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1.
Various coated metal samples with different pretreatments were investigated by electrochemical impedance spectroscopy (EIS). Variables were the substrate (cold-rolled steel and hot-dipped galvanized steel), phosphate system (iron and zinc phosphate), post rinse (chromate and silane/zirconium rinse) and paint systems. The corrosion performance was determined on the basis of coating degradation, water uptake and interface delamination of the tested samples. The zinc phosphate performed better than iron phosphate on CRS. The silane/Zr rinse did not perform well in the CRS/iron-phosphate system. However, it showed a better performance than the chromate when used as a post rinse of zinc phosphate. Salt spray test (SST) and adhesion test results of the same samples are also reported in this paper and compared to the EIS data. The correlation among three test methods was poor. 相似文献
2.
L. Fathyunes M. Azadbeh M. Tanhaei S. O. R. Sheykholeslami 《Journal of Coatings Technology and Research》2017,14(3):709-720
Coating with dense and fine particles containing fewer cracks and lower porosity shows more improved protective properties due to limiting pathways between the environment and base metal. The main aim of present research is to introduce an innovative method that is called rephosphating to achieve this morphology. The outstanding point of the present investigation is to highlight the significant effect of surface pretreatment by secondary grinding of phosphated surface and then rephosphating of this surface to obtain a coating with appropriate properties. The SEM observations showed that this method has an obvious influence on the formation of a very uniform zinc phosphate coating on the plain carbon steel compared with the traditional method of phosphating. Furthermore, the protecting properties of phosphated and rephosphated samples were described and compared using the neutral salt spray and the electrochemical polarization tests. The results showed that rephosphating method had a beneficial effect on improving the corrosion resistance. As well, improved paint adhesion of rephosphated sample was observed compared with that of the phosphated sample. Finally, it was concluded that when rephosphating method can be used to repair damaged phosphated areas, the coating with more compact morphology and improved properties can be achieved. 相似文献
3.
C. Kavitha T. S. N. Sankara Narayanan K. Ravichandran Il Song Park Min Ho Lee 《Journal of Coatings Technology and Research》2014,11(3):431-442
The present work aims at the development of an energy-efficient and eco-friendly approach for the deposition of zinc phosphate coatings on steel. The study describes the possibility of preparing zinc–zinc phosphate composite coatings by cathodic electrochemical treatment using dilute phosphoric acid as an electrolyte and zinc as an anode. The methodology enables the preparation of coatings with different proportions of zinc and zinc phosphate by suitably varying the applied current density, pH, and treatment time. Adhesion of the coating on mild steel and adhesion of paint film on the phosphate coating were found to be good. The surface morphology of the coatings exhibited platelet-type features and small white crystals (agglomerated at some places) which represented zinc and zinc phosphate, respectively. An increase in current density (from 20 to 50 mA/cm2) increased the size of the zinc crystals, and coatings prepared at 40 and 50 mA/cm2 resembled that of electrodeposited zinc. Since the proportions of zinc and zinc phosphate could be varied with applied current density, pH, and treatment time, it would be possible to use this methodology to prepare coatings that would offer different degrees of corrosion protection. 相似文献
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The influence of dissolved ozone (O3) and its concentrations on the formation of phosphate coatings on carbon steel in phosphate bath, as well as the protective
properties of phosphate coatings in a 5 wt% NaCl solution have been studied. The structure, surface morphologies, and phase
compositions of the phosphate coating on the carbon steel substrate was investigated by SEM, XRD. It is shown that the phosphate
coating became more dense with fewer microholes and an increasing concentration of ozone in phosphate bath in the range of
0.0 to 1.62 mg/L. The coating compositions were Zn3(PO4)2 · 4H2O (hopeite) and Zn2Fe(PO4)2 · 4H2O. Potentiodynamic polarization and immersion tests were used to evaluate the corrosion properties of the treated samples.
The coating showed good corrosion resistance properties. 相似文献
8.
T.S.N. Sankara Narayanan S. Jegannathan K. Ravichandran 《Progress in Organic Coatings》2006,55(4):355-362
The formation of phosphate coatings by cathodic electrochemical treatment using graphite and steel anodes and evaluation of their corrosion resistance is addressed in this paper. The type of anode used, graphite/steel, has an obvious influence on the composition of the coating, resulting in zinc–zinc phosphate composite coating with graphite anode and zinc–iron alloy–zinc phosphate–zinc–iron phosphate composite coating with steel anode. The corrosion resistance of the coating is found to be a function of the composition of the coating. The deposition of zinc/zinc–iron alloy along with the zinc phosphate/zinc and zinc–iron phosphate using graphite/steel anodes has caused a cathodic shift in the Ecorr compared to uncoated mild steel substrates. The icorr values of these coatings is very high. EIS studies reveal that zinc/zinc–iron alloy dissolution is the predominant reaction during the initial stages of immersion. Subsequently, the formation of zinc and iron corrosion products imparts resistance to the charge transfer process and increases the corrosion resistance with increase in immersion time. The corrosion products formed might consist of oxides and hydroxychlorides of zinc and iron. The study suggests that cathodic electrochemical treatment could be effectively utilized to impart the desirable characteristics of the coating by choosing appropriate anode materials, bath composition and operating conditions. 相似文献
9.
