Out-gassing problem

Question NASA has asked us to model a transient out-gassing problem for a thin plastic plate containing a volatile substance that will gradually effuse from the plate over time when exposed to the vacuum of space. Obtain an approximate expression for the time it takes for the concentration of this substance to decrease to 1/10 of its initial value at the mid point of the plate upon exposure to the space vacuum. Assume that at time t = 0 exposure to the space vacuum fixes c = 0 on the two faces of the plate, while the initial concentration of the species inside the plate starts at a uniform value of c° and the plate has a thickness of L. 

Normal (synthetic) paint can usually create serious problems for MCS patients. It s thus best to look for natural paint, namely those kinds based in minerals or plants. Some paints contain a natural solvent and others use water for dilution. Even natural solvents can sometimes cause allergic reactions in sensitive people, so be careful. Natural paints based in water are without a doubt the safest for MCS patients. In any case, always first put some paint on a small out-gassed board and place it in your home to see if you react to it (perhaps even put the board next to your bed). Never paint your entire home or safe room in one go First do the board test, then paint a wall, then paint a room and see if everything is still all right. Only then should you proceed with other rooms. See Part VIfor several natural and organic solutions or go to www.the-abc-of-mcs.com under Living. ... 

CVD eliminates the problems of solution based synthesis techifiques such as solvent retention and contamination. Retention of volatile solvents subsequent to film formation can cause out gassing resulting in formation of pinholes, voids etc. Also, substituent groups used to provide solubility frequently result in degradation of the material properties of the host polymer. These problems are absent in CVD. Further, the dry nature of CVD results in high... 

Also, as the thickness of the adhesive bondline increases, read through problems become worse. The heat resistance of urethane-bonded SMC composites has also been a problem. This is believed to be due to the out-gassing of volatiles from the plastic which decreases the bond integrity. This is evidenced in Table VI, which compares the heat resistance of metal-metal bonds and SMC composites prepared with urethane adhesives. It can also be seen that the composition of the SMC has a significant affect on the heat resistance. The urethane-modified SMC was also reported to give off less volatiles than the unmodified SMC. Recent work has indicated that certain primers may be able to protect the adhesive from the substrate. 

The problems of out-gassing are further illustrated when the essentially non-structural bonding of the satellite mirrors is considered. Here a silicone adhesive is used and, rather than using conventional acetic acid-based chemistry, which would fail the out-gassing criteria, oxime chemistry is employed. 

New cables and recently coated fittings can cause problems. Always keep some old or gassed-out cables, fittings and wires in your shed or storage area often it can take months before a new cable is properly gassed out. An alternative is to wrap the cable with aluminum foil tape see entry 149. 

New carpets, laminate, parquet, vinyl, and so on are not suitable for MCS patients, because the varnishes, glues, synthetic substances, formaldehyde and other chemical substances can cause severe problems. Gassing out these chemicals can take months if not years. It s therefore best to play it safe and go with materials that are less harmful, such as organically produced cotton. An untreated hardwood floor or other hard floor coverings, like stone, ceramic or porcelain tile, are also good options. Make sure you do not react to the specific wood by first testing a sample thoroughly ... 

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