OXIDATION OF USED LUBRICANTS BY FT-IR USING PEAK AREA INCREASE CALCULATION: ASTM D7214
EXPLANATION
The peak area increase (PAI) is representative of the quantity of all the compounds containing a carbonyl function that have formed by the oxidation of the lubricant (aldehydes, ketones, carboxylic acids, esters, anhydrides, etc.). The PAI gives representative information on the chemical degradation of the lubricant which has been caused by oxidation. This test was developed for transmission oils and is used in the CEC-L-48-A-00 test as a parameter for the end of test evaluation. However, the test method is not intended to measure an absolute oxidation property that can be used to predict performance of an oil in service. The test may be used for other than in-service transmission oils also; however, the stated precision may not apply.
TEST SUMMARY
FT-IR spectra of the fresh and the used oils are recorded in a transmission cell of known pathlength. Both spectra are converted to absorbance mode and then subtracted. Using this resulting differential spectrum, a baseline is set under the peak corresponding to the carbonyl region around 1650 cm(-1) and 1820 cm(-1) and the area created by this baseline and the carbonyl peak is calculated. The area of the carbonyl region is divided by the cell pathlength in mm and this result is reported as peak area increase.
INTERFERENCES - Some specific cases (very viscous oil, use of ester as base stock, high soot content) may require dilution of the sample and a specific area calculation as described in the method. The results of this test method may be affected by the presence of other components with an absorbance band in the zone of 1600 to 1800 cm(-1). Low PAI values may be difficult to determine in those cases.
TEST PRECISION
Repeatability: 0.029(x + 9)
Reproducibility: 0.26(x + 35)
Where x is the average of two results.
The bias of this test method cannot be determined because there is no certified reference standard for these properties available.