The St-37 type steel substrates were pretreated with Cr(VI) and Cr(III) conversion coatings where the latter was then post-treated with Co(II) and Ni(II) chemical treatments. The epoxy coatings containing 3.5 wt% nano-sized ZnO particles were applied over the chemically treated steel samples. The corrosion resistance of the samples was studied by a DC polarization technique. A scanning electron microscope (SEM) was utilized to investigate the morphology of the pretreated and post-treated samples. Electrochemical impedance spectroscopy (EIS) was utilized to investigate the corrosion resistance of the epoxy nanocomposites for different immersion times in 3.5 wt% NaCl solution. The adhesion strengths of the coatings were measured before and after 120 days of immersion in the corrosive electrolyte using a pull-off test. The cathodic delamination (CD) of the painted samples was also investigated. Results showed that conversion coatings can significantly increase the corrosion resistance and adhesion strength of the epoxy coating on the steel, and also reduce the rate of CD in comparison with an untreated sample. The adhesion strength and corrosion resistance of the epoxy coating on the Cr(III) pretreated samples were significantly greater than on the Cr(VI) sample. The increase in adhesion strength and corrosion resistance was more pronounced on the samples that were post-treated with Co(II) and Ni(II) chemical treatments. The cathodic disbonded areas of the Cr(III)–Co(II) and Cr(III)–Ni(II) post-treated samples were significantly lower than the Cr(III) and Cr(VI) pretreated samples. Results showed that Cr(III)-based conversion coatings can improve the anticorrosion performance and reduce CD compared with those with Cr(VI). 相似文献
10.
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 Ecorr 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 icorr 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. 相似文献
11.
The corrosion resistance of carbon steel specimens was compared, using different surface treatment methods such as blasting and zinc phosphate treatment on carbon steel followed by application of different coating thickness. Specimen surface morphology was observed by SEM. The corrosion performance of epoxy coated carbon steel was examined by electrochemical impedance spectroscopy (EIS), along with immersion test in 0.5N-NaCl solution and NORSOK M 501 cyclic test, respectively. EIS results showed that higher thickness of epoxy coating and zinc phosphate treatment on carbon steel showed better corrosion protection than rest of the specimens. Specimens with no treatment and blasting treatment followed by epoxy coating, showed poor corrosion protection. Results of NORSOK M 501 cyclic test showed similar trend as those of EIS results however degradation of specimens was more severe than those from immersion test. 相似文献
12.
An attempt has been made to investigate the effect of phosphating time and vanadium additive on the anticorrosion and surface properties of ambient temperature zinc phosphate coatings. Zinc phosphate coatings with different phosphating times and vanadium concentrations were applied to low carbon steel samples. A potentiostatic polarization test in 3.5 wt% NaCl solution was carried out to investigate the electrochemical properties of coated samples. Field emission scanning electron microscopy, energy-dispersive spectroscopy, and atomic force microscopy were utilized to evaluate the microstructure, chemistry and roughness of coatings. Surface properties such as wettability, surface tension, and work of adhesion were measured. Results indicate that the sample which was immersed for 30 min in the phosphating bath exhibits the lowest corrosion current density, one tenth of bare steel, due to formation of a compact coating while having a low number of microcracks. Addition of 500 ppm vanadium to the coating in a secondary bath decreases the corrosion rate of zinc phosphate coating remarkably, by almost 80%. Microstructural results reveal that vanadium-rich precipitates are formed and enhance the coating coverage on the steel substrate. Vanadium addition increases the surface roughness, surface free energy, and work of adhesion of the phosphate coating. 相似文献
13.
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. 相似文献
14.
Cecilia Deyá 《Journal of Adhesion Science and Technology》2013,27(14):1548-1562
Coatings are one of the most used protection methods for metals. Metallic coatings, such as zinc and its alloys, are used to protect steel in mild corrosive environments. In aggressive environments, on the other hand, organic coatings must be employed in the so-called duplex systems. However, the galvanized steel/organic coating adhesion is a problem and many attempts had been done to solve it with the incorporation of a chromate-based or phosphate-based interlayer. Nowadays, the use of these compounds is questioned due to their environmental impact and new adhesion promoters, like silanes, are being investigated. The aim of this paper was to study the adhesion and the anticorrosive behavior of a duplex system with a layer of glycidoxypropyltrimethoxysilane (γ-GPS) between the zinc and the coating. Polarization tests and corrosion potential measurements were done on the γ-GPS/galvanized steel to select the better anticorrosive pretreatment conditions for the application of an organic traditional paint. Dried and wet adhesion of the coating to the pretreated substrate was studied by the standard tape test. Salt spray test and electrochemical noise technique were employed to study the corrosion behavior of the duplex systems. Results showed that the films of γ-GPS formed on galvanized steel diminished the corrosion current of the metal, but they do not protect the substrate by a barrier effect. The incorporation of the pretreatment in the duplex system increased the adhesion of the paint, especially when the pretreated substrate was cured 1?h at 200?°C. 相似文献
15.
