What Are the Properties of Helium?

Helium, English name Helium, symbol He, colorless and odorless, non-flammable gas, the content of air is about 5.2 parts per million. Chemically inactive, usually not combined with other elements or compounds. On July 10, 1908, Dutch physicist Onis first liquefied helium.

Chinese name: Helium
English name: Helium
Chemical formula: He
Molecular weight: 4.003
CAS Registry Number: 275-187-7
Melting point: 1.0K (0.26MPa)
Boiling point: 4.3K (0.1MPa)
Water soluble: Hardly soluble in water

Density: 0.1786g / L (0 ° C, 0.1MPa)
Exterior: colorless
Security description: Non-flammable gas
Content: About 5.2 parts per million in air
Types of: Rare gas element
Critical temperature: 5.19K
Critical pressure: 0.228MPa
Evaporation heat: 20.4kJ / kg (boiling point)

History of Helium

As early as 1868, the French astronomer Janssen PJC (1824-1907) observed a yellow line D on the solar spectrum when observing a total solar eclipse, which is two parts of the already known sodium spectrum D1 and D2 The lines are different. At the same time, the British astronomer Lockyer JN (1836-1920) also observed this yellow line D. At that time, astronomers believed that this line was only available to the sun, and also considered a metallic element. Therefore, Lockyer called this element Helium, which is composed of two words. Helio means the Greek sun god, and the suffix -ium refers to the metal element. The Chinese translation is called helium.

In 1895, Lymesy cooperated with another British chemist, Travers MW (1872-1961). When treating pitch uranium ore with sulfuric acid, an inert gas was produced, which was spectroscopically identified as helium. It has been confirmed that helium is also a rare gas, which is also found on earth, and helium is a non-metallic element. ^[1] ^[2]

Physical and Chemical Properties of Helium

Physical properties of helium

At room temperature and atmospheric pressure, helium is a colorless, odorless gas. It is doing

Helium The volume content in the air is 5.24 × 10-6. It is the substance with the lowest critical temperature found by human beings. It is dark yellow when performing low voltage discharge.

Helium cannot be solidified simply by cooling a saturated liquid to absolute zero degrees. For helium to solidify, corresponding pressure must be applied. At 2.173K, helium will transform or more or less from a normal liquid into a fluid with unique properties. A liquid with a temperature above 2.173K is called helium I. Liquids below this temperature are called helium II. Helium II is a superfluid. Its entropy is zero, its thermal conductivity is extremely high, and its viscosity is almost zero.

Due to the low temperature of liquid helium, the resistance of the metal or metal compound will completely disappear by cooling some metals or metal compounds with liquid helium. This phenomenon is called superconductivity, and this temperature is called the critical temperature.

Because helium can propagate sounds about three times faster than air, people who breathe helium can speak at higher frequencies. This interesting phenomenon makes people who breathe helium squeak and squeak like old-fashioned cartoon characters. ^[3]

Chemical properties of helium

Helium is a monoatomic gas and is chemically inactive. Helium generally does not produce compounds, and it can form He + 2, HeH ions and molecules when excited in a low-pressure discharge tube.

Helium applications

Helium is widely used in military, scientific research, petrochemical, refrigeration, medical, semiconductor, pipeline leak detection, superconducting experiments, metal manufacturing, deep-sea diving, high-precision welding, and optoelectronic product production. ^[4]

1. Low temperature cold source: Utilizing the low boiling point of -268.9 of liquid helium, liquid helium can be used for ultra-low temperature cooling. The ultra-low temperature cooling technology has a wide range of applications in superconducting technology and other fields. Superconducting materials need to exhibit superconducting characteristics at low temperatures (about 100K). In most cases, only liquid helium can achieve such extremely low temperatures relatively easily. . Superconducting technology is widely used in magnetic levitation trains in the transportation industry and in magnetic resonance imaging equipment in the medical field.

