Corrosion inhibition of flaky aluminium powders prepared through sol–gel process

In order to prevent corrosion of aluminium pigment in water, coated flaky aluminium powder was prepared through the sol–gel process, in which tetraethoxysilane (TEOS) and tris(2-methoxyethoxy)vinylsilane (VTMOEO) were adopted as precursors. The influences of the dosage of precursors, ethylenediamine, water and ethanol, as well as the reaction temperature and reaction time on the corrosion inhibition efficiency were investigated. Under the optimum conditions, the corrosion inhibition efficiency reached 99.2% in alkaline media of pH 11. The analysis with SEM, FTIR, EDS and XPS showed that sol–gel coatings had successfully encapsulated on the surface of clear flaky aluminium powders.     

Aminomethylenphosphonsäuren als Korrosionsinhibitoren für Aluminiumpigmente in wäßrigen Medien

Aminomethylenephosphonic acids as corrosion inhibitors for aluminum pigments in aqueous media Flakelike aluminum pigments (aluminum content >99.5%) are corroded in aqueous alkaline mixtures of water and butyl glycol. Aminomethylenephosphonic acids inhibit this corrosion reaction. The temporal progress of the corrosion is determined by volumetric analysis of the evolved hydrogen. Direct comparison of aminomethylenephosphonic acids with analogous aminomethylenecarboxylic acids shows that the phosphonic acid group inhibits the corrosion significantly better than the carboxylic group. The actual corrosion inhibitors are in both cases (soluble) aluminum(III)-chelates, which are formed by a chemical reaction of the aminomethylenphosphonic resp.-carboxylic acids with the aluminum surface. This is proved by measuring the concentration of dissolved aluminum(III) in the corrosion medium with the help of atomic absorption spectroscopy and by using aluminum(III)chelates as corrosion inhibitors.     

Corrosion protection of aluminum pigments by sol-gel coatings

New sol-gel coatings for the corrosion protection of aluminum pigments were developed. To this end, the pigment particles are first coated with a silica layer by phosphoric acid-catalyzed sol-gel processing of Si(OEt)₄, to which either hexadecyltrimethoxysilane or dimethyldimethoxysilane is condensed. The coated pigments have excellent anticorrosive properties in alkaline solutions as well as under boiling water conditions.     

溶胶-凝胶制备的Al_2O_3-SiO_2复合陶瓷涂层抗原子氧侵蚀性能研究

采用溶胶-凝胶法,以异丙醇铝、正硅酸乙酯为原料制得了稳定、均一的溶胶,浸涂在聚酰亚胺表面干燥后获得了致密透明的涂层.采用空间综合环境地面模拟设备对试样进行了原子氧(Atomic Oxygen, AO)暴露实验.测试表明,溶胶-凝胶制备的Al_2O_3-SiO_2涂层抗原子氧侵蚀性能优异,抗原子氧侵蚀性能比聚酰亚胺基体提高了2个数量级以上.经原子氧暴露后的复合陶瓷涂层质量几乎没有发生变化.经FTIR和XPS分析表明,在原子氧暴露后涂层表面产生的是Al_2O_3-SiO_2复合物.SEM分析表明,无涂层的聚酰亚胺原子氧暴露后表面非常粗糙且表面呈现地毯状形貌,而涂覆涂层的试样暴露前后表面形貌没有发生变化.采用紫外-可见光-近红外分光光度计对涂覆溶胶-凝胶复合陶瓷涂层后的试样分析表明原子氧暴露前后试样表面的光学性能也未发生变化.     

Electrochemical characterization and CFD simulation of flow-assisted corrosion of aluminum alloy in ethylene glycol-water solution

An impingement jet system was used to study flow-assisted corrosion (FAC) of 3003 aluminum (Al) alloy in ethylene glycol-water solutions that simulates the automotive coolant by corrosion potential and electrochemical impedance spectroscopy (EIS) measurements as well as computational fluid dynamics (CFD) simulation. The effects of solution pH and fluid impact angle on Al FAC were determined. An increase of solution pH enhances the activity of Al due to dissolution of Al oxide film in alkaline environment. Moreover, Al activity decreases with the increasing fluid impact angle to the specimen. A CFD simulation shows that, with the increase of impact angle, the electrode area under high-velocity flow field decreases and that under low-velocity flow field increases. Consequently, the shear stress generated on electrode surface and the resultant mechanical effect on electrode activity decreases. Therefore, the electrode is more stable than that impacted at a smaller impact angle. There is an essential role of fluid hydrodynamics in corrosion of Al electrode, which is confirmed by corrosion potential and EIS measurements as well as CFD analysis.     

