硅酸钠封闭后处理对磷化热镀锌钢耐蚀性的影响

将热镀锌钢板磷化后再用硅酸钠（水玻璃）溶液封闭后处理,以进一步提高磷化膜的耐蚀性.用SEM、EDS、NSS试验和电化学极化测量研究了硅酸钠封闭后处理对磷化膜组成和耐蚀性的影响.结果表明,经硅酸钠封闭处理后,磷化镀锌钢板表面磷酸锌晶体间的孔隙被含Si、P、Zn的新膜填补,形成了连续完整的复合膜;复合膜的耐蚀性能明显提高,且与硅酸钠溶液的浓度及封闭时间有关;硅酸钠浓度为5 g/L、封闭10 min时形成的复合膜的耐蚀性最佳,NSS试验6个周期（天）后仍不出现腐蚀;试样的阳极极化和阴极极化阻力均显著增强,腐蚀电流密度明显减小,极化电阻增大了一个多数量级.     

几种改进磷化膜耐蚀性对比和自修复性初探

研制了钼酸钠添加剂改进磷化膜及钼酸钠、硝酸铈、硅酸钠溶胶封闭后处理改进磷化复合膜,拟替代高毒性铬酸盐钝化膜。采用中性盐雾试验、Tafel极化和电化学阻抗测试对比分析了这4种改进磷化膜与几种传统无铬转化膜、铬酸盐钝化膜耐蚀性的差异;用SEM和EDS研究带划痕试样经盐雾腐蚀后划痕表面的组织形貌和化学成分,初步探讨了改进磷化复合膜的自修复性。结果表明:3种改进磷化复合膜的耐蚀性优于铬酸盐钝化膜,具有自修复作用,有望成为铬酸盐钝化膜的替代品;硅酸钠溶胶封闭后处理改进磷化复合膜的耐蚀性最优。     

硝酸铈处理对磷化膜组织和耐蚀性的影响

为了发挥磷化膜和铈盐膜的优势,采用硝酸铈前处理或硝酸铈后处理对热镀锌层上的磷化膜进行改进,通过SEM,EDS,NSS和Tafel极化研究了硝酸铈改进磷化膜的显微组织和耐蚀性,并与铬酸盐钝化膜进行了比较。结果表明:硝酸铈前处理或后处理改进磷化膜均为含P,O,Ce和Zn化合物的复合膜,基本上克服了单一膜层的缺陷,使得复合膜的耐蚀性明显增强;硝酸铈后处理改进复合膜的耐蚀性优于铬酸盐钝化膜,有望成为高毒性铬酸盐钝化膜的替代品。     

LF21铝合金稀土转化膜的开裂及其钼酸盐后处理

用化学沉积法在LF21铝合金表面制备了均匀连续的稀土铈化学转化膜,通过电镜、能谱、极化曲线测试和盐雾试验等方法研究了膜的开裂行为以及钼酸盐后处理对膜耐蚀性能的改善作用.结果表明,沉积时间对膜的开裂倾向有显著影响,随沉积时间延长,开裂倾向增大,裂纹更深更宽.在10 g/L的钼酸钠溶液、50℃、浸泡30min的条件下对稀土转化膜进行后处理以后,裂纹程度有所减弱,耐蚀性能明显改善,维钝电流下降约一个数量级,耐盐雾性能也明显提高.钼酸盐后处理提高稀土转化膜耐蚀性的机理可能包括钼酸盐膜在裂纹部位的沉积、钼酸盐的缓蚀作用和稀土转化膜的"自封闭"作用.     

2024铝合金化学转化膜与磷化底漆耐蚀性的研究

通过盐雾实验、稳态阳极极化曲线和电化学阻抗谱3种测试方法，对磷化底漆和阿洛丁(1200)化学转化膜进行了测试，结果发现磷化底漆的耐蚀性明显优于阿洛丁化学转化膜．在中性盐雾实验10个周期中，阿洛丁化学转化膜腐蚀明显，而磷化底漆完好如初．在稳态和弱极化区，两者抗蚀性能相似，而在强极化区，磷化底漆明显优于阿洛丁化学转化膜、在电化学阻抗谱上，磷化底漆极化电阻(Rp)比阿洛丁转化膜高1个数量级．     

镀锌板上丙烯酸树脂复合膜的制备和表征

在镀锌钢板表面制备了丙烯酸树脂复合膜,用扫描电子显微镜观察膜层的微观形貌.用傅里叶变换红外光谱表征膜层的分子结构,用中性盐雾试验和电化学方法测试其耐蚀性,并用划痕浸泡实验测试膜层的自修复性能.结果表明:丙烯酸树脂复合膜表面致密平整;耐中性盐雾腐蚀达72 h;阻抗值和极化电阻值均较大,说明丙烯酸树脂复合膜能有效抑制腐蚀电化学反应;划痕浸泡试验证明丙烯酸树脂复合膜具有自修复功能.成膜过程中碳酸锆铵能够和丙烯酸树脂分子上的羟基和羧基发生交联反应,形成互穿网络结构,提高膜层内部的交联密度,有效地阻挡外界环境的侵蚀,当膜层破损时钼酸盐和磷酸盐与锌反应形成难溶盐吸附在破损处,起到自修复作用.     

