NMR Diffusion and Relaxation for Monitoring of Degradation in Motor Oils

Abstract

Different nuclear magnetic resonance (NMR) methods such as spectroscopy, diffusometry and relaxometry are applied with the aim to monitor motor oil degradation. Chemical degradation is detected by ¹H NMR spectroscopy. With respect to quality control, low-field NMR is the established technique, which mostly uses relaxation and diffusion. Conventional methods such as mono-exponential data modeling lead to inadequate description of relaxation and diffusion data of complex fluids like motor oils. Inverse Laplace transform has difficulties in quantification, comparability and interpretation. Therefore, various data processing approaches are investigated to obtain the physico-chemically and numerically most correct description of the data. The gamma distribution model for diffusion and also for T₁ and T₂ relaxation data numerically describes the data with high accuracy. Three differently degraded motor oils were exemplarily investigated with regard to spectroscopic, relaxation and diffusion parameters.