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101.
The use of electrochemical noise methods (ENM) to study thick, high impedance coatings 总被引:2,自引:0,他引:2
Gordon P. Bierwagen Carol S. Jeffcoate Junping Li S va Balbyshev Dennis E. Tallman Douglas J. Mills 《Progress in Organic Coatings》1996,29(1-4):21-29
Thick, high impedance organic coatings are those class of coatings used to provide corrosion protection to naval vessels, pipelines, gasoline storage tanks, and other large structures such as bridges and plant structures. These coatings, especially the newest generations now being used in practice, can provide exceptional protection and lifetime of performance such that properly and accurately assessing and differentiating among competing coatings is a very difficult task. The standard protocol of salt fog testing (ASTM B117), immersion testing, and outdoor exposure in a corrosive environment with subjective evaluation of a coating's performance durings and after testing, does not adequatcly rank and predict coating lifetimes for new coating systems, especially for the environmentally compliant coating systems such as powder coatings (especially the thick, fusion bonded epoxy (FBE) coatings used for pipelines), two component epoxy and urethane coatings and waterborne coatings. New, objective test methods are desperately needed by users and manufacturers of coatings. A relatively new electrochemical test procedure, electrochemical noise methods (ENM), as developed by Skerry and Eden, has been shown in our laboratory to be very successful in the ranking and prediction of relative coating performance. We have used the method successfully on naval ship coatings, several pipeline coatings and other related systems, and Skerry has used them successfully on industrial maintenance coatings. We have used these methods in conjunction with electrochemical impedance spectroscopy, d.c. resistance measurements and cyclic salt fog testing of the ProhesionTM type. In our studies of pipeline coatings, we needed to investigate thermal effects because of their extended range of use temperature. In these studies, we have discovered that electrochemical methods can be used for an in situ measurement of the Tg of coatings in electrolyte immersion. Further, the ‘plasticizing’ effect of aqueous electrolyte absorption as well as its relative irreversibility has been shown. For all coatings studied, ENM provided useful, objective, numerical data which rapidly ranks coatings and provides useful information on the relative lifetime prediction of coatings which may provide up to 30 years of service. 相似文献
102.
103.
In this work diamond-like carbon films were deposited on the Ti–6Al–4V alloy, which has been used in aeronautics and biomedical fields, by electrical discharges using a magnetron cathode and a 99.999% graphite target in two different atmospheres, the first one constituted by argon and hydrogen and the second one by argon and methane. Films deposited using the argon/hydrogen mixture were called a-C:H, while films deposited using the argon/methane mixture were called DLC. Raman spectroscopy was used to study the structure of the films. The Raman spectra profile of the a-C:H films is quite different from that of the DLC films. The disorder degree of the graphite crystalline phase in a-C:H films is higher than in DLC films (a-C:H films present small values for the the ID/IG ratio). Potentiodynamic corrosion tests in 0.5 mol l−1 NaCl aqueous solution, pH 5.8, at room temperature (≈25 °C) were carried out as for the a-C:H as for the DLC coated surfaces. Comparison between the corrosion parameters of a-C:H and DLC coated surfaces under similar deposition time, showed that DLC coated surfaces present bigger corrosion potential (Ecorr) and polarization resistance than those coated with a-C:H films. Electrochemical impedance spectroscopy (EIS) was also used to study the electrochemical behavior of a-C:H and DLC coated surfaces exposed to 0.5 mol l−1 aqueous solution. The EIS results were simulated with equivalent electrical circuit models for porous films. The results of these simulations showed similar tendency to the one observed in the potentiodynamic corrosion tests. The DLC film resistance and the charge transfer resistance (Rct) for the DLC coated surface/electrolyte interface were bigger than the ones determined for the a-C:H coated surfaces. 相似文献
104.
The corrosion behavior of Cr-N coated steels with different phases (-Cr, CrN and Cr2N) deposited by cathodic arc deposition on AISI H13 steel was investigated in a 3.5% NaCl solution at ambient temperature. Potentiodynamic polarization tests, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) were the techniques applied to characterize the corrosion behavior. It was found that the CrN coating had a lower current density from potentiodynamic polarization tests than others. The porosity, corresponding to the ratio of the polarization resistance of the uncoated and the coated substrate, was higher in the Cr2N coating than in the other Cr-N coated steels. EIS measurements showed, for most of the Cr-N coated steels, that the Bode plot presented two time constants. Also, the Cr2N coating represented the characteristic of Warburg behavior after 72 h of immersion. The coating morphologies were examined in planar view and cross-section by SEM analysis and the results were compared with those of the electrochemical measurement. The CrN coating had a dense, columnar grain-sized microstructure with minor intergranular porosity. From the above results, it is concluded that the CrN coating provided a better corrosion protection than the other Cr-N coated steels. 相似文献
105.