电镀锌板钼酸盐体系钝化膜的制备和腐蚀性能研究

采用钼酸盐作为主成膜物质对电镀锌板进行钝化处理,采用低浓度铬酸盐作为对比试验。用硫酸铜点滴试验、电化学交流阻抗、极化曲线和金相显微镜观察等方法检验膜层的腐蚀性能。结果表明:钼酸盐-硅烷、钼酸盐-硅烷-有机酸复合钝化可有效提高电镀锌层的腐蚀电位,降低腐蚀电流密度,抑制腐蚀的电化学过程,所以提高了镀锌板的耐腐蚀性,而且比低浓度铬酸盐钝化膜耐蚀性更好。     

热镀锌层上磷酸锌转化膜的生长与耐蚀性

热镀锌钢板在pH3.0、45℃的磷酸锌溶液中磷化2～600s,用扫描电镜、能谱仪和X射线衍射仪分析磷化膜的组织形貌和成分,并探讨膜层的生长行为。结果表明:磷酸锌晶体在锌晶粒内及晶界处均可成核,开始是以接近平行的片状生长,并逐渐向多方向生长成扇骨状的晶片。随着磷酸锌晶体的成核和生长,磷化膜的覆盖率增加,但晶体之间的孔隙难以完全消除;长大的磷酸锌晶片容易折断脱落,导致磷化后期膜层的质量增量减小;磷化膜主要由Zn3(PO4)2.4H2O组成。热镀锌钢板经磷化处理后,耐蚀性显著提高,磷化膜的耐蚀性随磷化时间和膜层覆盖率的增加而提高。     

铝合金表面钼酸盐改进植酸转化膜的耐蚀性能

目的通过钼酸钠(SM)添加剂、SM前处理、SM后处理三种方案对铝合金表面植酸转化膜进行改进研究,以进一步提高其耐蚀性。方法通过动电位极化测试研究改进后铝合金在3.5%(质量分数)Na Cl溶液中的耐蚀性。结果随着SM添加剂浓度的增加,铝合金表面植酸转化膜的耐蚀性先增强再减弱,SM质量浓度为30 g/L时的腐蚀保护效率Pe最大,达95.5%,而不含SM时的Pe仅为86.8%。p H值太大(p H=8.0)或太小(p H=3.0)都不利于形成耐蚀性更好的膜层,p H值为6.0时的Pe达98.6%。SM后处理会严重影响植酸转化膜的耐蚀性,腐蚀电流密度Jcorr大幅增大;SM前处理可提高植酸转化膜的耐蚀性,Pe达98.2%;SM前处理与添加剂同时应用时,植酸转化膜耐蚀性提高幅度更显著,Jcorr仅为0.042μA/cm2,极化电阻Rp达222 kΩ·cm2,Pe达99.5%。结论 SM添加剂和SM前处理均可明显提高铝合金表面植酸转化膜的耐蚀性,且复合作用时的效果更显著,而SM后处理不能提高铝合金表面植酸转化膜的耐蚀性。     

室温磷化加速剂的选择

采用几种金属盐，在不含其它氧化促进剂的磷化基础液里进行了试验，从而筛选出成膜速度快，耐蚀性好的钼酸盐作为室温磷化成膜加速剂，获得性能稳定的磷化法。     

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.     

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.     

Growth and corrosion resistance of molybdate modified zinc phosphate conversion coatings on hot-dip galvanized steel

The modified zinc phosphate conversion coatings（ZPC） were formed on hot-dip galvanized（HDG） steel when 1.0 g/L sodium molybdate were added in a traditional zinc phosphate solution. The growth performance and corrosion resistance of the modified ZPC were investigated by SEM, open circuit potential（OCP）, mass gain, potentiodynamic polarization and electrochemical impedance spectroscopy（EIS） measurements and compared with those of the traditional ZPC. The results show that if sodium molybdate is added in a traditional zinc phosphate solution, the nucleation of zinc phosphate crystals is increased obviously; zinc phosphate crystals are changed from bulky acicular to fine flake and a more compact ZPC is obtained. Moreover, the mass gain and coverage of the modified ZPC are also boosted. The corrosion resistance of ZPC is increased with an increase in coverage, and thus the corrosion protection ability of the modified ZPC for HDG steel is more outstanding than that of the traditional ZPC.     

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.     

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.     

