From Localized Electrochemical Behavior to Interfacial Reaction Mechanisms: Evaluation of Corrosion Inhibitors for Active Pb-Containing Phases in Sanxingdui Embrittled Gold Masks

Abstract

The Sanxingdui gold masks are Au–Ag–Pb ternary alloys in which preferential corrosion of intergranular active Pb-containing phases causes severe embrittlement and threatens long-term preservation. Here, corrosion inhibitors for these vulnerable microdomains were evaluated by integrating microstructural characterization, scanning electrochemical cell microscopy (SECCM), and density functional theory (DFT) calculations. Sodium cysteinate (NaCys), sodium hexametaphosphate (SHMP), sodium silicate (NaSi), and sodium salts of saturated fatty acids (NaCn, C6–C18) were screened on simulated Au–Ag–Pb alloys. NaCys and SHMP induced pronounced Pb depletion, while NaSi formed a hydrophilic, cracked deposit with limited protection. In contrast, NaCn showed a pronounced but non-monotonic carbon-chain-length dependence. NaC9, NaC10, and NaC12 exhibited the best overall performance, with NaC10 providing the highest and most stable localized inhibition. Shorter chains produced less ordered and less hydrophobic films, whereas longer chains were limited by poor effective solubility and interfacial accessibility. DFT calculations showed that inhibition cannot be predicted from adsorption strength alone. By combining adsorption energy, Pb defect formation energy, and interfacial retention energy, we established an interfacial reaction criterion distinguishing stable film formation from inhibitor-induced Pb extraction, thereby introducing the concept of effective inhibitor interfacial reactivity for mechanism-guided conservation. This approach provides a targeted strategy for protecting Sanxingdui gold masks and other complex multiphase metallic heritage objects.