10
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July - August 2015
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www.machinerylubrication.com
COMPONENT SPECTRAL LOCATION MEASUREMENT TRADITIONAL MEASUREMENT SENSITIVITY
Soot 2000 Carbon Load Total Insolubles Insensitive
Oxidation 1750 Oil Degradation BN, AN, Viscosity Partially
Nitration 1630 Oil Degradation BN, AN, Viscosity Partially
Sulfation 1150 Oil Degradation BN, AN, Viscosity Partially
Water 3400 Contaminant Karl Fischer Partially
Glycol 880 Contaminant Gas Chromatography (GC) Very
Diesel 800 Contaminant Flash Point, Viscosity, GC Extremely
Gasoline 750 Contaminant Flash Point, Viscosity, GC Extremely
ZDDP (AW) 980 Additive Elemental Spectroscopy Extremely
Abs
New Oil Spectrum
Used Oil Spectrum
Difference Spectrum
1-
2-
1-
0.2-
0.4-
0.6-
0.8-
2-
3-
3500
4000
Water
(3400)
Wavenumber
Soot
(200)
Oxidation
(1740)
Nitration
(1630)
Sulfation
(1150)
Glycol
(1040)
Diesel
Fuel
(800)
3000
2500
2000
1500 1000
FTIR is a valuable
addition to any oil
analysis program.
To minimize the effects of the base oil and additive molecular
resonances, FTIR analysis of used oil samples is a three-stage
process. The fi rst stage is to record the FTIR spectrum of a new oil
sample to obtain a baseline FTIR trace. The second stage is to record
the same FTIR spectrum of the used oil sample. The third and fi nal
stage is to subtract the new oil baseline, often referred to as the new
oil reference, from the used oil spectrum to obtain the difference
spectrum. In theory, the difference spectrum allows the changes in
both the chemical composition of the oil, such as oil oxidation
(represented by an increase in a peak centered around 1740 cm-1),
and any contaminants to be measured without interference from the
new oil molecular resonances.
The one major limitation of this difference spectrum procedure is
that it is often not practical to send a sample of new oil with the
used oil sample each time analysis is required. In order for the proce-
dure to be accurate, the new oil reference for this purpose should
not only be the same type, brand and grade as the used oil, but also
from the same manufactured batch of oil.
Another area where FTIR can prove extremely valuable is in
determining signifi cant changes in oil chemistry, such as what might
