热镀锌钢表面铈盐与硅烷处理后的耐蚀性能

将热镀锌(HDG)钢板经20g/L的Ce(NO3)3·6H2O溶液处理后浸涂5%(体积比)硅烷,研究膜层的耐蚀性能。5%NaCl溶液中的电化学极化曲线测试结果和中性盐雾试验(NSS)结果表明,单独的铈盐处理或浸涂硅烷膜都能够提高热镀锌层的耐蚀性,而经过该铈盐处理后再浸涂硅烷形成双层膜后能够明显地抑制腐蚀过程中的阴极和阳极反应,极化电阻Rp较HDG试样增加40多倍,也是单一膜层处理试样的5~9倍,膜层的耐蚀性能明显提高。俄歇电子谱(AES)分析表明,热镀锌试样经过两步处理后,在表面形成了双层膜,外层是富含C、Si、O的均匀硅烷膜层,里层是富含Ce的稀土转化膜层。     

Preparation and Corrosion resistance of Cerium-based Chemical Conversion Coating on AZ91 Magnesium alloy

采用Ce(NO3)3为主盐的稀土盐处理溶液，在AZ91镁合金表面形成无毒，无污染的铈盐化学转化膜，并研究成膜规律及其耐蚀行为。利用对膜层的外加扰动小，更易得到重复性高结果的电化学阻抗谱技术评价膜层耐蚀性能。初步优化了处理时间、温度、Ce(NO3)3液浓度和促进剂等因素对膜层结构和膜层耐蚀性能的影响，并获得了最好的成膜条件：温度35℃，时间为30min，处理液主盐Ce(NO3)3的浓度为0.02mol/l和4ml/l成膜促进剂。结果表明：优化后的工艺能够在AZ91镁合金表面获得宏观黄色致密，微观具有微小裂纹并分层的膜层，内层膜Ce含量较外层的低但致密。工艺优化制备的稀土化学转化膜能有效提高镁合金的耐蚀性能，有效抑制阴阳极反应，自腐蚀电位提高240mV，自腐蚀电流密度降低达到2个数量级。     

AZ91镁合金表面铈基稀土转化膜的制备及腐蚀电化学行为

考察了铈盐溶液中的AZ91镁合金电化学行为,包括开路电位,阴、阳极极化行为等,并据此开展了Ce(NO3)3为主盐的稀土盐转化膜研究,在AZ91镁合金表面形成无毒、无污染的铈盐化学转化膜,并研究成膜规律及其耐蚀行为.采用电化学阻抗谱技术优化了处理时间、温度、Ce(NO3)3液浓度和促进剂等因素对膜层结构和膜层耐蚀性能的影响,并获得了最好的成膜条件:处理温度为35℃,时间为30 min,主盐Ce(NO3)3的浓度为0.02 mol/L和促进剂H2O2浓度为4 mL/L.结果表明:采用优化后的工艺能够在AZ91镁合金表面获得宏观黄色致密、微观具有微小裂纹并分层的膜层,表层Ce含量较高.工艺优化制备的稀土化学转化膜能有效提高镁合金的耐蚀性能,有效抑制阴、阳极反应,自腐蚀电位提高250 mV,自腐蚀电流密度降低2个数量级.长期全浸实验结果表明,转化膜能有效提高镁合金的耐腐蚀性能,浸泡60 h后,保护性大大降低.     

热镀锌钢表面硅烷膜的腐蚀电化学性能

将热镀锌钢板在7 %(体积比)、pH＝4的乙烯基三甲氧基硅烷溶液中40 ℃下处理2 min,获得了硅烷膜试样.应用极化曲线和电化学交流阻抗谱(EIS)评价了硅烷膜在5 % NaCl溶液中的耐蚀性能,采用俄歇电子能谱(AES)分析了膜层的成分和结构特性.结果表明,硅烷膜主要由C、O、Si等元素组成,硅烷分子并非是简单地以物理吸附的方式存在于热镀锌层上,而是通过Si-O-Zn键使得硅烷界面层与热镀锌层紧密结合在一起.硅烷膜能同时抑制Zn腐蚀过程中的阳极和阴极反应,其极化阻抗值Rp可达5.53 kΩ·cm2.硅烷膜的低频与高频容抗弧几乎合成一个弧,表明腐蚀过程中硅烷膜层已经很致密,界面电容很大,Cl﹣难以通过膜层间隙到达Zn基体表面.     

