Liquid Helium is the preferred cooling agent for Type I superconductors, such as Lead and Aluminum, due to its ability to reach temperatures below their critical points. Liquid Nitrogen, boiling at 77K, is insufficient for cooling these materials as it cannot achieve the necessary low temperatures required for superconductivity. For Aluminum, which has a bulk critical temperature (Tc) of 1.2K, advanced cooling techniques like pumping on He-3 or utilizing adiabatic demagnetization cooling are necessary. This discussion highlights the limitations of Liquid Nitrogen and the complexities involved in cooling Type I superconductors.
PREREQUISITESPhysicists, materials scientists, and engineers involved in superconductivity research and cryogenic applications will benefit from this discussion.
Hence, another reason why people prefer Type II superconductors.f95toli said:No, because liquid nitrogen boils at 77K, and even if you pump on it the temperature will only go down a few K before it goes solid (I can't remember the exact temperature, 68K or so at 1 Bar?)
Hence, liquid nitrogen only works for high-Tc superconductors, and they are all type II.
Also, for aluminium you can't even use liquid helium (bulk Tc=1.2K), you need something more elaborate; you need to e.g. pump on He-3 (or He-3/He-4 mixtures) or use adibatic demagnetization cooling.