Oxygen plays a crucial role in numerous scenarios, including industrial production, scientific research, and daily life. Oxygen exists in two forms: liquid and gaseous, and they have significant differences in characteristics, preparation methods, application fields, etc. A thorough understanding of these distinctions helps us make more rational choices under different requirements.

I. Basic Understanding of Oxygen Atoms

Oxygen is the second – most abundant element in the Earth’s atmosphere, accounting for approximately 21% of the air by volume. Its atomic number is 8, and the chemical symbol is O. Oxygen atoms have strong oxidizing properties. In combustion reactions, they can react violently with fuels to release a large amount of energy. At the same time, it has a relatively high electronegativity. When forming compounds, it tends to attract electrons and thus carry a negative charge.

In the biological world, oxygen is an essential substance for biological respiration. Through respiration, organisms inhale oxygen and participate in the oxidation process within cells, thereby releasing the energy required to maintain life activities. In the industrial field, oxygen plays a key role in the steel – making process. It reacts with iron to remove impurities and effectively improve the quality of steel.

II. Characteristics and Applications of Liquid Oxygen

Liquid oxygen is the liquefied form of oxygen at extremely low temperatures. It is usually prepared by the air – separation method. First, the air is compressed and cooled to a liquefied state. Utilizing the difference in boiling points between oxygen and nitrogen, oxygen is separated through distillation and further cooled to become liquid.

Liquid oxygen appears as a pale blue and transparent substance. Its boiling point is – 183°C, and its density is 1.14g/cm³. It has a high expansion ratio. Approximately 800 liters of gaseous oxygen can be produced when 1 liter of liquid oxygen vaporizes. In the aerospace field, liquid oxygen is often paired with fuels such as liquid hydrogen as the oxidizer for rocket engines, providing powerful thrust for spacecraft. In the steel – making industry, liquid oxygen can increase the furnace temperature, accelerate the reaction process, and thus improve the quality and efficiency of steel production. In the medical field, liquid oxygen is used in some special medical operations that require extremely low – temperature environments.

III. Characteristics and Uses of Gaseous Oxygen

Gaseous oxygen is the most common form of oxygen under normal temperature and pressure. It consists of two oxygen atoms bonded together by a covalent bond, with the molecular formula O₂. The large – scale production of gaseous oxygen mainly adopts the air – separation technology, and it can also be prepared by the electrolysis of water.

Under normal temperature and pressure, oxygen is a colorless and odorless gas. It has an active chemical property and can react with many substances in an oxidation reaction, especially more violently in a high – temperature environment. In the medical field, oxygen is used for oxygen supply in hospital beds to treat various hypoxic conditions, such as respiratory diseases and carbon monoxide poisoning. In chemical synthesis, oxygen is used as an oxidant in the production of chemicals such as sulfuric acid and nitric acid, promoting reactions and improving production efficiency. In the metal processing industry, oxygen is mixed with combustible gases to form a high – temperature flame for metal welding and cutting.

IV. Significant Differences between Liquid Oxygen and Oxygen

(I) Physical State

Liquid oxygen is in a liquid state at extremely low temperatures. This state makes it suitable for occasions that require ultra – low – temperature environments or as a strong oxidizer, such as in aerospace propulsion systems. Oxygen, on the other hand, exists in a gaseous state under normal temperature and pressure, which is more convenient for participating in various chemical reactions and biological processes under daily conditions.

(II) Storage and Transportation

The storage and transportation of liquid oxygen require special low – temperature insulated containers, such as Dewar flasks or large – scale liquid oxygen tanks, to prevent its rapid vaporization. During transportation, strict thermal insulation measures must be taken, and professional equipment is required. In contrast, oxygen can be conveniently stored in high – pressure gas cylinders, which is convenient for flexible transportation and operation.

(III) Cost

The production and storage of liquid oxygen require a large amount of energy to maintain a low – temperature environment, and the investment and maintenance costs of related equipment are also high. Therefore, its cost is relatively high. The production and storage costs of oxygen are relatively low, especially for low – purity and small – batch usage scenarios, the cost advantage is more obvious.

(IV) Safety Risks

The low temperature of liquid oxygen can cause serious frostbite. Moreover, when it vaporizes, a large amount of gas is rapidly generated, which may cause the local oxygen concentration to be too high, triggering fire or explosion risks. Although oxygen itself is non – flammable, as an oxidizer, in a high – concentration environment, it is likely to fuel the fire and trigger an explosion. Therefore, when using and storing oxygen, it must be kept away from fire sources and flammable substances.

V. Methods of Obtaining Liquid Oxygen and Oxygen

(I) Methods of Obtaining Oxygen

1. Pressure Swing Adsorption (PSA): This method takes advantage of the different adsorption capacities of solid adsorbents for different gases. Under a certain pressure, the adsorbent adsorbs impurity gases, allowing oxygen to pass through the adsorption bed. The impurities are desorbed by reducing the pressure to achieve the enrichment of oxygen. A two – bed or multi – bed alternating cycle can be used for continuous production.
2. Cryogenic Method: Compress and cool the air to liquefy it. Utilize the difference in boiling points between liquid nitrogen and liquid oxygen to separate them in a distillation tower. Liquid nitrogen vaporizes first, and liquid oxygen remains at the bottom of the tower.
3. Membrane Separation Method: Separate based on the different permeation rates of gases through polymer membranes. Under a pressure difference, smaller oxygen molecules permeate faster than larger molecules, and the enrichment of oxygen is achieved through a hollow – fiber membrane module.

(II) Methods of Obtaining Liquid Oxygen

1. Cryogenic Liquid – Oxygen Production Method: Similar to the cryogenic oxygen – production process, first deeply cool and liquefy the air. During the distillation process, liquid oxygen is separated. Then, further cool and compress the oxygen, and pressurize it to liquefy it below the critical temperature. Finally, store it in a low – temperature insulated container.
2. Oxygen – First – Then – Liquefaction Method: First, obtain oxygen using the pressure swing adsorption method or membrane separation method. Then, use special equipment to compress and cool it to convert it into a liquid state. This process requires an efficient refrigeration system and a pressurized liquefaction device.

VI. Advantages and Disadvantages of Liquid Oxygen and Oxygen

(I) Liquid Oxygen

1. Advantages: It has strong oxidizing properties and is an efficient oxidizer, capable of providing powerful thrust for rockets, etc. Its low – temperature characteristics are suitable for special processes such as superconducting research and material cryogenic treatment.
2. Disadvantages: The storage and transportation conditions are harsh, the cost is high, and there are risks of frostbite and safety hazards.

(II) Oxygen

1. Advantages: It is essential for maintaining life and plays an irreplaceable role in medical first – aid. It is widely used in industries such as chemical engineering and metal processing, promoting chemical reactions and improving production efficiency.
2. Disadvantages: In application scenarios that require extremely low temperatures or high – energy density, it cannot replace liquid oxygen. Improper operation or storage can easily lead to safety accidents such as fires.

VII. Conclusion

Both liquid oxygen and gaseous oxygen have their unique properties and advantages, and they play important roles in different fields. In practical applications, we should carefully choose the appropriate form of oxygen according to specific needs and scenarios to ensure the smooth progress of production, scientific research, and daily life.