防止银器文物变色的唑系复合缓蚀剂Ⅱ. SERS法研究唑系缓蚀剂防银变色的作用机理

测定了 PMTA、MBO、MBI的普通拉曼光谱 ( NRS) ,利用表面增强拉曼散射光谱( SERS)研究了几种唑系缓蚀剂防止银器文物变色的表面成膜过程 ,复合缓蚀剂组分与银的相互作用 ,并讨论了其防变色作用的机理。实验结果表明 ,PMTA、MBI和 MBO与银表面存在着较强的相互作用 ,由于杂环结构的差异 ,不同缓蚀剂在银表面上呈现不同的吸附取向 ,形成了更为致密的防变色保护膜。在成膜溶液中 ,p H值较小时有利于缓蚀剂吸附 ,处理时间应不少于 1 2 0 min。成膜溶液和含缓蚀剂的硫化钠溶液中 ,银电极阴极极化时 (外加阴极电位≤ 60 0 m V的测试范围内 ) ,复合缓蚀剂的 SERS响应均随电位负移而增强 ,表明其可有效防止银在腐蚀介质中的变色行为

Azoles as Composite Corrosion Inhibitor for Anti tarnishing of Silver Antiques II. Mechanism of the Azoles for Anti tarnishing of Silver

The normal Raman spectra (NRS) of PMTA, MBO and MBI were measured. Surface enhanced Raman scattering (SERS) was used to study the surface filming processes of these azoles corrosion inhibitors for anti tarnishing of silver, and the interactions between components of composite corrosion inhibitor and silver surface. The mechanism of anti tranishing of silver was also discussed. The experimental results show that there are strong interactions between corrosion inhibitors and silver surface. As constituents of the composite inhibitor with different cycle configuration take on different adsorption directions on the silver surface, much more compact anti tarnishing film is formed. In the pretreatment solution , weak acid pH value is beneficial to the adsorption of corrosion inhibitor and pretreatment time should not be less than 120 min. Under the condition of cathodic polarization with additional potential less than 600mV, in the pretreatment solution and the solution of sodium sulfide, the SERS response ofcomposite corrosion inhibitor becomes stronger as the potential becomes lower. It is proved that the com posite corrosion inhibitor can prevent silver tarnish effectively from corrosion medium.