Nanocalorimeter Cell

Description

Nanocalorimetry, that is, differential scanning calorimetry (DSC) applied to nanogram sample masses, is used to measure latent-heat and specific-heat during in-situ thermal annealing of materials at high resolution (< 10 nJ/K) and high heating and cooling rates (> 1,000,000 K/s). Due to the much higher heating and cooling rates available in comparison to conventional DSC, the technique is particularly well-suited for distinguishing phase transformations which may be obscured--either due to overlapping transition temperatures or low enthalpic changes. A familiar example is the use of nanocalorimetry to determine glass-transitition temperatures in semi-crystalline polymers. These may have distinct features due to bulk amorphous interactions and local interactions at amorphous/crystalline phase boundaries. Accordingly, nanocalorimetry has become an important diagnostic tool for the identification and evaluation of metastable or transitory phase transitions -- particularly in materials which are structurally or compositionally complex.

A nanocalorimetry measurement involves recording electric power and sample temperature as functions of time, and the subsequent conversion of these signals into thermophysical quantities. The measurement principle is derived from basic thermodynamic considerations regarding the balance of heat energy within a control volume consisting of: (1) an electric heater, (2) a thin membrane, (3) sample, and (4) the environment. An electric current pulse is passed through the heater, raising its temperature almost instantaneously due to Joule heating, as well as the sample temperature via heat transfer through the thin membrane. As the sample temperature increases, the energy supplied (E = I2R*t) and the associated rise in temperature can be used to determine its apparent heat capacity. By varying the current amplitude, the rate of temperature increase can be varied, allowing kinetic information to be obtained. A conceptual diagram is shown below.

If the membrane is made sufficiently thin, the temperature of the heater, membrane and sample will be congruent, and the sample temperature will be determined primarily by the amplitude and duration of the pulse. Long pulses induce isothermal sample heating whereas for short pulses, the temperature rise is approximately linear, producing a nearly constant heating rate (for non-isothermal annealing experiments). The maximum heating rate is limited by the thermal time constant of the control volume--a smaller mass producing a smaller time constant and therefore a larger heating rate. Commercial systems, such as the Mettler-Toledo Flash DSC 1, can reach heating rates of up to 20,000 K/s in a lab setting, although rates approaching 1,000,000 K/s have been demonstrated by academic researchers.

References

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2. Ultrafast thermal processing and nanocalorimetry at heating and cooling rates up to 1MK∕s: Review of Scientific Instruments: Vol 78, No 7 https://aip-scitation-org.prx.library.gatech.edu/doi/abs/10.1063/1.2751411 (accessed 2018 -04 -28).

3. Liu, Y.; Hu, Z.; Suo, Z.; Hu, L.; Feng, L.; Gong, X.; Liu, Y.; Zhang, J. High-Throughput Experiments Facilitate Materials Innovation: A Review. Sci. China Technol. Sci. 2019, 62 (4), 521–545. https://doi.org/10.1007/s11431-018-9369-9.

4. Fitzharris, E. R.; Rosen, D. W.; Shofner, M. L. Fast Scanning Calorimetry for Semicrystalline Polymers in Fused Deposition Modeling. Polymer 2019, 166, 196–205. https://doi.org/10.1016/j.polymer.2019.01.083.

5. Poel, G. V.; Istrate, D.; Magon, A.; Mathot, V. Performance and Calibration of the Flash DSC 1, a New, MEMS-Based Fast Scanning Calorimeter. J. Therm. Anal. Calorim. 2012, 110 (3), 1533–1546. https://doi.org/10.1007/s10973-012-2722-7.

6. Allen, L. H.; Ramanath, G.; Lai, S. L.; Ma, Z.; Lee, S.; Allman, D. D. J.; Fuchs, K. P. 1 000 000 C/s Thin Film Electrical Heater: In Situ Resistivity Measurements of Al and Ti/Si Thin Films during Ultra Rapid Thermal Annealing. Appl. Phys. Lett. 1994, 64 (4), 417–419. https://doi.org/10.1063/1.111116.