Liquefied

Liquefied is a term used to describe a substance that has been transformed into a liquid state from a solid or gaseous state. In physics and engineering, liquefaction most commonly refers to turning a gas into a liquid by cooling and/or applying pressure, a process that reduces volume and increases density. The specific conditions needed depend on the substance and are represented in phase diagrams with critical temperature and pressure.

Gas liquefaction is energy-intensive and typically achieved through cryogenic cooling or high-pressure techniques. Liquefied natural gas (LNG) is natural gas cooled to about −162 degrees Celsius, turning it into a dense liquid suitable for long-distance transport and storage in insulated tanks. LNG must be regasified before use. Other liquefied gases include liquefied nitrogen, oxygen, and carbon dioxide, produced for industrial, medical, or research applications; these are usually kept at very low temperatures.

Liquefaction also describes a geological phenomenon during earthquakes: saturated soils can temporarily lose strength and behave like liquids when pore water pressure rises, a process known as soil liquefaction. This can lead to ground failure, settlement, and damage to structures.

Safety and handling are important considerations with liquefied materials. Cryogenic liquids can cause severe cold burns and may pose asphyxiation, flammability, or pressure hazards. Proper containment, insulation, venting, and adherence to safety standards are essential in storage and transport.