Effect of adsorbent on vacuum degree at low temperature of vacuum valve

For vacuum multi-layer insulation valves, the vacuum in the interlayer will gradually decrease as the use time increases. The gas in the interlayer is not a type of gas molecule, but a mixture of a plurality of gases. The main source of the interlayer gas is the outgassing of the inner and outer stainless steel tubes, the winding layer, the inner and outer tube support, and the deflation of other solid impurities. Metal venting is the main source of interlayer gas, and the main component of metal venting is hydrogen.

The experiment samples and analyzes the residual gas of the vacuum valve. The content of gas in the interlayer is hydrogen, nitrogen, oxygen, argon, water vapor, carbon dioxide and helium. The highest hydrogen content can reach 95%.

At the liquid hydrogen temperature, in addition to hydrogen and a very small amount of ruthenium, all other gases such as nitrogen, oxygen, argon, water vapor, carbon dioxide, etc. are condensed into a solid, and at the same time, only a small amount of hydrogen exists in the interlayer due to the action of the adsorbent. At liquid oxygen temperature, the molecular sieve has a poor adsorption capacity for hydrogen, and all other impurity gases are adsorbed by the molecular sieve or solidified. Since hydrogen is derived from the residual gas and the helium gas detected by the helium mass spectrometer when the vacuum valve is sealed, the content of niobium is extremely small, and it can be approximated that all of the vacuum interlayer is hydrogen at the liquid oxygen temperature. At liquid oxygen temperature, the adsorption capacity of 5A molecular sieve for hydrogen is very poor, and the amount of hydrogen adsorbed per gram of molecular sieve is only 0.01cm3 (standard state), which can be considered as non-adsorption.

At liquid oxygen temperature, molecular sieves have a fairly good adsorption capacity for oxygen, nitrogen and argon. At the liquid hydrogen temperature, the adsorption capacity of the molecular sieve for hydrogen becomes very strong. At 20K temperature and 1.33×10-4 Pa, the adsorption capacity of the molecular sieve for hydrogen is greater than 160 cm 3 (standard state) / g. Because the higher the pressure, the stronger the adsorption capacity of the molecular sieve, so at the liquid oxygen temperature, when the interlayer pressure is higher (>1.33×10-4 Pa), the adsorption capacity of the molecular sieve for oxygen, nitrogen and argon should be at least 1 cm3. State) / g.