Glass-to-metal seal absorb the stresses from thermal expansion mismatches. Due to its very low vapor pressure, indium finds use in glass-metal seals used in vacuum technology. Gallium is a soft metal with melting point at 30 °C. It readily wets glasses and most metals and can be used for seals that can be assembled/disassembled by just slight heating. It can be used as a liquid seal up to high temperatures or even at lower temperatures when alloyed with other metals (e.g. as galinstan). Mercury is a metal liquid at normal temperature. It was used as the earliest glass-to-metal seal and is still
Liquid hydrogen The first synthesis of the stable isomer form of liquid hydrogen, parahydrogen, was achieved by Paul Harteck and Karl Friedrich Bonhoeffer in 1929. The two nuclei in a dihydrogen molecule can have two different spin states. Parahydrogen, in which the two nuclear spins are antiparallel, is more stable than orthohydrogen, in which the two are parallel. At room temperature, gaseous hydrogen is mostly in the ortho isomeric form due to thermal energy, but an ortho-enriched mixture is only metastable when liquified at low temperature. It slowly undergoes an exothermic reaction to become the para isomer, with enough energy released as