Measuring Enthalpy of Sublimation of Volatiles by Means of Piezoelectric Crystal Microbalances

Piezoelectric Crystal Microbalances (PCM's) are widely used to study the chemical
processes involving volatile compounds in any environment, such as condensation process.
Since PCM's are miniaturized sensor, they are very suitable for planetary in situ missions,
where can be used to detect and to measure the mass amount of astrobiologically significant
compounds, such as water and organics. This work focuses on the realization and testing of a
new experimental setup, able to characterize volatiles which can be found in a planetary
environment. In particular the enthalpy of sublimation of some dicarboxylic acids has been
measured. The importance of dicarboxylic acids in planetology and astrobiology is due to the
fact that they have been detected in carbonaceous chondritic material (e.g. Murchinson), among
the most pristine material present in our Solar System. In this work, a sample of acid was heated
in an effusion cell up to its sublimation. For a set of temperatures (from 30 °C to 75 °C), the
deposition rate on the PCM surface has been measured. From these measurements, it has been
possible to infer the enthalpy of sublimation of Adipic acid, i.e. ?H = 141.6 ± 0.8 kJ/mol and
Succinic acid, i.e. ?H = 113.3 ± 1.3 kJ/mol. This technique has so demonstrated to be a good
choice to recognise a single compound or a mixture (with an analysis upstream) even if some
improvements concerning the thermal stabilization of the system will be implemented in order
to enhance the results' accuracy. The experiment has been performed in support of the VISTA
(Volatile In Situ Thermogravimetry Analyzer) project, which is included in the scientific
payload of the ESA MarcoPolo-R mission study