首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
Glass-like sol-gel coatings have been investigated as corrosion protective coatings on stainless steel. Magnesium- and borosilicate coatings with thickness of about 100–700 nm and methyl-modified SiO2 coatings with a thickness of about 2 m were deposited on stainless steel plates by dip-coating. The coatings were densified between 400°C and 500°C in different atmospheres (N2, air) for 1 h. The corrosion protection against gaseous attack was investigated by accelerated corrosion tests, at 800°C in air for 1 h. A corrosion protection factor was calculated from the relation Fe/Fe2O3, determined by XRD on the surface of coated and uncoated samples. Methyl-modified SiO2 coatings showed a protection factor, which was 2 orders of magnitude higher than for the other coatings. Electrochemical investigations were performed on samples submerged in a NaCl solution for 200 h. The corrosion propagation, polarization resistance and impedance vector were measured. For accelerated corrosion tests, polarization intensity curves were determined for high potentials of up to 1 V. Again excellent results were obtained for the methyl-modified SiO2 coatings, which remained passive for 200 h. Results of the salt spray corrosion test, however, showed no corrosion protection by the sol-gel coatings. After 2000 h in the salt spray chamber the steel was corroded and the coatings peeled off. It is concluded that for the further development of these coatings an improved interfacial passivation will be required.  相似文献   

2.
Inorganic–organic hybrid coatings by sol–gel process are very suitable for fighting corrosion. Inorganic sols in hybrid coatings not only increase adhesion by forming chemical bonds between metals and hybrid coatings, but also improve comprehensive performances of polymer in the coatings. Different organic polymers or organic functionalities are introduced into gel network to achieve tailored properties, such as hydrophobic properties, increasing cross-linking density, etc. As for corrosion protection of metals organic components of hybrid coatings are selected to repel water and form dense thick films and reduce coating porosity. The factors, such as the ratio of inorganic and organic components, cure temperature, pigments in hybrid coatings, need to be optimized for attaining hybrid films with the maximum corrosion resistance. Electro-deposition technique offers relatively thick homogeneous defect-free hybrid coatings in comparison to dip or spin coating techniques. Green cerium ions and non-ionizable organic inhibitors are more developed in hybrid coatings nowadays than other corrosion inhibitors. Long-term corrosion resistance techniques of inhibitors are discussed. The inhibitors entrapped in the nanocontainers are doped in hybrid films to prolong release of the inhibitors to damaged zones, which is discussed in detail. Among all the nanocontainers of corrosion inhibitors the prospective techniques which show superior corrosion protection are cyclodextrin/organic inhibitor inclusion complexes and layer by layer assembly of organic corrosion inhibitors in nanocontainers. Super-hydrophobic property of hybrid coatings derives from low surface tension and surface roughness of hybrid coatings, which endues the films with excellent corrosion protection for metals, but the durable property of super-hydrophobic coatings needs to be improved for industrial application. An ideal multiple model of hybrid coatings for superior anti-corrosion of metals proposed is a combination of super-hydrophobic hybrid coatings and underlying hybrid coatings doped with sustained release of corrosion inhibitors on metal substrates.  相似文献   

