ASTM D6186 Test Method for Oxidation Induction Time of Lubricating Oils
ASTM D6186 Standard Test Method for Oxidation Induction Time of Lubricating Oils by Pressure Differential Scanning Calorimetry (PDSC)
5. Apparatus
5.1 Pressure Differential Scanning Calorimeter (PDSC), equipped with the following items:
5.1.1 Sample Enclosure, with capability to 3.5 +/- 0.2 MPa (500 +/- 25 psig) at 210°C and pressure gage graduated ainintervals of 200 KPa (28.6 psig) or less.
5.1.2 Thermal Analyzer.
5.1.3 Aluminum Solid Fat Index (SFI) Sample Pan - See Note 1.
5.1.4 Oxidation Stability Software.
5.1.5 Calibration Software.
5.1.6 Calibrated Flowmeter, with a capacity of at least 200 mL/min and graduated in intervals of 5 mL or less.
5.1.7 Sample Encapsulation Press.
NOTE 1 - It has been found that when oil samples are prepared with SFI pans which have more consistent surface areas than standard flat bottom pans, reproducibility is improved.
NOTE 2 - Stainless steel or copper tubing is compatible with oxygen.
NOTE 3 - See Fig. 1 for a diagram of a typical test unit.
6. Reagents and Materials
6.1 Oxygen, a minimum purity of 99.5 % oxygen by volume.
NOTE 4 - Warning: Oxidizer. Gas under pressure.
6.2 Indium, of not less than 99.9 % indium by mass.
7. Calibration
7.1 Sample Temperature Calibration:
7.1.1 Weigh approximately 10 mg of indium into an aluminum sample pan, insert a lid and crimp the lid to the pan using the encapsulation press. Place the crimped pan onto the sample platform in the pressure cell. Seal an empty pan in the same manner and place it on the reference platform. Set the cell cover in place and close the cell.
7.1.2 Open the oxygen cylinder valve slightly and set a pressure of 3.5 +/- 0.2 MPa (500 +/- 25 psig) on the cell inlet line with the pressure regulator. Partially open the inlet valve on the cell and allow the pressure to slowly build up in the cell. This requires approximately 2 mins. Using the outlet valve, adjust and maintain the oxygen purge rate through the flowmeter at 100 +/- 10 mL/min.
7.1.3 Set the thermal analyzer to heat from ambient temperature (approximately 22°C) to 180°C at a programmed rate of 10°C/min. After completion of the run measure the melting temperature of the indium. If the melting temperature differs from 157.4 +/- 0.2°C (see Note 5) correct the difference by using either the hardware or software calibration procedure described in the manufacturer's instruction manual. If the hardware calibration procedure is used, perform the temperature correction under 3.5 MPa (500 psig) oxygen pressure with a 100 mL/min purge rate. A typical melting calibration curve is shown in Fig. 2.
NOTE 5 - The melting temperature of indium is 156.6°C at atmospheric pressure, but has been found to be elevated to 157.4°C under the 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 +/- 0.2 MPa (500 +/- 25 psig) oxygen and adjust the purge rate to 100 +/- 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 temperature. If, after 10 mins., the displayed cell temperature differs by more than +/- 0.2°C from the selected temperature, slowly adjust the temperature controller until they agree. After making an adjustment, wait at least 5 mins. to make certain that the temperature is stable before continuing. If the PDSC equipment does not have this function, the control calibration shall be followed according to the equipment manufacture's recommendations.
7.3 Cell Base Pressure Gage Calibration - Conduct the calibration using a calibrated pressure transducer or a previously calibrated gage according to the pressure cell manufacturer's instructions.
