1、Designation: D 7214 07An American National StandardStandard Test Method forDetermination of the Oxidation of Used Lubricants by FT-IRUsing Peak Area Increase Calculation1This standard is issued under the fixed designation D 7214; the number immediately following the designation indicates the year of
2、original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.INTRODUCTIONThis test method was jointly developed with “Groupement Fr
3、ancais de Coordination” (GFC),technical committee LM5 and “Coordinating European Council” (CEC) Surveillance Group T-048 forthe purpose of monitoring the oxidation stability of artificially aged automotive transmission fluids.This test method has been used in the CEC L-48-A-00 method as an end of te
4、st measurementparameter.1. Scope*1.1 This test method covers the determination of the oxida-tion of used lubricants by FT-IR (Fourier Transform InfraredSpectroscopy). It measures the concentration change of con-stituents containing a carbonyl function that have formedduring the oxidation of the lubr
5、icant.1.2 This test method may be used to indicate relativechanges that occur in an oil under oxidizing conditions. Thetest method is not intended to measure an absolute oxidationproperty that can be used to predict performance of an oil inservice.1.3 This test method was developed for transmission
6、oilswhich have been degraded either in service, or in a laboratorytest, for example a bulk oxidation test. It may be used for otherin-service oils, but the stated precision may not apply.1.4 The results of this test method may be affected by thepresence of other components with an absorbance band in
7、 thezone of 16001800 cm-1. Low PAI values may be difficult todetermine in those cases. Section 6 describes these possibleinterferences in more detail.1.5 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.6 This standard does not
8、 purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards
9、:2D 4057 Practice for Manual Sampling of Petroleum andPetroleum ProductsD 4177 Practice for Automatic Sampling of Petroleum andPetroleum ProductsD 6299 Practice for Applying Statistical Quality AssuranceTechniques to Evaluate Analytical Measurement SystemPerformanceE 131 Terminology Relating to Mole
10、cular SpectroscopyE 1421 Practice for Describing and Measuring Performanceof Fourier Transform Mid-Infrared (FT-MIR) Spectrom-eters: Level Zero and Level One TestsE 1866 Guide for Establishing Spectrophotometer Perfor-mance Tests2.2 CEC Standard:CEC L-48-A-00 Oxidation Stability of Lubricating OilsU
11、sed in Automotive Transmissions by Artificial Aging33. Terminology3.1 DefinitionsFor terminology relating to molecularspectroscopic methods, refer to Terminology E 131.3.2 Definitions of Terms Specific to This Standard:1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Pro
12、ducts and Lubricants and is the direct responsibility of SubcommitteeD02.96 on In-Service Lubricant Testing and Condition Monitoring Services.Current edition approved July 15, 2007. Published August 2007. Originallyapproved in 2006. Last previous edition approved in 2006 as D 721406.2For referenced
13、ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from Coordinating European Council (CEC), c/o Interlynk Admin-istr
14、ative Services, Ltd., P.O. Box 6475, Earl Shilton, Leicester, LE9 9ZB, U.K.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.1 carbonyl region, nregion of the FT-IR
15、spectrumcorresponding to the absorbance of compounds containing acarbonyl function. Depending on the nature of the carbonylcompounds, this region is usually located between approxi-mately 1820 cm-1and 1650 cm-1.3.2.2 differential spectrum, nFT-IR absorbance spectrumresulting from the subtraction of
16、the fresh oil from the used oil.3.2.3 PAI (peak area increase), narea of the carbonylregion of the differential FT-IR spectrum, divided by the cellpathlength in millimetres. In this standard, PAI refers to arelative measurement of the oxidation of a used lubricant byFT-IR.4. Summary of Test Method4.
