Differential scanning calorimetry on micro hotplates for temperature calibration and mass quantification

Abstract

In this work a novel calibration method for micro hotplates is developed and tested. The method is based on phase change processes of applied testing materials, which can be identified due to their phase change enthalpy in the power needed for the hotplate to linearly heat up. For traceability and reproducibility tests a ceramic heating element (Umweltsensortechnik GmbH, Geschwenda, Germany) including a Pt100 sensing element was used. Using the melting process of Hexatriacontane and different temperature ramps the feasibility of the method was tested, and the onset point of the phase change was identified as the best feature for temperature calibration. On this substrate we achieved an absolute deviation of 5 °C to literature values and a relative uncertainty of 0.3 °C. Pyrazine, which can be removed more easily, showed an absolute deviation of 2.5 °C to literature values and a relative uncertainty of again 0.3 °C for temperature calibration. The sublimation process of Hexamethylenetetramine was also tested but did not yield stable results. The two materials successfully tested on the ceramic heater were then transferred to MEMS membrane heaters (AS-MLV-P2 and AS-MLV, both metal oxide semiconductor gas sensors, ams AG, Premstätten, Austria) showing the applicability of the method for MEMS device calibration and yielding relative uncertainties for the calibrated heater resistance of 0.17 Ω (corresponding to 0.39 °C). For Hexatriacontane on the ceramic hotplate we also show the possibility of mass quantification through evaluating the phase change enthalpy.