that for pure ER coating fell below 10⁶ Ω cm² after only 30 or 40 days. Immersion tests on coated steel-copper galvanic couple showed that EB/ER coating offered 100 times more protection than ER coating against steel dissolution and coating delamination on copper, which was mainly attributed to the passive metal oxide films formed by EB blocking both the anodic and cathodic reactions. Salt spray tests showed that 100 μm EB/ER coating protected steel-copper couple for at least 2000 h.     

钢铁表面钛盐化学转化膜研究

研究了一种用于钢铁表面的环保型钛盐化学转化膜处理工艺,给出了工艺流程、钝化液配方及工艺条件,并采用金相显微镜、EDS和盐雾试验等方法对膜的表面形貌、元素组成和耐腐蚀性进行了测试.结果表明,钢铁经此工艺钝化后防腐性能明显提高,其膜层主要由三氧化二钛组成.     

Mercapto functional azole compounds as organic corrosion inhibitors in a polyester-melamine coating

The corrosion inhibition of two mercapto functional azole compounds including 2-mercaptobenzimidazole (MBI) and 2-mercaptobenzoxazole (MBO) for mild steel in 1 M NaCl solution was studied by electrochemical impedance spectroscopy (EIS), then their impact on the protective performance of a polyester-melamine coating was evaluated using salt spray. EIS results revealed a higher corrosion inhibitive activity of MBI compared to that of MBO. Corrosion products were examined by SEM-EDX and FTIR. The results showed modification of the corrosion products in the presence of MBI and MBO. The salt spray results revealed an improved corrosion protection of the coatings formulated with MBI and MBO. There was almost no impact of MBI and MBO on adhesion strength and glass transition temperature of the coatings, meaning that their impact on the corrosion protection performance of the formulated coating could only be attributed to their effect on the corrosion products.     

In-situ phosphatizing coatings III: A water-reducible alkyd baking enamel

We report the successful formulation of stable and compatible in-situ phosphatizing coatings (ISPCs) for a waterborne alkyd-amino baking enamel applied on bare cold-rolled steel (CRS), iron phosphated Bonderite 1000 (BD), and iron phosphated plus Parcolene 60 chromated (BD+P60) coupons. The enhanced coating adhesion of water-based ISPCs is confirmed by the cathodic delamination measurements. After 100 hr of salt spray (fog) test, the corrosion resistance performance (measured by the corrosion disbondment across the “X” scribe, d in mm) of the water-based ISPC on CRS panel (d=4.0−7.0 mm) outperformed that of the control alkyd paint on B-1000 (d=26 mm) and also on BD+P60 (d=14 mm) coupons. The superior coating performance of water-based ISPCs is believed to result from the in-situ metal surface phosphatization as detected by the reflectance FTIR technique. Department of Chemistry and Biochemistry, DeKalb, IL 60115-2862.     

Corrosion protection of mild steel by nano-colloidal polyaniline/nanodiamond composite coating in NaCl solution

The polyaniline/nanodiamond (PANI/ND) nanocomposite coating was synthesized on mild steel via electrochemical polymerization using cyclic voltammetry technique. The ultrasonic irradiation was used for effectively dispersing ND particles in electropolymerization solution. The prepared nanocomposite films were found to be nano-colloidal, and very adherent with low porosity. X-ray diffraction and FTIR techniques confirmed the intercalation of the nanoparticles in PANI matrix. The corrosion performance of the coatings was investigated in 3.5% NaCl solution by electrochemical impedance spectroscopy (EIS), polarization, and salt spray methods. The obtained results showed that the presence of ND particles significantly enhanced the corrosion protection performance of the PANI films in corrosive medium. EIS and polarization measurements indicated that the coating resistance and corrosion resistance values for the PANI/ND nanocomposite coating were much higher than that of pure PANI-coated electrode. Also, the results obtained revealed that the protection efficiency of PANI/ND-coated mild steel is achieved about 90% after 3 days. The porosity in PANI/ND nanocomposite coating is almost 18 times lower than that of the PANI coating.     

Influence of uniaxial deformation on the corrosion performance of pre-coated packaging steel

The influence of uniaxial deformation on the corrosion performance of electrolytic chromium-coated steel (ECCS) in both the presence and absence of a polymer coating was studied using scanning electron microscopy (SEM), open circuit potential (OCP), potentiodynamic polarization (PP) measurements and electrochemical impedance spectroscopy (EIS). The individual and combined contribution of chromium-chromium(III) oxide and the polymer coating was investigated. Specimens were uniaxially deformed to maximum strains of 5, 10 and 25%, respectively. After deformation Lüders bands were observed on the surface of the metal substrates. The corrosion resistance of the ECCS was shown to be better than that of the bare steel, due to the protective properties of the chromium-chromium(III) oxide layer on the surface. The corrosion resistance of the ECCS was found to decrease with strain, to be attributed to the introduction of local defects in the coating leading to increasing exposure of the more active underlying steel with deformation. The PETG (a glycol-modified amorphous PET) coating as such proves to be a very effective barrier layer in protecting the underlying substrate, however, in combination with the bare steel its protective properties decrease with time of exposure and deformation. Combining the individual contributions of the chromium-chromium(III) layer and the PETG coating it was shown that the corrosion performance of the polymer-coated ECCS is significantly better than the polymer-coated bare steel after deformation, which can be also attributed to the good corrosion resistance of the chromium-chromium(III) oxide layers and the improved adhesion of the coating.     

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.