Pumping characteristics of the St707 nonevaporable getter (Zr70V24.6-Fe5.4wt%)

The room temperature pumping speeds of the St707 nonevaporable getter (NEG) have been measured both for individual gases and for gas mixtures as a function of the quantities of gas pumped. The interesting feature of this NEG consists in its moderately low activation temperature. Therefore particular attention has been devoted to defining the optimum temperature and duration of the activation process to obtain the highest possible pumping speed in a given practical situation. It has been found that heating at 400 degrees C for about 1 h, or at 350 degrees C for one day, results in pumping speeds of about 1000 l s(-1) m(-1) for H-2, 2000 l s(-1) m(-1) for CO, and 450 l s(-1) m(-1) for N-2, values very close to those obtained after activation at the higher temperature of 740 degrees C. The St707 NEG is therefore particularly suitable for passive activation during bakeout of stainless steel vacuum systems, avoiding the need for electrical insulation and feedthroughs which are mandatory when activation is carried out by resistive heating. (C) 1996 American Vacuum Society.