Solid hydrogen

Solid hydrogen is hydrogen frozen into a crystalline solid, usually made of H₂ molecules. Its structure and properties vary with temperature and pressure, including transitions to dense phases at high pressure.

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Hydrogen phase diagram: A map of hydrogen’s stable phases as functions of temperature and pressure. It charts the conditions under which hydrogen freezes and transforms between solid structures.
James Dewar: Scottish chemist and physicist known for pioneering low-temperature research and inventing the Dewar flask. His cryogenic work enabled the liquefaction and eventual solidification of hydrogen.
Jupiter: The largest planet in the Solar System, composed mainly of hydrogen and helium. Models of Jupiter’s deep interior depend on hydrogen’s behavior under extreme pressure.
Gaseous hydrogen: Hydrogen in a gaseous state, consisting predominantly of mobile H₂ molecules under ordinary conditions. Gas molecules move freely, whereas solid hydrogen confines them to an ordered lattice.
Quantum solid: A solid whose particles show significant quantum motion even near absolute zero. Light hydrogen atoms retain large zero-point motion within the crystal.
Liquid hydrogen: Hydrogen in its liquid state, used as a cryogenic fluid and rocket propellant. Cooling liquid hydrogen below its freezing point produces ordinary solid hydrogen.
Saturn: The sixth planet from the Sun, composed mainly of hydrogen and helium. Hydrogen phase transitions help explain Saturn’s interior structure and thermal evolution.
Atomic hydrogen: Hydrogen consisting of individual H atoms rather than H₂ molecules. Most solid hydrogen remains molecular until compression may dissociate its molecules.
Molecular crystal: A crystal whose lattice sites are occupied by discrete molecules held together by intermolecular forces. Ordinary solid hydrogen is built from H₂ molecules rather than isolated atoms.
Absolute zero: The lowest possible temperature, at which a system has minimal thermal energy. Solid hydrogen’s persistent zero-point motion makes its behavior unlike a classical crystal near this limit.