Investigation of corrosion behavior of aluminum flakes coated by polymeric nanolayer: Effect of polymer type

Protection of aluminum pigments from corrosion phenomenon has been extended by an encapsulating polystyrene (PS) and poly(acrylic acid) (PAA) nanolayers. Flakes were first coupled with 3-methacryloxypropyltrimethoxysilane (MPS) and in situ polymerizations of styrene and acrylic acid, initiating with Azobisisobutyronitrile (AIBN) were performed. The encapsulated flakes were characterized by Fourier transform infrared (FTIR), energy-dispersive X-ray spectroscopy (EDX), and transmission electron microscope (TEM). Also, polymer chains were analyzed by gel permeation chromatography (GPC). Subsequently the chemical stability of the pigments in alkaline and acidic aqueous media was examined. Results indicated that polystyrene coating remarkably improved flakes’ anticorrosion property while PAA evolved hydrogen.     

An evaluation of Acacia mearnsii tannin as an aluminum corrosion inhibitor in acid,alkaline, and neutral media

The electrochemical behavior of aluminum in tannin from Acacia mearnsii bark was evaluated by potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) in media under three different pH conditions: acid, alkaline, and neutral. A relationship among pH, polymerization grade (PG), zeta potential, surface, and electrochemical properties was observed in the inhibition performance of the tannin. At high pH, the oligomer structure of the tannin was affected, resulting in a low PG (4) and high zeta potential (−75 mV), and consequently, the inhibition efficiency decreased (68%) in comparison with that in acid (99%) and neutral media (96%). The values obtained indicate a physisorption mechanism for the aluminum corrosion inhibition in the studied conditions.     

硅烷偶联剂改性的纳米二氧化硅包覆铝颜料的制备及其耐碱性能

在醇/水体系中,采用溶胶/凝胶法制备了硅烷偶联剂改性的纳米二氧化硅包覆的铝颜料,并采用SEM、FTIR等分析方法对包覆效果进行表征,检测了包覆产物的耐碱性,并对过程机理进行了分析。结果表明,硅烷偶联剂改性的二氧化硅可以在铝颜料表面形成一层包覆层,且硅烷偶联剂的含量越高,包覆层中颗粒物的含量越少,而有机膜的含量越高。硅烷偶联剂改性二氧化硅包覆铝颜料在pH值为11的碱性水溶液中,经720 h后,析出的氢气量为未包覆产品的2.7%,表明用此方法制备的铝颜料具有良好的耐碱性。硅烷偶联剂和二氧化硅并不是简单的混合,而是彼此缩合形成了均一的杂化材料。     

紫外辐射对2024铝合金表面钛盐转化膜形成的影响

采用由硫酸氧钛、氟化钠为主盐的转化液,在60℃,pH 5～5.5及紫外光照射条件下处理5min,在2024铝合金表面制备了一种钛盐转化膜,中性盐雾时间超过96h。EDS和XPS分析结果表明,转化膜主要由O,Ti,Al,F,Mg及Cu等元素组成,转化膜中的Ti主要以TiO2的形式存在。电化学测试结果表明,紫外照射条件下,转化反应处理的2024铝合金腐蚀电位正移和阳极钝化区形成,使得2024铝合金惰性、防腐性能显著增强。     

Magnetron sputtered Au-Pd-In alloys: microgravimetric and electrochemical characterisation in simulated physiological solutions

