共查询到20条相似文献,搜索用时 15 毫秒
1.
B. RamezanzadehM.M. Attar 《Surface & coatings technology》2011,205(19):4649-4657
Hot-dip galvanized steel (HDG) samples were chemically treated by Cr(III), Cr(VI), Cr(III)-Co(II) and Cr(III)-Ni(II) conversion coatings. Epoxy nanocomposites were prepared using 2 wt.%, 3.5 wt.%, 5 wt.% and 6.5 wt.% nano-ZnO. Electrochemical impedance spectroscopy (EIS), pull-off adhesion tester and scanning electron microscope (SEM) were utilized to evaluate epoxy coatings properties on the surface of pre-treated HDG samples. Results showed that addition of nano-ZnO particles (specially 3.5 wt.%) can significantly improve the corrosion resistance of the epoxy coating on HDG. Decrease of contact angle (φ) and increase of surface roughness (Ra) of the pre-treated HDG samples were obtained. Decrease of the value of φ was more pronounced when the Cr(III) pre-treated samples were post-treated by Cr(III)-Co(II) and Cr(III)-Ni(II) conversion coatings (CCs). The dry and wet adhesion strengths of the epoxy coating to HDG were significantly increased after the surface treatment of the samples. Increase of the adhesion strength and decrease of the adhesion loss were more pronounced on Cr(III)-Co(II) and Cr(III)-Ni(II) post-treated samples. The corrosion resistance of epoxy coating was also increased on the surface of pre-treated HDG samples. Increase of the corrosion resistance of the Cr(III) pre-treated HDG samples was more pronounced on the samples which were post-treated by Co(II) and Ni(II). 相似文献
2.
Yu-Tsern Chang Niann-Tsyr Wen We-Kun Chen Ming-Der Ger Guan-Tin Pan Thomas C.-K. Yang 《Corrosion Science》2008,50(12):3494-3499
The main purpose of this paper is to develop a dynamic and non-destructive method to quantify and correlate the microstructure changes of the Cr(III) layer by electrochemical techniques. The open circuit potential (OCP) analysis reveals the nucleation growth mechanisms of the Cr(III) layer and the dissolution phenomena of Zn. In addition, the effects of immersion time to the corrosion behavior of Cr(III)-based conversion coatings (TCCCs) on electrogalvanized steel were studied using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) in a 3.5% NaCl solution. Furthermore, surface morphology of the Cr(III) coatings under different immersion times was examined using both a scanning electron microscope and an atomic force microscope.From the potentiodynamic polarization experiment, the corrosion current density (Icorr) of the specimen with immersion time of 60 s was found appreciably small, representing the inheritance of the best anticorrosion performance. Additionally, the corrosion resistance of the Cr(III)-coating for the specimens obtained between 30 s and 60 s is two order higher than those of the untreated specimen from the EIS experiments. Results show that the quality of Cr(III)-based conversion coatings was strongly influenced by the immersion time of Cr(III) solution. And the optimal immersion time is recommended in the range of 30–60 s. 相似文献
3.
The influence of drying temperature on the corrosion performance of chromate coatings on electro‐galvanized (EG) steel has been investigated using electrochemical impedance spectroscopy (EIS) and potentiodynamic measurements in 3.5% NaCl solutions. The chromate coatings were applied to the EG steel in a solution (pH 1.2) containing sodium dichromate and sulfuric acid at room temperature. The coatings were dried in an oven at three different temperatures: 60, 110 and 210°C. The surface of the chromate coatings was analyzed using atomic force microscopy (AFM) and scanning electron microscopy (SEM) combined with energy‐dispersive spectrometry (EDS). The results show that the drying temperature significantly affects the morphology of the chromate coatings and consequently affects their corrosion behavior. The chromate coatings dried at 110°C had few cracks and the lowest corrosion current. The chromate coatings dried at 60°C showed passivity. The EIS results show that the chromate coatings dried at 60°C has the largest impedance in a neutral 3.5% NaCl solution. Drying at higher temperature (210°C) degrades the chromate coatings by widening the cracks and reducing soluble Cr(VI) in the chromate layer. The favorable drying temperature for the chromate coatings on the EG steel is between 60 and 110°C. 相似文献
4.
