CHARACTERIZATION OF A HISTORICAL CANNONBALL FROM THE FORTRESS OF SAN JUAN DE ULUA EXPOSED TO A MARINE ENVIRONMENT

摘要

Metallurgical analyses and chemical characterizations were carried out on historical cannonballs from the Fortress of San Juan de Uhia, Veracruz, Mexico. Cannonballs dating from the 18th and 19th centuries share metallurgical characteristics similar to those of material coming from a shipment of ammunition found in the wreck of a sunken French ship from the battle of Trafalgar. The analyses show that the base material is grey cast iron with a carbon equivalent of 4.94 and a ferritic-perlitic matrix, in which the high phosphorus content has led to the formation of iron phosphide compounds in conjunction with a homogeneous distribution of carbon graphite flakes of Type C. In addition, corrosion products from samples revealed the presence of various crystalline iron compounds (X-ray diffraction), mostly highly chlorinated iron compounds identified as akaganeite. X-ray fluorescence identified various characteristics of the corrosion products as a function of the sampling depth. FT-IR spectroscopy revealed that the main difference between the corrosion products (internal and external) is determined by the number of organic species. Differential scanning calorimetry corroborated that these corrosion products are thermally stable compounds at elevated temperatures.