In-Process Substance Thermal Stability Test Description
Test Purpose
This test is used to determine the reaction of samples when subjected to a mildly elevated temperature (75°C) for a specific period of time (48 hours). At the completion of the test, the sample is examined for discoloration, weight loss, and dimensional change as evidence of decomposition. Any evidence of explosion is also criteria for a positive result (i.e. fails the test). Materials that fail this test should be considered to have a mass explosion hazard.
Equivalence
This test is equivalent to UN Test 3 (c) in the UN Manual of Tests and Criteria.
Key Parameters
| Key Parameter | Objectives | Origin | Specs |
|---|---|---|---|
| Test temperature and time of exposure to that temperature | Determine the stability of a substance using exposure time and temperatures that represent worst-case in-process conditions and/or provide accelerated aging | A possible origin may be the accelerated aging principles set forth in STANAG 4147 Test 1, Vacuum Thermal Stability; specifically, reduction in the test temperature by 10°C increases the effective time by a factor of 2.5. In other words, results obtained in 48 hours at 75°C should be representative of those obtained in 120 hours at 65°C. | 75°C for 48 hours |
| Sample holder | Glass readily permits the sample to be visually inspected | 35mm diameter, 50mm high beaker or equivalent | |
| Watch glass | Provide witness if fuming occurs (watch glass may be discolored); watch glass allows venting but limits absorption of moisture while cooling (masking mass loss) | Uncovered samples can absorb moisture from the air while cooling | 40mm diameter watch glass or equivalent |
| Sample mass | Provide sufficient mass to enable accurate detection of thermal instability | 50-100 grams | |
| Test oven | Ensure adequate temperature control and protection against thermal runaway |
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| Self-heating temperature change | Parameter for characterizing the thermal stability of a material | 3°C or greater |
Indicators
| Indicators | Detection Method | Assessment* |
|---|---|---|
| Ignition or explosion | Visual post-test inspection | Damage to sample holder, flame traces, consumption of sample, etc. Mass explosion hazard |
| Fuming or decomposition | Visual post-test inspection | Discoloration of watch glass or sample |
| Substance temperature (not always required) | Thermocouple | Difference between reference and sample of 3°C or greater is evidence of self-heating. Mass explosion hazard |
*OR relationship
