DECOMPOSITION TEST DYNAMIC (GREWER AIR)
[VDI 2263, Part 1]
Approx. 8 ml of the test substance and of graphite powder as reference are filled into small wire baskets and then heated in an air stream surrounding the sample with constant rate (as a rule 1,2 °C/min).
The temperature difference between the sample and the reference (DT-signal) is recorded and plotted against the reference temperature.
The test can be carried out in a temperature range up to 10 °C below the melting point.
The lowest temperature, at which the DT signal deviates from the baseline in positive direction is defined as the begin (onset) of the first exothermic reaction.
This value can be used to determine safe drying temperatures in convection dryers (e.g., fluid bed dryers, spray dryers).
Depending on the dryer type the recommended maximum drying temperature is about 60-110 °C below the onset of the first exothermic reaction in this test.
Very often these values are too conservative (because they result from a simple screening test).
For a more precise evaluation of safe drying temperatures, additional tests, e.g., isoperibolic tests in a 400 ml wire basket, are recommended.