An electrochemical quartz crystal microbalance (EQCM) has been applied in corrosion sensing of magnetron sputtered Au-Pd-In alloy in simulated physiological solutions. The piezoelectric resonators were prepared by alloy deposition on quartz substrates by a DC magnetron-sputtering (MS) technique. X-ray photoelectron spectroscopy (XPS) analysis showed that the deposit composition was similar to that of the MS target, which was a commercially available casting alloy. X-ray diffraction indicated that the sputtered alloy has a crystalline structure. Measurements by using impedance spectroscopy and DC voltammetry showed some differences in electrochemical behaviour of both sputtered and cast alloy; however, these data did not indicate superior corrosion resistance of the sputtered specimen. Alloy corrosion has been studied by EQCM in three simulated physiological solutions: 0.9 N NaCl, 0.1 N NaCl+0.1 N lactic acid and artificial saliva. The EQCM indicated corrosion as increase in electrode mass, which was due to accumulation of corrosion products on the surface. The mass gain curves were similar in both neutral (pH 6) and acidic (pH 2.2) solutions, what implies dissolution of corrosion products in both media to be insignificant. XPS analysis showed that In₂O₃ was the main corrosion product on the surface. Corrosion current calculations from the mass curves were undertaken, which yielded the same corrosion rate assuming different oxides on the surface. The average corrosion rates in oxygenated 0.9 N NaCl and 0.1 N NaCl+0.1 N lactic acid solutions were similar and about twice as high as that in saliva.     

Korrosion von Zinkpigmenten im alkalisch wäßrigen Medium

Corrosion of zinc pigments in alkaline aqueous medium Zinc pigments corrode in an alkaline mixture of water and butyl glycol in the ratio 9 : 1 by the evolution of hydrogen. The corrosion rate decreases in the series flakelike non-leafing zinc pigment > flakelike leafing zinc pigment >spherical zinc dust. The relative high stability of the zinc dust can he explained by its low surface area. The chemical structure of the base which is used for adjusting the pH value has a significant influence on the corrosion rate of the flakelike leafing zinc pigment; the corrosivity falls in series ammonia > sodium hydroxide > 2-(dimethylamino)ethanol > triethylamine. The corrosion rate of the flakelike non-leafing zinc pigment depends only on the pH value and not on chemical structure of the examined bases. The determination of the concentrations of dissolved zinc(II) in the corrosion media by atomic absorption spectroscopy shows that the corrosion rate grows with increasing solubility of zinc(II) approximately.     

Saccharide und deren Derivate als Korrosionsinhibitoren für Aluminiumpigmente in wäßrigen Medien

Saccharides and their derivatives as corrosion inhibitors for aluminum pigments in aqueous media Aluminium pigments (Al-content >99,5%) were corroded in aqueous, slightly alkaline metallic coating compositions. The temporal progress of the corrosion can be determined easily by volumetric analysis of the evolved hydrogen. As simple model systems for testing mono-, di- and polysaccharides and their derivatives as corrosion inhibitors two water/butyl glycol-mixtures were chosen the pH of which was elevated to 10 to accelerate the corrosion reaction. In addition it was tried to establish structure-efficiency-relations by comparison with model compounds. Two classes of compounds were active:

• 1. Reducing mono- and disaccharides were inhibiting the corrosion reaction presumably by their in the equilibrium existing endiol structure element.
• 2. The examined hydroxycarboxylic acids are forming chelate complexes which seem to be the corrosion inhibitors.

The most effective of all tested compounds was the strong reducing agent ascorbic acid.     

高压输电耐张线夹用铝在中性溶液中的交流腐蚀行为

目的研究高压输电耐张线夹用铝在0.1 mol/L的中性Na2SO4溶液中的交流腐蚀行为。方法在耐张线夹端部截取块状腐蚀试样并包覆、打磨、清洗,利用自制设备测量试样在交变电流腐蚀作用下的Tafel曲线、交流阻抗谱和腐蚀速率,采用扫描电子显微镜分析微观腐蚀形貌,采用X射线衍射仪、能谱仪和X射线光电子能谱仪对腐蚀区元素及物相进行分析。结果交变电流密度为0~40 A/m2时,Tafel曲线负向移动;50 A/m2时,发生逆转,曲线正向移动;随交变电流密度增加,交流阻抗谱Nyquist图由单弧逐渐变为双弧,出现Warburg阻抗,Bode-Phaze图由单峰逐渐变为双峰;表面出现较多的点蚀坑和层状脱落痕迹;腐蚀产物为Al(OH)3和Al2O3。结论交变电流作用下试样的腐蚀倾向加深,腐蚀表面具有较多的空洞,垂直腐蚀和平行腐蚀交替进行,呈现层状脱落方式向基体演进,腐蚀产物与一般铝腐蚀产物相同,均为Al(OH)3和Al2O3,腐蚀速率在交变电流密度低于50 A/m2时相对较低,高于50 A/m2时大幅提高。     

