Liquid nitrogen refers to the liquid obtained from inert, colorless, odorless, noncorrosive and nonflammable nitrogen at extremely low temperature.Liquid nitrogen is inert, colorless, tasteless, low viscosity, noncorrosive, nonflammable, and extremely low temperature transparent liquid. When vaporizing, a large amount of endothermic contact will cause frostbite.nitrogenIt forms the majority of the atmosphere (78.03% by volume and 75.5% by weight).Under normal pressure, the boiling point of nitrogen is - 196.56 ℃, and 1 cubic meter of liquid nitrogen can expand to 696 cubic meters of pure gaseous nitrogen (21 ℃).If pressurized, liquid nitrogen can be obtained at a higher temperature.If the human body is exposed to liquid nitrogen without protective measures, the skin may be severely frostbitten.If the nitrogen produced by vaporization under normal pressure is excessive, it may reduce the partial pressure of oxygen in the air and cause hypoxia and asphyxia.
Chinese name
liquid nitrogen
Foreign name
Liquid nitrogen
chemical formula
Ntwo
molecular weight
twenty-eight point zero one
CAS login number
7727-37-9
EINECS login number
231-784-9
Melting point
-210 ℃
Boiling point
-195.79 ℃
Water solubility
Slightly soluble in water
Density
0.81 g/cm³
Appearance
Colorless Transparent Liquid
Application
Rapid freezing and transportation of food, freezing anesthesia, substance protection agent, synthetic ammonia, nitric acid production, etc
Precautions for operation: closed operation, providing good natural ventilation conditions.Operators must be specially trained and strictly abide by the operating procedures.The temperature of liquid nitrogen at normal pressure is very low. Once it comes into contact with the surface of an object, it will quickly boil, and at the same time, it will quickly take away a lot of heat energy.Therefore, when using liquid nitrogen, extra attention should be paid to avoid direct contact with skin.Wear protective equipment, such as antifreeze gloves, when filling.Do not use cotton gloves. Cotton gloves will absorb a large amount of liquid nitrogen by capillary phenomenon, causing gloves to freeze.The cylinder and accessories shall be handled with care to prevent damage.Provide leakage emergency treatment equipment.
Precautions for storage: store in a cool and ventilated warehouse.The warehouse temperature should not exceed 30 ℃.The storage area shall be equipped with leakage emergency treatment equipment.
Engineering control: closed operation, providing good natural ventilation conditions.
Respiratory system protection: no special protection is generally required.However, when the oxygen concentration in the air of the workplace is less than 18%, you must wear an air respirator, oxygen respirator or a long tube mask.
Eye protection: wear safety mask.
Body protection: wear cold clothing.
Hand protection: wear cold proof gloves.
Other protection: avoid high concentration inhalation and frostbite.
danger
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Liquid nitrogen will quickly volatilize into nitrogen at room temperature, and change from liquid to gas.At the same time, the volume will expand rapidly, and gas explosion may be caused when stored in non pressure closed containers.If it is a non positive pressure storage drum, do not store liquid nitrogen in a sealed container at room temperature.
Nitrogen is an inactive substance. If liquid nitrogen is used in a confined space, the nitrogen vaporized from liquid nitrogen will fill the whole space, slowly replacing the oxygen in the air, reducing the oxygen concentration and suffocating. Therefore, liquid nitrogen must be used in an open space.
emergency measure
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First aid measures
Skin contact: take off all clothes that restrict blood circulation in frostbitten areas.Do not rub the frozen part to avoid injury to muscle tissue.Put the injured part in warm water at 38~42 ℃ for rewarming, and immediately ask a doctor for treatment.The muscle tissue of frostbite is painless, and presents a waxy yellow color.When it begins to thaw, the skin will feel swollen, painful, and prone to infection.If the frostbitten part of the body has been thawed, it must be covered with a dry sterile cloth and wrapped with a large protective cover for medical treatment.For large areas of frostbite, first take off your clothes, then rinse with warm water, and ask a doctor for treatment.
Inhalation: quickly leave the site to a place with fresh air.Keep the respiratory tract unobstructed.If breathing is difficult, give oxygen.If breathing stops, perform artificial respiration immediately.Get medical attention.
Fire fighting measures
Hazard characteristics: In case of high heat, the internal pressure of the container will increase, which may cause cracking and explosion.
Hazardous combustion products: This product is nonflammable.
Fire extinguishing method: This product is nonflammable.Use foggy water to keep containers cool in the fire.The vaporization of liquid nitrogen can be accelerated by spraying atomized water, but the water gun shall not shoot liquid nitrogen.
