Boiling temperature measurement

What is boiling?

The vaporization of a compound corresponds to its change of state between the liquid state and the gaseous state. The inverse transformation is called condensation.

Vaporization can take place in two distinct ways: by evaporation and by boiling. Boiling takes place at a specific temperature called the boiling temperature. This depends very strongly on the ambient pressure. Boiling is a sudden change in state of the liquid: bubbles of vapor form and rise to its surface.

Unlike boiling, evaporation takes place more slowly and more or less quickly at all temperatures as long as the gaseous phase above the liquid is not saturated with the vapor of the compound in question (we speak of then pressure or vapor tension).

How to measure the boiling temperature?

This measurement can be carried out by calorimetry, and more particularly by DSC. The sample is placed in a crucible under controlled pressure and undergoes a rise in temperature. Without change of state, the measured heat flux corresponds only to the heat necessary for heating the liquid (Heat Capacity). When the boiling point is reached, a very large endothermic heat flux is measured. The location of this enthalpy peak is determined by the so-called “onset” method, and defines the boiling point at the measurement pressure (see figure).

Commonly boiling temperature measurements are made at atmospheric pressure. However, Calnesis also performs boiling temperature measurements at controlled sub-atmospheric pressure (between 10 mbar and 1 bar) by DSC. These measurements allow in particular the plotting of the phase diagram of the samples, very useful in the dimensioning of the evaporation processes.

To study liquid/gas balances or changes of state, other solutions can be implemented to adapt to your needs and to get as close as possible to your process. Do not hesitate to contact us to discuss it.