目的 为提高镁合金耐蚀性并进一步探究缓蚀剂的作用机理,选取紫脲酸（PPA）有机缓蚀剂应用于AZ31B镁合金。方法 采用电化学技术、析氢测试以及静态失重法测试紫脲酸在质量分数为3.5%的NaCl溶液中对AZ31B镁合金的缓蚀效果,并利用扫描电镜观察表面形态,利用XRD和XPS研究表面膜层结构和成分,进而深入分析PPA的缓蚀机理。结果 失重测试、析氢测试和电化学测试显示PPA对AZ31B具有较好的缓蚀作用。25 ℃时,由失重法得到的缓蚀效率为74.9%,由析氢法得到的缓蚀效率为59.6%,由电化学阻抗得到的缓蚀效率为73.5%,由动电位极化得到的缓蚀效率为53.9%。缓蚀效率的不同是由于测试方法不同导致的。随着实验温度的升高和浸泡时间的延长,PPA的缓蚀效率增加,由失重法得到的缓蚀效率最高可到93.9%（50 ℃,72 h）。SEM-EDS、XRD和XPS结果表明AZ31B镁合金表面保护膜层为PPA阴离子插层的Mg Al-LDH,膜层致密。结论 PPA对AZ31B镁合金的缓蚀机理为：在3.5% NaCl溶液中加入PPA后,PPA分子电离出氢离子,使溶液变为酸性,而PPA变为阴离子。由于阴极发生析氢反应,溶液的pH会升高,最终稳定在pH=10,碱性环境下促进了镁基体表面Mg Al-LDH的生成,PPA则以阴离子形式插入Mg Al-LDH的层间,在AZ31B镁合金表面生成了具有PPA阴离子插层的Mg Al-LDH保护膜,隔绝了镁基体与腐蚀介质的直接接触,减缓了腐蚀。
Abstract
In order to improve the corrosion resistance of magnesium alloys and gain a deeper understanding of the corrosion inhibition mechanism of corrosion inhibitors, this work explores the application of purple polyamide (PPA) as an organic corrosion inhibitor for AZ31B magnesium alloys. Magnesium alloys such as AZ31B are widely utilized in structural and transportation applications due to their low density and excellent mechanical properties. However, their inherently poor corrosion resistance in chloride-rich environments, such as marine and physiological media, remains a major barrier to their broader application. So, the development of effective, environmentally benign corrosion inhibitors is of significant scientific and industrial interest. In this work, the corrosion inhibition behavior of PPA in 3.5% NaCl solution was systematically investigated through a combination of electrochemical testing, including potentiodynamic polarization and electrochemical impedance spectroscopy (EIS), hydrogen evolution measurements, and static weight loss experiments. At 25 ℃, the corrosion inhibition efficiency of PPA was determined to be 74.9% by weight loss measurement, 59.6% by hydrogen evolution, 73.5% by EIS, and 53.9% by potentiodynamic polarization. This discrepancy reflected the different sensitivities and evaluation principles of each technique. With the increase of temperature and immersion time, the inhibition efficiency of PPA improved significantly, indicating enhanced adsorption stability and protective film integrity under elevated conditions, reaching a maximum of 93.9% (as determined by the weight loss method) at 50 ℃ and 72 h. To understand the underlying inhibition mechanism, detailed surface characterizations were carried out. Specifically, a scanning electron microscopy (SEM) was employed to visualize changes in surface morphology before and after PPA treatment, revealing a more compact and uniform film in the presence of the inhibitor. On the contrary, a loose magnesium hydroxide layer was formed on the surface of AZ31B alloy in 3.5% NaCl solution. Energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analyses further confirmed the presence of a dense protective layer composed of Mg-Al layered double hydroxides (LDHs) intercalated with PPA species. These layered structures were known to offer barrier properties that physically isolated the metallic substrate from the aggressive chloride-containing environment.
Mechanistically, the inhibition effect of PPA was attributed to its ability to form a stable, compact, and adherent interfacial layer. Upon dissolution in 3.5% NaCl solution, PPA molecules ionized and released protons, thereby acidifying the environment. This proton release transformed PPA into negatively charged anionic species. During corrosion, the hydrogen evolution reaction at the cathodic sites of AZ31B alloy surface increased the local pH, which eventually stabilized at approximately pH = 10. This alkaline environment promoted the in-situ formation of Mg-Al LDH on the surface of the alloy. Simultaneously, the PPA anions became intercalated within the interlayer galleries of the LDH structure, effectively becoming an integral part of the protective film. This synergistic interaction between the inhibitor molecules and the LDH host not only reinforced the integrity of the protective LDH layer, but also enhanced its stability against dissolution and mechanical degradation. Consequently, the resulting PPA-intercalated LDH film served as a robust barrier that blocked the diffusion of corrosive species such as Cl- ions to the AZ31B surface, significantly retarding the corrosion process.
关键词
紫脲酸 /
AZ31B /
镁合金缓蚀剂 /
MgAl-LDH /
缓蚀机理
Key words
purple polyamide /
AZ31B /
corrosion inhibitor for magnesium alloy /
MgAl-LDH /
inhibition mechanism
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