Trelic’s picture of the week – 05/2017

Can you guess what does this picture represent?

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The picture shows a setup phase of a differential scanning calorimetry (DSC) measurement. The automatic robot arm is transferring a sample pan to the DSC furnace.

DSC is a thermal analysis technique used for material characterization. It can be used to measure several materials parameters. Of all the thermal analysis methods, DSC is the most widely used and easily available. DSC measures temperature difference (or heat flow to be more precise) between a sample of interest and an inert reference sample. Heating causes enthalpy (internal energy) changes, which are either endothermic (sample is absorbing energy) or endothermic (sample is releasing energy). As a result, parameters such as glass-transition temperature (Tg), crystallization and curing degree can be determined.

How is the measurement done in practise? A very small piece (for example in our DSC typically between 1mg and 10mg) of material is placed inside a pan and the heat flow is measured either as a function of temperature ramp or at constant temperature (isothermal), typically under nitrogen atmosphere.

Below is an example of the DSC run for an epoxy adhesive. The sample is measured twice: first run (blue curve) shows Tg of the partially uncured adhesive as well as curing peak whereas the second run (green peak) shows Tg of the fully cured adhesive. The curing peak can be used to calculate the curing degree of the adhesive, which can be useful when optimizing process parameters. Partially uncured materials can cause reliability problems for example with stability. The Tg temperatures of the two runs also show that the glass transition temperature tends to be lower for uncured materials (18°C) than for fully cured materials (51°C).