17、1 FT-IR spectra of the fresh oil and of the used oil arerecorded in a transmission cell of known pathlength. Bothspectra are converted to absorbance and then subtracted. Usingthis resulting differential spectrum, a baseline is set under thepeak corresponding to the carbonyl region around 1650 cm-1an
18、d 1820 cm-1and the area created by this baseline and thecarbonyl peak is calculated. The area of the carbonyl region isdivided by the cell pathlength in millimetres and this result isreported as Peak Area Increase (PAI).5. Significance and Use5.1 The PAI is representative of the quantity of all thec
19、ompounds containing a carbonyl function that have formed bythe oxidation of the lubricant (aldehydes, ketones, carboxylicacids, esters, anhydrides, etc.). The PAI gives representativeinformation on the chemical degradation of the lubricant whichhas been caused by oxidation.5.2 This test method was d
20、eveloped for transmission oilsand is used in the CEC L-48-A-00 test (Oxidation Stability ofLubricating Oils Used in Automotive Transmissions by Artifi-cial Aging) as a parameter for the end of test evaluation.6. Interferences6.1 Some specific cases (very viscous oil, use of ester asbase stock, high
21、soot content) may require a dilution of thesample and a specific area calculation, which are described in14.1-14.3. In those cases, the result is corrected by a dilutionfactor, which is applied to the sample.7. Apparatus7.1 FT-IR Spectrophotometer, suitable for recording mea-surements between 1650 c
22、m-1and 1820 cm-1and with aresolution of 4 cm-1.7.2 Transmission Cell, with windows of potassium bromide,having a known pathlength of approximately 0.025 to 0.1 mm.7.3 Syringe, or Other Automated or Semi-Automated De-vice, with adequate volume to fill the cell, for example, 2 mL.8. Reagents and Mater
23、ials8.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall reagents shall conform to the specifications of the commit-tee on Analytical Reagents of the American Chemical Society,where such specifications are available. Other grades
24、 may beused, provided it is first ascertained that the reagent is ofsufficiently high purity to permit its use without lessening theaccuracy of the determination.8.2 Heptane, used as cleaning solvent. Other solvents andsolvent mixtures may be used provided they adequately cleanthe cell(s) between sa
25、mples. A 50/50 mixture of cyclohexaneand toluene has been found to be useful in cleaning cells afterhighly contaminated and degraded samples have been run.(WarningFlammable.)8.3 PAO4, used as dilution oil (PAO4: PolyAlphaOlefinwith a kinematic viscosity at 100C of approximately 4 mm2/s)9. Calibratio
26、n and Standardization9.1 Calculation of the Cell PathlengthUse a cell with aknown pathlength of approximately 0.025 to 0.1 mm. Calibratethe infrared cell pathlength using the interference fringemethod:9.1.1 Acquire the background infrared spectrum. Insert theempty infrared cell into the infrared spe
27、ctrometer samplecompartment and acquire the cell infrared spectrum. The finalspectrum is obtained by subtraction of the background spec-trum from the cell spectrum.NOTE 1This computation is generally an integral part of the infraredspectrometer software.9.1.2 Choose 2 minima separated by about 20 me
28、asurableinterference fringes as shown in Fig. 1. Count the number ofinterference fringes between the lower and the higher wave-numbers, referred to as l1and l2.NOTE 2The spectral range may be chosen freely in an area where thefringes are regular.9.1.3 The cell pathlength is calculated by the formula
29、:e 55nl12l2!(1)where:e = the pathlength in mm, andn = the number of fringes between l1and l2.9.2 Instrument Performance Checks:9.2.1 Periodically, the performance of the FT-IR instrumentshould be monitored using the Level 0 procedure of PracticeE 1421. If significant change in performance is noted,
30、thentesting should be suspended until the cause of the performancechange is diagnosed and corrected.9.2.2 Alternative instrument performance tests conformingto the recommendations of Guide E 1866 may be substitutedfor the Practice E 1421 test.10. Conditioning10.1 Before using the infrared cell ensur
31、e that it is clean bywashing through with a suitable solvent, for example, heptane.Dry the cell using dry air or nitrogen, if necessary. Calibratethis cell as described in Section 9.11. Preparation of Sample of Used Oil11.1 Refer to Practice D 4057 (Manual Sampling) or Prac-tice D 4177 (Automatic Sa
32、mpling) for proper sampling tech-niques.11.2 When sampling used lubricants, the specimen shall berepresentative of the system sampled and shall be free ofD7214072contamination from external sources. As used oil can changeappreciably in storage, test samples as soon as possible afterremoval from the
33、lubricating system and note the dates ofsampling and testing.11.3 If the sample of used oil contains visible sediment, heatto 60 6 5C in the original container and agitate until all of thesediment is homogeneously suspended in the oil. If the originalcontainer is a can or if it is glass and more tha