M. M. Musiani F. Furlanetto P. Guerriero J. Heitbaum 《Journal of Applied Electrochemistry》1993,23(10):1069-1075
Phenol electropolymerization to polyoxyphenylene coatings on phosphated steel and phosphated galvanized steel, normally impossible under the conditions allowing effective coating formation on either steel or zinc, is activated by cathodic deposition of zinc. A critical zinc amount has been found to be necessary to suppress electrochemical processes competitive with electropolymerization and induce coating formation with nearly 100% efficiency. SEM analysis showed that this critical amount of zinc corresponded to the formation of a low number of zinc nuclei emerging at the surface of the phosphate layer, on which, however, polyoxyphenylene was formed as a continuous coating. A.c. impedance tests showed that initial barrier properties are worse for coatings grown on zinc-plated phosphated samples than for those grown on steel from the same solutions. However, the long term corrosion resistance is much better in the former case, the improvement being largely associated with zinc cathodic protection 相似文献
16.
Improved corrosion resistance of pulse plated nickel through crystallisation control 总被引:1,自引:0,他引:1
P. T. Tang T. Watanabet J. E. T. Andersen G. Bech-Nielsen 《Journal of Applied Electrochemistry》1995,25(4):347-352
When electrodeposition of nickel is used for corrosion protection of steel two aspects are important: the porosity of the coating and the resistance against corrosion provided by the coating itself. Using simple pulsed current (PC) plating, the size of the deposited crystals can be significantly smaller, thereby reducing porosity correspondingly. This usually also leads to improved hardness of the coating. Introducing pulse reversal (PR) plating, the most active crystals are continuously dissolved during the anodic pulse, providing a coating with improved subsequent corrosion resistance in almost any corrosive environment. This correlation between film texture and corrosion resistance will be discussed. 相似文献
17.
不同材料表面镍-磷-锌盐纳米复合化学镀层性质的比较 总被引:2,自引:0,他引:2
研究比较了D310硅钢片和A3钢片表面Ni-P-Zn3(PO4)2,Ni-P-ZnSnO3和Ni-P-ZnSiO3纳米复合化学镀层的外貌和性质。用扫描电子显微镜(SEM)观察外貌:称重法测定厚度,通过10%NaCl溶液,1%H2S气体加速腐蚀试验,10%,CuSO4溶液点滴试验,饱和KCl溶液循环伏安(CV)试验,抗粘性试验及抗高温氧化试验等多种手段测定其性能。结果表明:纳米复合化学镀层的性能优于镍-磷镀层和其它微米复合镀层。 相似文献
18.
Khalid Abdalla Azmi Rahmat A. Azizan 《Journal of Coatings Technology and Research》2013,10(1):133-139
Zinc phosphate coating is widely used for corrosion protection of metallic materials, mainly mild steel. In the present study, the effect of pretreatment with copper acetate solution on zinc phosphate layer properties was investigated via scanning electron microscopy, energy-dispersive spectroscopy, and X-ray diffraction. The corrosion resistance of the coating was evaluated using polarization curves and electrochemical impedance spectroscopy in an aerated 3.5% NaCl solution. The pretreatment resulted in a compact and uniform phosphate coating with smaller crystal size and greater surface coverage. Electrochemical results showed better corrosion resistance for the pretreated phosphate layer compared with the untreated one. 相似文献
19.
Two types of phosphate fillers (nanosized aluminum phosphate and microsized aluminum–zinc phosphate) were tested as anticorrosive fillers in 2 K solvent-borne polyurethane paints based on commercial acrylic resin with OH groups and an isophorone diisocyanate-type hardener. Three coating compositions containing commercial fillers (mica/quartz, TiO2, wollastonite, talc) and also mentioned nanosized aluminum phosphate or microsized aluminum–zinc phosphate were prepared using a pearl-mill as well as a laboratory dissolver, applied onto a steel substrate and cured at room temperature for 14 days. An influence of the type and content of a phosphate filler on properties of polyurethane paints and coatings has been investigated. Incorporation of nanosized aluminum phosphate into coating compositions increases their viscosity while cured paints exhibit reduced adhesion to steel substrates. The results of corrosion tests in a salts spray chamber as well as immersion in an aqueous NaCl solution indicated that the paint system with 9.8 wt.% of applied nanofiller had similar protective properties to a polyurethane coat containing a higher dose (i.e. 15.6 wt.%) of commercial microsized aluminum–zinc phosphate. 相似文献