Corrosion behavior of metallic surfaces in biodiesel evaluated by Atomic Force Microscopy, Vickers Micro Hardness, and Copper Strip Test

The biodiesel presents advantages as a fuel compared with diesel, being an alternative to replace fossil fuels. It can be produced with renewable sources, for example, vegetal oils, animal fats, and sugarcane ethanol. The main problems of biodiesel are affinity with water, low oxidative stability, and free fatty acids that can increase the corrosiveness of this fuel. In this work, it was evaluated the corrosiveness of biodiesel on metallic samples by Atomic Force Microscopy, Vickers Micro Hardness, and Copper Strip Test. Different biodiesel samples were produced and characterized by water concentration, specific mass, acid index, ester concentration, and copper corrosivity. Simulations of storage tanks were performed during 30 and 60 days, with metallic samples (Stainless Steel, Carbon Steel 1020, Iron, Copper, and Piston parts) immersed in biodiesel. The results of Copper Strip Tests did not show corrosion. The Vickers Micro Hardness did not indicate modification of the metallic samples. The Atomic Force Microscopies indicated that the biodiesel samples corroded the metallic surfaces (Copper, Iron, and Piston) and the samples with higher water concentration and higher acidity showed higher corrosive activity. The 60 days simulation showed corrosion and indicated that even quality biodiesel can affect metallic surfaces and piston parts.