Biodiesel is a renewable fuel consisting of alkyl esters, which show a higher corrosive behavior when compared with a diesel fuel. The corrosive processes by biodiesel affects the processing infrastructure of this biofuel and mechanical parts of automotives. Valves, engine blocks, and cylinder liners are gray cast iron components affected by biodiesel corrosion. The corrosion resistance of niobium carbide (NbC) coatings deposited using thermoreactive diffusion (TRD) on gray cast iron in continuous contact with diesel fuel and palm biodiesel was studied. Both coated and uncoated samples were subjected to immersion tests, cyclic oxidation at 473 K, and an electrochemical impedance spectroscopy (EIS) test. The coatings were characterized by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD). Both the rate of corrosion by immersion and the resistance to polarization via EIS showed the favorable behavior of niobium carbide coatings against the corrosion of palm biodiesel. The corrosion rate on samples coated with niobium carbide was three times lower than that of the gray casting samples. These results allow the conclusion that niobium carbide coatings could be a viable alternative to lessening the corrosive effects of palm biodiesel in the applications where gray cast iron is used in continuous contact with biofuel.

Palm biodiesel is a currently used biofuel, principally as an additive or substitute of diesel fuel in vehicular internal combustion engines. In the present work, vanadium carbide (VC) coatings were deposited on gray cast iron (GCI) using the thermoreactive diffusion process (TRD) to evaluate the corrosiveness of palm biodiesel and compare it with gray cast iron corrosion behavior. VC coated and uncoated gray cast iron samples were tested by immersion corrosion tests (291 K and 313 K), cyclic oxidation test (CO), and the electrochemical impedance spectrometry test (EIS). The corrosion test showed the reduction of the corrosion rate for the VC coating when compared to gray cast iron. EIS tests of coated samples showed higher values of polarization resistance when compared with uncoated gray cast iron samples. Results confirmed that while biodiesel was more corrosive than diesel on both coated and uncoated gray cast iron, the VC coating was efficient in protecting the substrate exposed to both fuels.