The modified zinc phosphate conversion coatings(ZPC) were formed on hot-dip galvanized(HDG) steel when 1.0 g/L sodium molybdate were added in a traditional zinc phosphate solution. The growth performance and corrosion resistance of the modified ZPC were investigated by SEM, open circuit potential(OCP), mass gain, potentiodynamic polarization and electrochemical impedance spectroscopy(EIS) measurements and compared with those of the traditional ZPC. The results show that if sodium molybdate is added in a traditional zinc phosphate solution, the nucleation of zinc phosphate crystals is increased obviously; zinc phosphate crystals are changed from bulky acicular to fine flake and a more compact ZPC is obtained. Moreover, the mass gain and coverage of the modified ZPC are also boosted. The corrosion resistance of ZPC is increased with an increase in coverage, and thus the corrosion protection ability of the modified ZPC for HDG steel is more outstanding than that of the traditional ZPC. 相似文献
5.
The effect of a silicate conversion coating, which was applied on electrogalvanized steel (EG) and hot dip galvanized steel (HDG), on zinc passivation and dissolution is investigated by atomic emission spectroelectrochemistry (AESEC) using anodic/cathodic cycles in a neutral borate buffer solution. We are able to decompose the total zinc oxidation rate into a soluble (dissolution) and insoluble (passivation) component. It is found that the silicate conversion coating reduces the soluble component with no measurable effect on the insoluble component. The results imply that zinc passive film formation occurs unhindered underneath the silicate film but the film effectively blocks zinc dissolution. 相似文献
6.
Effect of molybdate post-sealing on the corrosion resistance of zinc phosphate coatings on hot-dip galvanized steel 总被引:3,自引:0,他引:3
The technique of post-sealing the phosphated hot-dip galvanized (HDG) steel with molybdate solution was addressed. The composition and corrosion resistance of the improved phosphate coatings were investigated by SEM, EDS, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements, and neutral salt spray (NSS) test. The results showed that molybdate films were formed in the pores of phosphate coatings, and the compact and complete composite coatings composed of phosphate coatings and molybdate films were formed on the zinc surface, resulting in that both the anodic and cathodic processes of zinc corrosion were inhibited remarkably; the corrosion protection efficiency values were increased; and the electrochemical impedance values were enhanced at least one order of magnitude. The low frequency impedance values for the composite coatings were increased at the initial stages of immersion in 5% sodium chloride solution, indicating the self-repairing activity of the composite coatings. 相似文献
7.
ABSTRACTNew protective coatings with satisfactory performance and low impact are required by the surface treatment industry as effective Cr(VI)-free substitutes. Recently conversion coating systems containing Zr/Ti have shown great promise particularly for zinc finishes on steel and in this paper, we study the influence of bath conditions (e.g. pH and time) on conversion layers composed of a Zr-based film. The coating formation was studied by simultaneous monitoring of open circuit potential and surface pH using a novel cell design. Samples were subsequently characterised by electrochemical impedance spectroscopy in NaCl over a 24-hour period. The system demonstrates a correlation between pH of formation and corrosion resistance. 相似文献
8.
M. Mosia?ek G. Mordarski P. NowakW. Simka G. NawratM. Hanke R.P. SochaJ. Michalska 《Surface & coatings technology》2011,206(1):51-62
Conversion coatings on the magnesium alloy AZ81 were prepared using the phosphate-permanganate baths differing in composition. The corrosion behavior of the coated and uncoated alloys has been investigated by electrochemical impedance spectroscopy (EIS) and linear polarization methods. The choice of proper electric equivalent circuit (EEC) is discussed. The effect of temperature, bath composition and time of conversion as well as etching in acids before application on the corrosion resistance of the coated alloy has been evaluated. The best corrosion resistance was obtained for the samples coated in the bath containing 25 g KMnO4, 150 g Na2HPO4 and 50 ml H3PO4 in 1 dcm3, applied at 80 °C. Differences in the morphology and composition of coated surfaces were investigated by the scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) techniques and correlated with the corrosion resistance of the samples. 相似文献
9.
