Corrosion Characteristics of XVII Century Portuguese Cast Iron Cannon from Goa (India) Using Spectroscopic Analysis

The study investigates the corrosion behavior and microstructural changes in seventeenth-century cast iron cannons exhibited at the Archaeological Museum in Goa. Chipped samples from four cannons underwent analysis for surface morphology, microstructure, and elemental composition using optical microscopy, SEM-EDX, and X-ray diffraction. FTIR spectroscopy was employed to identify the molecular structure of organic compounds, metal oxides, and oxyhydroxides on the surface. The findings reveal that the pearlite matrix of the cast iron contains graphite flakes, leading to a distinctive form of graphitic corrosion on the cannon surface. Highly localized graphitic corrosion areas on the surface have resulted in pits or series of pits, posing a potential risk to the structural integrity of the cannons over time. The study identifies the presence of chloride as a contributing factor to the corrosion process, working in tandem with graphitic corrosion of the cast iron. Understanding these corrosion mechanisms is crucial for developing strategies to ensure the long-term preservation of these historical artefacts.