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Chip Calorimetry

chip-calorimetry-zoom.jpgt0-5 holder.jpgsensor 13 box 1 - 5 wt 100 rpm crop 3on2.jpg

Conceptually, the fast scanning chip calorimetry technique is similar to DSC and RHC in that a differential heat flow is measured. Like DSC and RHC, it is a differential technique, i.e. a sample and a reference are subjected to the same temperature program, so that the influence of non-sample effects such as heat losses and addenda heat capacities (due to e.g. the membrane) is reduced. In practise, a closed tube containing an oven with both reference and sample sensors is submerged in liquid nitrogen. The oven is kept at a constant temperature, which will be the base temperature for all measurements. The liquid nitrogen acts as a heat sink, allowing cryogenic base temperatures.

The thin membrane chips consist of a 1 µm thick freestanding SiNx membrane of 900 µm by 900 µm, supported by a silicon frame. In the centre of this membrane an active area can be found where the sample is placed. The size of the active area depends on the type of chip, and will determine the maximum scanning rates that can be attained. Depending on its size, the active area will contain 1 or 2 on-chip resistive heaters and a number of polysilicon p-n thermopiles.

The very high heating and cooling rates that can be achieved using this technique can be used to avoid all kinds of undesirable non-isothermal effects (e.g. reordering), making it possible to investigate metastable structures. This technique has so far been succesfull for the study of crystallization kinetics of rapidly crystallizing materials, in bulk or in thin layers.