Pumping of methane by St707 at low temperatures

A simple means of pumping small leak rates of methane is frequently required in long-term sealed-off devices such as evacuated solar absorbers. In this paper we examine, in this context, a chemisorption or catalytic pump the SAES getter St707. After suitable activation in an ultrahigh vacuum system a small sample of St707 (2.7 x 3 cm), with heater external to the vacuum system, was exposed to a methane leak as the sample temperature was raised in steps from room temperature to 400 0C, the highest temperature used. Pumping was first detected at 100 0C and at 400 0C the pumping speed was 2 x 10-3 l s-1 cm-2 (pumping area assumed 8 cm2), after 0.34 Torr l of methane had been pumped. Care was taken to distinguish these small pumping speeds from ionic pumping by the gages. The conclusion is that the St707 getter is suitable as a methane pump of low speed at low temperatures and pressures