2. Balloon inflation: Because the density of helium is much smaller than that of air (the density of air is 1.29kg / m ³ and the density of helium is 0.1786kg / m ³ ), and its chemical properties are extremely inactive and safer than hydrogen (hydrogen can be in air (Combustion may cause explosion), helium is often used to fill gas in spacecraft or advertising balloons. ^[1]

3. Inspection and analysis: The superconducting magnet of the nuclear magnetic resonance analyzer commonly used in instrument analysis needs to use liquid helium to cool down. Helium is often used as a carrier gas in gas chromatography analysis. It uses the characteristics of good permeability and non-flammability of helium. Used in vacuum leak detection, such as helium mass spectrometer.

4. Protective gas: Utilizing the inert chemical properties of helium, helium is often used as a protective gas for welding of metals such as magnesium, zirconium, aluminum, and titanium. ^[1]

6. Other aspects: Helium can be used as a high-pressure device for high-vacuum devices, nuclear reactors ^[5] on rockets and spacecrafts to transport liquid hydrogen, liquid oxygen and other liquid propellants. Helium is also used as a cleaning agent for atomic reactors, in breathing gas mixtures for marine development, and as filling gas for gas thermometers. ^[5]

Preparation method of helium

1. Condensation method: Condensation method for helium extraction from natural gas is industrially used. The method includes pretreatment and purification of natural gas, crude helium production, and helium refining, etc., to obtain 99.99% pure helium. ^[6]

2. Air separation method: The crude helium and neon mixed gas is generally extracted from the air device by the decondensation method. Pure helium is produced from the crude helium and neon mixed gas. The neon mixed gas is separated and purified to obtain 99.99% pure helium. . ^[6]

3. Hydrogen liquefaction method: Industrial use of hydrogen liquefaction method to extract helium from synthetic ammonia tail gas. The process of this method is to remove nitrogen at low temperature and purify the crude helium with oxygen to catalyze hydrogen removal and helium purification by distillation, to obtain 99.99% pure helium. ^[6]

4. High-purity helium method: 99.9999% of high-purity helium is obtained by further purifying 99.99% of pure helium with activated carbon. ^[4]

Helium Toxicology

If a large amount of helium is inhaled, the oxygen in the body will be replaced by helium, resulting in hypoxia (respiratory reflex is driven by excessive carbon dioxide in the receptor, and it is not sensitive to hypoxia), and it may even die. In addition, if helium is directly inhaled from a high-pressure gas cylinder, its high flow rate will seriously damage lung tissue. Large amounts of high pressure helium and oxygen can cause high pressure tension symptoms (HPNS), but a small amount of nitrogen can handle this problem. Large and prolonged inhalation of helium can cause brain damage and even death. A small amount of helium is also contained in most French fries packaging, but don't worry, it is not harmful. ^[7]

Helium precautions

1. The pressure is usually 15 MPa. When using it, use a pressure reducer such as YQY-12 or 152IN-125 to reduce the pressure. Use soap water to check the gas pipeline before use to ensure that the gas pipeline is not leaking.

2. Ensure that helium is not leaked and the workplace is kept ventilated. When the helium content increases and the oxygen content is lower than 19.5%, the patient first appears to have accelerated breathing, lack of concentration, and ataxia; followed by fatigue, irritability, and restlessness. , Nausea, vomiting, coma, convulsions, and death.

3. When the exhaust gas of each bottle of helium is used, the residual pressure in the bottle should be kept at 0.5MPa, and the minimum residual pressure should not be lower than 0.25MPa. The valve of the bottle should be closed to ensure the gas quality and use safety.

4. Bottled helium should be sorted and stacked during transportation, storage, and use. It should not be placed near open flames and heat sources. It should be kept away from fire, exposed to oil and wax, exposed to the sun, not thrown away, and not bumped. For arc starting or arcing, brutal loading and unloading is strictly prohibited. Short-distance moving helium cylinders should use special carts for cylinders. Long-distance moving cylinders should be transported by dangerous goods transport vehicles. The temperature of liquid helium is 4.25K, which can cause severe frostbite when in contact with the skin.

