Monitoring of Lubricating Oil Degradation Via Fast Field Cycling NMR Relaxometry

Abstract

Motor oils are composed of a hydrocarbon mineral or synthetic blend (base oil), conveniently combined with specific chemicals aimed to prevent degradation and improve their functionality and lifespan. Oxidation, nitration, sulphating and contamination are the most common factors to consider, while thermal stress is one of the most aggressive chemical degrading mechanisms. The fast field-cycling NMR relaxometry technique has been successfully used to characterize chemical degradation in oil bases and lubricants. Our studies have suggested that the spin–lattice relaxation rate R1 measured at low field (Larmor frequencies lower than 2 MHz) and preferably at room temperature (or lower) meets optimal analytical conditions that are vastly superior to spin–spin relaxation R2 analytics at low temperatures (−10 °C to 10 °C) in the MHz frequency range. The proposed theoretical relaxation model has shown good consistency with pulsed field-gradient measurements of diffusion and other relaxation experiments performed on fixed-field instruments. Among others, applications in a short time include detection of adulteration and other forensic needs related to oils, fingerprint fast testing, efficiency and durability testing of additives and quality determination of mineral or synthetic bases.