In low temperature physics and industrial applications, liquid nitrogen (LN₂) and liquid oxygen (LOX) play an important role. Although they both exist in liquid form and are made by cooling the gas to extremely low temperatures, there are significant differences in physical properties, application scenarios and safety risks. This article will systematically sort out the difference between liquid nitrogen and liquid oxygen from four aspects: basic properties, preparation methods, main uses and safety precautions.
Comparison of basic properties
1. Chemical composition
Liquid nitrogen is composed of nitrogen molecules (N₂), and liquid oxygen is composed of oxygen molecules (O₂). Both are rich in nature and are both gases under normal conditions.
2. Boiling point and melting point
The boiling point of liquid nitrogen is -195.8°C (77 K), and the melting point is -210°C; the boiling point of liquid oxygen is -183°C (90.2 K), and the melting point is -218.8°C. Liquid nitrogen has a lower boiling point, making it easier to achieve and maintain liquid state.
3. Density
The liquid nitrogen density is about 0.808 g/cm³, while the liquid oxygen is 1.141 g/cm³. Therefore, under the same volume, the mass of liquid oxygen is greater.
Preparation method
Liquid nitrogen and liquid oxygen are usually prepared by an air separation device (ASU). This technology uses the differences in boiling points of various components in the air to achieve gas separation through compression, cooling and expansion processes. Due to the higher boiling point of liquid oxygen, it is collected in ASU at a relatively high temperature zone, while liquid nitrogen is obtained in a lower temperature zone.
Application areas
The main uses of liquid nitrogen include:
- Food industry: used for rapid freezing, maintaining food quality and nutrition;
- Medical field: applied to cryotherapy and cryogenic storage of biological samples (such as cells, tissues);
- Scientific research: As a cooling medium in superconducting experiments and low temperature physics research.
The main uses of liquid oxygen include:
- Space propulsion: used as an oxidant in rocket engines;
- Metallurgical industry: assists combustion during steelmaking to increase furnace temperature;
- Medical oxygen supply: Provide high concentration of oxygen support for patients with respiratory disorders.
Safety precautions
Both have extremely low temperatures and direct contact can lead to severe frostbite. also:
- Liquid oxygen is a strong oxidant, and contact with combustible substances can easily cause combustion or explosion;
- Although liquid nitrogen is not an oxidant, it will replace air in large quantities after vaporization, which may cause the risk of hypoxia and asphyxiation in confined spaces.
Although liquid nitrogen and liquid oxygen are both low-temperature liquids, their physical properties, uses and safety requirements are significantly different. Correct understanding of the difference between the two is of great significance to scientific choice and safe use. Whether in industrial, scientific research or medical scenarios, operating procedures must be strictly followed and protective measures must be taken to ensure the safety of personnel and equipment.