3.
Electroless Ni-P composite coatings have gained a good deal of popularity and acceptance in recent years as they provide considerable improvement of desirable qualities such as hardness, wear, abrasion resistance, etc. The disagreement among researchers on the corrosion behaviour of these coatings warrants a thorough investigation. Among the various techniques available for the determination of corrosion resistance, electrochemical impedance spectroscopy (EIS) is considered to be superior as it provides not only an assessment of the corrosion resistance of different deposits but also enables the mechanistic pathway by which the deposits become corroded to be determined. The present investigation focuses on the evaluation of the corrosion resistance of electroless Ni-P and Ni-P-Si3N4, Ni-P-CeO2 and Ni-P-TiO2 composite coatings produced using an acidic hypophosphite-reduced electroless nickel bath, using EIS. The study makes evident that the same fundamental reaction is occurring on all the coatings of the present study but over a different effective area in each case. The charge transfer resistance of electroless Ni-P and Ni-P composite deposits are in the range 32,253–90,700 Ω cm2, whereas the capacitances of these coatings are in the range 11–17 μF/cm2. The improved corrosion resistance obtained for electroless Ni-P and Ni-P composite coatings is due to the enrichment of phosphorus on the electrode surface, which enables the preferential hydrolysis of phosphorus over that of nickel. The better corrosion resistance obtained for electroless Ni-P composite coatings can be ascribed to the decrease in the effective metallic area prone to corrosion. Among the three electroless Ni-P composite coatings, the corrosion resistance is in the following order: Ni-P-CeO2=Ni-P-Si3N4>Ni-P-TiO2. Electronic Publication  相似文献   

4.
Smart epoxy coatings modified with different additives were applied on AA2024. The following three different systems were studied: a reference consisting of an epoxy coating containing chromate active pigments and two “smart” coatings modified with containers loaded with corrosion inhibitor—layered double hydroxides filled with mercaptobenzothiazole and tubular halloysites (HS) filled with 8-hydroxyquinoline. The thickness of the coatings was determined by scanning electron microscopy. The barrier properties and the average corrosion resistance were assessed by electrochemical impedance spectroscopy (EIS). The long-term corrosion repair ability of the various coatings was confirmed by EIS measurements carried for a period of 3 weeks in scratched samples. The ability of the smart additives to inhibit corrosion over defects with different sizes and geometry was studied at the microscale by using localized impedance spectroscopy (LEIS) and the scanning vibrating electrode technique. The results demonstrate that the additives provide effective corrosion inhibition on defects of various sizes. Moreover, the LEIS measurements give some important highlights concerning the mechanisms and kinetics of inhibition of each system.  相似文献   

5.
The corrosion behavior of electrodeposited nanocrystalline (NC) zinc coatings with an average grain size of 43 nm was investigated in 3.5% NaCl solutions in comparison with conventional polycrystalline (PC) zinc coatings by using electrochemical measurement and surface analysis techniques. Both polarization curve and electrochemical impedance spectroscopy (EIS) results indicate that NC and PC coatings are in active state at the corrosion potentials, and NC coatings have much higher corrosion resistance than PC ones. The corrosion products on both coating surfaces are mainly composed of ZnO and Zn5(OH)8Cl2·H2O, but the corrosion products can form a relatively more protective layer on NC coating surfaces than on PC coatings. The EIS characteristics and corrosion processes of PC and NC zinc coatings during 330 h of immersion were discussed in detail.  相似文献   

6.
Composite electrochemical coatings based on nickel, zinc, and chromium were studied. The dispersed phase of these coatings is constituted by graphite, diamond, and polytetrafluoroethylene produced from wastes formed in manufacture of fluoroplastic and ultradispersed diamond produced from industrial waste. The conditions in which high-quality coatings with best characteristics, such as microhardness and corrosion resistance, were determined. The wear resistance was additionally found for the chromium-diamond coating.  相似文献   

7.
Possibility of depositing zinc-fluoroplastic composite electrochemical coatings from ammonium chloride electrolytes, with the role of a dispersed phase played by liquid wastes from production of fluoropolymers and secondary suspensions of F-4D and F-4MD fluoroplastics, was studied. The optimal deposition parameters of composite coatings were determined. The effect of liquid wastes on the buildup of internal stresses in coatings and on the corrosion resistance of zinc-fluoroplastic composite electrochemical coatings was examined.  相似文献   

