IP 418: Determination of relative volatility of automotive lubricating oils by isothermal thermogravimetry

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  • Method adopted/last revised: 1996
  • Method reapproved: 2004
  • REF/ISBN: IP418-2934869
  • Status: Current
  • First printed in STM books: January 2004


This standard specifies two methods of determining the relative volatility of base oils and unused formulated lubricating oils for automotive use. The relative volatility is determined relative to a reference material (squalane). Only a very small sample mass (10 mg) is required for carrying out the methods.

NOTE 1 The relative volatility determined using this standard can be correlated with the evaporation loss as determined by the Noack method (see annex A and B.1).

NOTE 2 The rate of vaporization of a pure liquid is the mass loss per unit area per unit time. For mixtures there is an additional factor: the composition can change significantly if one component vaporizes faster than another. This effect is reduced by increasing the volume-to-area ratio of the sample.

NOTE 3 In general, the measurements depend on the experimental configuration, and data can only be compared with those from an identical experiment. For example, two correctly calibrated thermogravimetric analysers can give very different results due to differences in the shape of the pan, the pan suspension arrangement, the furnace diameter and the gas flow rate. However, this dependency on experimental configuration can be eliminated by measuring relative to a reference material and setting the operating temperature so that the vaporization rate for the reference material is the same for different instruments.

NOTE 4 Method A has a longer run time and is more precise than the shorter method B which can be useful for quick screening tests where the precision of results is not as critical.

NOTE 5 The precision for method A has been determined in the range 0,6 to 2,2 volatility relative to squalane, using mineral base oils and mineral-based formulations with Noack values ranging from 7 % to 26 % provided by the CEC PL-34 Panel. The precision for method B was determined on the same runs using data obtained from the shorter run time in the range 0,7 to 3,1 relative volatility.

NOTE 6 Round robin data show that relative volatility is independent of the differences in temperature calibration, flow rate, sample pan type (see note 9) and any other variable between different models of instrument.

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