PerkinElmer OilExpress 4, User Manual

Page: 11 / 152

Introduction . 11
Introduction to Oil Analysis by Infrared
Spectroscopy
The OilExpress 4 System is an automated system that uses infrared (IR) analysis to monitor
additive depletion, contaminant build-up and base-stock degradation of in-service lubricants
and hydraulic fluids. A range of analysis methods for measuring these parameters are
supplied, including standard methods for Mineral Oils, Synthetic Oils, the Joint Oil Analysis
Program (JOAP) and ASTM. Within OilExpress 4 software, methods can be added or deleted,
and the existing methods customized.
Infrared Absorption
The chemical bonds within organic molecules are in a state of continual vibration, with bonds
stretching and contracting as well as bending relative to each other. When an infrared beam
falls on a molecule, waves of specific frequencies are absorbed from the beam by the
molecule. The actual frequencies absorbed depend on the types of bonds present in the
molecular structure. Chemical bonds within a molecule are said to exhibit “characteristic
infrared absorptions”.
A record of the frequencies at which absorption takes place for an organic compound is
called its infrared spectrum. An infrared spectrum of a compound will reveal information
about its molecular structure, as the existence of specific groups of atoms may be confirmed
from the presence of their characteristic absorptions. The spectrum of a mixture of
compounds contains contributions from all of the compounds.
As a lubricant wears, its composition changes as additives are depleted and contaminants
and breakdown products accumulate. As each of these compounds has a distinct infrared
spectrum, the spectrum of the lubricant will change and these changes can be used to assess
the condition of the lubricant.
An example of the changes seen as a lubricant wears is shown in Figure 2.
4000 550 3500 3000 2500 2000 1500 1000
1.5
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
cm-1
A
Figure 2 Spectra of unused and used diesel engine oil
Used oil
New oil
Water
Soot
Oxidation
Nitration
Phosphate
antiwear