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ASTM D2668-07(R2021) pdf free download

ASTM D2668-07(R2021) pdf free download.Standard Test Method for 2,6-di-tert-Butyl- p-Cresol and 2,6-di-tert-Butyl Phenol in Electrical Insulating Oil by Infrared Absorption
1. Scope
1.1 This test method covers the determination of the weight percent 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 its absorbance at the specified wavelengths in the infrared spec- trum. 1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard. 1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appro- priate safety, health, and environmental practices and deter- mine the applicability ofregulatory limitations prior to use. 1.4 This international standard was developed in accor- dance with internationally recognized principles on standard- ization established in the Decision on Principles for the Development of International Standards, Guides and Recom- mendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
3. Significance and Use
3.1 The quantitative determination of 2,6-ditertiary-butyl paracresol and 2,6-ditertiary-butyl phenol in a new electrical insulating oil measures the amount of this material that has been added to the oil as protection against oxidation. In a used oil it measures the amount remaining after oxidation has reduced its concentration. The test is also suitable for manu- facturing control and specification acceptance. 3.2 When an infrared spectrum is obtained of an electrical insulating oil inhibited with either of these compounds there is an increase in absorbance of the spectrum at several wave- lengths (or wavenumbers). 2,6 ditertiary-butyl paracresol pro- duces pronounced increases in absorbance at 2.72 µm (3650 cm −1 ), and 11.63 µm (860 cm −1 ). 2,6 ditertiary-butyl phenol produces pronounced increases in absorbance at 2.72 µm (3650 cm −1 ) and 13.42 µm (745 cm −1 ). 3.3 When making this test on other than a highly oxidized oil or when using a double-beam spectrophotometer, it has been found convenient to obtain the spectrum between 2.5 µm (4000 cm −1 ) and 2.9 µm (3450 cm −1 ) because the instrument is compensated for the presence of moisture and the band is not influenced by intermolecular forces (associations). However, when testing a highly oxidized oil or when using a single-beam instrument better results may be obtained if the scan is made between 10.90 µm (918 cm −1 ) and 14.00 µm (714 cm −1 ). 3.4 Increased absorption at 11.63 µm (860 cm −1 ) or 13.42 µm (745 cm −1 ) or both, will identify the inhibitor as 2,6- ditertiary-butyl paracresol or 2,6-ditertiary-butyl phenol re- spectively (Note 1). N OTE 1—The absorbance at 745 cm −1 for 2,6-ditertiary-butyl phenol and at 860 cm −1 for 2,6-ditertiary-butyl paracresol for equal concentra- tions will be in the approximate ratio of 2.6 to 1.
6. Calibration and Standardization
6.1 When the manufacturer of the oil is known and the base oil is available, use it to prepare the standards. For oils of unknown origin, use base oils which meet the requirements of Specification D3487. Some base oils may provide a better match than others and therefore it is desirable to have several available. 6.2 Prepare standards containing between 0.05 and 0.4 weight percent of 2,6-ditertiary-butyl paracresol or 2,6- ditertiary-butyl phenol dissolved 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 investigated are believed to contain greater amounts of inhibitor. Obtain a spectrum, at the desired band, of each standard in accordance with Practices D2144. Cells with a standard path length of 0.3 to 1.0 mm are recommended. Other path lengths may be found more suitable for different instruments or particular wave lengths. Other sample path lengths may be used provided the instrument sensitivity can be adjusted to compensate for this change. The dip in the curve for the inhibited oil should provide a distinctive increase in the absorbance at the critical wavelength or frequency (Note 3). Repeat the procedure on each of the standards making at least three scans on each standard. (See Note 2) Record all settings of the spectropho- tometer used in obtaining the respective spectra (Note 4).

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