Real time mapping of corrosion activity under coatings

Current accelerated testing of aircraft coating systems for corrosion protection relies heavily on salt spray methods. Electrochemical techniques such as electrochemical impedance spectroscopy (EIS) and electrochemical noise methods (ENM) provide insight into the global properties of a coating system, and both techniques are being used on a limited basis. However, there is a need to investigate corrosion events with greater spatial resolution under coatings at the metal/coating interface. Such corrosion activity may be related to coating defects and variations in the surface chemistry of the underlying metal.

The scanning vibrating electrode technique (SVET) has been developed to allow high spatial resolution investigation of localized corrosion activity that may be associated with coating defects or galvanic coupled regions of the metal surface. The SVET offers high resolution in current measurements of the order of 0.5 μA/cm² and is able to detect in-situ initiation and progress of corrosion activity under a protective coating. Using the SVET, minute variations in d.c. current associated with localized corrosion activity are detected and used to map both anodic and cathodic corrosion activities in a localized area. The difference in initial corrosion activity under various coatings can be correlated to the performance life of the coatings. The application of SVET to aircraft coatings and corrosion is reported to demonstrate the utility of this important new electrochemical tool.

In the current study, the SVET was used to discriminate the corrosion protection performance of selected sol–gel based coating systems. Sol–gel based surface treatments are being developed as part of an environmentally compliant coating system alternative to the currently used chromate-based systems. The SVET results are compared with data obtained from chromium inhibition coating systems. The SVET analyses are compared with electrochemical impedance measurements. The comparison of such data will provide the basis to adopt SVET measurements as an early performance discriminator for newly developed coating systems.     

Contribution of acoustic emission technique for monitoring damage of rubber coating on metallic surfaces: Comparison with electrochemical measurements

Chlorobutyl coatings are industrially applied on metallic inner walls of HCl storage tanks, in order to protect steel against corrosion. Rubber coating constitutes an efficient barrier against HCl penetration up to metallic surface; yet, traces of monochlorobenzene (MCB) into HCl solutions can locally damage the coating and induce both acid infiltration and rapid corrosion of steel under the coating. Acoustic emission (AE) technique, due to its non-intrusive feature and its sensitivity, is a potential technique for the detection of polymer coating damage as well as metallic corrosion under the coating. In that context, this technique was coupled and compared to electrochemical measurements at least for metal damage evaluation. AE signals produced by corrosion of bare metal in HCl solution were first characterized, and then AE and electrochemical results obtained during metal and/or coating damage were compared, in the case of physical or chemical deteriorations of the coating, in an HCl solution containing traces of monochlorobenzene. In case of physical coating damaging, AE and polarisation resistance measurements are in good correlation as soon as metallic corrosion starts. When polymer coating suffers a solvent impregnation, previously to HCl solution contact, acoustic activity increases as soon as corrosion under the coating occurs, whereas polarisation resistance measurements do not allow detecting corrosion of steel.     

涂层防腐蚀的电化学研究

综述了国内外现行的涂层防腐蚀性能研究的电化学方法,说明了电化学方法评价涂层性能的一般规律和特点,指出电化学方法评价涂层性能具有快速、准确、方便的优点。     

High performance reaction-induced quasi-ceramic silicone conversion coating for corrosion protection of aluminium alloys

Regulations posed by the Environmental Protection Agency on the use of chromate conversion coatings have triggered the need to find alternative materials for the corrosion protection of aluminium and its alloys. A simple four-step process of creating a quasi-ceramic coating has been developed. The coating, which is made of environmentally safe chemicals, should be easily and safely manufactured for bulk production. Here, we describe the synthesis, characterization and evaluation of a silicone conversion coating for aluminium metal and its alloys. The spectroscopic techniques utilised in this study have shown the mode of the bonding mechanism between the metal and the coating. Thermal analysis of the material was conducted to evaluate its stability, while nano-mechanical properties were determined and correlated with the surface morphology of the coating. Results obtained from FTIR and XPS spectroscopic techniques suggested that the coating adhered to the metal substrates through active surface functionalities, and thermal analysis showed that the coatings contained volatile solvents including water that evaporated at lower temperatures. Nano-mechanical tests suggested that the coating had elastic properties. Accelerated corrosion and immersion tests were also performed on coated and uncoated aluminium alloys. Coated and uncoated aluminium alloys were also exposed to soil containing sulphate-reducing bacteria. Coated coupons showed excellent corrosion protection and antifouling characteristics indicating that the coatings were impervious and of high integrity.     

