Helium is widely used in military industry, scientific research, petrochemical, refrigeration, medical treatment, semiconductor, pipeline leak detection, superconductivity experiment, metal manufacturing, deep-sea diving, high-precision welding, optoelectronic product production, etc. (1) Low temperature cooling: Using the low boiling point of liquid helium of -268.9 °C, liquid helium can be used for ultra-low temperature cooling. Ultra-low temperature cooling technology has a wide range of applications in superconducting technology and other fields. Superconducting materials need to be at low temperature (about 100K) to show superconducting properties. In most cases, only liquid helium can easily achieve such extremely low temperature. . Superconducting technology is widely used in maglev trains in the transportation industry and MRI equipment in the medical field. (2) Balloon inflation: Since the density of helium is much smaller than that of air (the density of air is 1.29kg/m3, the density of helium is 0.1786kg/m3), and the chemical properties are extremely inactive, which is safer than hydrogen (hydrogen can be in the air flammable, possibly explosive), helium is often used as a filling gas in spaceships or advertising balloons. (3) Inspection and analysis: The superconducting magnets of nuclear magnetic resonance analyzers commonly used in instrument analysis need to be cooled by liquid helium. In gas chromatography analysis, helium is often used as a carrier gas. Taking advantage of the good permeability and non-flammability of helium, helium It is also used in vacuum leak detection, such as helium mass spectrometer leak detectors. (4) Shielding gas: Utilizing the inactive chemical properties of helium, helium is often used as shielding gas for welding of magnesium, zirconium, aluminum, titanium and other metals. (5) Other aspects: Helium can be used as a pressurized gas for transporting liquid propellants such as liquid hydrogen and liquid oxygen on rockets and spacecraft in high vacuum devices and nuclear reactors. Helium is also used as a cleaning agent for atomic reactors, in the mixed gas for breathing in the field of marine development, as a filling gas for gas thermometers, etc.