热镀锌钢表面铈转化膜的表征与腐蚀电化学行为

将热镀锌钢在20 g/L Ce(NO3)·6H2O溶液(pH=4,25℃)中处理10s~24 h,获得铈转化膜试样.应用极化曲线和电化学交流阻抗谱(EIS)研究铈转化膜试样和空白热镀锌试样在5%NaCl溶液中的耐蚀性能.利用扫描电镜(SEM)和X射线光电子能谱(XPS)研究转化膜的形貌和组分.结果表明:经硝酸铈溶液处理后的镀锌钢板,其腐蚀电流密度下降,极化电阻升高,同时,锌腐蚀过程中的阳极和阴极反应受到抑制,腐蚀保护效率显著提高;低频阻抗值随成膜时间的增加而先增大后减小,表明腐蚀电解质在转化膜层孔隙中扩散的难易程度先增加后下降;当成膜时间在30 min～1 h之间时,所得转化膜的阻抗值最大可达8~9 kΩ·cm2,耐蚀性最佳.铈转化膜随处理时间的增加首先在锌晶粒晶界附近发生开裂,逐渐形成"干涸的河床"样形貌.铈转化膜含铈、锌、氧等元素,主要由CeO2、Ce(OH)4(或CeO2·2H2O)、ZnO和少量Ce2O3、Ce(OH)3(或Ce2O3·2H2O)等混合组成.     

镀锌钢表面硅烷膜的耐蚀性能研究

采用浸涂技术,在热镀锌（HDG）钢板表面制备3-氨丙基甲基二乙氧基硅烷膜。通过电化学方法研究硅烷膜在3．50％的氯化钠溶液中的耐蚀性能,并用SEM研究存在硅烷膜的镀锌钢在腐蚀前后的形貌变化。结果表明,形成硅烷膜的镀锌钢在3．50％的氯化钠溶液中的自腐蚀电流密度下降到2．434×10^-8A·cm^-1自腐蚀电位正移。经SEM测试表明,硅烷膜在腐蚀前后的形貌几乎不变,耐蚀性能明显优于空白样镀锌钢。     

热镀锌层柠檬酸改进型铈盐转化膜的生长机理

将热镀锌钢板浸入含有25 g/L Ce(NO3)3·6H2O、4~6 g/L H2O2(30%)、15~20 g/L H3Cit的处理液中,在70℃下处理10 s~240 min,从而在其表面获得铈盐转化膜。采用中性盐雾试验(NSS)和电化学极化曲线来分析膜层耐蚀性能,确定最佳成膜时间范围。采用扫描电镜(SEM)观察膜层的微观形貌,利用能谱仪(EDS)、X射线光电子能谱仪(XPS)、红外吸收光谱仪(IR)分析膜层的化学组成。结果表明:处理时间为10 min左右的铈盐转化膜耐腐蚀性能最优,最佳工艺条件下得到的铈盐转化膜的耐蚀性能与铬酸盐转化膜的相当;随着处理时间的延长,膜的厚度增加,膜层的裂纹变宽;处理时间超过10 min后膜层逐步产生脱落,耐腐蚀性能也随之降低;转化膜的生长过程中,前期以柠檬酸铈吸附膜的沉积为主,后期以Ce(OH)3/Ce2O3及Ce(OH)4/CeO2的沉积占主导。     

冷轧钢表面植酸-硅烷双膜复合层的耐蚀性能

为了研究植酸-硅烷复合膜对冷轧钢腐蚀行为的影响,采用浸泡法在冷轧钢板表面分别制备了植酸化学转化膜、硅烷膜层及植酸-硅烷复合膜层。采用扫描电子显微镜观察冷轧钢板表面经植酸转化膜和植酸-硅烷复合膜层处理之后的形貌;运用红外光谱和X-射线光电子能谱方法研究植酸转化膜及植酸-硅烷复合膜层的化学组成;采用极化曲线、电化学阻抗谱、盐雾试验研究植酸-硅烷复合膜层的耐蚀性能及在3.5%氯化钠腐蚀溶液中的稳定性。结果表明:植酸-硅烷复合膜层的耐腐蚀性能及在氯化钠溶液中的稳定性明显高于单一的硅烷膜层。其作用机理在于植酸转化膜一方面可以提高硅烷膜层与金属基体的结合力,另一方面可以与硅烷膜层协同作用提高复合膜的耐腐蚀性能。     

双一[γ一（三乙氧基硅）丙基]四硫化物处理热镀铝锌层的耐蚀性研究

采用双-[γ-(三乙氧基硅)丙基]四硫化物(BTESPT)硅烷钝化液对热镀铝锌钢板进行了钝化处理.研究了在5%NaCl溶液中未钝化、硅烷钝化及铬酸盐钝化热镀铝锌钢板的极化曲线和电化学交流阻抗谱.通过中性盐雾试验比较了硅烷钝化膜与铬酸盐钝化膜的耐蚀性能.结果表明:经硅烷钝化液钝化后的热镀铝锌钢板,其腐蚀电位和电流密度下降,极化电阻增大,硅烷钝化膜抑制了热镀铝锌钢板的腐蚀过程,使得耐蚀性能远远高于铬酸盐钝化后的热镀铝锌钢板.     

