Rate of outgassing

It can therefore be accepted that the rate of outgassing at normal temperature is extremely low, although the actual rates are not known. In fact molybdenum disulphide has been used satisfactorily in many applications in space vacuum, some of which were listed in Table 1.1. 

Overall mass transfer coefficient (Aoi) Variable that relates air-water flux rate of a chemical to the gradient between water concentration and air concentration divided by Henry s Law constant. Also called the transfer velocity and the piston velocity because in the case where air concentration is zero, the rate of outgassing would be equal to the flux that would result if a hypothetical piston were to move vertically through the water column at the speed of /foi-... 

The pretreatment conditions were the same as those for IR study of adsorbed pyridine. The sample pretreated in a vacuum was exposed to ca. 300Torr D2 at different temperatimes for 1 h. After cooling to room temperature, the sample was outgassed for 10 min prior to TPD run. TPD was run at a heating rate of lOK min 1, and the desorbed gases were analyzed by mass spectrometry. 

A cylindrical vacuum chamber has an internal diameter of 70 cm and a length of 2.5 m. It is made of cleaned stainless steel and evacuated with a combination of diffusion and rotary vacuum pumps. Measurements of the outgassing rate of the chamber material, cleaned according to the same method, give the following data ... 

When a vacuum system is suspected of having a leak, one of the first tests is to determine whether the leak may be caused by outgassing. An easy way to determine this is to chart the rate of pressure loss versus time. To chart this rate, obtain the lowest vacuum you can in a reasonable amount of time, then close the section in question from the pumping section by a stopcock or valve. Next, periodically over a few minutes, or an hour or two (or three), note the pressure and elapsed time. As seen in Fig. 7.55, a real leak will indicate a constant rate of pressure rise over time while an outgassing problem will indicate a decreasing rate of pressure rise over time. 

The rate of adsorption measurements at 90° and 77° K reported in this paper were bracketed between values of the outgassing rate that decreased steadily from 0.008 to 0.005 jumole per hour at 600° C. for a 20-gram sample. 

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