Dedicated NMR sensor to analyze relaxation and diffusion in liquids and its application to characterize lubricants.

Abstract

A dedicated NMR sensor was designed for the analysis of liquids. The magnets are arranged in a V-shape, creating a spatially dependent magnetic field in the gap. Measurements of samples with diverse diameters are possible under defined magnetic field gradients at a given position. The magnet thus combines properties of single sided NMR with high static magnetic field gradients and classical TD devices with lower to almost zero gradients. The sensor can easily be adapted to the requirements of the considered investigation, probes can be customized. On the example of lubricants and their aging, the added value and applicability of this sensor in quality control is highlighted in this publication. Relaxation and diffusion were measured by CPMG while varying the echo time τe and quantified via numerical modelling. Especially relaxation shows a high sensitivity towards aging of lubricants such as particulate abrasion and changes in molecular dynamics induced, for example, by additive depletion. The applicability of this NMR-sensor in quality control is demonstrated on the example of engine and transmission oils as well as of lubrication greases.