Oxygen (O2) is a colourless and odourless gas. It is vital for most life forms on earth. We absorb oxygen through the air we breathe. Medical oxygen is essential in hospital and clinical care for resuscitation and surgery and for various therapies. It is also mixed with nitrogen or helium to create underwater diving mixtures.
Oxygen is obtained on a commercial scale through the liquefaction and distillation of ambient air at air separation plants. A second purification process may be necessary if ultra-high purity levels are required. High-purity oxygen can also be produced through the electrolysis of water. Membrane techniques are suited to lower-purity requirements.
The main industrial application of oxygen is combustion. Many materials that do not normally burn in air will burn in oxygen so mixing oxygen with air greatly enhances combustion efficiency in iron and steel, non-ferrous, glass and concrete industries. It is widely combined with a fuel gas for cutting, welding, brazing and glass blowing, offering much higher flame temperatures and thus greater efficiency than just air. With oxyfuel, plasma and laser processes, a jet of gaseous oxygen is used to cut steel. Oxygen is also popular in thermal lancing to drill or cut through materials such as concrete, brick, stone and various metals.
Due to its ability to help stabilise the arc and reduce surface tension, oxygen is used as an ingredient in some shielding gas mixtures. The chemical industry relies on pure oxygen to increase the efficiency of oxidation reactions, for instance. High-purity oxygen is used in laboratories, process-control operations, gas-cooled nuclear reactors, metal analysis instruments, and in semiconductor and optical fibre production.
On the water treatment front, oxygen is an effective way of purifying waste water and treating sewage. Other applications include sealing glass ampoules in the pharmaceutical industry, oxygenation of water for aquaculture, modified atmosphere packaging (MAP) mixtures and liquid explosives.