Enhanced Corrosion Resistance of Carbon Steel in Hydrochloric Acid Solution by Polyoxometalate-Estertin Derivatives

The development of
acid-resistant and efficient corrosion inhibitors
is of great significance for metal protection in many industrial processes.
In this work, eight cases of sandwich-type polyoxometalate (POM)-based
inorganic–organic hybrids, namely, carboxyethyltin and transition
metal (TM) cofunctionalized tungstoantimonates and tungstobismuthates,
formulated as NaxK10–x[(SnR)2(TM­(H2O)3)2(B-β-SbW9O33)2]·mH2O and NayK10–y[(SnR)2(TM­(H2O)3)2(B-β-BiW9O33)2]·nH2O (abbreviated
as SbW9-TM-SnR and BiW9-TM-SnR; TM = Mn, Co, Ni, and Zn; m = 18, 24, 24, and 22; n = 30, 25, 20, and 21; SnR = Sn­(CH2CH2COO)) are first used as green corrosion inhibitors for 20# carbon steel in 0.5–2.0 M HCl solutions. Weight loss and
electrochemical experiments prove that the corrosion inhibition efficiency
is all above 81% for these POM-based corrosion inhibitors at 150 mg
L–1, and SbW9-Mn-SnR shows
the highest efficiency of 96.9% at 150 mg L–1 after
immersion in a 0.5 M HCl solution for 10 h. Scanning electron microscopy–energy-dispersive
X-ray spectroscopy and X-ray photoelectron spectroscopy analyses show
that these POM-based inhibitors form films on the carbon steel and
the adsorption mechanism obeys the Langmuir adsorption model. The
thermodynamic activation parameters were calculated, proving the occurrence
of both chemical and physical adsorptions. The film-forming mechanism
was also analyzed. This work provides guidance for synthesizing new
lacunary POM-based materials to protect metals from corrosion in HCl
pickling.

耐酸高效缓蚀剂的开发对于众多工业过程中的金属防护具有重要意义。
本工作中，8例基于夹心型多金属氧酸盐（polyoxometalate, POM）的无机-有机杂化物，即羧乙基锡与过渡金属（transition metal, TM）共同功能化的钨锑酸盐与钨铋酸盐，其化学式分别为NaxK10–x[(SnR)2(TM(H2O)3)2(B-β-SbW9O33)2]·mH2O与NayK10–y[(SnR)2(TM(H2O)3)2(B-β-BiW9O33)2]·nH2O（缩写为SbW9-TM-SnR与BiW9-TM-SnR；其中TM=Mn、Co、Ni、Zn；m=18、24、24、22；n=30、25、20、21；SnR=Sn(CH2CH2COO)），首次被用作20#碳钢在0.5~2.0 mol/L盐酸溶液中的绿色缓蚀剂。
失重实验与电化学实验结果表明，上述多金属氧酸盐基缓蚀剂在投加量为150 mg/L时，缓蚀效率均可达81%以上；其中SbW9-Mn-SnR在0.5 mol/L盐酸溶液中浸泡10 h后，缓蚀效率最高可达96.9%。
扫描电子显微镜-能量色散X射线能谱与X射线光电子能谱分析显示，此类多金属氧酸盐基缓蚀剂可在碳钢表面成膜，且其吸附机制符合朗缪尔吸附模型。通过计算得到的热力学活化参数证实，该过程同时存在化学吸附与物理吸附。本研究还对成膜机制进行了分析。
本工作为合成新型缺位型多金属氧酸盐基材料以保护金属免受盐酸酸洗腐蚀提供了指导思路。