Proton Field Cycling NMR Relaxometry of Comercial Lubricants

M. BALLARI; E. ANOARDO; F. BONETTO

Torino, Italia

Conferencia; 3º Conference on Field Cycling Relaxometry; 2003

Universidad de Torino, Italia

Engineering performance of lubricants is closely related to its molecular structure and functionality of additives. Relationships between bulk macroscopic properties and molecular dynamic or structure are still not clearly understood. Aging and degradation of motor-oil lubricants are still less clear from a microscopic point of view. Standard quality analysis of lubricants includes the use of Fourier-transform infrared (FTIR) spectroscopy. This method allows to quantify some components in a chemical mixture (either organic or inorganic),  most used to get fingerprints of selected patrons, later used to compare and identify components in the spectrum of an unknown sample. In lubricant analysis, FTIR is commonly used to monitor oxidation, nitration, sulfating, production of carbonyl-containing species, fuel dilution, water component, additive depletion, soot, and glycol, between others. Other important and commonly used analysis in lubricant quality control are determination of wear metals and cinematic viscosity. Therefore, any NMR study aimed to investigate possible links between the macroscopic properties and the microscopic behavior, can be compared with FTIR results and the macroscopic parameters. On these grounds, we started to consider the use of NMR relaxometry as a potential tool for inquiring about degradation processes than may alter the molecular dynamics in motor-oil lubricants. A first striking and promising result was the fact that differences between new and aged specimens manifest in the low frequency range. T1 dispersions were studied in two different commercial lubricants (each one new and used) and interpreted in terms of self-diffusion and molecular rotations. The analysis revealed a noticeable sensitivity of the involved correlation times with the oil aging. From a comparison with qualitative FTIR spectroscopy analysis and different measurements like cinematic viscosity, flash and flame points, we were able to correlate the relaxation dispersions with the dominant aging factors.