ASTM D4419 Method for Measurement of Transition Temperatures of Petroleum Waxes
ASTM D4419 Standard Test Method for Measurement of Transition Temperatures of Petroleum Waxes by Differential Scanning Calorimetry (DSC)
11. Procedure
11.1 Weigh 10 ± 1 mg of the wax pieces into a sample pan, and insert the pan in the calorimeter sample compartment.
NOTE 3 - Intimate thermal contact, sample-to-pan and pan-to-sensor, is essential. Ensure that pan bottoms are flat and also that sensor surfaces where pans rest are clean. If the equipment is available, it is advantageous to ensure maximum sample-to-pan thermal contact by crimping a metal cover against the pan with the sample sandwiched in between. A thermal precycle (see section 10.3 ) improves pan contact and establishes the same thermal history for every sample.
11.2 Flush the sample compartment of the test cell with inert gas throughout the test; a flow of 10 to 50 mL/min is typical.
11.3 Perform a thermal precycle (Note 3). Heat the test cell at 10 ± 1°C/min to 20 ± 5°C beyond the end of melting, beyond the return to the base line (Note 4 and Note 5). Then cool the test cell to 15 ± 5°C at 10 ± 1°C/min. Hold the test cell at 15°C for 30 s.
NOTE 4 - During the precycle heating scan, note the height of the first thermo transition peak, and adjust instrument sensitivity so it is 50 to 95 % of full scale.
NOTE 5 - The exposure of the sample to high temperatures should be minimized to prevent decomposition. Hold the maximum temperature only for the time required to prepare for cooling.
11.4 Perform and record the thermal scan of record. Heat the test cell at 10 ± 1°C/min to 20 ± 5°C beyond the end of melting (Note 6). Record the DSC curve using a heating rate of 10 ± 1°C/min from 15°C to 20 ± 5°C beyond the end of melting.
NOTE 6 - A cooling (solidification) scan is also possible, but the transition peak apex will be several degrees celsius lower than that obtained using a heating scan.
12. Calculation
12.1 Several transitions may be present. Number them consecutively in order of appearance. Draw tangents to each transition peak (see Fig. 1). The transition peak apex (TA) is located by the intersection of the tangents to the peak slopes (Note 7 and Note 8).
NOTE 7 - The extrapolated onset (TO) and end (TE) temperatures are located by the intersection of the peak tangents with the base line (see Fig. 1). The difference between the onset and end temperatures of each transition peak is a measure of peak width.
NOTE 8 - Some microcrystalline waxes may exhibit shoulders on the transition peaks. If this occurs, exclude the shoulder in drawing in the extrapolated onset (TO) and end (TE) temperatures.
12.2 Read the temperature associated with each transition peak apex from the curve, and apply any correction indicated by the temperature-scale calibration.