稀土元素对机械镀锌层性能的影响

采用机械镀锌工艺,在镀层形成过程中添加某种稀土盐获得机械镀锌层。测定了镀层的电化学腐蚀参数、镀层孔隙率、元素谱线及镀层断面形貌。讨论了稀土含量对镀锌层电化学腐蚀性能、孔隙率的影响。研究结果表明:稀土能显著改善机械镀锌镀层的耐蚀性能和提高镀层的致密性;镀层耐蚀性随稀土添加量增加呈先提高后降低趋势;当稀土加入量为2%时,锌镀层耐蚀性最好,致密性最高。     

基于不同胶凝材料钢筋混凝土耐腐蚀性试验研究

针对混凝土结构中钢筋的锈蚀问题,以普通硅酸盐水泥和镁水泥作为胶凝材料,制作了钢筋裸露和涂有环氧树脂涂层的4种钢筋混凝土试件,将其浸泡在氯盐、硫酸盐及镁盐的耦合溶液中,利用电化学方法得到极化曲线和交流阻抗谱,通过塔菲尔外推法进行非线性最小二乘法拟合计算得到腐蚀电流密度、腐蚀电位、腐蚀速率等相关评价指标来衡量混凝土中钢筋锈蚀情况.结果表明:长期浸泡在耦合盐溶液中,普通硅酸盐水泥和镁水泥钢筋混凝土试件都发生了较严重的腐蚀,普通硅酸盐水泥的抗腐蚀性优于镁水泥;在钢筋表面涂有GHT涂层可极大地降低钢筋的腐蚀速率;镁水泥GHT涂层混凝土试件的抗腐蚀性能劣于硅酸盐GHT涂层混凝土试件但优于硅酸盐裸露钢筋混凝土.     

Development and characterization of silicone/phosphorus modified epoxy materials and their application as anticorrosion and antifouling coatings

Epoxy resin is chosen for our present study owing to its exceptional combination of properties such as easy processing, high safety, excellent solvent and chemical resistance, toughness, low shrinkage on cure, good electrical, mechanical and corrosion resistance with excellent adhesion to many substrates. This versatility in formulation made epoxy resins widely applied for surface coatings, adhesives, laminates, composites, potting, painting materials, encapsulant for semiconductor and insulating material for electric devices. There are numerous paint/coating systems based on epoxy resin available for corrosion and fouling prevention. They however are not completely satisfactory in field applications, where high corrosion, fouling and flame resistance are required. The demand for epoxy resin as corrosion/fouling resistant coatings is restricted mainly due to its inferior characteristics like poor impact strength, high rigidity, and moisture absorbing nature besides inadequate flame retardant properties. It is for this reason that silicones and phosphorus-based compounds are used as modifier in this work by intercrosslinking network mechanism (ICN) to obtain epoxy resin with desired properties ideally suitable for field applications for preventing corrosion and fouling with flame retardantancy. The present work involves the development of solvent free silicone/phosphorus modified epoxy coating systems, since solvent free coating systems are widely used for numerous applications due to their lower cost per unit film thickness, freedom from fire and pollution hazard and ability to provide better performance. For the development of coating systems, epoxy resin (X) serves as base material, hydroxyl terminated polydimethylsiloxane (HTPDMS) as modifier, γ-aminopropyltriethoxysilane (γ-APS) as crosslinking agent and dibutyltindilaurate (DBTDL) as catalyst. Polyamidoamine (A), aromatic amine adducts (B) and phosphorus-containing diamine (C) were used as curing agents. The study also describes the evaluation of corrosion resistant behaviour of unmodified epoxy and siliconized epoxy coatings by potentiodynamic polarization method, electrochemical impedance spectroscopy (EIS), salt-spray and antifouling tests. The results are discussed.     

