Can you guess what does this picture represent?
The last week’s picture gave a short introduction to differential scanning calorimetry (DSC). This week’s picture is digging deeper the same topic. Typical DSC measurement is done in nitrogen atmosphere and the sample is measured within a closed pan (typically a tiny hole is added for possible evaporation). The picture of this week shows a pile of open DSC pans used in oxidative induction time/temperature (OIT) measurements.
OIT measurements give important information about the stability of a material in thermo-oxidative environment. This kind of exposure causes aging with combination of high temperature and oxidative atmosphere such as air, often leading to corrosion or degradation of materials.
OIT is a quick and easy method for example to compare stability of different materials and for quality control. However, any extrapolation of long-term stability should be avoided and determined with other techniques.
An example of OIT DSC run for PET grade Mylar is shown below. Blue curve shows the traditional DSC measurement for the material in nitrogen atmosphere, showing glass transition at 80°C and melting around 250°C. The OIT measurement done in air is shown with green curve. As can be seen, the two curves are identical until 260°C at which the oxidation starts to occur.