5. The use and inspection of steel cylinders for helium storage shall be in accordance with the provisions of the "Cylinder Safety Supervision Regulations" of the State Bureau of Quality and Technical Supervision, and the cylinder inflation pressure shall not exceed the prescribed pressure. Safety helmets must be installed at all times, a protective gas valve, gas cylinders are inspected every three years (except for special cases) for appearance inspection and hydrostatic test. They can be used again after passing the test. The inspection is performed in the inflation unit. ^[8]

Emergency Helium Disposal

In the event of a leak, the personnel in the leak-contaminated area should be evacuated to the upper reaches and isolated, and access strictly restricted. It is recommended that emergency handlers wear self-contained positive-pressure respirators and general work clothes. Cut off the source of the leak if possible. Reasonable ventilation to accelerate diffusion. If possible, use it immediately. The leaking container should be properly handled, and used after repairing and inspection. ^[9]

Analysis of helium content

Determined by gas chromatography. Conditions: The column is a stainless steel column with a length of 6m and an inner diameter of 4mm. Filler is PoraPakQ, or similar. The carrier gas is hydrogen [99.99% (V / V)], and the flow rate is 40ml / min. Use the loop injector. The detector is a thermal conductivity detector. The column temperature was 60 ° C. The detector temperature was 130 ° C. Operation: Send the sample helium to the gas chromatograph through the gas injection valve. Select the GC operating conditions so that the standard peak signal is equivalent to not less than 70% of the full-scale reading, so that nitrogen and oxygen can be completely separated from helium (nitrogen and oxygen may not be distinguishable from each other). The residence time shown by the peak response value obtained from the sample sample should be equivalent to the peak response obtained from the air-helium calibration standard sample (1.0% air mixed with industrial-grade helium, provided by the manufacturer), and it should not exceed 1.0% air volume (volume), and He content should not be less than 99.0% (volume). ^[4] ^[10]

Domestic status of helium

Helium is one of the rare strategic materials indispensable for the development of defense military industry and high-tech industries. Helium-containing natural gas is still the only source of helium for industrial production. China's helium resources are quite scarce, the content is very low, the extraction is difficult, and the cost is high. Therefore, while protecting the limited helium resources, research and development of advanced natural gas helium extraction technology is of great significance for improving the economics of helium production, ensuring the safety of national helium use, and promoting the development of China's natural gas helium extraction industry. According to the analysis and introduction of helium extraction technology, the low-temperature condensation method is more mature, but the energy consumption and cost are higher; other helium extraction technologies such as adsorption method, absorption method and membrane permeation method have their own characteristics, but cannot be scaled to the industry due to applicable conditions application. With the development of new materials and new technologies, natural gas helium extraction technology has been continuously improved and innovated. Adsorption methods, membrane permeation methods, and other helium extraction technologies have developed rapidly. The combined production method and the combined method process have good application prospects. The development of helium technology provides new ideas. ^[11-12]

Helium purity

Helium Industry Helium

Project name indicators

Helium purity: 99%

Neon (hydrogen), oxygen (argon), nitrogen, methane

Moisture content, dew point, -43

Pure helium

Project name indicators

First-rate quality products

Helium purity,% 99.99599.99399.99

Neon content, ppm152540

Hydrogen content, ppm357

Oxygen (argon) content, ppm355

Nitrogen content, ppm101725

Carbon monoxide, ppm111

Carbon dioxide, ppm111

Amount of methane, ppm111

Water content, ppm101520

High purity helium

The purity of helium is> 99.999%,

Impurity content (ppm):

O20.5,

N21.0,

CO0.5,

CO20.5,

CH40.5,

H2O0.5,

Ne8.0;

Helium ultrapure helium

The purity of helium is> 99.9999%,

Impurity content (ppm):

N20.5,

O20.5,

Ne0.5,

CO0.1,

CO20.1,

THC0.1,

H2O0.2;