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

Abstract

A dedicated nuclear magnetic resonance (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 underdefined magnetic field gradients at a given position. The magnet thus combines properties of single sided NMR with high static magnetic field gradients and classical time domain (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 are highlighted in this publication. Relaxation and diffusion were measured by Carr–Purcell–Meiboom–Gill (CPMG) while varying the echo time τe and quantified via numerical modeling. 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.

Influence of Parasitic Electric Currents on an Exemplary Mineral-Oil-Based Lubricant and the Raceway Surfaces of Thrust Bearings

“…[33,34]), Nuclear Magnetic Resonance (NMR) spectroscopy (cf. [35,36], or dielectric spectroscopy) can detect the influence of the electrical load and which interactions occur between individual additives and the electrical fields resulting from the electrical load is not shown by the series of tests presented here.…”

Combined nuclear magnetic resonance methods in quality control of lubricants in green energy production

“…The two resulting distributions of transverse relaxation represent to a first approximation, the base oil CH 2 and CH 3 functional groups. [ 10 ] Mean diffusion coefficients <D CH2 > and < D CH3 > calculated from these data are identical, leading to the focus on <D CH2 > in the following.…”

“…A dedicated NMR sensor introduced in Rudszuck et al [ 10 ] was used for relaxation and diffusion measurements. It was equipped with a probe with a diameter of 42 mm operating at a Larmor frequency of 11.5 MHz.…”