有机－无机杂化涂层制备及耐腐蚀性能研究

采用溶胶-凝胶法，以甲基三乙氧基硅烷(MTEOS)和正硅酸乙酯(TEOS)为原料，用浸渍-提拉法，在LY12铝合金基体表面成功制备了有机-无机杂化涂层.涂层表面光滑、平整、致密、无裂纹.通过液态浸渍实验、盐雾腐蚀实验和电化学腐蚀实验研究了有机-无机杂化涂层的耐腐蚀性能.结果表明，有机-无机杂化涂层耐腐蚀性能优良，具有很大的应用前景，使此杂化膜替代对环境有害的铬酸盐转化膜成为可能.     

盐沉积条件下CO2对LY12铝合金大气腐蚀的影响

目的研究在有/无CO_2存在的恒温恒湿条件下,表面有沉积盐的LY12铝合金的大气腐蚀行为与腐蚀机理,搞清CO_2对其大气腐蚀的影响。方法将LY12铝合金表面分别沉积不同浓度的NaCl和MgCl_2,分别进行通/不通CO_2的恒温恒湿实验,借助扫描电镜(SEM/EDS)、X射线衍射(XRD)和X光电子能谱(XPS)等表面技术以及腐蚀失重分析方法,研究盐沉积条件下CO_2对LY12铝合金大气腐蚀的影响。结果在试验条件下,MgCl_2造成的LY12铝合金腐蚀都以点蚀为主,失重高于NaCl造成的。以MgCl_2为介质时,主要腐蚀产物都为(Mg1–xAlx(OH)_2)x+(Cl~–,CO~(2–))x×mH_2O(简写为LDH);以NaCl为介质时,主要腐蚀产物都为Al_2O_3或Al(OH)_3。两种介质的腐蚀产物都出现了Cu元素的富集。结论无论是否存在CO_2,Mg元素都参与了腐蚀产物的形成。合金元素Cu的存在及其富集,是造成CO_2对纯铝和LY12铝合金腐蚀行为不同影响的主要因素。     

咪唑啉季铵盐缓蚀剂的复配机理

通过电化学测试确定咪唑啉季铵盐(IM)和辛基酚聚氧乙烯醚(OP)两种缓蚀剂的最佳复配比,利用X射线光电子能谱(XPS)分析高温高压CO_2腐蚀条件下缓蚀剂在L245钢表面的吸附特性,结合分子动力学计算研究了复配缓蚀剂的缓蚀机理。结果表明:复配后IM缓蚀剂分子在金属表面吸附量增加,同时OP分子的吸附提高了IM缓蚀剂分子在金属表面的吸附覆盖程度,形成致密的保护膜,阻碍溶液中腐蚀性介质对金属表面的侵蚀,有效保护基体减缓腐蚀,从而使得IM和OP复配后的缓蚀率明显升高;IM与OP复配后缓蚀剂分子在Fe(001)表面的吸附强度增大,说明缓蚀剂分子的缓蚀性能本质上是由缓蚀剂分子与金属表面的电子转移行为所决定的。     

Novel anti-corrosion nano-sized vanadia-based thin films prepared by sol–gel method for aluminum alloys