8.
Organically modified silicate (Ormosil) coatings have been synthesized through the sol–gel method for corrosion protection of aluminum alloy. Silica-based unmodified coatings were also designed to investigate the effect of tetraethoxysilane (TEOS) content on the properties of the coatings. The surface morphology of the coatings was characterized by scanning electron microscopy. The corrosion resistance was evaluated by immersion test, electrochemical impedance spectroscopy and potentiodynamic polarization measurements. In addition, the surface potential differences of the coated samples were determined by scanning Kelvin probe. The results showed that a better corrosion resistance of unmodified coating was prepared by controlling the TEOS/EtOH/H2O molar ratio of 0.109/1/1.52. Ormosil coatings provided excellent barrier properties and corrosion resistance in comparison with the unmodified sol–gel coatings. The Ormosil coating modified with triethoxyoctylsilane exhibited corrosion resistance properties superior to the other Ormosil coatings after exposure to 3.5 wt% NaCl solution for 10 days.  相似文献   

9.
The Zn-Ni+Ni coatings were deposited under galvanostatic conditions at the current density range from 20 to 60 mA cm?2. The influence of deposition current density on surface morphology, chemical and phase composition and corrosion resistance of obtained coatings, was investigated. Structural investigations were conducted by X-ray diffraction method. Surface morphology and surface chemical composition of the obtained coatings were determined by a scanning electron microscope. Studies of electrochemical corrosion resistance were carried out in the 5% NaCl solution, using potentiodynamic and Scanning Kelvin Probe (SKP) methods. A possibility of incorporation of nickel powder from a suspension bath to the Zn-Ni matrix, during galvanostatic deposition was demonstrated. The results of chemical composition analysis show that the Zn-Ni + Ni coatings contain approximately 15?C18% at Ni. It was found that surface morphology, surface chemical and phase composition of Zn-Ni + Ni coatings depend in small degree on deposition current density. However, the current density influences distribution of nickel powder on the surface of these coatings. The optimal values of current density on account of corrosion resistance, are found to be j = 40?C50 mA cm?2.  相似文献   

10.
AISI 304 Stainless Steel is widely used in different industrial fields because of its mechanical and corrosion properties. However, its tendency to corrosion in presence of halide ions limits the applications. One strategy to improve the corrosion resistance is the use of coatings barriers containing corrosion inhibitors in their formulation. The lanthanides present attractive green and corrosion properties for the substitution of chromates, which are the most common substances used as corrosion protection. However, these compounds are highly toxic, and an intense effort is being undertaken to replace them. Cerium is a good alternative because of its relatively low cost and abundance. It fulfils the basics requirements for being considered an alternative inhibitor: the ions form insoluble hydroxides and they present low toxicity. Inorganic and hybrid sol-gel coatings have been developed to increase the corrosion resistance of metals and they provide an excellent vehicle for the incorporation of secondary phases including particles and metal ions as cerium ions. The aim of this work was to study the influence of the incorporation of cerium ions in hybrid silica sol-gel coatings deposited on AISI 304 stainless steel as substrate as a potential replacement of chromate treatments. This system should combine the barrier protection effect of silica coating with the corrosion inhibitor effect of the cerium ions inside the coatings. After 7 days of immersion in NaCl, coated substrates showed lower current densities than the bare steel, although the coatings produced from Ce (III) salts experience a slight weakening in time and those obtained from Ce (IV) chemicals evidence an enhance in the coating performance, probably due to the plugging of corrosion products in the defective areas of the film.  相似文献   

11.
A chrome‐free conversion coating treatment for magnesium by phytic acid solution was developed. The immersion experiments were used for evaluating the effects of the processing parameters (such as conversion temperature and time, concentration and pH value of phytic acid solution) on the corrosion resistance of the phytic acid conversion coating. The morphologies and compositions of the coatings were determined by SEM and EDS respectively. The experimental results indicated that the corrosion resistance of the conversion coating formed in the solution containing 0.5% phytic acid at 25°C and pH=4 for 30 min was higher than that of natural oxide, and the conversion coating formed on the surface of magnesium was of multilayer mainly consisting of Mg, C, O and P. The thicknesses of the conversion coatings were approximately 1.0–15 µm and the conversion coatings presented obvious network‐like cracks. The electrochemical potentiodynamic polarization experiment indicated that the free corrosion potential of the magnesium with phytic acid conversion coating was increased, and its corrosion current and corrosion rate declined in 3.5% NaCl solution. Phytic acid conversion coating could improve the electrochemical property of magnesium and provide effective protection, which can improve the corrosion resistance of magnesium.  相似文献   