Conversion coatings on zinc surfaces (Zn and electrogalvanized steel) were obtained with tungstate baths acidified by phosphoric acid under different experimental conditions. Open circuit potential and local pHs were monitored during the conversion processes. The conversion layers were submitted to immersion tests monitored by open circuit potential and electrochemical impedance spectroscopy. Scanning electron microscopy and energy dispersive X-ray complemented the electrochemical measures. The local pH measurements have evidenced that the conversing process occurs at a specific value of pH. Electrochemical impedance has detected similarities between the deterioration process of tungstate and chromate conversed zinc surfaces. 相似文献
10.
In this work, a Cr-free conversion layer based on molybdate–phosphate–silicate (MPS) was synthesised on a galvanized steel by simple immersion and its corrosion behaviour was compared to that of a typical chromate layer. Stationary electrochemical techniques and electrochemical impedance spectroscopy (EIS) were employed to highlight the corrosion mechanisms of both coatings in different NaCl concentrations, immersion times and pH. Contrary to the chromate layer, the MPS coating showed good electrochemical stability even in concentrated NaCl solutions and remarkable electrochemical efficiency. With increasing time, two corrosion stages were associated with the two likely sublayers of the MPS coating. Furthermore, the MPS coating behaved better than the chromate layer in acidic and alkaline pH, especially the latter as a compact corrosion product layer formed. Finally, each coating/electrolyte interface was characterised by an electrical equivalent circuit giving a satisfactory correlation between the experimental and the calculated impedance. It derived that the MPS could be an environmentally friendly alternative to chromating. 相似文献
11.
G. Ruhi 《Surface & coatings technology》2009,204(3):359-365
A stable boehmite sol was synthesized using Al-isopropoxide as a precursor in an appropriate ratio with water. Afterwards, the 9Cr-1Mo steel specimens were coated with prepared boehmite sol by dip coating technique. AFM analysis of the coated specimens confirmed the presence of nano sized particles (8-12 nm) in the coating. Electrochemical measurements like potentiodynamic and potentiostatic polarisations, electrochemical impedance spectroscopy (EIS) in different concentrations of Cl− ions indicated that the sol-gel alumina coating is able to make an appreciable improvement in the corrosion resistance of the base alloy. It was also observed that the sol-gel coatings can control the pitting attack up to a certain extent in 100 ppm Cl− containing solution. However, the coatings become susceptible towards pitting attack in 200 ppm Cl− bearing solution. The SEM micrographs of the corroded surfaces revealed the occurrence of severe pitting on the uncoated specimens in 100 ppm Cl− solution and also on the coated specimen in 200 ppm Cl− solution. 相似文献
12.
The conversion coating can be obtained by using a solution containing titanium tetrachloride, fluorosilicate acid and nitric acid. The results of X-ray photoelectron spectroscopy (XPS) showed that the titanium conversion coating consisted of ZnO, TiO2 and Zn4Si2O7(OH)2. The formation process of the titanium conversion coating was studied. Effects of the immersion time, pH value and solution temperature on the corrosion resistance and the chemical composition of the titanium conversion coating were investigated by the salt spray test (SST) and XPS, respectively. The results of XPS and SST showed that the titanium conversion coating displayed better corrosion resistance with higher contents of Si and Ti. Results of corrosion tests (the salt spray and electrochemical test) indicate that the corrosion resistance of the conversion coating by titanium solution is better than that of the conversion coating using the traditional chromate solution. 相似文献
13.
为了提高冷轧镀铝锌钢板表面晶花质量,在连续热浸镀生产线制备了4种不同成分的Al-Zn-Mg-Si镀层样板,采用体视显微镜、扫描电镜、电子探针、X射线衍射仪和电子背散射衍射等方法,研究了Mg含量对镀层凝固组织和耐腐蚀性能的影响。结果表明:随Mg含量的增加,镀层晶花尺寸先减小后增大,耐腐蚀性先降低后增高;在Mg质量分数为1.0%时,镀层质量最佳,晶花细小均匀,平均晶粒尺寸为1.2 mm,镀层截面组织中含质量分数为68.3%的富铝相、质量分数为26.1%的富锌相、少量富硅相和富镁相,在60 d内的平均失重速率为0.05 g/(m2·d)。 相似文献
14.
