目的 在电解海水苛刻腐蚀环境中（6 mol/L NaOH,2 mol/L NaCl,90 ℃）,对比研究钼酸钠（Na2MoO4）、钨酸钠（Na2WO4）、磷酸钠（Na3PO4）、五氧化二钒（V2O5）四种无机缓蚀剂对316L奥氏体不锈钢（316L SS）与2205双相不锈钢（2205 DSS）的缓蚀效果与作用机理。方法 通过动电位极化曲线、电化学阻抗谱（EIS）测试和腐蚀浸泡实验,研究四种无机缓蚀剂的缓蚀效率。结合扫描电子显微镜（SEM）、光学轮廓显微镜（OP）和X射线光电子能谱（XPS）等表面分析方法,研究无机缓蚀剂对不锈钢表面形貌及膜层的影响。结果 电化学与腐蚀浸泡实验结果表明,四种无机缓蚀剂能够提高不锈钢在高温碱性盐水中的耐腐蚀性,并随着浓度的增加,缓蚀效率提升。V2O5具有最好的缓蚀效果,在0.05 mol/L时,缓蚀效率达到79.90%（316L SS）和89.58%（2205 DSS）,Na3PO4次之,缓蚀效率为83.33%（2205 DSS）,Na2MoO4和Na2WO4的缓蚀效果最差;SEM和OP结果显示,添加V2O5和Na3PO4后,不锈钢表面腐蚀产物减少,表面粗糙度降低;XPS分析表明,V2O5体系中的四价、五价钒和Na3PO4体系中的磷酸根均参与不锈钢表面膜层的构建,形成富钒/磷酸盐复合膜层。结论 V2O5和Na3PO4在模拟电解海水环境中具有优异的腐蚀防护效果,通过在不锈钢表面参与形成致密的富钒/磷酸盐复合膜层,抑制界面电荷转移过程,增强材料的耐蚀性。
Abstract
During alkaline seawater electrolysis for hydrogen production, the equipment operates for long periods in a high-temperature, highly alkaline, and chloride-rich environment. Structural materials are therefore prone to severe corrosion, which directly affects the long-term stability and service life of the electrolytic system. The work aims to compare the inhibition performance of four inorganic inhibitors including sodium molybdate (Na2MoO4), sodium tungstate (Na2WO4), sodium phosphate (Na3PO4), and vanadium pentoxide (V2O5) on 316L austenitic stainless steel (316L SS) and 2205 duplex stainless steel (2205 DSS) in a simulated electrolytic seawater electrolyte (6.0 mol/L NaOH, 2.0 mol/L NaCl, 90 ℃), and propose mechanistic explanations supported by film chemistry evidence.
Inhibition performance was firstly evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). A 14-day static full-immersion weight-loss test was then used to verify long-term protection, yielding the corrosion rate (CR) and inhibition efficiency (IE). Post-corrosion surface morphology and roughness evolution were analyzed by scanning electron microscopy (SEM) and optical profilometry (OP) to reveal corrosion-product coverage, pit development, and surface roughening. X-ray photoelectron spectroscopy (XPS) was employed to determine the elemental composition and valence states of surface films, thereby linking electrochemical responses with film chemistry.
For both stainless steels, V2O5 and Na3PO4 produced the most pronounced improvements, whereas Na2MoO4 and Na2WO4 were less effective in this highly alkaline chloride environment. EIS fitting showed that V2O5 markedly increased the film resistance (Rf) and charge-transfer resistance (Rct), indicating enhanced barrier protection and suppressed charge-transfer kinetics. For 316L SS, 0.05 mol/L V2O5 gave Rct = 29 770 Ω·cm2 and Rf = 923.50 Ω·cm2, and the CPEf parameter Y0 was the lowest with n = 1, suggesting reduced dispersion and a denser, more uniform film. Na3PO4 also increased interfacial impedance. For 316L SS, when Na3PO4 increased from 0.01 to 0.05 mol/L, Rct rose from 26 480 to 28 680 Ω·cm2 and Rf increased from 185.60 to 478.80 Ω·cm2, while IE increased from 69.49% to 72.10%. For 2205 DSS, the IE of 0.05 mol/L Na3PO4 was 58.38%. The IE values of Na2MoO4 and Na2WO4 were lower.
The 14-day immersion results further demonstrated the best inhibition performance of V2O5. For 316L SS, the CR in the inhibitor-free solution was 0.020 9 mm/a, indicating severe damage to the native passive film at 90 ℃ in 6.0 mol/L NaOH, 2.0 mol/L NaCl. After addition of V2O5, the CR decreased to 0.005 5 mm/a (0.01 mol/L) and 0.004 2 mm/a (0.05 mol/L). For 2205 DSS, the CR was 0.004 8 mm/a. After addition of V2O5, it decreased to 0.001 1 and 0.000 5 mm/a, corresponding to IE values of 77.08% and 89.58%. SEM/OP results showed that 316L SS in the inhibitor-free solution was covered with loose, piled corrosion products and exhibited typical uniform corrosion. After addition of Na3PO4 and especially V2O5, corrosion products were greatly reduced, and surface roughness decreased. For 2205 DSS, pitting dominated in the inhibitor-free solution. After addition of Na3PO4 or V2O5, pit density decreased, indicating improved film integrity.
XPS showed coexistence of V4+ and V5+ in the V2O5 system, together with changes in Fe 2p binding energy, indicating that vanadium participated in film construction and altered the local chemical environment of Fe in the film. In the Na3PO4 system, PO43--related signals appeared and the Fe spectra changed accordingly, supporting the formation of a phosphate-containing composite film. Based on electrochemical, immersion, and characterization evidence, it is concluded that the superior performance of V2O5 and Na3PO4 in the coupled high-temperature, highly alkaline, chloride-rich environment arises from their ability to build denser composite protective films (V-rich or phosphate-containing), which enhances barrier properties and suppresses interfacial charge transfer. By contrast, Na2MoO4 and Na2WO4 mainly act through passivation/deposition and are more susceptible to chloride competition and film destabilization under these conditions, resulting in weaker overall protection.
关键词
电解海水 /
无机缓蚀剂 /
316L不锈钢 /
2205双相不锈钢 /
腐蚀电化学
Key words
electrolysis of seawater /
inorganic corrosion inhibitor /
316L stainless steel /
2205 duplex stainless steel /
corrosion electrochemistry
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基金
国家重点研发计划（2023YFB4005100）; 国家自然科学基金青年科学基金项目（C类）（52201088）
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