12.
用热分析仪研究非晶态材料的晶化动力学有两大类方法:等温法和变温法.变温法测定动力学参数的优点是简便,需要的样品量少,能在反应开始到结束的整个温度范围内连续计算动力学参数.晶化反应是一种相变反应.反应前后没有重量的变化,因此,只能采用差热分析法D’fA或差示扫  相似文献   

13.
《印度化学会志》2023,100(4):100966
In the present study, tribological and corrosion behaviour of electroless Ni–B–W (ENB-W) coatings prepared from stabilizer-free baths and deposited on AISI 1040 steel substrates were examined. Three distinct coating bath temperatures (85 °C, 90 °C, and 95 °C) were varied for coating deposition. The coatings showed nodular morphology. Thermogravimetric study of ENB-W coatings revealed improved thermal stability attained at 95 °C bath temperature. The microhardness of ENB-W coating was 645, 690, and 720 HV100 at bath temperatures of 85 °C, 90 °C, and 95 °C respectively. The inclusion of W to Ni–B coating enhanced the hardness by ∼150 HV100. On a pin-on-disc tribometer, wear test was conducted. The precipitation of Ni (111) and its borides occurred post sliding wear at high temperatures (300 °C). Ni (111) crystallite size decreased because of high temperature sliding wear at 300 °C with an increase in coating bath temperature. With a reduction in crystallite size at high temperatures, both wear rate and COF decreases. The scratch hardness and first critical load of failure of the coatings was determined using a scratch tester. Using potentiodynamic polarization, corrosion resistance of ENB-W coatings in 3.5% NaCl was investigated. ENB-W coatings could provide shielding to AISI 1040 steel from corrosion. Though the corrosion resistance is poor with respect to lead stabilized coatings.  相似文献   

14.
Sol-Gel-Derived Hybrid Coatings for Corrosion Protection   总被引:5,自引:0,他引:5  
The corrosion resistance of sol-gel-derived, organic-inorganic, silica-based hybrid coatings was studied. Hybrid sols were prepared by copolymerizing tetraethylorthosilicate (TEOS) and 3-methacryloxypropyltrimethoxysilane (MPS) with a two-step acid-catalyst process. Hybrid coatings were dip-coated on 304 and 316 stainless steel substrates and annealed at 300°C for 30 minutes. The adhesion, flexibility, and biocompatibility of the coatings were examined. Hybrid coatings were found to be relatively dense, uniform and defect free. Electrochemical analyses showed that the coatings provided excellent corrosion protection by forming a physical barrier, which effectively separated the anode from the cathode. In addition, further experimental results revealed that the corrosion patterns are strongly dependent on the nature of the stainless steel substrates. Some possible mechanisms for corrosion breakdown associated with each type of substrate are also introduced.  相似文献   

15.
16.
在高强钢表面制备了防护性溶胶凝胶涂层,并研究了不同浓度二氧化硅纳米粒子的加入对于涂层形貌、耐蚀性和硬度的影响。采用扫描电子显微镜(SEM)和电子能谱(EDS)观察了涂层的微观结构和成分;采用显微硬度计测试了涂层的硬度;采用电化学方法研究了二氧化硅纳米粒子的浓度对于涂层耐蚀性能的影响;采用傅里叶红外光谱研究涂层的化学结构,进而探讨了二氧化硅纳米粒子对于涂层的强化机理。结果显示涂层加入二氧化硅纳米粒子的最佳浓度为500 mg.L-1,此条件下的涂层表面均匀致密,有较高的硬度并且在3.5%NaCl溶液中体现出较好的耐蚀作用。纳米粒子在溶胶中反应形成活性羟基基团并与硅烷发生反应生成空间网状结构,从而强化涂层。  相似文献   

