Demystifying and Understanding Lubricants
Tags: industrial lubricants
Fourier transform infrared (FTIR) spectroscopy is an analytical technique used to determine chemical components in new and used oils using a single instrument. Information about the state of oxidation, nitration and sulfation of the oil and the levels of soot, moisture, glycol and various additives, among other things such as acid number, base number and moisture are detectable with FTIR.
This second article of a two-part series discusses some actual examples using the methodology written in Part 1.
The initial example illustrates the use of FTIR in a commonly used oil analysis application.
Example 1 - Spectral Subtraction
An example of spectral subtraction for a new and an in-service compressor lubricant is presented in Figure 1. This is often employed in used oil analysis to determine the relative progression of oxidation of an oil in service.
The new spectrum (a) could have been obtained by scanning a sample of the new oil by the laboratory performing the routine analysis, or it could have been retrieved from the COAT®1 System spectral library of benchmarked oils.
The in-service spectrum (b) was obtained by scanning a sample of the exact same compressor oil in service.
Spectrum (c) was generated by subtracting spectrum (a) from (b), the differential spectrum. It is beyond the scope of this article to determine the specific causes of peaks in the subtracted spectrum (c), but computer software is available to instantly crunch this data and report a snapshot of the lubricant condition.
The following examples illustrate the use of FTIR in a research environment.
Example 2 - Identifying Unknown Fluid
In Figure 2, an unknown "magic" fluid was marketed as a "biodegradable nontoxic diesel fuel conditioner and power booster". Using powerful software and a spectral library of known fluids and commercially available additives, an unknown fluid can be identified with reasonable accuracy. Spectral subtraction can be employed to determine the makeup of the material indicated by the remaining peaks in the spectrum. A simple visual analysis of the spectra demystifies most of the magic. Further analysis will break down the details of the formulation.
The FTIR determined this to be an oil based on vegetable oils, such as Canola oil with a cetane improver (alkylated nitrate) present in the concentration range of five to 10 percent.
Analysis of an aftermarket lubricant additive (ALA) marketed as a metal conditioner boasts the following performance benefits:
1. Provides a lubricity between moving components, which improves tolerances to the appropriate degree and increases efficiency with less wear.
2. Penetrates metal to form a tough, slippery, residual coating to all friction points.
3. Eliminates the rapid oxidation of motor oils.
4. Prevents buildup of engine contaminants and prepares deposits to be entrapped by the motor oil filter.
5. Gas mileage may increase by as much as eight to 10 percent with long-term use.
6. Circulates throughout the oil system to seal costly and dangerous leaks, reaching all gaskets to increase their seal protection and service life.
An initial hypothesis was formed based on the performance benefits listed above. Each comment below corresponds directly to the corresponding performance benefit listed above.
1. The ALA additive definitely contains oil, of which adequate amounts are already present in the motor oil.
2. The ALA additive possibly contains an ester base oil or additive (a polar molecule that adheres to and coats or wets metallic surfaces) and also possibly PTFE (Teflon™ ) because:
a. It is considered slippery.
b. The product itself does not appear black, thus eliminating molybdenum disulfide (MoS2) and graphite.
c. Contrary to this claim, PTFE will not form a residual coating.
3. The ALA additive likely contains an antioxidant, although adequate amounts already exist in the motor oil.
4. The ALA additive likely contains a detergent/dispersant additive, although again, adequate amounts are already present in the motor oil. It is the normal function of detergents and dispersants to "prepare deposits" to be eliminated by the filter. There is nothing unusual about this claim.
5. The gas mileage may - or may not - be increased.
6. The esters in the ALA additive will wet and penetrate seals. The product circulates with the oil and reaches all oil-wetted parts. Esters will increase the flexibility of gaskets if they dry out and will slightly swell seals and gaskets which may stop a leak.
An FTIR spectrum was taken of this metal conditioner and compared to the spectral library of lubricant additives and lubricants in Figure 3. Using UMPIRE®2 software, the program was able to identify components of the metal conditioner on the basis of their spectral fingerprints.
In Figure 3, specific regions in the spectrum of the metal conditioner are indicated in spectrum D. Note the peaks labeled phenol antioxidant, ester and halocarbon. These support the hypothesis above.
Spectrum A depicts a commercially available antioxidant that closely matches the peak of spectrum D.
Spectrum B depicts a commercially available colloidal suspension of PTFE in mineral oil and ester base oil. Notice how the spectrum appears similar to spectrum D.
Spectrum C is a spectrum of one percent A and B.
Dispersants/detergents additives, rust inhibitors, defoamers, etc. were also found using the same methodology, and were co-added to create a more complete spectrum match.
It is now evident that the fingerprint of D may be successfully reproduced from its likely components. However, most of the ingredients in the bottle of ALA additive are already present in premium motor oil, and are functioning in their intended jobs.
References
1 COAT® System FTIR based oil analyzer is a registered trade mark of Thermal-Lube Inc.
2 UMPIRE® proprietary software is a registered trade mark of Thermal-Lube Inc.
Given the power of FTIR spectroscopy and newly available IR spectra libraries, the potential exists for this tool to be more useful in oil analysis and identifying components of complex chemical mixtures.