Single-run determination of the saturation vapor pressure and enthalpy of vaporization/sublimation of a substance undergoing successive solid-solid and solid-liquid phase transitions: the case of $N$-methyl acetamide

TL;DR

This study introduces a method for single-run measurement of vapor pressure and enthalpy of vaporization/sublimation of a substance with multiple phase transitions, demonstrated on N-methyl acetamide.

Contribution

It presents a novel dynamical measurement technique that captures vapor pressure and enthalpy data across phase transitions in a single experiment.

Findings

Accurate vapor pressure data obtained in a single run.

Determined enthalpies of sublimation and vaporization for different phases.

Method applicable to substances with complex phase behavior.

Abstract

We report on the dynamical measurement of the saturation vapor pressure of $N$-methyl acetamide in the temperature range $-30^\circ$C to $34^\circ$C. This is achieved by monitoring the pressure inside a vacuum chamber in which a precooled sample of the substance slowly thermalizes to the chamber temperature, undergoing first a phase transition between two crystalline structures around $1^\circ$C and then a solid-liquid phase transition around $30^\circ$C. Such a measurement provides in a single run accurate data for the saturation vapor pressure and the enthalpies of sublimation and vaporization of the different phases of the investigated substance.