Chromate conversion coatings have been widely applied for the corrosion protection of aluminum alloys. However, the waste containing Cr6+ has many limitations due to the environmental consideration and health hazards. Vanadates are among the proposed alternatives to chromating. Series of specimens were prepared under the following conditions: (a) as polished, (b) directly treated with vanadia, (c) etched, (d) oxide thickened, and (e) etching followed by oxide thickening. After surface preparation, the specimens were dipped in vanadia solution prepared via sol gel method. Electrochemical impedance spectroscopy (EIS) and polarization measurements have been used to evaluate the coating performance in 3.5% NaCl. The optimum conditions under which vanadia treatments can provide good corrosion protection to the aluminum substrate were determined. The surface morphologies of the treated samples were investigated using SEM and EDS. Optical microscope was also used to investigate the occurrence of pitting corrosion. The surface preparation prior to vanadia treatment was found to have a marked effect on the corrosion protection of AA6061 T6. Generally, vanadia treatments improve the corrosion resistance due to formation of highly protective vanadium oxides. According to the EIS and polarization measurements, a combination between etching and oxide thickening prior to vanadia treatment plays an important role on the corrosion protection mechanism.     

NY-400 型耐张线夹内部交流腐蚀形貌及产物研究

目的研究老旧高压输电耐张线夹内部交流腐蚀。方法截取已运行35 a的耐张线夹并解剖,采用扫描电子显微镜分析腐蚀区的微观形貌,采用X射线衍射仪、能谱仪和X射线光电子能谱仪对腐蚀区元素及物相进行分析鉴定,分析线夹内部腐蚀损伤演化过程。结果线夹内表面与铝线表面局部出现大量白色腐蚀产物和黑色覆盖物,白色腐蚀物呈粉末和片层两种形态。分析表明,腐蚀产物相组成为Al2O3,Al O(OH)和Al OOH;黑色覆盖物随深度增加而减少,黑色区域主要元素为Al,O和C,物相组成为Al2O3,C(graphite)和含C有机物。钢芯锌层破坏区的内层铝线更易腐蚀,腐蚀区呈灰黑色,微观形貌为富铁元素颗粒镶嵌在其它腐蚀产物中,区域的主要元素为Al,C,O,Fe和Zn,Fe元素存在形式为Fe2O3;钢芯表面镀锌层局部腐蚀严重,呈现平面型点蚀形貌,主要元素为Zn,Al,C和O,Zn腐蚀产物为六边纤锌矿结构Zn O。结论内部交流腐蚀原因为液体渗入,同时腐蚀产生大量的热致使材料分解。     

Enhancement of the anti-corrosion efficient of hybrid nanostructure coating using copper phthalocyanine self-assembled monolayers

A self-assembled films (SA) of cupper phthalocyanine (CuPh) chemisorbed on the mild steel surface was coated by an inorganic-organic sol gel hybrid coating. Hybrid sol was synthesized via acid catalyzed hydrolysis and condensation of methacryloxypropyl trimethoxysilane (TMSM) and tetraethoxysilane (TEOS) at the molar ratio of 1: 1. The morphology of mild steel coated with TMSM/TEOS and CuPh was examined by SEM. The surface chemistry of the hybrid sol-gel coatings was investigated with polarization scans and electrochemical impedance spectroscopy (EIS) in aerated 0.5 mol L^–1 HCl solution. Self assembled CuPh films coated under the hybrid coating showed a strong influence on its corrosion resistance, mainly when the samples have 24 h immersion time and 1 mM concentration.     

Electrodeposition of sol–gel films on Al for corrosion protection

Sol–gel films were electrodeposited on aluminum electrodes following the methodology we have developed and is based on applying negative potentials. This increases the pH at the surface, causing acceleration of the polymerization. Our process follows the “two step method”, in which the monomer is first hydrolyzed in acidic solution (pH 4) and only then the negative potential is applied, which consumes protons and releases hydroxyl ions, thus enhancing the condensation.Films made of different monomers, i.e., tetraethoxysilane (TEOS), methyl trimethoxysilane and phenyl trimethoxysilane (PTMOS), were prepared, characterized and examined for their corrosion inhibition properties. Potentiodynamic polarization, electrochemical impedance spectroscopy, optical and scanning electron microscopy as well as atomic force microscopy have been used as a means of film characterization. Hydrophobic and steric silanes, such as PTMOS showed a considerable corrosion inhibition capacity as compared to the capacity exhibited by less hydrophobic and steric derivatives such as TEOS. The difference between the conventional dip-coating method and the electrodeposition approach for depositing sol–gel films was also examined, indicating a clear advantage of the latter.