1、Designation: D2668 07 (Reapproved 2013)Standard Test Method for2,6-di-tert-Butyl- p-Cresol and 2,6-di-tert-Butyl Phenol inElectrical Insulating Oil by Infrared Absorption1This standard is issued under the fixed designation D2668; 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 () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of the weightperc
3、ent of 2,6-ditertiary-butyl paracresol (DBPC) and 2,6-ditertiary-butyl phenol (DBP) in new or used electrical insu-lating oil in concentrations up to 0.5 % by measuring itsabsorbance at the specified wavelengths in the infrared spec-trum.1.2 The values stated in SI units are to be regarded asstandar
4、d. No other units of measurement are included in thisstandard.1.3 This standard does not 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
5、-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D923 Practices for Sampling Electrical Insulating LiquidsD2144 Practices for Examination of Electrical InsulatingOils by Infrared AbsorptionD3487 Specification for Mineral Insulating Oil Used inElectrical Appar
6、atus3. Significance and Use3.1 The quantitative determination of 2,6-ditertiary-butylparacresol and 2,6-ditertiary-butyl phenol in a new electricalinsulating oil measures the amount of this material that hasbeen added to the oil as protection against oxidation. In a usedoil it measures the amount re
7、maining after oxidation hasreduced its concentration. The test is also suitable for manu-facturing control and specification acceptance.3.2 When an infrared spectrum is obtained of an electricalinsulating oil inhibited with either of these compounds there isan increase in absorbance of the spectrum
8、at several wave-lengths (or wavenumbers). 2,6 ditertiary-butyl paracresol pro-duces pronounced increases in absorbance at 2.72 m (3650cm1), and 11.63 m (860 cm1). 2,6 ditertiary-butyl phenolproduces pronounced increases in absorbance at 2.72 m (3650cm1) and 13.42 m (745 cm1).3.3 When making this tes
9、t on other than a highly oxidizedoil or when using a double-beam spectrophotometer, it hasbeen found convenient to obtain the spectrum between 2.5 m(4000 cm1) and 2.9 m (3450 cm1) because the instrument iscompensated for the presence of moisture and the band is notinfluenced by intermolecular forces
10、 (associations). However,when testing a highly oxidized oil or when using a single-beaminstrument better results may be obtained if the scan is madebetween 10.90 m (918 cm1) and 14.00 m (714 cm1).3.4 Increased absorption at 11.63 m (860 cm1) or 13.42m (745 cm1) or both, will identify the inhibitor a
11、s 2,6-ditertiary-butyl paracresol or 2,6-ditertiary-butyl phenol re-spectively (Note 1).NOTE 1The absorbance at 745 cm1for 2,6-ditertiary-butyl phenoland at 860 cm1for 2,6-ditertiary-butyl paracresol for equal concentra-tions will be in the approximate ratio of 2.6 to 1.4. Apparatus4.1 With equipmen
12、t description referring to compliance, theequipment shall be in accordance with Section 6 of PracticesD2144. Accordingly, the use of Fourier-transform rapid scaninfrared (FTIR) spectrophotometers is permitted by referenceto that test method.5. Sampling5.1 Obtain the sample in accordance with Practic
13、es D923.6. Calibration and Standardization6.1 When the manufacturer of the oil is known and the baseoil is available, use it to prepare the standards. For oils ofunknown origin, use base oils which meet the requirements ofSpecification D3487. Some base oils may provide a bettermatch than others and
14、therefore it is desirable to have severalavailable.1This test method is under the jurisdiction of ASTM Committee D27 onElectrical Insulating Liquids and Gases and is the direct responsibility of Subcom-mittee D27.03 on Analytical Tests.Current edition approved Nov. 1, 2013. Published December 2013.
