This article briefly introduces tips on sample dosage for thermal analysis techniques such as thermogravimetry, differential thermal analysis, differential scanning calorimetry, thermogravimetric-differential thermal analysis, and thermogravimetric-differential scanning calorimetry, which are commonly used in thermal analysis. When preparing an experiment, one of the primary parameters is the amount of sample, and how to choose the right amount of sample has a very important impact on the reliability of the experimental results.
1. Small sample size.
The temperature gradient within the sample is small, which is conducive to the diffusion of gas products, making the chemical equilibrium to the positive development, narrower peak shape, lower peak temperature, but more “real” some DSC peak shape is smaller, adjacent peaks (platform) separation ability is enhanced.
2. Large sample size.
Can increase the DSC detection signal, which is conducive to the detection of small thermal changes.
The temperature gradient within the sample is larger, the gas product diffusion is also slightly worse, the peak shape is broadened, and the peak temperature drifts too high temperature. This phenomenon is especially evident for samples with relatively poor thermal conductivity, such as polymers, where adjacent peaks (plateaus) tend to merge and peak separation ability decreases. Overall, in most cases, due to the adequate sensitivity of DSC and thermal balance, measurements with smaller sample volumes are appropriate.
However, for some special applications, such as adsorption/desorption, catalysis, antioxidant properties studies, etc., large sample volumes are more favorable. In addition, for such applications, more attention is paid to the sample and gas contact area, which cannot be fully satisfied by the usual crucible.
A pair of contradictions: sensitivity vs. resolution.
How to improve sensitivity and detect weak thermal effects: increase the ramp-up rate and increase the sample volume.
How to improve resolution and separate adjacent peaks (plateaus): use a slow ramp-up rate and a small sample volume.
Since increasing the sample volume has a large effect on sensitivity and a small effect on resolution, and accelerating the ramp rate has a large effect on both, it is common to choose a slower ramp rate (to maintain good resolution) and an appropriate increase in sample volume to improve sensitivity in the case of weak thermal effects.
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