F.X. Wang X.P. Gao Z.W. Lu S.H. Ye J.Q. Qu F. Wu H.T. Yuan D.Y. Song 《Journal of Alloys and Compounds》2004,370(1-2):326-330
In this work, effects of partial substitution of Mg, Ni with AB2 in Mg-based alloy and subsequent surface modification by further ball-milling with carbon nanotubes (CNTs) on electrochemical properties were investigated. Mg1.9(AB2)0.1Ni0.8 (AB2=LaNi2, LaNiCo and LaNiMn) alloys were prepared by solid-state diffusion method, the nanocrystalline Mg-based alloys were prepared by ball-milling the mixture of obtained Mg1.9(AB2)0.1Ni0.8 alloys and nickel powder. It was found that the electrochemical capacities of nanocrystalline Mg1.9(AB2)0.1Ni1.8 alloys were measured to be 460–490 mAh/g. The nanocrystalline Mg-based alloys containing carbon nanotubes (10 wt.%) obtained by ball-milling after 60 min were demonstrated to show improved electrochemical properties with respect to the original nanocrystalline Mg-based alloys. The electrochemical reaction activity was detected by electrochemical impedance spectra (EIS). Raman and X-ray photoelectron spectroscopy (XPS) proved the interaction between Mg1.9(AB2)0.1Ni1.8 alloys and carbon nanotubes after ball-milling, which resulted in an increase in the surface Ni/Mg ratio. 相似文献
106.
电化学法处理废硬质合金直接回收金属钴和碳化钨 总被引:4,自引:0,他引:4
首次采用电化学法处理废硬质合金直接回收金属钴和碳化钨,工艺简单可靠,具有较好的环境和经济效益。 相似文献
107.
Chan-Yeol Seo Seung-Jun Choi Jeon Choi Choong-Nyeon Park Paul. S. Lee Jai-Young Lee 《Journal of Alloys and Compounds》2003,350(1-2):324-331
AB5-type intermetallic compounds were prepared by arc-melting in argon atmosphere. The composition of a stoichiometric compound LaNi3.6Al0.4Co0.7Mn0.3 with a hexagonal CaCu5 structure was varied by stoichiometric and nonstoichiometric addition of Ti. With the increase of the Ti y0.05 content in LaNi3.6Al0.4Co0.7Mn0.3Tiy, the hydrogen storage capacity is enhanced, whereas when y=0.1–0.3, it is decreased. The discharge capacity and cyclability are increased considerably by addition of titanium in the range of 0.02–0.1 with a maximum value at about 0.1%. The highest maximum capacity is achieved for a nonstoichiometric addition of 0.05% Ti. The kinetic properties are also additionally improved by the formation of a titanium-rich second phase. This can explain the improvement of the capacity for alloys with low Ti content. The decrease in capacity for high Ti content was also correlated with the amount of the Ti-rich phase. Therefore, the improvement of kinetics are due to the catalytic effect, grain boundary diffusion effect or more pronounced alloy pulverization upon cycling. This study has been aimed to improve the electrode properties of a series of multicomponent LaNi3.6Al0.4Co0.7Mn0.3Tiy (y=0.0, 0.02, 0.05, 0.1, 0.2, 0.3) alloys which have mutual complementary properties. All the prepared alloys have been subjected to analyses by EDS, SEM and XRD. In order to determine the hydrogen storage capacity, the pressure composition isotherms (P–C–T curves) have been used. The metal hydride electrodes were characterized by galvanostatic cycling test. 相似文献
108.
The effect of corrosion inhibiting pigments on environmentally assisted cracking of high strength aluminum alloy 总被引:2,自引:0,他引:2
The effects of some corrosion inhibiting pigments on environmentally assisted cracking of 7075-T76 aluminum alloy were examined in 3.5% NaCl (pH=6.2) solution. In order to study the inhibition mechanism of these pigments in environmentally assisted cracking of aluminum alloy, electrochemical polarization tests were carried out in 3.5% NaCl (pH=6.2 and 3) and 0.1 M HCl solutions respectively with the presence and absence of these pigments. The results showed that the effects of the pigments on environmentally assisted cracking of aluminum alloy were exhibited mainly at crack initiation and the early stage of crack propagation. A nontoxic compound, composed of phosphate, molybdate, citrate, and thiazole/imidazole derivatives, was a promising pigment to inhibit environmentally assisted cracking of the alloy. 相似文献
109.
应用多重动电位扫描极化技术测评有机涂层/金属体系的耐腐蚀性 总被引:1,自引:0,他引:1
林昌健 《中国腐蚀与防护学报》1994,14(4):315-321
应用多重动电位扫描极化技术测评有机涂层/金属体系的耐腐蚀性林昌健(固体表面物理化学国家重点实验室,厦门大学厦门361005)T.Nguyen(美国国家标准与技术研究院)1引言有机聚合物涂层/金属体系的腐蚀已成为腐蚀界的一个研究热点[‘-‘].影响有机... 相似文献
110.
Fa-Liang Zhang Yong-Chun Luo Jiang-Ping Chen Ru-Xu Yan Jian-Hong Chen 《Journal of Alloys and Compounds》2007,430(1-2):302-307
Hydrogen strorage alloys with formula La1.5Mg0.5Ni7 were prepared by induction melting followed by different annealing treatments (1073, 1123 and 1173 K) for 24 h. The alloy composition, alloy microstructure and electrochemical properties were investigated, respectively. The results showed that the multi-phase structure of as-cast alloy was converted into a double-phase structure (Gd2Co7-type phase and Ce2Ni7-type phase) through annealing treatments. Mg atoms were mainly located in Laves unit of Gd2Co7-type unit cell and Ce2Ni7-type unit cell. The electrochemical capacity of alloy electrodes after annealing treatment could be up to 390 mAh/g. The cyclic stability of alloy electrodes was significantly improved by annealing treatments; After 150 charge/discharge cycles, the capacity retention ratio of alloy annealed at 1173 K was the highest (81.9%). The high rate dischargeability of alloy electrodes was also improved due to annealing treatment. 相似文献