Recently, people have tried to use phenyl silicone rubber to solve the problem that the O-ring installed on the siphon of liquid nitrogen dewar bottle is not tightly sealed. The O-ring is not in direct contact with liquid nitrogen, but the neck temperature of Dewar bottle is very low. Therefore, when using Dewar bottle, the current O-ring will still become very fragile and lead to poor sealing effect.


It is well known that the boiling point of liquid nitrogen is very low, which is - 196 ° C (or - 321 ° F）。 At present, the minimum temperature that thermosetting rubber can withstand is about - 104 ℃ ° C. Such as phenyl silicone rubber. Of course, sometimes the most difficult part of choosing a rubber material is to understand the exact temperature at which the rubber needs to be sealed and work.


Because the temperature of liquid nitrogen is too low, and the temperature loss from convection to environment or conduction to equipment, the temperature will drop sharply when liquid nitrogen is gasified. Therefore, only when the temperature of liquid nitrogen is within the tolerance range of the rubber material, the rubber material can seal it.


Sealing performance is directly related to rubber deformation and sealing ability. At low temperature, the modulus of rubber will increase when it reaches the glass transition temperature. As the rubber hardens, the ability to deform and seal may be reduced enough to allow leakage. Table 1 shows the low temperature test for different types of silicone materials（ Note: when testing rubber at low temperature, there will be some deviation according to the application.)