Application of contaminant species separation by TGA/MS to unraveling outgassing physics and laws

Progress was performed recently on the separation and characterization of the chemical species outgassed by space materials, relying on the assessment of thermogravimetric analysis (TGA) peaks by mass spectrometry (MS). A companion communication reports on this experimental technique and the first level processing of these MS data, which often allows determining which are the outgassed species, and their MS spectra. This communication focusses more on the second analysis step, i.e. the study of the MS data acquired during the initial outgassing phase. Ancient simpler outgassing analyses based on total mass measurements only, most of the time on quartz crystal microbalances (QCMs), cannot realistically determine the separate contribution of different species, even though some models consider the contribution of several species, which are indeed more "mathematical species" than physical ones. In contrast, this new approach, also taking into account the MS measurements during the outgassing, and known species spectra (from the TGA/MS analysis done previously), allows a more realistic determination of the contribution of each real chemical species to the total outgassing. Even though results are not yet final and perfect, measured outgassing fluxes from several species and materials are presented. Their physical analysis, through comparison and tit by diffusion or other possible outgassing laws are also presented. At this level, they clearly point to diffusion laws, rather than to any other outgassing law, although not necessarily always Fickian diffusion. This method was applied to typical US or European outgassing approaches, with either isothermal ASTM-1559 outgassing tests or multi-temperature VBQC-type tests.