15、Originallyapproved in 1967. Last previous edition approved in 2007 as D2668 07. DOI:10.1520/D2668-07R13.2For referenced 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 standard
16、s Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States16.2 Prepare standards containing between 0.05 and 0.4weight percent of 2,6-ditertiary-butyl paracresol or 2,6-ditertiary-butyl phenol dissolved
17、 in an uninhibited base oil.Alternatively, the range of prepared standards may be in-creased to 0.5 weight percent if certain oils to be investigatedare believed to contain greater amounts of inhibitor. Obtain aspectrum, at the desired band, of each standard in accordancewith Practices D2144. Cells
18、with a standard path length of 0.3to 1.0 mm are recommended. Other path lengths may be foundmore suitable for different instruments or particular wavelengths. Other sample path lengths may be used provided theinstrument sensitivity can be adjusted to compensate for thischange. The dip in the curve f
19、or the inhibited oil shouldprovide a distinctive increase in the absorbance at the criticalwavelength or frequency (Note 3). Repeat the procedure oneach of the standards making at least three scans on eachstandard. (See Note 2) Record all settings of the spectropho-tometer used in obtaining the resp
20、ective spectra (Note 4).NOTE 2The current method precision is based on manually deter-mined results where exactly three scans were determined for eachstandard. Newer instruments are capable of automatically performingscans much more rapidly, which can reduce the variability of resultsdetermined. In
21、such cases, it is recommended that the number of scans beincreased to statistically compensate for any outliers. Laboratories willneed to determine the minimum number of scans that should be used intheir instrument standardization and test specimen analyses to satisfy theirtesting needs.NOTE 3Where
22、desired, a chart having a non-linear wavelength scaleas the abscissa may be used.NOTE 4In making these tests, transmission-scaled charts may be used,but in this case special rulers and nomographs or logarithmic tables willbe necessary for determining the intensity measurements. Alternatively,instrum
23、ent software capable of recording all settings of the spectropho-tometer used in obtaining the respective spectra, may be used.6.3 The quantitative determination is made from the follow-ing equation which is derived from Beers law:Absorbance 5 A 2 Aowhere:Ao= absorbance units of base oil, andA = abs
24、orbance units of oil containing 2,6-ditertiary-butylparacresol or 2,6-ditertiary-butyl phenol.6.4 Manual Plotting Routine for Generating CalibrationCurveDesignate the point of maximum absorbance of theabsorbance band as Point A. Draw a tangent to the spectrumcurve and a second line through Point A p
25、erpendicular to theabsorbance lines, as shown in Fig. 1. Designate the intersectionof these two lines as Point Ao. Read the values of absorbanceat these points on the charts of the three scans made on eachtest specimen to the nearest 0.001 absorbance unit (with the aidof a reading glass) and subtrac
26、t the values of Aofrom those ofA. When the average of the three values for each of thespecially prepared test specimens is plotted against theconcentration, a straight line is obtained. The best straight linethrough the calibration data points should be drawn or deter-mined by linear regression anal
27、ysis. This is the calibrationcurve from which the unknown concentration of the 2,6-ditertiary-butyl paracresol or 2,6-ditertiary-butyl phenol in atest specimen may be determined. One such calibration curveis shown as Fig. 2. Fig. 3 and Fig. 4 illustrate sections ofdifferential scans. Figs. 5-7 show
28、FTIR scans of uninhibited, asimilar oil with 0.55 % DBPC and the resulting FTIR differ-ential scan.6.4.1 Automatic Plotting Routine for Generating Calibra-tion CurveFor instruments capable of automatically generat-ing a standard calibration curve, follow manufacturers instruc-tions. Perform at least
29、 three scans for each standard analyzedacross the calibration range of interest (see Note 2). Develop acalibration curve which has a minimum correlation value of0.99 to ensure the linearity of the calibration curve.6.5 When frequent determinations are made on a routinebasis, periodic checks of one o
30、r more standards arerecommended, since the characteristics of electronics compo-nents in spectrophotometers change with time. If the absor-bance of the standards differ from the calibration curve bymore than the limits given in 8.2, a new curve should beobtained. Some laboratories have developed tig