Emergency Management
Emergency treatment: quickly evacuate the personnel in the leakage contaminated area to the windward place, isolate them, and strictly restrict access.It is recommended that emergency personnel wear self-contained positive pressure respirators and cold clothing.Do not touch the leakage directly.Cut off the leakage source as much as possible.Use exhaust fan to send the leaked air to the open area.Leaking containers shall be properly treated, repaired and inspected before reuse.
Treatment method for liquid nitrogen leakage
When the concentration of inhaled nitrogen is not too high, the patient initially feels chest tightness, shortness of breath, and weakness;Then there are restlessness, extreme excitement, running, shouting, absent-minded, unsteady gait, called "nitrogen intoxication", which can lead to lethargy or coma.Inhalation of high concentration can lead to rapid coma and death due to respiratory and cardiac arrest.
1. Quickly evacuate the personnel in the leakage pollution area to the windward place, and set isolation area to strictly restrict access.
4. Avoid leaking liquid into the basement or other enclosed manned working space. If it cannot be avoided, immediately notify the relevant department.
5. Do not contact the leakage directly.
6. Cut off the leakage source as far as possible.
7. Fog water spray can be used to accelerate the evaporation of liquid, but the water gun shall not be allowed to shoot liquid.
8. Prevent the gas from accumulating in the low concave place, and use the exhaust fan to send the leaked gas to the open place.
9. Personnel are prohibited to stay in low-lying or downwind areas.
purpose
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Industrial use
In industrial production, liquid nitrogen is obtained by compressed liquid air fractionation, which can be used as deep refrigerant. Because of its chemical inertia, it can directly contact with biological tissue, and be frozen immediately without destroying biological activity, so it can be used for[1]：
(1) Quickly freeze and transport food, or make ice products.
(2) In surgery, rapid freezing can be used to help stop bleeding and remove the superficial part of the skin surface that needs to be cut.
(3) Preservation of living tissue, biological samples andspermandeggStorage of.
(4) Can be usedcryogen, used to quickly freeze biological tissue to prevent tissue damage.
Food preservation
During the freezing process, the formation of ice crystals will cause the decline of product quality. The shorter the time for food to pass through the maximum ice crystal formation zone, the smaller the ice crystals generated, and the less damage to food.The boiling point of liquid nitrogen under normal pressure is - 195.8 ℃.Liquid [FZ1] nitrogen quick freezing technology makes use of the ultra low temperature heat absorption characteristics of liquid nitrogen, contacts liquid nitrogen with food, and carries out intense heat exchange at a temperature difference of more than 200 K, with extremely fast freezing speed and cooling rate of 7~15 K/min[2]。
Because liquid nitrogen is frozen at low temperature in a short time, small and evenly distributed ice crystals are formed inside the food, which will cause little damage to cells and reduce juice loss after thawing, and can maintain the nutrition, taste and original flavor of the food.At the same time, the evaporation of liquid nitrogen replaces the air with nitrogen, which can reduce the oxygen concentration and reduce food respiration and nutrition during the freezing process.When liquid nitrogen contacts food with irregular shape, it can minimize heat transfer resistance[3]。
Cryotherapy
Liquid nitrogen cryotherapy is a new technology in the field of modern therapeutics.liquid nitrogenCryotherapyIt is a comprehensive effect of cryobiology[4]。Normal cells will be irreversibly damaged when they are extremely frozen.It is to quickly kill the cells in the diseased area under the extremely frozen state, so that the diseased area can recover normally.Generally used for treatmentWart、CornsAnd skin diseases[5]。
Cryosurgery is also used to treat breast cancer.IceCure, an Israeli medical company, developed the latest technology of cryotherapy for breast cancer in 2012, which uses liquid nitrogen to freeze and kill breast cancer cells. The company is conducting clinical trials on it.If the trial is successful, breast cancer patients will be able to "remove" the tumor in the body without undergoing surgery in the future[6]。
Subcooled liquid nitrogen cooling system
When the temperature of liquid nitrogen is lower than the saturation temperature corresponding to its saturation pressure, it turns into supercooled liquid nitrogen, and the lower the temperature, the better the cooling effect.The subcooled liquid nitrogen cooling system (SLNCS) designed based on the requirements of the object to be cooled and the nature of liquid nitrogen has the advantages of stable pressure, controllable flow and continuous operation, and has been widely used in low-temperature permanent magnet undulatorsSuperconducting cable, high temperature superconducting motors and other fields. When the magnet material of the cryogenic permanent magnet undulator is cooled to the liquid nitrogen temperature zone, it can obtain higher peak field strength and anti radiation demagnetization ability. Superconducting cables can enter the superconducting state in the liquid nitrogen temperature zone, and the resistance disappears, almost realizing lossless transmission[7]Superconducting materials in high-temperature superconducting motors can exhibit unique properties at low temperatures, which helps to improve motor efficiency and stability[8]。
