Liquid nitrogen

Liquid nitrogen (LN2) is nitrogen in a liquid state at extremely low temperatures.

It is a colorless and mobile liquid. It is much thinner than water. Its viscosity is about one-tenth that of acetone. This makes it roughly one-thirtieth as thick as water at room temperature. Because it stays so cold, it is widely used as a powerful coolant. It is essential for many scientific, medical, and industrial tasks.

Liquid nitrogen is produced through a process called fractional distillation of liquid air.

First, an air compressor squeezes filtered air to a high pressure. The high-pressure gas is then cooled back to ambient temperature. Next, the gas is allowed to expand to a low pressure. This expansion causes the air to cool greatly due to the Joule–Thomson effect. Through further stages of expansion and distillation, the air is separated into nitrogen, oxygen, and argon. Large modern plants can produce 3000 tons of liquid air products every day.

At a molecular level, nitrogen is a diatomic molecule, meaning it consists of two nitrogen atoms. The molecules have a weak van der Waals interaction between them. This means there is very little interatomic attraction. This weak connection is the cause of nitrogen's unusually low boiling point. If the liquid is placed in a vacuum chamber, a vacuum pump can reduce its temperature to its freezing point. This ability to maintain extreme cold is what makes it so useful.

When liquid nitrogen touches a much warmer object, it boils immediately. This creates a layer of nitrogen gas bubbles around the object. This phenomenon is known as the Leidenfrost effect. The gas layer acts as an insulating layer between the liquid and the warm surface. While this can provide a moment of insulation, faster cooling is often achieved by using a slush of both liquid and solid nitrogen. This ensures more direct and efficient heat transfer.

History shows how much we have learned about this substance. Polish physicists Zygmunt Wróblewski and Karol Olszewski first liquefied nitrogen. They achieved this at the Jagiellonian University on April 15, 1883. Industrial production grew significantly over time. Air-liquid plants began to be built in the 1930s. However, they became much more common after the Second World War. Today, we use specialized vacuum flasks to store it. These flasks can hold the temperature at 77 K through slow boiling. Modern pressurized, super-insulated vessels can reduce losses to 2 percent per day or less.

Liquid nitrogen has many diverse applications. In medicine, doctors use cryotherapy to remove skin lesions like warts or actinic keratosis. It is also used for the cryopreservation of blood, sperm, eggs, and other biological samples. In industry, it can freeze water and oil pipes to allow for repairs when a valve is missing. This is known as cryogenic isolation. It is even used in tunnel construction to stabilize loose soil by freezing the water within it. This increases the ground's bearing capacity so it will not collapse during excavation.

In the culinary world, chefs use it to create frozen desserts like ice cream.

Because it cools food so rapidly, it forms smaller ice crystals. This results in a much smoother texture. Some bartenders use it to create a smoky effect in cocktails. This happens as tiny droplets of the liquid condense the vapor in the surrounding air.

However, this must be done with extreme care. Accidental swallowing of the liquid can cause severe or even fatal damage to the body.

Safety is the most important factor when handling this cryogenic fluid. It can rapidly freeze living tissue and cause cold burns.

Workers should always use special gloves. There are also risks involving pressure and air quality. The liquid-to-gas expansion ratio is 1:694 at certain temperatures. This means a massive amount of force can be generated if it vaporizes in a closed space. Furthermore, as it evaporates, it can reduce oxygen levels in a room. This can lead to asphyxia, which is a lack of oxygen, without any warning.