ASTM D6186-98

NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: D 6186 – 98
Standard Test Method for
Oxidation Induction Time of Lubricating Oils by Pressure
Differential Scanning Calorimetry (PDSC)
This standard is issued under the fixed designation D 6186; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope oxidation stability. This test method is faster than other oil
oxidation tests and requires a very small amount of sample. It
1.1 This test method covers the determination of oxidation
may be used for research and development, quality control, and
induction time of lubricating oils subjected to oxygen at 3.5
specification purposes. However, no correlation has been
MPa (500 psig) and temperatures between 130 and 210°C.
established between the results of this test method and service
1.2 The values stated in SI units are to be regarded as the
performance.
standard.
1.3 This standard does not purport to address all of the
5. Apparatus
safety concerns, if any, associated with its use. It is the
5.1 Pressure Differential Scanning Calorimeter (PDSC),
responsibility of the user of this standard to establish appro-
equipped with the following items:
priate safety and health practices and determine the applica-
5.1.1 Sample Enclosure, with capability to 3.5 60.2 MPa
bility of regulatory limitations prior to use.
(500 6 25 psig) at 210°C and pressure gage graduated
2. Terminology ainintervals of 200 KPa (28.6 psig) or less.
5.1.2 Thermal Analyzer.
2.1 Definitions of Terms Specific to This Standard:
5.1.3 Aluminum Solid Fat Index (SFI) Sample Pan—See
2.1.1 extrapolated onset time, n—a time determined on a
Note 1.
thermal curve, as the intersection of the extrapolated baseline
5.1.4 Oxidation Stability Software.
and a line tangent to the oxidation exotherm constructed at its
5.1.5 Calibration Software.
maximum rate.
5.1.6 Calibrated Flowmeter, with a capacity of at least 200
2.1.2 oxidation induction time, (OIT), n—a period of time
mL/min and graduated in intervals of 5 mL or less.
during which the oxidation rate accelerates from zero to a
5.1.7 Sample Encapsulation Press.
maximum and which corresponds to the extrapolated onset
time.
NOTE 1—It has been found that when oil samples are prepared with SFI
2.1.3 thermal curve, n—a graph of sample heat flow versus pans which have more consistent surface areas than standard flat bottom
pans, reproducibility is improved.
time.
NOTE 2—Stainless steel or copper tubing is compatible with oxygen.
NOTE 3—See Fig. 1 for a diagram of a typical test unit.
3. Summary of Test Method
3.1 A small quantity of oil is weighed into a sample pan and
6. Reagents and Materials
placed in a test cell. The cell is heated to a specified
6.1 Oxygen, a minimum purity of 99.5 % oxygen by vol-
temperature and then pressurized with oxygen. The cell is held
ume.
at a regulated temperature and pressure until an exothermic
reaction occurs. The extrapolated onset time is measured and NOTE 4—Warning: Oxidizer. Gas under pressure.
reported as the oxidation induction time for the lubricating oil
6.2 Indium, of not less than 99.9 % indium by mass.
at the specified test temperature.
7. Calibration
4. Significance and Use
7.1 Sample Temperature Calibration:
4.1 Oxidation induction time, as determined under the
7.1.1 Weigh approximately 10 mg of indium into an alumi-
conditions of this test method, may be used as an indication of
num sample pan, insert a lid and crimp the lid to the pan using
the encapsulation press. Place the crimped pan onto the sample
This test method is under the jurisdiction of ASTM Committee D-2 on
platform in the pressure cell. Seal an empty pan in the same
Petroleum Products and Lubricants and is the direct responsibility of Subcommittee
D02.09 on Oxidation.
Current edition approved June 10, 1998. Published August 1998. Originally
Rhee, In-Sik, “Development of New Oxidation Stability Test Method for
published as D 6186–97. Last previous edition D 6186–97.
Lubricating Oils Using a Pressure Differential Scanning Calorimeter (PDSC),”
NLGI Spokesman, Vol 65, No. 3, June 2001, pp. 16–23.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
D6186–98
conditions of this test method, 3.5 MPa (500 psig) of oxygen.
7.2 Temperature Controller Calibration:
7.2.1 Remove both the sample pan and the reference pan
from the cell, then close the cell. Slowly pressurize the cell
with 3.5 6 0.2 MPa (500 6 25 psig) oxygen and adjust the
purge rate to 100 6 10 mL/min using the cell outlet valve.
Select the desired test temperature (either 210, 180, 155, or
130°C).
7.2.2 Program the cell to maintain the selected test tempera-
ture. If, after 10 mins., the displayed cell temperature differs by
more than 6 0.2°C from the selected temperature, slowly
adjust the temperature controller until they agree. After making
FIG. 1 PDSC Test Unit
an adjustment, wait at least 5 mins. to make certain that the
temperature is stable before continuing. If the PDSC equip-
ment does not have this function, the control calibration shall
manner and place it on the reference platform. Set the cell
be followed according to the equipment manufacture’s recom-
cover in place and close the cell.
mendations.
7.1.2 Open the oxygen cylinder valve slightly and set a
7.3 Cell Base Pressure Gage Calibration—Conduct the
pressure of 3.5 6 0.2 MPa (500 6 25 psig) on the cell inlet line
calibration using a calibrated pressure transducer or a previ-
with the pressure regulator. Partially open the inlet valve on the
ously calibrated gage according to the pressure cell manufac-
cell and allow the pressure to slowly build up in the cell. This
turer’s instructions.
requires approximately 2 mins. Using the outlet valve, adjust
and maintain the oxygen purge rate through the flowmeter at
8. Procedure
100 6 10 mL/min.
8.1 Before starting a test, the control thermocouple calibra-
7.1.3 Set the thermal analyzer to heat from ambient tem-
tion shall be conducted at the test temperature (either 210, 180,
perature (approximately 22°C) to 180°C at a programmed rate
155, or 130°C) according to 7.2.1 and 7.2.2. When the test
of 10°C/min. After completion of the run measure the melting
temperature is not known, conduct the calibration at 210°C.
temperature of the indium. If the melting temperature differs
8.2 Weigh 3.0 6 0.2 mg of oil into a new sample pan.
from 157.4 6 0.2°C (see Note 5) correct the difference by
Spread the sample evenly upon the flat portion. Do not spill
using either the hardware or software calibration procedure
any of the sample into the trough portion of the pan. A flat
described in the manufacturer’s instruction manual. If the
bottom pan can be used if the sample is placed upon a 0.5 cm
hardware calibration procedure is used, perform the tempera-
diameter circle in the center of the pan.
ture correction under 3.5 MPa (500 psig) oxygen pressure with
8.3 Place the uncovered pan containing the sample onto the
a 100 mL/min purge rate. A typical melting calibration curve is
platform of the cell according to the PDSC manufacturer’s
shown in Fig. 2.
instructions for placing the sample pan. Place a new empty pan
NOTE 5—The melting temperature of indium is 156.6°C at atmospheric
of the same configuration onto the cell platform according to
pressure, but has been found to be elevated to 157.4°C under the
the PDSC manufacturer’s instructions for placing the reference
pan. Clo
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