31、hter limits thanthese. A new curve should also be obtained whenever there isa change in operating conditions, such as a change in lightsource, scan speed, and so forth.NOTE 5It is recommended that the solutions of known concentrationbe stored in amber-colored bottles for a period not to exceed one y
32、ear inorder to facilitate a quick check of the characteristics of the spectropho-tometer in relation to the calibration curve.FIG. 1 Spectrum of an Electrical Insulating Oil Inhibited with 2,6-Ditertiary-ButylParacresol Showing Location Points Aoand AD2668 07 (2013)27. Procedure7.1 Using the quantit
33、ative scan mode, make at least threescans (see Note 2) of the test specimen on which the determi-nation of the 2,6-ditertiary-butyl paracresol or 2,6-ditertiary-butyl phenol content is to be made, at the desired band. Do thisin accordance with Practices D2144, except that cells havingpath lengths as
34、 specified in 6.2 are preferred. Use the same cellthat was used in obtaining the spectra for the calibration curve.For the Differential Method, fill the reference cell with anappropriate base oil free of oxidation inhibitors. Use a spec-trophotometer which meets the requirements specified inSection
35、6 of Practices D2144 and instrumental conditionsidentical to those used in obtaining the spectra for the calibra-tion curve. In particular, it should be noted that Fourier-transform rapid scan infrared spectrophotometers may also beused and in some cases are preferred for the measurement.7.2 For rou
36、tine tests, a single scan of the test specimen isadequate as long as the instrument is capable of meeting thecriteria of 8.2 using single scans to replace average values. Forreferee purposes, use the average of three scans of the testspecimen performed manually or the average of the samenumber of sc
37、ans used to standardize the instrument for the testspecimen, if performed automatically.7.3 Manually Determined ResultsRead the values of ab-sorbance at points Aoand A on each of the three spectra to thenearest 0.001 absorbance unit; obtain the differences andaverage them. Using this average value,
38、determine the concen-tration from the calibration curve.7.4 Automatically Determined Results Using the averagevalue of the absorbance difference between A and Aothat isdetermined automatically by the instrument for the sameFIG. 2 Calibration Curve for Determining the Percent by Weight of 2,6-Diterti
39、ary-ButylParacresol in Electrical Insulating OilFIG. 3 Section of Differential Scan-AD2668 07 (2013)3number of scans performed on the test specimen as for thestandards, determine the concentration of the test specimenfrom the calibration curve.FIG. 4 Section of Differential Scan-BFIG. 5 Example of a
40、 FTIR Scan of an Uninhibited Transformer OilD2668 07 (2013)48. Precision and Bias8.1 Checking Limits of Range (A Ao)Determine thehighest and lowest values of A Aoresulting from the three ormore scans and subtract one from the other. If the resultingquantity exceeds 0.010, reject the results as exces
41、sively vari-able and repeat the test.8.2 Repeatability The difference between two determina-tions for DBPC and DBP, each obtained from the average ofthree scans determined manually, obtained by the same opera-tor with the same apparatus under constant operating condi-tions on identical test material
42、 would, in the long run, in thenormal and correct operation of the test method, exceed thevalue of 0.04 % by only one case in twenty.8.3 Reproducibility The difference between two determi-nations for DBPC and DBP, each obtained from the average ofthree scans determined manually, obtained by differen
43、t opera-tors in different laboratories on identical test material would, inthe long run, in the normal and correct operation of the testmethod, exceed the value of 0.04 % by only one case in twenty.8.4 No statement is made about bias of this test method formeasuring ditertiary-butyl paracresol or di
44、tertiary-butyl phenolas it has not been determined.9. Keywords9.1 2,6-ditertiary-butyl paracresol; 2,6-ditertiary-butyl phe-nol; electrical insulating oil; infrared absorptionFIG. 6 Example of a FTIR Scan on a Transformer Oil with 0.55 % DBPCFIG. 7 Example of the Differential Scan Showing 0.542 % WT
45、 % DBPC InhibitorD2668 07 (2013)5ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof
46、 infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this s
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48、r views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org). Permission rights to photocopy the standard may also be secured from the ASTM website (www.astm.org/COPYRIGHT/).D2668 07 (2013)6
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