The lifetime assessment of low infrared emissivity composite coatings in chloride environments

The microstructural-electrochemical model is employed to predict the lifetime of low infrared emissivity composite coatings in chloride environments. Electrochemical data collected in 3.5 wt.% NaCl solution is presented for the low infrared emissivity coating, and these values are used as inputs for a mechanistic-based corrosion model which yields the salt spray life of the coating. To check the calculated results, the model predictions were compared with the results of salt spray tests. The current work showed that the model was able to predict lifetime of low infrared emissivity coating under salt spray, but tended to under-predict lifetime at short times and over-predict at long times. Under-prediction may be associated with corrosion protection of metallic pigment particles by polymer. Over-prediction by the model at longer exposure times may be associated with the fact that an influence of porosity is not included as a part of this simple model.     

Corrosion resistance and infrared emissivity properties of EPDM (EPDM-g-MAH) film on low infrared emissivity PU/Cu coating

In order to improve the corrosion resistance of low infrared emissivity polyurethane (PU)/Cu coating, ethylene-propylene-diene monomer (EPDM) and maleic anhydride grafted EPDM (EPDM-g-MAH) were deposited on PU/Cu coating by spin coating, respectively. The ability of EPDM and EPDM-g-MAH to serve as corrosion protective films for PU/Cu coating was examined by evolved emissivity immersion test and potentiodynamic polarization measurements in 3.5% NaCl solution. And the chemical composition and surface morphology of PU/Cu coating before and after corrosion were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that all of the coated samples present a better corrosion resistance than bare PU/Cu coating due to indissolubility of Cu by aggressive ions, and the effect of EPDM-g-MAH is better than that of EPDM.     

Ca-Mn co-doping LaCrO3 coating with high emissivity and good mechanical property for enhancing high-temperature radiant heat dissipation

Two techniques, including spray drying and electrostatic spray, were applied to produce feedstocks for preparing Ca-Mn co-doping LaCrO₃ ceramic coatings with two different structures on Ni-based alloy by the atmospheric plasma spraying method. The results show that coating from feedstocks produced by spray drying exhibits lower roughness and porosity than the coating from feedstocks produced by electrostatic spray due to the full melting of smaller feedstocks. Higher proportion of melting zones is beneficial to enhance the ratio of hardness to modulus to improve wear resistance. The emissivity of the coatings with roughness from 0.65 µm to 4.6 µm is all above 0.9 in the waveband of 1–14 µm at room temperature. What’s more, structure-dependent emissivity is affected by surface roughness and pore size due to the infrared scattering. The temperature-dependent thermal infrared emissivity at 1–14 µm decreases with the increasing temperature, and is still above 0.67 at 1200 °C.     

海洋环境下GH907合金耐高温防腐蚀涂层技术研究

研究了一种在海洋环境下使用的新型低温固化耐高温防腐蚀涂料及其制备方法,确定了涂覆工艺,并对涂层进行了附着力、热震、盐雾、湿热及耐高温氧化等性能的测试。结果表明,制备出的涂层抗高温氧化性能高,耐盐雾腐蚀时间长,结合力优良,达到了在海洋环境下的防盐雾、防湿热、防霉菌及耐650℃高温氧化的要求。研究成果已应用于生产,产品质量稳定。     

不同颜色色浆对氟树脂/铝低红外发射率涂层的影响

研究了大红、深黄、水紫、黑色4种颜色色浆对氟树脂/铝低红外发射率涂层光泽、附着力、硬度、粗糙度、耐冲击性、色差、红外发射率、耐腐蚀性等性能的影响。研究结果显示:深黄色色浆涂层的发射率最低,约为0.1;不同色浆对氟树脂涂层色差明度影响不同,相对于其他色浆,水紫能够使涂层偏暗;大红、深黄、水紫色浆的涂层硬度均为6H;加深黄色浆的涂层附着力最好,其次是大红色浆和水紫色浆;深黄色浆对涂层的耐冲击性影响最大,其次是大红色浆和水紫色浆;相对于大红、深黄、黑色色浆,水紫色浆涂层具有最低的粗糙度,表面比较光滑;水紫色浆和深黄色浆的红外波峰比较持平,有利于减小表面发射率;水紫色浆氟树脂涂层的耐腐蚀性能最好。耐盐水腐蚀测试后4种涂层均没有明显失光,水紫涂层没有发生明显变色,深黄和黑色涂层起泡密度较低。水紫色浆因其粒径均匀细小,在氟树脂涂料中易分散,与氟树脂相容性好,因此具有相对较优的综合性能。     

