Thermal analysis of an aluminum standard and Iceland spar calcite. A) Heat flow vs. temperature data for the melting of an aluminum sample used to calibrate thermocouples. The endotherm for a pure metal has a very well defined onset temperature and a clear baseline on either side of the endotherm. In contrast, the decomposition of CaCO3
(B) has a much broader endotherm with a more ambiguous baseline (note the difference in scale on the x-axis). This results in a more subjective onset temperature as the baseline must be manually defined. Peak temperatures are also identified. Both samples were run at 30 mbar using a He carrier gas with a 3 sccm flow rate and a ramp rate of 35°C/minute.