Helium is also a gas that is extremely difficult to dissolve in water. 100 volumes of water can only dissolve 1 volume of helium at 0°C. In medicine, this property of helium is used to prevent "dive disease." Previously, when divers dived into the sea, the nitrogen in the air that was inhaled into the body dissolved as the pressure in the blood increased due to the huge pressure in the deep sea. When divers went to sea, the pressure dropped sharply, and the nitrogen that was originally dissolved in the blood was exhausted, causing blood vessel blockage and death. This disease is called "diving disease." Now people use helium mixed with oxygen , which is made in "artificial air" (79% helium, 21% oxygen) to provide divers with breathing. Since helium is rarely dissolved in the blood, even if divers dive below 100 meters, they will not suffer from "diving disease". This "artificial air" is also commonly used to treat bronchial asthma and suffocation. Since its density is only 1/3 of the air, breathing is much easier than breathing air, which can reduce the patient's difficulty in breathing.
Helium is the most difficult gas to liquefy. It was once considered a "permanent gas" until it finally liquefied in 1908. On the one hand, it starts to cool down as it throttles and expands. 250 ℃; on the other hand, its critical temperature is the lowest and can only be liquefied with liquid hydrogen after pre-cooling. Helium can only become liquid at -267.9℃, and can become "helium ice" at -272.2℃. Meanwhile, liquid helium is usually used as a coolant in the low-temperature industry.
Since helium is close to the ideal gas (absolute zero is about 273.16°C), it is an ideal filling material for precision gas thermometers.
helium has a high excitation potential. Helium is widely used as a filler gas in the electronic tube industry. It can also be used as incandescent lamp , extreme detector, high voltage display, etc. Using
Due to its chemical properties, helium is very inert and is difficult to combine with other elements. When welding metals magnesium, aluminum, titanium and stainless steel in the industry, it is used as a protective gas to isolate the air and prevent metal oxidation during welding. The helium content in the atmosphere of
is very low, only five parts per million per volume, but the content in natural gas is higher, up to 2-6%. Today, helium is mainly produced by natural gas in the industry.
