Liquid metal cooled reactor Clementine was the first liquid metal cooled nuclear reactor and used mercury coolant, thought to be the obvious choice since it is liquid at room temperature. However, because of disadvantages including high toxicity, high vapor pressure even at room temperature, low boiling point, producing noxious fumes when heated, relatively low thermal conductivity, and a high neutron cross-section, it has fallen out of favor. Sodium and NaK (a eutectic sodium-potassium alloy) do not corrode steel to any significant degree and are compatible with many nuclear fuels, allowing for a wide choice of structural materials. They do, however, ignite spontaneously on contact
Room-temperature superconductor of a Meissner effect at 250K may have appeared in magnetometer tests. In 1964, William A. Little proposed the possibility of high temperature superconductivity in organic polymers. This proposal is based on the exciton-mediated electron pairing, as opposed to phonon-mediated pairing in BCS theory. Room-temperature superconductor A room-temperature superconductor is a hypothetical material that would be capable of exhibiting superconductivity at operating temperatures above 0 °C (273.15 K). While this is not strictly "room temperature", which would be approximately 20–25 °C, it is the temperature at which ice forms and can be reached and easily maintained in an everyday environment.