ASTM D7098-08 (Reapproved 2015)
Designation: D7098 − 08 (Reapproved 2015)Standard Test Method forOxidation Stability of Lubricants by Thin-Film OxygenUptake (TFOUT) Catalyst B1,2This standard is issued under the fixed designation D7098; the number immediately following the designation indicates the year oforiginal 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 oxidation stability oflubricants by thin-film oxygen uptake (TFOUT) Catalyst B.This test method evaluates the oxidation stability of petroleumproducts, and it was originally developed as a screening test toindicate whether a given re-refined base stock could beformulated for use as automotive engine oil3(see Test MethodD4742). The test is run at 160 °C in a pressure vessel underoxygen pressure, and the sample contains a metal catalystpackage, a fuel catalyst, and water to partially simulate oilconditions in an operating engine. In addition, the test methodhas since been found broadly useful as an oxidation test ofpetroleum products.41.2 The applicable range of the induction time is from a fewminutes up to several hundred minutes or more. However, therange of induction times used for developing the precisionstatements in this test method was from 40 min to 280 min.1.3 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.3.1 Exception—Pressure units are provided in psig, anddimensions are provided in inches in AnnexA1 and AnnexA2,because these are the industry accepted standard and theapparatus is built according to the figures shown.1.4 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-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:5A314 Specification for Stainless Steel Billets and Bars forForgingB211 Specification for Aluminum and Aluminum-AlloyRolled or Cold Finished Bar, Rod, and WireD664 Test Method for Acid Number of Petroleum Productsby Potentiometric TitrationD1193 Specification for Reagent WaterD2272 Test Method for Oxidation Stability of Steam Tur-bine Oils by Rotating Pressure VesselD4742 Test Method for Oxidation Stability of GasolineAutomotive Engine Oils by Thin-Film Oxygen Uptake(TFOUT)E1 Specification for ASTM Liquid-in-Glass ThermometersE144 Practice for Safe Use of Oxygen Combustion Vessels3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 break point—the precise point of time at which rapidoxidation of the oil begins.3.1.2 oxidation induction time—the time until the oil beginsto oxidize at a relatively rapid rate as indicated by the decreaseof oxygen pressure.3.1.3 oxygen uptake—oxygen absorbed by oil as a result ofoil oxidation.4. Summary of Test Method4.1 The test oil is mixed in a glass container with four otherliquids used to simulate engine conditions: (1) an oxidized/nitrated fuel component (Annex A3), (2) a mixture of soluble1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility ofSubcommittee D02.09.0G on Oxidation Testing of Engine Oils.Current edition approved Oct. 1, 2015. Published December 2015. Originallyapproved in 2005. Last previous edition approved in 2008 as D7098 – 08ε1. DOI:10.1520/D7098-08R15.2While Catalyst B can be used for testing oxidation stability of many lubricanttypes, the mixture of fuel, nitro-paraffin, and catalyst components used in this testmethod simulates the Sequence IIIE Engine Test. Test results on several ASTMreference oils have been found to correlate with Sequence IIIE engine tests in hoursfor a 375 % viscosity increase. (See Ku, Chia-Soon, Pei, Patrick T., and Hsu,Stephen M., “A Modified Thin-Film Oxygen Uptake Test (TFOUT) for theEvaluation of Lubricant Stability in ASTM Sequence IIIE Test, SAE TechnicalPaper Series 902121, Tulsa, OK, Oct. 22-25, 1990.)3Ku, C. S. and Hsu, S. M., “A Thin Film Uptake Test for the Evaluation ofAutomotive Lubricants,” Lubrication Engineering, 40, 2, 1984, pp. 75–83.4Selby, Theodore W., “Oxidation Studies with a Modified Thin-Film OxygenUptake Test”, SAE Technical Paper Series 872127, Toronto, Ontario, Nov. 2-5,1987.5For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at service@astm.org. For Annual Book of ASTMStandards volume information, refer to the standard’s Document Summary page onthe ASTM website.Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1metal naphthenates (lead, iron, manganese, and tin naphthen-ates (Annex A4), (3) a nitro-paraffinic compound, and (4) TypeI reagent water.4.2 The glass container holding the oil mixture is placed ina pressure vessel equipped with a pressure sensor. The pressurevessel is sealed, charged with oxygen to a pressure of 620 kPa(90 psig), and placed in an oil bath at 160 °C at an angle of 30°from the horizontal. The pressure vessel is rotated axially at aspeed of 100 r ⁄min forming a thin film of oil within the glasscontainer resulting in a relatively large oil-oxygen contact area.4.3 The pressure of the pressure vessel is recorded continu-ously from the beginning of the test and the test is terminatedwhen a rapid decrease of the pressure vessel pressure isobserved (Point B, Fig. 1). The period of time that elapsesbetween the time when the pressure vessel is placed in the oilbath and the time at which the pressure begins to decreaserapidly is called the oxidation induction time and is used as ameasure of the relative oil oxidation stability.5. Significance and Use5.1 This test method was originally developed to evaluateoxidation stability of lubricating base oils combined withadditives chemistries similar to those found in gasoline engineoils and service.25.2 This test method is useful for screening formulated oilsbefore engine tests. Within similar additive chemistries andbase oil types, the ranking of oils in this test appears to bepredictive of ranking in certain engine tests. When oils havingdifferent additive chemistries or base oil type are compared,results may or may not reflect results in engine tests. Onlygasoline engine oils were used in generating the precisionstatements in this test method.6. Apparatus6.1 Oxidation Bath and Pressure Vessel—See appropriateAnnex (Annex A16or Annex A27) for detailed description ofapparatus and accessories for equipment described in this testmethod.NOTE 1—To reduce vapor odors when opening pressure vessel after use,a hood may be desirable.6.2 Precision Pressure Gauge—Use a certified precisionpressure gauge to accurately control the oxygen feed to thepressure vessel. The gauge shall have a sufficient range toencompass 0 kPa to 650 kPa (~90 psig) required by the testmethod with division 2.0 kPa (~0.5 psig) or better to enablereadings to be made to 2.0 kPa (~0.25 psig).7. Reagents7.1 Purity of Reagents—Reagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall reagents shall conform to the specifications of the Commit-tee onAnalytical Reagents of theAmerican Chemical Society.87.2 Purity of Water—Unless otherwise indicated, referencesto reagent water shall be understood to mean distilled watermeeting requirements of reagent water as defined by Type I ofSpecification D1193.7.3 Acetone, CH3COCH3.7.4 Air, containing 2000 ppm nitrogen dioxide, NO2(com-mercially available compressed gas mixture, certified within65 %).7.5 Cyclo-hexane, C6H12, Practical Grade or other suitablehydrocarbon solvent. (Warning—Highly flammable. Skin ir-ritant on repeated contact. Aspiration hazard.)7.6 Isopropyl Alcohol, CH3CH(CH3)OH.7.7 Oxygen, 99.8 %.8. Materials8.1 TFOUT Catalyst B Package:76The sole source of supply of the apparatus known to the committee at this timeis Koehler Instrument Co., Inc., 1595 Sycamore Ave., Bohemia, NY11716 andStanhope-Seta, London St., Chertsey, Surrey, KT16 8AP, U.K. If you are aware ofalternative suppliers, please provide this information to ASTM InternationalHeadquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee,1which you may attend.7The sole source of supply of the apparatus known to the committee at this timeis Tannas Co., 4800 James Savage Rd., Midland, MI 48642. If you are aware ofalternative suppliers, please provide this information to ASTM InternationalHeadquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee,1which you may attend.8Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. For Suggestions on the testing of reagents notlisted by the American Chemical Society, see Annual Standards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.FIG. 1 Pressure versus Time Diagram of the Oxidation TestD7098 − 08 (2015)28.1.1 Fuel Component—The fuel component is a nitratedgasoline fraction or organic equivalent. This component maybe prepared in accordance with the procedures described inAnnex A3.8.1.2 Soluble Metal Catalyst Mixture—This catalyst is amixture of soluble metal catalysts (lead, iron, manganese, andtin). The catalyst may be prepared according to the proceduresdescribed in Annex A4.8.1.2.1 Other oxidation stability test methods have demon-strated that soluble metal catalyst supplies may be inconsistentand have significant effects on the test results. Thus, for testcomparisons, the same source and same batch of metalnaphthenates shall be used.NOTE 2—It is good research practice to use the same batches of catalystcomponents when closely comparing engine oils.NOTE 3—Slow, steady reactivity of some of the catalyst chemicals canbe a problem. Such problems can be reduced by storing the closed catalystvials in a refrigerator at approximately 5 °C. The catalyst chemicalsremain