Effects of readsorption on outgassing rate measurements

摘要: Outgassing rates from the walls of a vacuum chamber are usually measured by one two methods, (1) throughput method, where outgassing rate is derived pressure drop across known conductance during evacuation, or (2) rise method (aka gas accumulation method) sealed off at low and in with time measured. A model analyzed to show that readsorption desorbed results Qm being considerably less than intrinsic Qi (the absence readsorption). The ratio Qm/Qi varies pumping parameter S/A (S speed adsorbing area) sticking probability s. found vary zero coverage s0, except when a/As0≪kt−1, effective area orifice, area, k constant involving heats adsorption, t time. Measurements pressure‐rise on stainless steel systems evolved hydrogen, linear for as long 103 h increasing factor large 106, indicating rate. It shown if occurs then p(t) curve will be nonlinear. proposed explain observed constancy apparent which assumes (a) desorption limited (b) diffusion H atoms surface much greater H2 arrival molecules phase empty sites.