Liquid nitrogen

Liquid nitrogen, written as LN₂, is nitrogen cooled down until it becomes a liquid. It stays liquid at very cold temperatures, with a boiling point of about −196 °C (−321 °F). Because it is extremely cold, liquid nitrogen is often used to keep things frozen or to cool machinery and experiments.

We can make liquid nitrogen by a process called fractional distillation of liquid air. This means separating the different gases in air by their boiling points. Liquid nitrogen looks clear and moves easily—it is not thick like water. In fact, it is much less thick than water at normal temperatures.

People use liquid nitrogen for many useful things. It works very well as a coolant, which means it helps keep things very cold. For example, scientists use it in laboratories, doctors use it to freeze and treat some skin problems, and it even helps keep food fresh for a long time.

Physical properties

Liquid nitrogen keeps its diatomic shape even when it turns into a liquid. Because the molecules of nitrogen don’t stick together very strongly, liquid nitrogen has a very low boiling point.

You can make liquid nitrogen even colder by putting it in a special vacuum chamber. However, when liquid nitrogen touches something warmer, it quickly turns into gas, forming a layer that slows down cooling. This is called the Leidenfrost effect. Cooling things faster can be done by using a mix of liquid and solid nitrogen.

Main article: Leidenfrost effect

Handling

Liquid nitrogen is a cryogenic fluid that can freeze living tissue very quickly, so special care is needed when handling and storing it. It is usually kept in vacuum flasks, which help maintain its extremely cold temperature by allowing slow boiling. These flasks can keep liquid nitrogen cold for several hours to a few weeks, depending on their size and design. New technology has improved storage, allowing liquid nitrogen to be kept for even longer periods with very little loss.

Uses

Liquid nitrogen is very cold and can keep things frozen, making it useful for many jobs. It is often used to freeze food, store cells for science, and keep medical samples safe. It can also freeze water in pipes so workers can fix them without turning off the water.

Liquid nitrogen is also used to cool machines, like cameras used to look at stars, and to help make very cold chemicals for experiments. It can even make metals fit together better when building machines. It is also used in making ice cream very quickly, giving it a smooth texture. However, it must be handled carefully because it can be dangerous if swallowed.

See also: Ice cream § Cryogenics

History

Nitrogen was first turned into a liquid on 15 April 1883. Two scientists from the Jagiellonian University, Zygmunt Wróblewski and Karol Olszewski, made this discovery. They showed that nitrogen could exist as a liquid, which happens at very cold temperatures.

Safety

Liquid nitrogen can be very dangerous if not handled properly. When it turns from liquid to gas, it expands quickly and can create a lot of pressure. This pressure can cause containers to burst, which can be very unsafe.

Because liquid nitrogen is extremely cold, touching it or things cooled by it can cause serious burns. Special gloves should always be used when handling liquid nitrogen. Also, liquid nitrogen can reduce the amount of oxygen in the air, especially in small spaces, which can make it hard to breathe. Workers often use special sensors to check for low oxygen levels when using liquid nitrogen.

Never ingest liquid nitrogen, as it can freeze tissues inside the body and cause very serious injuries. Always follow safety instructions when working with this very cold substance.

Production

Main article: Air separation

Liquid nitrogen is made from air that has been cooled and compressed. This process uses special equipment to separate different gases found in air, such as oxygen and nitrogen. When air is cooled to very low temperatures, it turns into a liquid, and then the different parts can be separated. This method has been used since the 1930s and is now common in many factories. Large plants can make thousands of tons of liquid nitrogen every day.