When cooled to -183 ° C and a pressure of 760 mm Hg. of Art. oxygen becomes a pale blue liquid with no odor, and when -218,8 ° C - freezes.
Oxygen is the most common on Earth. The Earth's crust (about 47% by mass) exists in a bound form in the atmosphere (about 23% by weight) - free.
The main methods of oxygen production:
- from the air by means of its purification from mechanical impurities, moisture and carbon dioxide, compressed in the compressors, cooling to liquefaction and subsequent separation of oxygen and nitrogen in a slow increase of temperature, nitrogen, having a lower boiling point, evaporates and is discharged into the environment, and the oxygen is stored in liquid (cryogenic distillation);
- electrolysis of distilled water flowing through the formal reaction: 2H 2 O → O 2 ↑ + 2H 2 ↑; because almost clean water does not conduct, it added electrolytes, for example, KOH or NaOH;
- in the laboratory - the catalytic decomposition of hydrogen peroxide H 2 O 2 , the decomposition by heating oxides of heavy metals (eg mercury oxide HgO), potassium permanganate, KMnO 4 , potassium chlorate KClO 3 , etc.
V = K 1 • V b ,
where K 1 - the coefficient, V b - capacity of the container in dm 3 (liter).
Thus, the new tank (150 kg / cm 2 at 20 ° C) of 40 l containing 6.24 m 3 of oxygen under normal conditions.
Liquid oxygen technology, according to GOST 6331-78, also issued the first and second grades. It is stored and transported in Dewar flasks and other cryogenic storage tanks (tank).
Dewars are spherical or cylindrical. The inner and outer casing is made of aluminum alloy tube (neck), which is suspended inside the vessel - Kh18N10T steel having a low coefficient of thermal conductivity. In the space between the walls is usually generated by a vacuum-powder insulation of technical vacuum and a mixture of powdered airgel with a bronze powder. The adsorbent is cooled by liquid oxygen and absorb residual gases between the walls cavity, creating a vacuum in it up to a pressure of 10 -4 -10 -3 mm Hg. of Art.
In the evaporation of 1 liter of liquid oxygen produces about 860 liters of gas (at normal atmospheric pressure and temperature of 20 ° C). When transporting liquid oxygen tare weight attributable to 1 kg of oxygen, more than 10 times smaller than the transport of gas. Storage, transportation and gasification of liquefied natural gas to its inevitable loss of evaporation.
Hazards and safety measures
- Oxygen is not toxic by itself is not explosive or flammable, but is a strong oxidant and actively supports the combustion of various materials, especially organic and other combustible materials, and therefore to work in contact with oxygen should only be allowed for this material;
- in contact pressure of compressed oxygen for more than 30 kgf / cm 2 with fats and oils is their instantaneous oxidation, accompanied by the release of heat that can cause them to ignite, and under certain conditions - to the explosion, and in this connection when dealing with the oxygen necessary to monitor to tanks, equipment and clothing of personnel had no traces of fats and oils;
- substances such as wood, coal, paper, asphalt, etc., impregnated with liquid oxygen, are able to detonate;
- to avoid fires of oxygen in the air of working premises must not exceed 23% by volume, area, where possible exceeding the volume fraction of oxygen, must be equipped with ventilation and controls air in these areas is necessary to limit the presence of people and to exclude the presence of flammable substances;
- after being in an environment with high oxygen content is prohibited to approach the fire, smoke, should be ventilated garment for 30 minutes;
- Liquid oxygen affects the mucous membrane of the eye, and in contact with skin causes frostbite tissue samples of liquefied natural gas should be in protective glasses and gloves;
- tanks and piping intended for transporting oxygen, can not be used for storage and transport of other gases, measures should be taken to prevent contamination of cylinder oil, and their collisions, falls, and the need to protect them from the heat source of heat and precipitation.
Oxygen - a key gas for welding and cutting. The combustion of fuel gas in the air formed a flame at a temperature not exceeding 2000 ° C, and in technically pure oxygen, it can not exceed 2500-3000 ° C. This is precisely the temperature of the flame is practically suitable for the welding of many metals.
In flame treatment is commonly used to surround the oxygen content of 99,2-99,5% and above. For non-critical types of gas welding, soldering, surface hardening, and other methods of heating the gas flame can be used pure oxygen is 92-98%.
For welding and cutting using oxygen in the gaseous form, coming from the cylinder, gasification unit (SSU-1, MSP-4, MSP-7K, 8K, SSU, GC-0, 75, MCC-3, etc.) or stand-alone stations ( IGOS-150, K-0, 15, K-0, 4, K-0, 5, etc.). If significant amounts of oxygen consumption and economically sound stored and transported in liquid rather than gaseous form, despite the inevitable loss by evaporation of liquefied gas.
The transformation of liquid oxygen in the gas is carried out in the gasification plants - pumping or beznasosnyh. An example of the pumping unit can serve as a permanent installation of SSU-1 is designed for the gasification nepereohlazhdennogo oxygen content and recipients of cylinders under a pressure of 240 kgf / cm 2 (24 MPa).
Along with the processes of flame treatment of the oxygen is also used:
- as an auxiliary gas laser cutting of materials;
- for oxygen cutting with the support of a laser beam;
- as the plasma gas in plasma cutting;
- when cutting with a spear;
- for the addition of small amounts of the protective gas (argon, carbon dioxide) for some arc welding of steels and metals (in order to improve performance, prevent porosity, etc.).
gas-oxygen welding
gas-oxygen cutting
oxygen lance cutting
plasma cutting of metal
laser cutting of metal
Welding materials:
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