Influence of silane coupling agent on corrosion-resistant property in low infrared emissivity Cu/polyurethane coating

Surface of copper (Cu) powder was chemically modified using silane coupling agent (KH550) in order to improve the interfacial interaction between Cu and polyurethane (PU) polymer, and therefore, expectable corrosion resistance of the Cu/PU coating with low infrared emissivity was acquired. Infrared spectra reveal an obvious interaction between Cu and PU induced by the addition of KH550. The corrosion behavior of Cu/PU coating has been investigated with potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Results have shown that the proper amount of KH550 is benefit to the dispersion of Cu and induces the strong chemical interfacial interaction, which often keeps the low infrared emissivity and increases the corrosion resistance of the Cu/PU coating.     

Preparation and characterization of a new low infrared-emissivity coating based on modified aluminum

A low infrared-emissivity coating was prepared using modified Al powder and polyurethane as metallic pigment and adhesive. Al powder was coated with polyethylene wax by the flux-capping method to reduce the emissivity and gloss of the coating. The surface morphology and chemical composition of pure and modified Al powders were characterized by scanning electron microscopy and X-ray diffraction. The infrared emissivity of the product was measured by an infrared emissometer. The influences of the modified Al powder content, substrate material, coating thickness, and aging time on infrared emissivity were systematically investigated. The results indicate that modified Al powder decreases not only the gloss of the coating, but also its emissivity within the wavelength range of 8–14 μm. The polyethylene wax/Al composites have a homogenous sheet structure at 30 wt.% Al content, and a lower infrared emissivity. The optimum content of modified Al powder is around 18 wt.%. The coating exhibits a lower emissivity value and excellent optical properties. The infrared emissivity of the composite coating significantly increases with increased thickness, and approaches a constant value when the thickness is more than 80 μm. Accelerated aging test results show that with increased aging time, the coating with modified Al powder has a better aging resistance and lower infrared emissivity than that with pure Al powder.     

铜基表面陶瓷涂层的制备与耐蚀性能研究

以Al2O3、TiO2和ZnO为骨料,钠水玻璃为粘接剂,在纯铜表面用热化学反应法制备了陶瓷涂层。X射线分析发现,陶瓷涂层热固化后,涂层内产生了NiAl2O4、Al2SiO5等新相,它提高了涂层与基体的结合强度。腐蚀实验表明,封孔后陶瓷涂层的耐酸、耐碱、耐盐等性能分别比纯铜基体提高了3.9、12.3和6.3倍;极化曲线表明,陶瓷涂层有明显的钝化区,其抗电化学腐蚀能力增强,抗盐雾腐蚀性比基体提高了5.0倍。     

无氰酸性镀镉在航空航天零部件上的应用

介绍了一种用于航空航天零部件的高耐腐蚀性镀镉层结构,包括金属基体、预镀层、中间镀层、镀镉层以及钝化层,其中所述金属基体为钢铁基体和铝合金基体。对镀层结构进行中性盐雾试验2064 h其表面无白色腐蚀物生成,耐盐雾性能比航天工业部标准QJ 453-1988《镀镉层技术条件》中96 h中性盐雾试验的要求高21倍。这种保护层在耐腐蚀性上取得了重大突破,能大幅度提高航空航天零部件的使用寿命。     

