- Method ASTM D6468
- Repeatability 22.42 - 0.2130x
- Reproducibility 44.04 - 0.4281x
- Blending non-linear
- Additive Correction No
This test will determine the relative stability of middle distillate fuels under high temperature aging conditions with limited air exposure. Thermal stability is defined as the products ability to resist oxidation and thermal stressing that will form undesirable degraded compounds.
To perform the test the two 50ml portions of the sample are filtered and then added to open test tubes. These tubes are then aged for either 90 or 180 minutes depending upon the specification. 90 minutes of aging will simulate a few months of storage time while 180 minutes will simulate 6months to a year. Once the tubes are removed from the heating bath they are placed in the dark to cool to room temperature. When the cooling is finished the samples are filtered through a small filter pad and rinsed with solvent. This pad containing the insoluble is then rated by using an instrument that measures the amount of light reflected. The less light that is reflected, the lower the numeric value and the higher the amount of insoluble deposits are contained on the filter. The heavier the deposits are the more likely the sample is to oxidize, polymerize, or otherwise degrade.
Another good use of this test is to measure the D1500 ASTM color of the product before and after. Many purchasers use this spec for a determination of how dark the product will become as it ages.