热镀锌钢上铈盐转化膜在含Cl-介质中的耐蚀性

将热浸镀锌钢浸渍在20 g·L~(-1)Ce(NO_3)_3·6H_2O溶液(pH=4,25℃)中10s~24 h,制备了铈盐转化膜试样。通过中性盐雾和盐水浸泡试验评价了转化膜在含Cl~-介质中的耐蚀性能。采用扫描电镜和X射线衍射能谱研究了转化膜的形貌和物相结构。结果表明,铈盐转化膜能显著推迟热浸镀锌层出现白锈的时间;随成膜时间的延长,转化膜的耐蚀性能先增加后下降;当成膜时间为30~60 min时,转化膜的耐蚀性能最佳。铈盐转化膜主要由非晶态结构的ZnO和CeO_2组成,在腐蚀介质中不易形成腐蚀微电池。     

CORROSION RESISTANCE OF HOT DIP GALVANIZED STEEL PRETREATED WITH BIS-FUNCTIONAL SILANES MODIFIED WITH NANOALUMINA

The corrosion behavior of hot dip galvanized steel pretrvated with bis-[triethoxysilylpropyl] tetrasulfide （BTESPT） modified with alumina particles was studied. The corrosion resistance of the passiving films was evaluated by Tafel polarization curve and electrochemical impedance spectroscopy. The films formed on the galvanized steel substrate were characterized by Fourier transform infrared spectroscopy and energy dispersive X-ray spectrometry. The surface morphology of the treated hot dip galvanized steel samples was observed by Field Emission Scanning Electron Microscope. The results show that the pretrvatments on the basis of silane films modified with nanoalumina particles have reduced both anodic and cathodic current densities, and increased total impedance in the measured frequency, consequently, improving corrosion protection for hot dip galvanized steel during immersion in NaCl solutions compared to chromate films and silane films.     

热浸镀锌层上钼酸盐转化膜的腐蚀电化学性能

    将热镀锌钢在含10 g/L Na₂MoO₄·2H₂O、pH为5的溶液中60℃下处理10~300秒,获得了钼酸盐转化膜试样.应用极化曲线和电化学交流阻抗谱(EIS)研究了转化膜层在5% NaCl水溶液的耐蚀性能.结果表明,经钼酸盐转化处理后的镀锌钢板,其腐蚀电流密度下降,极化电阻升高,阴极极化作用明显增强,腐蚀保护效率显著提高,电化学阻抗值提高了一个数量级;低频扩散阻抗值随处理时间的增加先增大后减小,表明腐蚀电解质在转化膜层孔隙中扩散的难易程度先增加后下降.     

A comparative study of molybdate/silane composite films on galvanized steel with different treatment processes

Two types of molybdate/silane composite films were obtained on the surface of hot-dip galvanized steel sheets by either directly immersing in a solution containing silane and molybdate as additive (single-step process), or firstly immersing in a molybdate solution, then in a silane solution (two-step process). The chemical compositions and microstructures of the films were examined by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and reflection absorption infrared spectroscopy (RAIR). The corrosion resistances were investigated by electrochemical measurements and neutral salt spray (NSS) test. The results showed that the molybdate/silane composite film formed in the single-step process had a similar double-layer structure as that obtained in the two-step process. The inner layer was composed mainly of the elements O, Mo, Zn, and P, similar to the single molybdate film; whereas the outer layer was composed mainly of the elements C, O and Si, similar to the single silane film. Compared with the single molybdate or silane film, the corrosion current of the composite films was reduced and the impedance of the films was increased. Accordingly, the corrosion resistance of the composite films was remarkably enhanced to a level which was comparable to or even surpassing that of the conventional chromate passivation film.     

