Outgassing materials

This paper reviews the systems studied to date with the HTFA and compares the HTFA results to those of other experiments when available. Initially, we limited studies to simple test systems. For a number of years only rate constants could be measured, in large part because the impurity ions from outgassing materials prevented branching fraction determinations. Fortunately, many of the reactions produced only one product (at least at lower temperatures) and this limitation did not often result in much information being missed. The early studies included most of the important ionospheric reactions with the exception of the reactions involving O atoms. The upper temperature limit for these studies was at least 1400 K and in some cases 1800 K. 

We determined the ratio of the magnetic moments of the proton and the deuteron with improved accuracy (37). We demonstrated that even thoroughly outgassed materials such as glass, quartz and metal wires retain a certain amount of hydrogen, the presence of which becomes evident by exchange with deuterium at elevated temperature (38). 

Analysis of RGA results provides a good indication of the sources and mechanisms for the generation of the outgassed materials. Table 6.4 shows RGA data of sealed packages containing various die-attachment materials and processing conditions. ... 

Thermogravimetric analyzers may be connected to a variety of chemical analyzers to determine the exact composition of the outgassed materials as they are evolved. 

Outgassed materials 5,000 ppm moisture (maximum) 3.5.3 Packages with an equivalent exposed adhesive to the application shall be analyzed after 24 hr and 1,000 hr 150°C 3.8.6... 

Thermogravimetric analyzers may be connected to a variety of chemical analyzers to determine the exact composition ofthe outgassed materials as they are evolved. Among chemical analysis methods are gas chromatography, infrared spectroscopy, and mass spectroscopy for example, a TGA apparatus may be coupled with a Fourier Transform Infrared (FTIR) spectrophotometer to measure the thermal oxidative stabilities of several fluorinated polyimides. 

By annealing of austenitic stainless steel doped with N, B, and Ce at 800°C under vacuum, the surface was covered in part with thin precipitated BN layers. From studies by reflection high-energy electron diffraction (RHEED) and transmission electron diffraction (TED) it was shown that the surface is covered with the basal planes of a-BN, which are more inert to gas adsorption than other planes. It was also shown that this is a new, low-outgassing material surface for improved ultrahigh vacuum use [59]. From optical spectra and CNDO model calculations it is assumed that the butadiene-iron tricarbonyl complex is adsorbed on a a-BN substrate via the butadienyl group [60]. 

No major instrument maintenance should be scheduled during the period of the experiment. No dirty samples like high-outgassing materials should be analyzed during the period of the experiment to avoid potential cross-contamination. 

Evaporation and sublimation into a vacuum system is defined as outgassing. Almost every material, solid, or liquid has a small vapor pressure, and their outgassing becomes important when the vacuum pressure falls below this vapor pressure. In a vacuum system, outgassing has the same effect as a leak and can limit the achievable vacuum. Outgassing materials may condense on nearby colder surfaces, which can be problematic if they obscure optical instruments or react with other materials. Therefore, outgassing is one of the great concerns for interplanetary space missions, where an obscured telescope or solar cell can ruin an expensive mission. 

Walls and floors should be coated with a low-outgassing material (Table 14.1) that is easily cleaned. In some cases the coating material should be electrically conductive to minimize electrostatic charge buildup. 

Assume that the density of the outgassing material is that of water 1 g/cm. A cube 1 cm on a side is shown in Figure 13.2. It would have a mass of 1 g, contain about 33 X 10 molecules 3 X 10 molecules along one edge, and 1 X 10 molecules on each face. The density of molecules in a monolayer is thus about 1 X 10 molecules per square centimeter. 

Thermal control materials must be selected that meet out-gassing requirements. Consideration must also be given to the fact that the outer surfaces and radiators, due to their relatively low temperatures, could be accumulation surfaces for outgassed materials. 

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