effective up to six months after the septum is punctured, if they arestored as noted above.8.1.3 Nitro-paraffın—This compound is made up of a nitri-alkane blend.NOTE 4—Suitably prepared catalyst packages may be purchased fromTannas Co.78.2 Varnish and Deposit Remover, water-soluble varnishremover or other engine varnish/deposit removers.8.3 Silicone Stopcock Grease.9. Preparation of Apparatus9.1 Glass Sample Container—A clean glass sample con-tainer is important for obtaining repeatable results. Thoroughcleaning can be accomplished by (a) rinsing with cyclo-hexaneor other suitable hydrocarbon solvent, (b) soaking in concen-trated solution of a water-soluble varnish remover, (c) thor-oughly rinsing with water, (d) rinsing with acetone, (e) andpermitting to dry.NOTE 5—A segmented glass reaction dish has been found suitable toprevent premature mixing of the catalyst components (see Fig. A2.4)9.2 Cleaning of Pressure Vessel—Fill with concentratedsolution of a water-soluble varnish remover and soak forsuitable time, rinse with water, rinse with acetone, and permitto dry.9.3 Cleaning of Pressure Vessel Stem—Periodicallydisassemble, inspect, and clean the pressure vessel stem. Rinsethe inside of the stem with isopropyl alcohol and blow dry withoil free compressed air. For users of apparatus described inAnnex A1, periodically insert a dry pipe cleaner into thetransducer line opening for removal of potential residuebuildup.NOTE 6—Replace O-rings when reassembling the pressure transducers.9.4 Periodically pressure test the pressure vessels at 690 kPa(~100 psi) with air or oxygen. If the pressure drops more than0.690 kPa (~0.1 psi) on the pressure gauge within 60 s, replacethe O-ring seals and inspect the valve seals according tomanufacturer’s directions. If the problem continues, contact thespecific equipment manufacturer.NOTE 7—Previous versions of this test method have called for hydro-static testing of the pressure vessel. This was found unnecessary at therelatively low pressures involved in running this test method.9.5 Cleaning of Catalyst Syringes—Use individual catalystsyringes for each catalyst component. Thoroughly clean anddry syringes prior to each use. (See Annex A5 for recom-mended procedure.)10. Procedure10.1 Weighing and Mixing Sample and Catalyst Compo-nents:10.1.1 Place the clean glass sample container onto theprecision balance and tare.10.1.2 Weigh 1.500 g 6 0.001 g of oil sample into thecontainer and tare.10.1.3 Add 0.045 g 6 0.001 g of the soluble metal catalystmixture into the glass sample container and tare.10.1.4 Add 0.030 g 6 0.001 g each of the fuel component,nitro-paraffin and reagent water to the glass sample containerand tare each time. It is easiest to add the distilled water lastand place on top of the oil sample.10.1.5 Just prior to inserting the glass sample container intothe pressure vessel, thoroughly mix the catalyst componentswithin the sample container by hand-rotation (approximatelyfive rotations) and proceed immediately to 10.2. Delay mayresult in variation of results.10.2 Pressure Vessel Assembly and Charging—Immediatelyand rapidly assemble and charge the pressure vessel in accor-dance with apparatus type (see A1.2 or A2.7).NOTE 8—Avoid releasing the oxygen too rapidly by decreasing thepressure to atmospheric in no less than 1 min to avoid possible foamingand overflow of the sample from the glass sample container.10.3 Oxidation—Before starting the test, bring the heatingbath to the test temperature at 160 °C and insert the pressurevessel(s) in accordance with apparatus type (see A1.3 or A2.8).10.3.1 Allow the bath temperature to level out at the testtemperature, which must occur within 15 min after insertion ofthe pressure vessel. Maintaining the test temperature within thespecified limits of 160 °C 6 0.3 °C during the entire test run isthe most important single factor ensuring both repeatability andreproducibility of test results. If the test temperature cannot bemaintained as specified, the test results shall not be consideredvalid.NOTE 9—The time for the bath to reach the operating temperature afterinsertion of the pressure vessel may differ for different apparatus assem-blies and shall be observed for each unit (a unit may carry one, two, three,or four pressure vessels). The objective is to find a set of conditions, whichdoes not permit a drop of more than 2 °C after insertion of the pressurevessel(s) and allows the pressure vessel pressure to reach plateau within15 min.10.4 Keep the pressure vessel completely submerged andmaintain continuous and uniform rotation throughout the test.A standard rotational speed of 100 r ⁄min 6 5 r ⁄min is re-quired; any v