工程机械产品用涂料与涂层体系的测试和选择

分析了大气腐蚀环境对工程机械表面涂装涂层的腐蚀(老化)作用,提出了定性的评价标准和涂层体系的指标;叙述了工程机械产品用涂料与涂层体系选择中的问题,探讨了检测和评定工程机械涂料和涂层体系的方法。     

片状玻璃对水性复合锌铝合金涂层耐蚀性的影响

为了改善水性锌铝合金涂层的耐蚀性能,在硅烷钝化液中加入玻璃粉制备了玻璃/水性锌铝涂层,采用中性盐雾试验、电化学阻抗谱、极化曲线等方法研究了玻璃粉用量对 Q235 钢表面该涂层耐蚀性能的影响,利用扫描电镜、能谱、X 射线衍射等技术分析了涂层的形貌、组成以及元素分布状况。结果表明,添加片状玻璃粉可以提高涂层的耐蚀性能。玻璃粉与金属粉以平行叠加的方式排列在锌铝合金涂层中,部分玻璃粉包覆在涂层的外围形成致密的网状结构。当玻璃粉的添加量为 20 g/L时,涂层的耐蚀性能最好,耐中性盐雾试验时间为 3 100 h,是不添加玻璃粉涂层的 5 倍。     

Assessment of protective properties of organic coatings by thermal cycling

Researchers’ efforts are focused on understanding how coatings can be tested in order to determine their real capabilities and selected for different purposes. Outdoor exposures are certainly reliable and offer a good representation of the actual service life. However, such tests cannot be considered quick.

On the other hand, a quick test, even if reliable, very often disagrees with the actual degradation mechanisms occurring under natural conditions. In fact, in order to determine an acceleration of the natural weathering, it is necessary to increase the effect of natural parameters affecting the protection properties of a coating.

The usual modern way to operate is to take advantage of ageing tests where temperature plays a big role in the ageing of the material, permitting to gather faster information for coating corrosion resistance evaluation.

Following the recent new experience realised by the Bierwagen group, we carried out different thermal cycling tests consisting in daily series of electrochemical measurements on coated samples, carried out using electrochemical impedance spectroscopy (EIS).

The cumulative effects of such a thermal cycling on the film, based on a large variety of theoretical explanations, should permit the ranking of a variety of materials, by constituents, characteristics and application purposes, in a short time while remaining objective and reliable.

The used ageing procedure and data evaluation allowed to quickly and precisely obtain information concerning both barrier properties and adhesion properties of the studied materials.     

聚苯胺基涂层在质子交换膜燃料电池金属双极板上的应用进展

聚苯胺具有独特的导电性和电化学性能,近年来随着燃料电池的发展成为双极板防护的重要材料。然而,聚苯胺涂层在质子交换膜燃料电池高温强酸的工作环境中长期耐蚀性仍无法满足要求,限制了该材料的规模应用。本文综述了聚苯胺基涂层在质子交换膜燃料电池双极板上应用的最新研究进展,包括通过掺杂和共聚改性的聚苯胺涂层、引入高分子材料和纳米材料制备的聚苯胺基复合涂层;分析了各类典型涂层的电化学测试性能结果,总结了聚苯胺基复合涂层的耐蚀机理。最后总结了聚苯胺基涂层研究中目前存在的问题,并对研究方向进行了展望,指出统一测试标准对材料性能评价和商业应用具有重要意义,且今后应重点加强纳米材料复合涂层的研究,并基于原位观测和表征技术对涂层机理进行深入解析。     

FeSO4对化学镀Ni-P工艺的影响

为了进一步改善化学镀Ni-P镀层的显微硬度和耐蚀性,将FeSO4加入到化学镀Ni-P镀液中.通过金相显微镜测试了FeSO4对Ni-P镀层表面形貌的影响;采用显微硬度计测试了镀层的显微硬度;采用电化学技术测试了FeSO4对镀层耐蚀性能的影响.结果表明:当镀液中FeSO4的质量浓度小于1.0 g/L时,镀层的沉积速率虽然降...     

Evaluating water transport through high solid polyurethane coating using the EIS method

Buried pipelines are commonly coated with high solid polyurethane to prevent corrosion. The diffusion of water through the coating plays an essential role in the performance and endurance of the coating. This study focuses on the evaluation of water diffusion through polyurethane coatings. The effects of thickness and ambient temperature on water diffusion through polyurethane, which is coated on mild steel and immersed in 3.5% (weight fraction) NaCl solution, are evaluated using electrochemical impedance spectroscopy (EIS). Experimental observations clearly indicate that the water diffusion coefficient strongly depends on service temperature and the thickness of coating. Higher temperature (lower than T _g) increases water uptake of the polymer but no measurable changes were observed for the temperature change studied. EIS results show that the mechanism of corrosion does not change in the range of thicknesses and temperature investigated in this study.     

