DSC isothermal experiments provide an indication of a material's stability at an elevated temperature. The purge gas, which surrounds the material, remains constant or is switched at the elevated temperature to generate a sample-atmosphere interaction (e.g., oxidative stability).
If you want to set up a DSC isothermal procedure, you can choose one of two techniques—the DSC Wizard or the Experimental View - Procedure Page. See the instructions below for each technique.
Isothermal (Start) Temperature: The acceptable range for the equilibration temperature in an isothermal experiment is cooler dependent. Hypothetically only isothermal temperatures within the operating range of the selected cooler can be used (e.g., –90 to 550°C for the RCS). However, prolonged experiments near the upper temperature limit for a specific cooler could affect the lifetime of the unit. Therefore, use of the Finned Air Cooling System (FACS) is recommended for isothermal work above 350°C. In addition, isothermal evaluations above 600°C should be performed with an inert purge gas. Standard test methods exist where the equilibration temperature is specified. For example, polyolefin oxidative stability analysis studies are specified at 200°C based on ASTM Method D3895-80.
CAUTION: We recommend that you do not use the RCS when running isothermal experiments above 400°C. Damage to the unit can occur if used at high temperatures for extended periods.
Switch to Gas 2 (requires a Mass Flow Controller): The option of switching gas after achieving the equilibration temperature provides the ability to measure material characteristics that are based on not only temperature, but also on the atmosphere around the material (e.g., stability in oxygen [resistance to oxidative degradation]).
Isothermal Time: The isothermal time should be set to a value that is greater than required to measure the event of interest. If the time required is unknown, a large value should be entered.
End Experiment When: No analysis time will be wasted provided a proper "End Experiment" condition is set. DSC isothermal experiments are usually stopped based on detecting heat flows (mW/minute) greater than a "threshold" value. This threshold should be large enough to ensure that a real event is occurring and that the extrapolated onset can be determined. 0.5 mW/minute is a good initial choice. Check the End Experiment When box and select the desired setting to use this option.
Additional Conditions: There are additional experimental conditions that can be changed to optimize specific situations. These are accessed using Advanced Parameters and Post-Test Conditions. For most experiments, the system default values shown are recommended.
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Enter the desired parameters, then select Next to proceed.
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Display the Procedure Page. Select the desired experiment from the list of available preprogrammed templates.
Enter the desired parameters. When you have finished setting up this procedure, you can enter more information by selecting the Notes Page and Summary Page for this run.
Click the Apply button when finished to save these changes or the Append button to save the changes to this run and add another run to the end of the sequence.
NOTE: You can use any test template as the basis for a custom test by selecting the desired test template from the list of tests, then click the Apply button and change the test to Custom. Then you can click on the Procedure Page and then the Editor button to make the changes desired.
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