Corrosion fatigue behavior of a steel with sprayed coatings 总被引:1,自引:0,他引:1
K. Tokaji T. Ogawa J. U. Hwang Y. Kobayashi Y. Harada 《Journal of Thermal Spray Technology》1996,5(3):269-276
This paper describes the corrosion fatigue behavior and fracture mechanisms of a steel with different sprayed coatings. Rotating
bending fatigue tests were conducted in 3% NaCl solution using specimens of a medium carbon steel with sprayed coatings of
a ceramic (Cr2O3), a cermet (WC-12%Co) and two metals (Ni-11 % P and Al-2% Zn). The corrosion fatigue process was basically the same for ceramic, cermet, and Ni-11 % P sprayed specimens. That is,
the corrosive media could be supplied from the specimen surface to the substrate through cracks initiated during fatigue cycling
and/or pores in the coatings, and thus corrosion pits were generated followed by subsequent crack initiation and growth in
the substrate. The corrosion fatigue strength of ceramic sprayed specimens was slightly improved compared to that of the substrate
steel because the under-coating (Ni-5%A1) could impede the penetration of the corrosive media although the ceramic coating
had a poor resistance to cracking under cyclic loading. Cermet sprayed specimens also exhibited improved corrosion fatigue
strength because of the high resistance to cracking and the low volume fraction of pores of the coating. In Ni-11 % Psprayed
specimens, cracks were initiated in the coating even at low stress levels; thus the corrosion fatigue strength was the same
as that of the substrate. Anodic dissolution took place in Al-2 % Zn coating because the coating was electrochemically poor,
and thus the substrate was cathodically protected. Therefore, the corrosion fatigue strength of Al-2 % Zn sprayed specimens
was enhanced to as high as the fatigue strength of the substrate in room air. Based on the experimental results, a dual-layer
coating consisting of WC-12%Co and Al-2%Zn was fatigue tested. The coating was effective at low stress levels and exhibited
long life under conditions where corrosion fatigue strength was critical. 相似文献
15.
16.
BH390钢热镀锌抑制层及其合金化镀层界面结构 总被引:2,自引:0,他引:2
利用SEM和TEM研究了铝含量不同的热镀锌镀层中抑制层的结构及抑制层在形成和生长过程中Zn-Fe-Al金属间化合物之间的反应过程;分析了铝含量不同的镀层合金化后镀层与BH390钢基体之间的界面结构。结果表明,随着锌液中铝含量的增加,镀层中抑制层的结构逐渐由晶粒粗大且不连续的Fe2Al5转变为晶粒细小相对致密的FeAl3。铝含量不同的热镀锌镀层在合金化过程中抑制层结构的变化和镀层中各相的形成及生长过程是不相同。随着锌液中铝含量的增加合金化镀层与钢基体界面结合处镀层结构的均匀性逐渐降低,在相同的合金化工艺条件下,随着锌液中铝含量的增加镀层的合金化时间延长。 相似文献
17.
F. Zucchi A. Frignani V. Grassi G. Trabanelli C. Monticelli 《Corrosion Science》2007,49(12):4542-4552
The formation of stannate and permanganate–phosphate conversion coatings on AZ31 magnesium alloy was investigated in situ by EIS measurements and their protective performances were studied by different electrochemical techniques in diluted (0.05 M) sodium sulphate solution.The influence that short or long treatment times exert on the performances of such conversion coatings is discussed. While permanganate–phosphate baths always built layers characterized by penetrating cracks, long stannate baths produced layers without interconnected porosity, but were defective. This accounted for the initial greater protectiveness achieved with the stannate treatment; nevertheless, the easy penetration of the electrolytic solution through such a layer quickly decreased its corrosion resistance. 相似文献
18.
19.
The structure, morphology and composition of conversion coatings grown in stannate bath on pure Mg were studied using potential–time, polarization curves, X-ray diffraction, scanning electron microscopy and photocurrent spectroscopy. The coating is manly constituted by crystalline magnesium–tin hydroxide, whose morphology and distribution depends on the conversion bath composition and temperature. The photoelectrochemical investigation allowed to estimate the band gap value of MgSn(OH)6 and flat band potential. A sketch of the metal/passive film/electrolyte junction formed during conversion on the metal substrate is reported to account for the overall photoelectrochemical behaviour. 相似文献