GROUND SIMULATION STUDIES OF OUTGASSING PARAMETERS FOR COMMERCIALLY AVAILABLE BLACK PAINTS

摘要

This work is dedicated to comparative ground simulation studies of black paints and coatings. Some of these materials are already in use in orbiting spacecrafts, mainly in optical systems, while others are considered for such applications. The paints and coatings discussed here are S2, PU1, and PNC manufactured by MAP (France), CV-1148 produced by NuSil (USA), and Acktar Vacuum Black coating developed by Acktar (Israel). S2, PNC, and CV-1148 are silicone-based materials and as such are known to be a threat as a source of contamination; PU1 is based on polyurethane and, therefore, may release hydrocarbons; an Acktar coating is inorganic but highly porous and, therefore, may aggregate fragments from its environment with a potential of desorption and contamination of neighboring parts in vacuum. The experimental evaluation of the paints started from general outgassing tests according to the ASTM E 595 standard to determine total mass loss (TML), collected volatile condensable material (CVCM), and water vapor regained (WVR). Then in situ monitoring of the contaminants by a quartz crystal microbalance (QCM) was performed. It involved the following stages: (a) holding the sample at high temperature while keeping the QCM at low temperature; (b) cooling the sample and keeping it at room temperature without changing the QCM temperature in order to isolate the contaminants re-evaporation process; and (c) increasing the QCM temperature to study the effect of the temperature on the re-evaporation kinetics. In addition, chemical identification of the residual contaminants was performed by FTIR spectroscopy. Considerable differences in the outgassing kinetic parameters and contamination potentials were detected between the discussed materials. For example, the Acktar coating, while having the highest TML shows the lowest contamination potential. The PNC paint is characterized by the shortest outgassing time among the siliconic paints and produces substantially lower mass of contaminants than its predecessor, S2. It has a higher re-evaporation rate of contaminants from the QCM, as well. An analytical model was developed to derive the outgassing and re-emission kinetic parameters from the experimental data.