Corrosion inhibitors of copper and its alloys based on plant raw materials and metal oxide nanoparticles

Abstract

The article examines the corrosion degradation of copper and tin bronze in the conditions of modern urban atmosphere, where the presence of sulfate, nitrate, and chloride ions leads to the formation of loose corrosion products and the development of local damages critical for roofing, facade, and decorative-sculptural elements. It is shown that replacing traditional synthetic inhibitors with more environmentally acceptable compositions is possible through the combination of phytochemical components of plant raw materials and metal oxide nanoparticles, forming hybrid organo-inorganic barrier layers. As a model material, bronze BrOF 10-1 (CuSn10P1) was used, tested in a city rain solution (Na2SO4/NaHCO3/NaCl at 0.2 g/L each, pH 4.5). Plant extracts of medicinal sage and wormwood were obtained by maceration; their phenolic pool and antioxidant characteristics were quantitatively compared (for sage: 145,8 mg GAE/g and 78,3% by DPPH), justifying enhanced adsorption capacity. ZnO and TiO2 nanoparticles were synthesized by the sol-gel method; zeta potentials close to the colloidal stability boundary (−28.4 and −31.6 mV) and average hydrodynamic diameters of 42.7 and 36.2 nm were established, determining the requirements for ultrasonic dispersion. Electrochemical evaluation revealed pronounced synergy: the Salvia/ZnO hybrid reduces the corrosion current density from 12,84 to 0.86 µA/cm² with 93,30% efficiency, while Salvia/TiO2 provides 91,04% (Icorr 1.15 µA/cm²); changes in Tafel slopes indicate a mixed inhibition mechanism with predominant effect on anodic processes. Cyclic voltammetry data show that the charge associated with surface transformations decreases from 18,42 to 2,15 µC/cm², interpreted as the formation of a dense dielectric barrier and restructuring of the energetics of interfacial reactions due to chemisorption. Microscopic analysis confirms pitting suppression: for optimal Salvia/ZnO, average depth decreases to 0,45 µm, affected area to 3,2%, roughness Ra to 0,65 µm. Adsorption is described by the Langmuir isotherm with modification of thermodynamic parameters upon nanoparticle introduction; comparison of data sets demonstrates high consistency and practical relevance for the protection and restoration of copper alloys in aggressive urban environments.