Work Item
ASTM WK77506
Revision of E537-20 Standard Test Method for Thermal Stability of Chemicals by Differential Scanning Calorimetry
Rationale
1. Add caution statements on pressure differential scanning calorimetry for thermal stability application in the standard. Generally, thermal stability of a substance is the stability to resist chemical degradation under high temperature operating conditions, so it is a property of a substance, not interaction with others, such as a gas. Pressure differential scanning calorimetry typically is used to study the reactivity between a liquid or solid sample with certain gas which stays in the large headspace of the instrument (e.g., oxidation induction time of a sample with oxygen or air). However, with this significantly large headspace compared to loaded sample size (e.g., TA 25P, 100ml headspace for ~10mg sample), pressure differential scanning calorimetry for degradation evaluation always gives false negative result due to the following reasons: 1, liquid sample will vaporize during temperature ramping and result in no exotherm but endotherm; 2, solid sample may melt and then vaporize. 3, gas sample is not concentrated on DSC sensor so that the reaction from a gas sample cant be detected in pressure DSC. Therefore, a caution statement on pressure differential scanning calorimetry for the scope of this standard has been added: Because of the large headspace to sample size in a pressure DSC, great care should be taken if it is used for the thermal stability of a solid or a liquid in an inert environment. Liquid vaporization can completely skew the results. 2. Limit the sample container to sealed high-pressure ones (able to hold at least 7MPa) for common DSC (not high pressure DSC). As shown in Fig 3 and Fig 4, open DSC container and low pressure sealed DSC container will give either false negative or no meaningful result. only the sealed high-pressure DSC container gives a reliable degradation activity.
Work Item Status
Date Initiated: 06-25-2021
Technical Contact: Min Sheng
Item: 001
Ballot: E27.02 (21-02)
Status: Negative Votes Need Resolution