Machinery Lubrication magazine published by Noria Corporation
Issue link: http://www.e-digitaleditions.com/i/544388
8 | July - August 2015 | www.machinerylubrication.com FROM THE FIELD JEREM Y WRIGH T | NORI A CORPOR AT ION ourier transform infrared (FTIR) spectroscopy is a versatile tool used to detect common contaminants, lube degradation byproducts and additives within lubri- cating oils. It has become a widely used technique for quickly assessing multiple lubricant characteristics, and yet many people don't fully understand how it works. When exposed to infrared radiation, molecules absorb radiation at very specifi c wave- lengths. Knowing this, you can pass infrared radiation through a sample and use a detector on the other side of the sample to identify the molecules found in that sample. Much like a fi nger- print, no two molecules produce the same pattern or wavelength. This is very useful in being able to identify the material composition of a sample. Qualitative analysis becomes easy because of this fact. When a software algorithm is used to plot the resulting spectrum, a visual representation is generated. This test method is relatively quick to perform and is capable of simultaneously detecting multiple parameters, including antioxi- dants, water, soot, fuel, glycol, oil oxidation and certain additives. Adding to the power of this qualitative measurement, the size of the peaks is a direct indication of the amount of the specifi c material found in the sample. For a better understanding, let's take a more in-depth look at the process and anatomy of analyzing a sample. The fi rst compo- nent in the system is the source. The source will emit infrared energy and send it through an aperture to control the amount being presented to the sample. Next, the beam enters the interferometer where it is "encoded" using a series of stationary and movable mirrors. This encoding is a way to produce a signal that consists of all the important infrared frequencies simultaneously. The beam then enters the sample, and certain frequencies of the energy are absorbed. The energy that escapes the sample is sent to the detector where it is measured. This measured signal is then sent to a computer where Fourier transformation takes place. Fourier transformation is a mathematical process where a waveform can be broken into an alternate representation for easy viewing. At this point, the results are plotted on the screen, and a simple analysis can be made by the technician. Since most used oil samples are complex mixtures of thousands of different molecules, including base oil molecules, additives, oil degradation byproducts, wear debris and contaminants, the infrared spectrum of the sample is typically complex and can be diffi cult to interpret with any degree of certainty, as some wave- numbers may overlap. Despite these drawbacks, FTIR still has great value in used oil analysis and is employed by the majority of oil analysis labs as a screening tool. BENEFITS of FTIR OIL ANALYSIS F Wavenumber Antioxidant Water Soot Oxidation Nitration Sulfation 3900 3500 3100 2700 2300 1900 1500 1100 700 Glycol AW Fuel 5. Computer Spectrum Interferogram Spectrometer 1. Source 3. Sample 4. Detector 2. Interferometer O i l A n a l y s i s Source Detector Energy Energy Wavelength Wavelength