Zn-5%Al-RE镀层耐蚀性能的研究

试验了在高碳钢丝表面上热浸镀Zn-5%Al-RE合金层。通过湿热试验、晶间腐蚀试验、盐雾腐蚀试验，研究了该合金镀层的耐蚀性能，并与镀锌钢丝的耐蚀性能进行了对比。在水蒸汽的晶间腐蚀试验表明，合金镀层还略逊于锌镀层，但是在采用模拟海水的湿热试验以及盐雾腐蚀试验中，合金热浸镀层的耐蚀性能明显优于普通锌镀层，阳极极化曲线表明，合金层的致钝电流密度小，致钝电位较低，且稳定钝化区较宽，这可能是合金热浸镀层在海水中具有较好耐蚀性能的主要原因。     

Epoxy powder coatings containing polyaniline for enhanced corrosion protection

Incorporation of polyaniline (PANI) in epoxy type powder coating formulations has not been attempted earlier. Using specific grade of PANI with low doping, it can be incorporated in epoxy powder coating formulations by twin screw extrusion process. The powder formulations were deposited on steel substrates by electrostatic spray coating at −60 kV and baked at 140 °C for 20 min. These were extensively tested for corrosion resistance by exposure to hot saline conditions followed by electrochemical impedance spectroscopy and also salt spray testing. PANI incorporated coatings showed no deterioration even after 1400 h of hot (65 °C) saline treatment. The coatings intentionally scratched also exhibited self healing property and there was no rust formation even after prolonged exposure to hot saline conditions. These results could be explained on the basis of additional crosslinking due to PANI, as confirmed by DSC results, which gave rise to improved barrier property and self healing was associated with the scavenging of ions by PANI which prevented corrosion of the underlying substrate.     

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.     

Effects of size, shape and floatage of Cu particles on the low infrared emissivity coatings

Low infrared emissivity coating was prepared by the copper (Cu) particles and ethylene–propylene–diene monomer (EPDM) binder. The effect of size, shape and floatage of Cu particles on infrared emissivity of the coatings was systematically investigated. The results indicated that the optimized Cu particles with the minimum coating emissivity are several micron-sized, flaky and high-leafing, exhibiting 0.78, 0.72 and 0.10 emissivity value, respectively. The formation of low infrared emissivity coatings depends strongly on the floatage of Cu particles, not the size or shape, and the results obtained by leafing aluminum (Al) and bismuth oxide (Bi₂O₃) pigment are in good agreement with this standpoint. A theoretical model was proposed to account for the mechanism, which indicated that the low porosity of the coatings with leafing pigments plays an important role in the formation of low emissivity coatings.     

十八胺改性纳米SiO2制备及在水性环氧防腐涂料中的应用

摘要：以正硅酸四乙酯（TEOS）、十六烷基三甲基溴化铵（CTAB）、γ-(2，3-环氧丙氧基)丙基三甲氧基硅烷（KH560）为原料，采用溶胶-凝胶法制备表面环氧基化的纳米SiO2，通过十八胺（ODA）的伯胺端基与纳米SiO2表面的环氧基进行反应得到ODA-SiO2，用于制备水性环氧防腐涂料。通过傅里叶变换红外光谱（FTIR）、热重测试（TG）、X射线光电子能谱仪（XPS）、扫描电镜（SEM）表征ODA成功接枝到SiO2表面；通过电化学测试、耐盐雾性能测试对水性环氧涂层的防腐性能进行了分析。结果表明，含0.3wt%ODA-SiO2的水性环氧涂层具有较好的防腐蚀性能，耐盐雾时间500h。     

钝化工艺对无氰镉-钛合金镀层性能的影响

为了获得无氰镀镉-钛合金的最佳后处理工艺,利用金相显微镜、电化学工作站和盐雾试验测试了三种钝化膜的外观及耐蚀性,并进行了比较。实验结果显示,三种钝化工艺获取的钝化膜经96 h中性盐雾试验后,均未出现白锈;电化学测试结果显示低铬钝化工艺获取的钝化膜自腐蚀电流密度最大,重铬酸钠钝化工艺获取的钝化膜自腐蚀电流密度最小。从环保和耐蚀性方面考虑,建议选用重铬酸钠+硝酸钝化工艺作为无氰镉-钛合金镀层的后处理工艺。     