电镀锌钝化处理耐蚀效果的电化学评估

采用线性极化电阻、开路电位及阳极极化曲线等电化学方法,评估了锌镀层经3种不同钝化液处理后在w=1%的NaCl溶液中的耐蚀性。结果表明,3种电化学方法测得的钝化膜耐蚀性与中性盐雾试验的结果相符,能够用于快速有效地评价电镀锌钝化处理的耐腐蚀效果。     

Aktuelle Fragen des Korrosionsschutzes durch Anstrichstoffe

Problems of Interest in the Protection against Corrosion Using Coating Agents Within the scope of this review the protective coating of steel as well as galvanized constructions have been dealt with. Starting with the economical loss due to corrosion, as exemplified by a few cases of damage experienced in the practice, the following topics have been treated: Relationships between the condition of the surface and the quality of coating; cleaning and derusting; methods for application of the coating; (brushing, spraying); influence of environmental conditions; attainable and required thickness of the layer; criteria for evaluation (cost and durability); multi-layer systems; thick-layer coatings; coatings on zinc layers; temporary protection against corrosion (protection of rolled steel); protection against corrosion by desirable coating procedures.     

电流密度对光亮镍-铁合金镀层表面形貌及耐蚀性的影响

通过电沉积方法制备光亮镍-铁舍金镀层,利用扫描电镜测定镀层表面显微形貌(SEM),X射线衍射仪测定合金饺层的相结构(XRD),然后对合金镀层进行浸泡腐蚀实验,观察其腐蚀行为,并测定其庸蚀速率.结果表明:镍-铁合金镀层在质量分数为3.5%的NaCl溶液中的腐蚀速率较在质量分数为5%的H2SO4溶液中的腐蚀速率小,即:在质量分数为3.5%的NaCl溶液中有较好的耐蚀性,最小的腐蚀速率为0.21 mg/(dm2·h),且在电流密度为4～6 A/dm2工艺条件下获得的舍金镀层在两种溶液中都具有较好的耐蚀性能.     

低温多效海水淡化铝合金传热管防腐涂层性能评价

分析了低温多效海水淡化工况下铝合金传热管防腐涂层的使用环境、腐蚀影响因素等,选择了一种专用铝合金传热管的纳米涂层作为研究对象,与同类防腐涂料对比其耐工况腐蚀性能,同时对纳米涂层铝合金传热管进行了换热方面的性能测试及经济性评价。     

热浸镀锌层表面偏钒酸盐转化膜

在热浸镀锌试样表面获得了一层均匀、完整的偏钒酸盐转化膜.成膜溶液成分及工艺条件为:NaVO3 5 g/L,pH 1.3,温度30 ℃,时间30 min.对比研究了偏钒酸盐转化膜和铬酸盐转化膜的耐蚀性能.结果表明,偏钒酸盐转化膜由Zn、O、V等元素组成,热浸镀锌层经偏钒酸盐转化处理后电化学阻抗和极化电阻增大,腐蚀电流密度...     

硅酸钠预处理对镀锌层稀土镧盐转化膜耐蚀性的影响

对热镀锌钢板先进行硅酸钠(水玻璃)预处理再镧盐钝化,以进一步提高镧盐转化膜的耐蚀性.用扫描电镜、能谱仪、盐雾腐蚀试验、塔菲尔极化曲线等方法研究了硅酸钠预处理对热镀锌层镧盐转化膜微观形貌和耐蚀性的影响.结果表明,硅酸钠预处理使得镧盐转化膜成膜均匀,膜层增厚且耐蚀性明显提高.通过正交试验得到最佳工艺为:先在室温下于0.5 ...     

涂层防腐蚀性能电化学快速评价方法

论述了目前评价涂层耐腐蚀性能与失效检测的常用电化学测试方法,指出研究涂层耐腐蚀性能实验室评定方法,是正确评估防腐蚀涂料使用寿命的最佳途径。