VISTA Instrument: A PCM-Based Sensor for Organics and Volatiles Characterization by Using Thermogravimetric Technique

VISTA (Volatile In Situ Thermogravimetry Analyser) is a μ-Thermogravimeter sensor developed by Consortium of Italian Institutes. ThermoGravimetric Analysis (TGA) is a widely used technique to monitor thermal processes involving volatile compounds, e.g. deposition/sublimation and absorption/ desorption. The instrument core is composed by a Piezoelectric Crystal Microbalance (PCM), equipped with built-in heater and built-in temperature sensor, and provided of its own Proximity Electronics (PE). The PCM oscillation frequency linearly depends on the mass deposited on its sensible area (according to Sauerbrey equation) while the PCM temperature can be increased by means of integrated heaters. Thus, mass and volatile composition can be inferred by the frequency change and by desorption temperature, respectively. The instrument is divided in two sensor heads: VISTA1, able to monitor outgassing processes in space, and VISTA2, able to reach higher temperatures, studying the dehydration and organics decomposition in minerals in different environmental conditions. An Engineering Model of VISTA1 and a laboratory breadboard of VISTA2 have been developed. Pure organic compounds and contaminant have been characterized by using deposition processes and TGA cycles obtaining some physical-chemical parameters, i.e. enthalpy of sublimation/evaporation, Δ
_Hsub,evap
, deposition rates, k and vapor pressures, P
_vap
. The instrument concept, the scientific objectives and the laboratory measurements are explained in this work.