不同腐蚀试验的电化学阻抗谱评价

采用电化学阻抗谱分析了环氧涂层的介质浸泡、ASTM-B117盐雾试验、PROHESION循环试验的性能变化。实验结果表明:介质浸泡更侧重考察涂层的屏蔽作用,对环氧-聚酰胺体系酸性电解质更容易导致涂层失效;而盐雾试验更容易导致涂层吸收水分,干湿交替增加了有机涂层吸水能力;划痕试验表明样板在ASTM-B117和PRO-HESION遵循不同的腐蚀机理。     

镀银层在氯化钠和硫化钠溶液中的耐蚀性研究

通过盐雾腐蚀试验、电化学腐蚀试验和硫化钠腐蚀试验,考察了镀银层在氯化钠和硫化钠溶液中的耐蚀性。结果表明:镀银层盐雾腐蚀前后的微观形貌没有明显的差别,而紫铜盐雾腐蚀前后的微观形貌发生了很大的变化;镀银层的自腐蚀电位为-0.205 V,较紫铜的自腐蚀电位正移了约18 mV;镀银层的自腐蚀电流密度为1.42×10^-7 A/cm²,较紫铜的自腐蚀电流密度降低了一个数量级;镀银层在硫化钠溶液中也具有良好的抗腐蚀能力。     

The effect of zirconia ions on corrosion performance of sol–gel coated galvanized steel

Currently, galvanized steel is treated with hexavalent chrome passivation. Sol–gel coating has been found to be a potential replacement for the hazardous hexavalent chrome passivation treatment. The aim of this work is to study the effect of zirconyl nitrate on corrosion behavior of sol–gel coating. Aminopropyl-trimethoxysilane and 3-glycidoxypropyltrimethoxysilane were employed as precursors to prepare the sol–gel-based silane coating. The sol–gel film was deposited on galvanized steel sheet by dip coating method. The chemical properties of sol–gel solution and coated films were analyzed by infrared spectroscopy. Morphology of the film was characterized by scanning electron microscope. The corrosion resistance of the coated samples was evaluated by electrochemical impedance spectroscopy, potentiodynamic polarization curve, and salt spray test. The results indicated that zirconia-doped coatings have better corrosion resistance in comparison with their undoped counterparts. The coating doped with 0.5% zirconyl nitrate provides better corrosion protection due to the inhibitive action of zirconia ion.     

High-density polyethylene coating on carbon steel by an electrostatic powder spray system

Plain carbon steel specimens were surface-treated mechanically and then chemically before applying high-density polyethylene (HDPE) coating. Pretreated specimens were coated with HDPE powder, both with and without a heat stabilizer (Irganox 1010), using a spray electrostatic technique. Effects of various variables, such as surface roughness, prephosphating treatment, addition of stabilizer, and the role of curing time and temperature were investigated. Mechanical and immersion tests were conducted to measure adhesion, ductility, and corrosion resistance of the coated specimens. Scanning electron microscopy and infrared spectroscopy were used to study the microstructure of produced coating and its interface with the substrate, as well as the possible chemical changes that occurred. The results obtained revealed that, pure HDPE can be coated on plain carbon steel with a good performance. It was further observed that an addition of 0.5 wt % of heat stabilizer to HDPE powder increases the performance of produced coating significantly. This was evidenced by the measurements of adhesion, ductility, and corrosion resistance in sulfuric acid, sodium hydroxide, ferric chloride, water, and salt spray, as well as scanning electron microscopic examinations and infrared spectra. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2507–2513, 1998     

三元乙丙橡胶低红外发射率涂层的制备与表征

为制备低红外发射率涂层,优选了三元乙丙橡胶(EPDM)为粘结剂、漂浮性片状铝粉(约15 μm)为填料,用流延自成膜法制备涂层.研究了溶剂种类和填料质量分数对涂层红外发射率的影响,并对涂层的物相和微观形貌进行了表征.研究结果表明:EPDM具有良好的红外透明性;二甲苯为溶剂时,涂层发射率最低为0.686;环己烷为溶剂时,铝粉显示出更好的漂浮性,涂层发射率可低至0.358;涂层在室温环境中具有一定的耐候性.制得的涂层可以用作低红外发射率隐身材料.