Liquid oxygen, often abbreviated as LOX, is oxygen cooled to extremely low temperatures, transforming it from a gas into a liquid. It is produced by cooling atmospheric air and then separating the oxygen through fractional distillation. Understanding its temperature characteristics is important due to its widespread applications and handling precautions.
The Boiling and Freezing Points
Its boiling point, the temperature at which it changes from liquid to gas at standard atmospheric pressure, is approximately -183°C (-297.3°F). Below this temperature, oxygen remains in a liquid state.
For oxygen to solidify, it must be cooled even further. Its freezing point is around -218.79°C (-361.82°F). At standard pressure, oxygen exists as a liquid within a very narrow temperature range between its boiling and freezing points.
Characteristics of Liquid Oxygen
It appears as a clear, pale blue liquid. This cryogenic liquid is slightly denser than liquid water, with a density of about 1.141 kg/L.
It is strongly paramagnetic, meaning it is attracted to a magnetic field, a property demonstrable by suspending it between the poles of a powerful magnet. The transition of oxygen to its liquid state occurs at “cryogenic” temperatures, defined as temperatures below -90°C (-130°F). This deep cooling process concentrates oxygen, making it useful despite the extreme conditions required to maintain its liquid form.
Everyday Uses
Liquid oxygen serves various practical applications across multiple sectors. In the aerospace industry, it functions as an oxidizer for liquid fuels in rocket engines, providing the thrust necessary for space travel.
In the medical field, liquid oxygen is a primary source for oxygen therapy systems and ventilators, particularly in hospitals and for patients requiring high-flow oxygen. Its compact storage and high purity make it a reliable option, as one liquid oxygen storage tank can replace numerous high-pressure gas cylinders. Industrially, it is used in processes like steel production to increase combustion rates, and in welding and metal cutting. Chemical manufacturers also utilize it as a reactant or catalyst in various operations.
Safe Handling Practices
Given its extreme cold and other properties, handling liquid oxygen requires strict safety measures. Direct contact with liquid oxygen or surfaces cooled by it can cause severe frostbite or cryogenic burns. Therefore, wearing appropriate personal protective equipment (PPE) is essential.
Recommended PPE includes a full faceshield over safety glasses, clean, loose-fitting thermal-insulated or leather gloves, long-sleeved shirts, and pants without cuffs. Proper ventilation is also crucial because liquid oxygen expands significantly when it vaporizes, producing approximately 860 volumes of gaseous oxygen from one volume of liquid. This rapid expansion can lead to oxygen enrichment of the surrounding atmosphere, where oxygen concentrations exceed 23.5%. An oxygen-enriched environment increases the risk of fire, as materials that do not typically burn in air can ignite intensely and spread rapidly.