超高真空領域におけるモレキュラシーブクライオソープションポンプの排気特性
1964 年 7 巻 12 号 p. 405-410
詳細
1964 年 7 巻 12 号 p. 405-410
In the development of a cryosorption pump being available in ultra-high vacuum, the pumping performances have been experimentally studied for two kinds of molecular sieves, 5A and 13X, at 77°K. The pumping speed has been measured on the adsorbent bed in the sample cell by the constant flow method as a function of time for nitrogen gas in the pressure range of 10-610-8 Torr. The results are as follows :
(1) Excluding the initial adsorption stage which succeds for a few minutes after introducing the adsorbate gas, the pressure in the cell increases linearly in the square root of time slowly. For this pumping stage, we call “steady pumping stage”.
(2) The initial pumping speeds of the steady pumping stage for both 5A and 13X are very large and independent of the pressure in the region below 1× 10-6 Torr. However, the speed for 5A depends on. the pressure in the higher region than 10-6 Torr. The decay of speed for 5A is much faster than that for 13X.
(3) The steady pumping speeds are indepedent of the thickness of the adsorbent bet and in proportion to the apparent area of the adsorbent bed.
(4) The decay of speeds in case of constant throughput are assumed to depend on the diffusion rate of adsorbed molecules into the adsorbent.
(5) The optimun condition of baking the molecular sieves is to heat them at 400°C for about 10 hours in high vacuum.