34、n three-fourthsfull, transfer the entire sample to a clear-glass bottle having acapacity at least one third greater than the volume of thesample. Transfer all traces of sediment from the originalcontainer to the bottle by vigorous agitation of portions of thesample in the original container.12. Proc
35、edure12.1 Record the background spectrum, and subtract it fromall subsequent spectra at least once per day.12.2 With a syringe or other injection device, fill the cellwith the fresh oil, and record its spectrum. Accumulate anadequate number of scans for a satisfactory signal to noise ratioof 2 mAbs
36、2000 cm-1.12.3 Empty and clean the cell with heptane, fill it with theaged oil and record its spectrum.NOTE 3It may happen that the aged oil is too viscous to fill the cell.Then it is possible to proceed to a dilution as described in 12.4.1.12.4 Convert fresh and aged oil spectra to absorbance andsu
37、btract them; a differential spectrum is obtained (see Fig. 2).Locate and zoom on the carbonyl region centered at 1720 cm-1.Processing may continue if the maximum absorbance of thiscarbonyl region is lower than 1.5.NOTE 4Since the carbonyl region absorption minima (close to 1820cm-1and 1650 cm-1) can
38、 vary with the type of oil sample being tested, itwas decided not to use fixed baseline limits for calculating the area A.NOTE 5The carbonyl band may consist of more than one peakmaxima.NOTE 6Do not calculate the differential peak area by difference of thepeak area of the aged oil with the peak area
39、 of the fresh oil.12.4.1 If the maximum absorbance of the carbonyl region ofthe differential spectrum is higher than 1.5: dilute with 1 %accuracy by weight both fresh and aged oils with the samedilution factor, D (PAO 4 is recommended as dilution oil). Forexample,D=2fora50%(1:1) wt/wt dilution. Reco
40、rd the twospectra, convert them to absorbance and subtract them. If themaximum absorbance of the carbonyl region is still higher than1.5, then use a higher dilution factor. This occurrence couldhappen in the case of ester or soot-containing oils.NOTE 7The cell pathlength may be changed to 0.05 mm or
41、 0.025 mmif absorbance in the assessment area is greater than 1.5.NOTE 8Dilution factors are commonly chosen between 2 and 10.12.4.2 If the maximum absorbance of the carbonyl region ofthe differential spectrum is lower than 1.5: draw a base lineconnecting the absorption minima located at each side o
42、f thisregion as shown on the spectrum in Fig. 2. These minima areusually close to 1820 cm-1and 1650 cm-1within 6 20 cm-1.Calculate and record the differential peak area as area A. (Thismay be done automatically with the spectrometer software.)FIG. 1 Example of Interference Fringes for Cell Pathlengt
43、h CalculationD721407313. Calculation of Results13.1 The results are reported as PAI (peak area increase):carbonyl region area, A multiplied by the dilution factor, D anddivided by the cell pathlength, e in mm:PAI 5area Ae mm!3 D (2)13.1.1 If no dilution was needed, the dilution factor, D is 1.14. Pr
44、ocedures for Interferences14.1 The results of this test method may be affected by thepresence of other components with an absorbance band in thezone of 16001800 cm-1. Low PAI values may be difficult todetermine in those cases. The following procedures may beused if interferences are present.14.2 Soo
45、t-Containing OilsThe presence of soot degradesthe spectra by decreasing the transmittance level. This casemay require a dilution as described in 12.4 in order to obtain anabsorbance lower than 1.5.14.3 Ester-Containing OilsThe ester functions containedin some lubricants, especially those formulated
46、with ester baseoil, interfere with the oxidation peak. Dilution may be neededwith these types of lubricants and it is recommended to use acell with a small pathlength (0.05 mm maximum). Check theshape of the spectrum before interpreting it. The residualpositive or negative peaks at 1740 cm-1showing
47、the presenceof ester function may make it difficult to correctly perform thesubtraction operation between the aged oil spectrum and thefresh oil spectrum. The different examples below show thedifferent cases that could be encountered and describe thebaselines settings needed to eliminate these ester
48、 residualinterfering peaks.14.3.1 Example 1 (see Fig. 3)This differential spectrum isrepresentative of a lubricant containing no ester base oil orcontaining ester but showing no interference. In this case, drawthe baseline between the absorption minima located on eitherside of this region as shown o
49、n the spectrum in Fig. 2. Theseminima are usually close to 1620 cm-1and 1850 cm-1within 20cm-1.14.3.2 Example 2 (see Fig. 4)There is a small residualnegative peak at 1740 cm-1. This negative peak does not crossthe baseline between 1650 and 1820 cm-1. Draw a first baselineclose to 1650 and 1820 cm-1as described in 12.4. This baselinecreates the area A1. Draw a second baseline above the residualpeak creating the area A2, representative of the ester interfer-ence. This second baseline has to be set in order to obtain apeak shape similar to a peak showing no int
