ASTM D6375 Standard Test Method for Evaporation Loss of Lubricating Oils by Thermogravimetric Analyzer (TGA) Noack Method
9. Procedure
9.1 Determination of Specimen Mass:
9.1.1 Determine the nominal internal diameter (in centimetres) of the specimen pans by measuring the internal diameter of 10 different pans and averaging the results. A caliper shall be used to make this measurement.
9.1.2 Calculate the specimen mass using following equation:
Ms = Specimen mass, mg (round to closest whole mg.)
ID = Nominal inside diameter of specimen pan, cm (see 9.1.1).
9.2 Air Flowrate - Set air flowrate to that recommended by the TGA manufacturer or higher if during the initial tests with the Noack reference oil there appears to be condensation on any part of the TGA balance mechanism or furnace lining. Repeat 8.1 with the new flow rate.
9.3 Temperature Program (see Note 2):
NOTE 2 - This section only needs to be done during the initial set up of the method in the TGA.
9.3.1 Using the correlation from 8.1, determine the final program temperature required to obtain a final specimen temperature of 249°C.
9.3.2 Program the TGA to heat the specimen from 50°C to the final program temperature determined in 9.3.1 at heating rate(s) that will simulate the specimen heating rate of the standard Noack methods (100°C/min to 220°C and 10°C/min from 220°C to 249°C). Some guidance on how to achieve acceptable heating rates can be obtained from the examples shown in Fig. 2. Maintain the final program temperature for 30 min (see Note 3).
NOTE 3 - The 30 min isothermal hold may be adjusted after the Noack reference oil has been tested and the Noack reference time for the instrument has been established (see 9.4). The isothermal hold can then be set to be 2 min longer than the measured Noack reference time.
9.3.3 Tare an empty specimen pan in accordance with the TGA operating manual.
9.3.4 Add the required mass (+/- 3 mg) (as determined in 9.1) of the Noack reference oil to the tared pan.
9.3.5 Place the pan on the TGA pan holder, and run specimen through the temperature program, as described in 9.3.2.
9.3.6 From the data obtained in 9.3.5, generate a plot of time versus specimen temperature. Determine whether at any time the specimen temperature was above 249°C. When this occurs, proceed to 9.3.8. When it does not occur, proceed to 9.3.7.
9.3.7 Temperature not over 249°C: Determine the Noack reference time in accordance with 9.4.6. When the Noack reference time is less than 7 min, return to 9.3.2 and the reduce heating rate to extend the Noack reference time beyond 7 min. Check the specimen temperature at the Noack reference time to be sure it is between 248 and 249°C. When it is lower, determine how much lower than 248.5°C and increase the final program temperature by this amount. Go to 9.4.
9.3.8 Temperature over 249°C: Modify the TGA temperature program to eliminate the temperature overshoot. This is generally accomplished by splitting the program into two stages, by reducing the heating rate by the final program temperature, or by a combination thereof. An example of how temperature overshoot was eliminated in a particular instrument is shown in Fig. 3. Repeat 9.3.3-9.3.6 until an appropriate temperature program has been obtained.
9.4 Determination of Noack Reference Time:
NOTE 4 - Important: This determination shall be completed each day prior to evaluating any test specimens.
9.4.1 Set air flowrate in accordance with 9.2.
9.4.2 Enter final temperature program established in 9.3.
9.4.3 Tare an empty specimen pan in accordance with the TGA operating manual.
9.4.4 Add the required mass (as determined in 9.1) of the Noack reference oil to the tared pan. Whether specimen is added volumetrically or gravimetrically, the actual mass shall be within +/-3 mg of the calculated specimen mass. Adjust specimen mass to meet this requirement.
9.4.5 Place the pan on the TGA pan holder, and run specimen.
9.4.6 From the thermogravimetric curve generated in 9.4.5, determine the time (if possible to the closest 0.01 min) required for the Noack reference oil to reach its Noack evaporative loss. This time is the Noack reference time. Record this time, as it will be used in 9.5 to determine the TGA Noack volatility of the test lubricants. An example of a TG curve for the Noack reference oil and how to use it to determine the Noack reference time is shown in Fig. 4 (Curve 1). The isothermal hold of the TGA temperature program can now be modified to the Noack reference time plus 2 min. This will expedite future determinations.
9.4.7 Check that the specimen temperature at the Noack reference time is between 247 and 249°C. When the temperature is outside this range, burn out TGA in accordance with 8.2 and repeat 9.4.
9.4.8 Compare the measured Noack reference time to those measured in prior days. When the difference is more than 10 %, check operation of the TGA in accordance with Section 8. When significant repairs or modifications, such as replacement of the balance mechanisms, temperature sensor, and so forth, have been made to the TGA since the previous time the Noack reference time was measured, the test method shall be repeated starting with Section 8.
9.5 Determination of TGA Noack Volatility of Test Lubricant:
9.5.1 Using a new specimen pan, repeat 9.4.1-9.4.5 using the test lubricant in place of the Noack reference oil.
9.5.2 Using the TG curve for the test lubricant and the Noack reference time from 9.4.6, determine the mass loss (in mass %) of the test lubricant at the Noack reference time. This is the TGA Noack volatility for the test lubricant. Examples of how to determine the TGA Noack volatility of test lubricants are shown in Fig. 4 (Curves 2 and 3). Check that the specimen temperature at the Noack reference time is between 247 and 250°C. When it is not, reinitiate the test starting with Section 8.
9.5.3 The TGA shall be burned out (see 8.2) on a regular basis. An estimate of how many tests can be done on a particular TGA before it needs to be burned out can be obtained by performing consecutive tests with the Noack reference oil until the difference in the Noack reference time between any of the determinations is greater than 10 %. The number of tests between burn outs may be increased by operating at a higher air flowrate (see 9.2).