17.
The filiform corrosion is a special-type atmospheric corrosion, which broadens below the organic coatings and is characterized by its manifestation in the form of fibres or filaments. An important factor for broadening the filiform corrosion involves also the barrier or chemical resistance of the organic coating. The paper deals with the modes of filiform-corrosion initiation and evaluation thereof under nonpigmented organic coatings based on various binder bases. Also the possibility of retardation of the filiform corrosion by means of zinc powder and the effects of lamellar pigment on the filament shapes are studied.  相似文献   

18.
A two-step procedure for synthesizing a new type of hybrid coating is presented. Coatings were synthesized from tetraethyl orthosilicate, 3-(trimethoxysilyl)propyl methacrylate and zirconium(IV) propoxide (ZTP). Zirconium(IV) propoxide was chelated with methacrylic acid. The synthesis, which proceeded at room temperature, was optimized using in situ Fourier transform infrared spectroscopy (FTIR). The effects of ZTP content, ageing and Zr/Si ratio were investigated. The viscosity of the sols increased with the ratio of Zr to Si. The terminal stability of the hybrid coatings was determined by thermogravimetric analysis and their composition and morphology analyzed by FTIR and scanning electron microscopy combined with energy dispersive X-ray spectroscopy. Sols were deposited on the aluminium AA7075-T6 substrate by spin-coating. The corrosion properties in dilute Harrison’s solution of samples coated by hybrid coatings were determined by electrochemical polarization methods. The coatings substantially improved the corrosion resistance of the substrate, as shown by a broad range of passivity extending up to high electrode potentials. The degree of protection was dependent on the content of zirconium and the time of ageing. The strong corrosion protection was ascribed to the bonding between silicon, oxygen and zirconium (Si–O–Si, Si–O–Zr), as proved by the FTIR analysis.  相似文献   

19.
Two types of electroless Ni–W–P coatings: nanocrystalline with low P and amorphous with higher P content are investigated. Scanning probe microscopy is applied to study their morphology. Textured nanocrystalline coatings consist of coarse pyramids built of nanometer thick lamellas. The surface morphology of amorphous coatings is much finer and uniform. Nanohardness of all coatings depends on W content. Microhardness is increasing during the heat treatment up to 350 °C due to nickel phosphide precipitation affected by tungsten also. The wear resistance of nanocrystalline Ni–W–P coatings is much higher than that of amorphous in spite of the similar tungsten content in both. Lower corrosion resistance of amorphous Ni–W–P coatings is found by weight loss method during long-term immersion in 5 % NaCl. Electrochemical tests by potentiodynamic polarization curves in two model corrosion media—solutions of 0.5 M H2SO4 and 5 % NaCl—are performed. The corrosion of bi-layered Ni–W–P/Ni–P and Ni–W–P/Ni–Cu–P deposits on mild steel is also investigated. The results prove that an electroless Ni–W–P coating on mild steel extremely improves its mechanical and corrosion behavior. It is demonstrated that in addition to deposit’s structure and composition, the distribution and chemical state of alloy ingredients are also responsible for its properties.  相似文献   

20.
电沉积非晶态铁—铬合金镀层的研究   总被引:7,自引:0,他引:7  
成旦红  徐伟一 《电化学》1997,3(2):202-205
本实验通过控制镀液组成和操作条件获得了非晶态铁-铬合金镀层,实验分析了PH值,电流密度以及镀层中铬含量对所形成镀层的非晶态结构的影响,阳极极化曲线测量结果表明,与晶态层相比,非晶态度层具有较高的耐蚀性。  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号