Growth and corrosion behavior of rare earth film on hot-dip galvanized steel

1Introduction For a long time,chromate compounds Cr(VI)have been used as effective and inexpensive corrosion inhibitors for zinc and zinc coating.However,with the advent of increasing environmental awareness,the toxicity and carcinogenic nature of Cr(VI)b…     

Synergistic corrosion protection for galvanized steel by phosphating and sodium silicate post-sealing

To improve the corrosion resistance of phosphate coatings, the phosphated hot-dip galvanized (HDG) sheets were post-sealed with sodium silicate (water glass) solutions. The morphology and chemical composition of the composite coatings was analyzed using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The effect of sodium silicate post-sealing treatment on the corrosion behaviors of phosphate coatings was investigated by neutral spray salt (NSS) tests and electrochemical measurements. The results show that after the silicate post-treatment the pores among zinc phosphate crystals are sealed with the films containing Si, P, O and Zn, leading to the formation of the continuous composite coatings on the surface of HDG steel. The corrosion resistance of the composite coatings depending on concentration of sodium silicate and post-sealing time is greatly improved by the silicate post-treatment. The optimum concentration of silicate and post-sealing time are 5 g/L and 10 min, respectively. Both the anodic and cathodic processes of zinc corrosion on the samples are suppressed conspicuously, and the synergistic protection effect of the single phosphate coatings and the single silicate films is evident. Moreover, the low frequency inductive loop in electrochemical impedance spectroscopy (EIS) is disappeared and the electrochemical impedance values are increased for more than one order of magnitude. The corrosion protection of the composite coatings is comparable to that provided by the chromic acid post-treatment.     

钼酸盐后处理提高热镀锌上磷化膜耐蚀性的探讨

将磷化后的热镀锌钢板用钼酸盐后处理,以提高磷化膜的耐蚀性。用SEM、EDS、电化学极化测量和盐雾试验研究了钼酸盐后处理对磷化膜组成和耐蚀性的影响。结果表明,经钼酸盐处理后,磷化膜上磷酸锌晶体间的孔隙被钼酸盐膜填补,从而在锌层表面形成了由磷化膜和钼酸盐膜构成的连续完整致密的复合膜;复合膜的极化电阻Rp显著增大,腐蚀电流密度显著减小,耐蚀性大大增强。磷化300s、后处理50s时复合膜的耐蚀性最优,Rp比单磷化膜的增加了一个数量级。     

Effect of silicate pretreatment, post-sealing and additives on corrosion resistance of phosphated galvanized steel

Sodium silicate （water glass） pretreatment before phosphating, silicate post-sealing after phosphating and adding silicate to a traditional phosphating solution were respectively carried out to obtain the improved phosphate coatings with high corrosion resistance and coverage on hot-dip galvanized（HDG） steel. The corrosion resistance, morphology and chemical composition of the coatings were investigated using neutral salt spray（NSS） tests, scanning electron microscopy（SEM） and energy dispersive spectroscopy（EDS）. The results show that pretreatment HDG steel with silicate solutions, phosphate coatings with finer crystals and higher coverage are formed and the corrosion resistance is enhanced. Adding silicate to a traditional phosphating solution, the surface morphology of the coatings is nearly unchanged. The corrosion resistance of the coatings is mainly dependent on phosphating time. Phosphating for a longer time （such as 5 min）, the corrosion resistance, increasing with concentration of silicate, is improved significantly. Post-sealing the phosphated HDG steel with silicate solutions, the pores among the zinc phosphate crystals are sealed with the films containing Si, P, O and Zn and the continuous composite coatings are formed. The corrosion resistance of the composite coatings, related to the pH value, contents of hydrated gel of silica and Si2O^2- 5 and post-sealing time, is increased markedly. The improved coatings with optimal corrosion resistance are obtained for phosphating 5 min and post-sealing with 5 g/L silicate solution for 10 min.     

Effect of molybdate post-sealing on the corrosion resistance of zinc phosphate coatings on hot-dip galvanized steel

The technique of post-sealing the phosphated hot-dip galvanized (HDG) steel with molybdate solution was addressed. The composition and corrosion resistance of the improved phosphate coatings were investigated by SEM, EDS, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements, and neutral salt spray (NSS) test. The results showed that molybdate films were formed in the pores of phosphate coatings, and the compact and complete composite coatings composed of phosphate coatings and molybdate films were formed on the zinc surface, resulting in that both the anodic and cathodic processes of zinc corrosion were inhibited remarkably; the corrosion protection efficiency values were increased; and the electrochemical impedance values were enhanced at least one order of magnitude. The low frequency impedance values for the composite coatings were increased at the initial stages of immersion in 5% sodium chloride solution, indicating the self-repairing activity of the composite coatings.