Tau-RMode

For correct kinetic analysis and for correct Purity Determination it is necessary to correct the DSC/DTA measurement regarding thermal resistance and regarding time constant of the measuring system.

The Indium melting peak, measured with DSC 204, shows the typical shape of a melting peak of a pure metal:

  • The endothermal peak increases nearly linearly up to the maximum. This behavior is caused by the so-called thermal resistance.
  • After the maximum the melting peak decreases nearly exponentially. A more precise analysis indicates that the decay is the sum of more then one exponential functions.

According to all standards, the temperature during DSC measurements is measured on the reference side. Therefore, the given temperature is not the temperature inside the sample.In order to receive the true sample temperature the measurement is to correct regarding to thermal resistance.

 

After correction regarding thermal resistance, the left front of melting peak increases nearly perpendicularly, indicating that the sample temperature is constant.

After correction regarding time constant the DSC curve is decreasing approximately perpendicularly to the baseline without overshooting.

After the complete correction, the shape of the DSC melting peak is nearly a delta-pulse, an indication that the sample temperature now is constant during the melting process and that the DSC peak ends very sharply. This special shape is only given in temperature scaling.

In time scaling it is visible that after both corrections the sample temperature is constant during the melting process. Now, the corrected DSC curve decreases perpendicularly to the baseline and partial area exhibits a clear end point of melting process.