The Influence of pH Value on Corrosion Behavior of Warring States Type Tin Bronze in Simulated Red Soil Solutions

ABSTRACT

Acidic red soils can destabilize corrosion‐product films on archeological tin bronzes, but the pH threshold for film failure remains unclear. Here, a Cu‐Sn alloy containing 9.8 wt.% Sn (Sn9.8), selected according to representative Warring States bronze weapons from Yunnan, was exposed to simulated red soil solutions with pH values of 3.5–5.5. Electrochemical measurements combined with SEM‐EDS, Raman spectroscopy, and XPS show a sharp transition at pH 4.0. At pH > 4.0, selective Sn oxidation promotes a hydrated Sn(IV)‐rich oxide/hydroxide film and increasing charge‐transfer resistance. At pH ≤ 4.0, high H ⁺ concentration destabilizes this film, exposes the Cu‐rich matrix, and promotes active dissolution with Cu‐rich chloride‐containing products. The results identify pH 4.0 as a critical acidity threshold and support pH control, dechlorination, and post‐excavation stabilization of bronze relics.