An evaluation of the corrosion resistance and adhesion properties of an epoxy-nanocomposite on a hot-dip galvanized steel (HDG) treated by different kinds of conversion coatings

Hot-dip galvanized steel (HDG) samples were chemically treated by Cr(III), Cr(VI), Cr(III)-Co(II) and Cr(III)-Ni(II) conversion coatings. Epoxy nanocomposites were prepared using 2 wt.%, 3.5 wt.%, 5 wt.% and 6.5 wt.% nano-ZnO. Electrochemical impedance spectroscopy (EIS), pull-off adhesion tester and scanning electron microscope (SEM) were utilized to evaluate epoxy coatings properties on the surface of pre-treated HDG samples. Results showed that addition of nano-ZnO particles (specially 3.5 wt.%) can significantly improve the corrosion resistance of the epoxy coating on HDG. Decrease of contact angle (φ) and increase of surface roughness (Ra) of the pre-treated HDG samples were obtained. Decrease of the value of φ was more pronounced when the Cr(III) pre-treated samples were post-treated by Cr(III)-Co(II) and Cr(III)-Ni(II) conversion coatings (CCs). The dry and wet adhesion strengths of the epoxy coating to HDG were significantly increased after the surface treatment of the samples. Increase of the adhesion strength and decrease of the adhesion loss were more pronounced on Cr(III)-Co(II) and Cr(III)-Ni(II) post-treated samples. The corrosion resistance of epoxy coating was also increased on the surface of pre-treated HDG samples. Increase of the corrosion resistance of the Cr(III) pre-treated HDG samples was more pronounced on the samples which were post-treated by Co(II) and Ni(II).     

Effect of SiO2:Na2O molar ratio of sodium silicate on the corrosion resistance of silicate conversion coatings

Passivation treatment by sodium silicate solution is considered as an alternative to chromium chemical conversion treatment to improve the corrosion resistance of hot-dip galvanized (HDG) steels. In this paper, a transparent silicate coating was formed on the surface of HDG steel by immersing in sodium silicate solution with SiO₂:Na₂O molar ratio in the range from 1.00 to 4.00. The parameter about the SiO₂:Na₂O molar ratio of silicate solution has been discussed using corrosion resistance and surface morphology. Tafel polarization, electrochemical impedance spectroscopy (EIS) measurements and neutral salt spray (NSS) test show that silicate coatings increase the corrosion resistance of HDG steels. From the results obtained, it is deduced that the optimum SiO₂:Na₂O molar ratio is 3.50. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction analysis (XRD), and reflectance absorption infrared spectroscopy (RA-IR) show that there are no obvious differences of the chemical composition and structure in various silicate coatings. The silicate coatings mainly consist of zinc oxides/hydroxides, zinc silicate and SiO₂. However, atomic force microscopy (AFM) images reveal that the surface of silicate coatings with a molar ratio of 3.50 is more compact and uniform than other silicate coatings.     

Effect of porosity of phosphate coating on corrosion resistance of galvanized and phosphated steels Part II: Evaluation of corrosion resistance

The effect of porosity of phosphate coatings on the corrosion resistance of ungalvanized (UG), electrogalvanized, and hot dip galvanized steels is evaluated in this study. The corrosion resistance of phosphatized and painted steel is related to the integrity and continuity of phosphate and paint layers, and pores in the phosphate layer affect the corrosion resistance of material. The porosity of the phosphate coating was evaluated by using the cathodic polarization electrochemical test. To evaluate the corrosion resistance of the phosphatized and painted steels, they were submitted to accelerated corrosion tests. As was expected, the creepback from the scribe increased with the increase in porosity. This behavior was evident for UG steel, but less evident for galvanized steels due to cathodic protection and/or barrier effect of the zinc coating.     

聚苯胺/磷酸锌/聚硅氧烷复合涂层自修复和耐蚀性能初探

目的初步探索由聚苯胺/磷酸锌有机-无机复合钝化填料和环氧-聚硅氧烷树脂制备的自修复涂层的修复和防腐性能。方法采用微区交流阻抗技术(LEIS)、扫描电子显微技术(SEM)和电化学阻抗技术(EIS),研究了聚苯胺/磷酸锌/聚硅氧烷复合涂层的防腐性能和在人工损伤部位的修复功能。结果由微区电化学阻抗和电化学阻抗测试可知,环氧-聚硅氧烷清漆具有自修复和优异的耐蚀性能;偶联剂处理的聚苯胺/磷酸锌有机-无机复合钝化填料(HCE),可显著提升环氧-聚硅氧烷涂层的自修复和耐蚀性能。当HCE的添加量为0.3%(以占环氧-聚硅氧烷涂料质量的百分比计)时,涂层的自修复和耐蚀性能最佳,缺陷部位修复后的阻抗值最大达到70 k?,是环氧-聚硅氧烷清漆的9倍。涂层阻抗值随浸泡时间的延长而增加,浸泡3750 h时,涂层阻抗值增至10~(11)?·cm~2。结论当涂层产生缺陷时,一方面聚苯胺/磷酸锌有机-无机复合填料发生氧化还原反应,生成新的氧化膜;另一方面,聚苯胺与环氧-聚硅氧烷树脂发生交联固化反应,在基体缺陷处成膜,提高了涂层的致密性;二者协同作用使HCE3涂层试样具有最佳的耐蚀性能和自修复功能。