Early Observations and the Importance of Oxygen
Before the discovery of oxygen as a chemical element, its properties and influence on combustion and respiration were practically known. People had long recognized that fire and life depended on air, but the precise role of oxygen remained unknown—it was not yet understood that oxygen was the key ingredient responsible for these phenomena.
- Antiquity:
Already in ancient times, thinkers such as Aristotle attempted to describe the composition of air. It was believed that it was homogeneous, and that the processes of combustion and respiration were associated with the "life-giving aether." - Phlogiston theory:
In the 17th and 18th centuries, the phlogiston theory was developed, which proposed that flammable substances contained "phlogiston" released during combustion. However, evidence for this hypothesis was lacking.
The discovery of oxygen
The discovery of oxygen as a chemical element is attributed to several scientists who independently conducted research on the composition of air and the combustion process.
1. Carl Wilhelm Scheele (1772–1773)
Swedish chemist Carl Wilhelm Scheele was the first to isolate oxygen by heating mercury oxides (HgO) and nitrates. He called it "fire air" because he observed that it supported combustion. However, his work was not published until 1777, several years after the discoveries of other chemists.
2. Joseph Priestley (1774)
English chemist Joseph Priestley independently isolated oxygen by heating mercuric oxide. He named the newly discovered gas "dephlogisticated air" because it supported combustion much better than ordinary air. Priestley was the first to publish his findings, which brought him wide recognition.
3. Antoine Lavoisier (1777)
French chemist Antoine Lavoisier played a key role in understanding the nature of oxygen. He rejected the phlogiston theory ( phlogiston is a hypothetical substance that, according to 17th-century theory, was present in all combustible materials. During combustion, phlogiston was supposed to be released into the air, leaving the ash or slag as a "pure" material. This theory prevailed until the 18th century) and showed that oxygen is a chemical element involved in combustion and respiration. In Latin, oxygen is called "oxygenium ," which comes from the Greek words "oxys" (acidic) and "genes" (generating). This name was introduced by Antoine Lavoisier, who mistakenly believed that oxygen was a key component of all acids. In the classification of chemical elements, oxygen is designated by the symbol O , and its Latin name is used in scientific nomenclature, particularly in the context of chemical compounds (e.g., "oxidum" - oxide).
Development of oxygen research
After its discovery, research on oxygen developed dynamically, which was of great importance for science and industry:
- 19th century: Oxygen has become a central element of chemical and biological research. It has been discovered that it plays a key role in the respiration of living organisms and in combustion processes.
- Cryogenics: In 1877, Louis Paul Cailletet and Raoul Pictet liquefied oxygen, which opened the way to its industrial separation and storage.
- Industrial Revolution: Oxygen began to be used in metallurgy (Bessemer process), medicine (oxygen therapy) and military technology.
Oxygen in metal alloys plays both a favorable and unfavorable role, depending on its concentration, technological conditions and alloy properties.
The influence of oxygen on the properties of alloys
Positive effects of the presence of oxygen
- Creating protective layers:
In some metal alloys, such as aluminum, titanium, or alloys containing chromium (e.g., stainless steels), oxygen reacts with the metal to form a thin oxide layer (e.g., Al₂O₃, TiO₂, Cr₂O₃). These layers are tight, durable, and act as a protective barrier against further oxidation or corrosion. - Improved resistance to high temperatures:
In the case of heat-resistant alloys, the presence of oxide layers (scales) increases resistance to oxidation at high temperatures, which is important in the energy and aviation industries. - Structural stabilization:
Oxygen in controlled amounts can stabilize the structure of metal oxide alloys, such as ceramic and metal alloys (metal-ceramic composites), increasing their mechanical strength and abrasion resistance.
Oxygen – negative effects of its presence
- Formation of oxide inclusions:
In some cases, oxygen in alloys can lead to the formation of oxide inclusions, which are structural defects. These can reduce the metal's mechanical properties, such as strength and ductility, and negatively impact its processing. - Brittleness of alloys:
Too high an oxygen concentration can lead to increased metal embrittlement, especially in materials such as titanium alloys, magnesium alloys, and some steels. Oxygen-induced embrittlement reduces the durability of structures and can lead to premature failure. - Problems in production processes:
Oxygen present in the casting or welding processes of alloys can lead to the formation of porosity, which reduces the quality of the product.
Control of oxygen content in metal alloys
To ensure optimal alloy properties, control of oxygen content is crucial in metallurgical processes:
- Degassing processes:
During metal smelting, vacuum or chemical degassing is used to minimize the oxygen content. - Addition of deoxidants:
In metallurgy, additives such as carbon, silicon or manganese are used, which react with oxygen to form oxides that are removed from the liquid metal. - Protection against air ingress:
Alloy manufacturing and processing processes are often carried out in protective atmospheres such as argon or nitrogen to prevent oxidation.
Examples of alloys with controlled oxygen presence
Aluminum alloys:
The formation of oxides on the surface of aluminum alloys results in a thin but very durable protective layer that significantly increases corrosion resistance. This phenomenon is particularly exploited in anodizing, an electrochemical process that strengthens this layer and provides additional properties, such as an aesthetic finish or increased surface hardness. Aluminum alloys are used in the aerospace, automotive, and construction industries due to their lightness, durability, and ease of processing.
Titanium alloys:
Oxygen in controlled amounts increases the mechanical strength of titanium alloys, particularly in applications requiring high strength under extreme conditions, such as in aerospace, medicine, and the chemical industry. However, excess oxygen can cause embrittlement, which limits the material's ductility. To prevent these negative effects, production processes are strictly controlled, particularly during melting and metallurgical processing.
Stainless steels:
The presence of chromium in stainless steel (minimum 10,5%) causes it to react with ambient oxygen, forming a thin, passive chromium oxide layer. This layer acts as a protective barrier that is self-healing – if scratched or damaged, it reacts with oxygen and reforms. These properties make stainless steel invaluable in humid, corrosive, and high-temperature environments, such as those found in the food, medical, and chemical industries.
Magnesium alloys:
Magnesium and its alloys are extremely lightweight, making them ideal for applications in the automotive, aerospace, and consumer electronics industries. However, excess oxygen can lead to accelerated oxidation of these alloys, resulting in a reduction in their mechanical properties. Therefore, during production and storage of magnesium alloys, special protective coatings or controlled atmospheres are used to limit oxygen exposure.
Copper alloys:
Oxygen in copper alloys, such as bronzes and brasses, can affect their structure and properties. A small amount of oxygen in bronzes can improve castability, but an excess leads to porosity, a weakened structure, and a decrease in electrical conductivity. Therefore, oxygen-free copper is used for applications requiring high electrical conductivity.
Nickel alloys:
Oxygen plays a key role in forming protective layers on the surface of nickel alloys such as Inconel and Hastelloy , which are widely used in high-temperature and aggressive chemical environments. The oxide layer of nickel or its combinations with chromium provides excellent corrosion and oxidation resistance, making these materials indispensable in gas turbines, industrial furnaces, and chemical reactors.
Cobalt alloys:
In some cobalt alloys used in medicine (e.g., implants), the presence of controlled levels of oxygen during the manufacturing process helps achieve optimal strength and abrasion resistance. However, excess oxygen can lead to undesirable embrittlement, which is why processes such as vacuum melting are used to produce these materials.
Zirconium alloys:
Oxygen is a key element in protecting zirconium alloys, which form a zirconium oxide layer of exceptional durability. This layer provides excellent corrosion resistance, particularly in aqueous and chemical environments, making zirconium indispensable in the nuclear and chemical industries. However, excess oxygen can lead to increased hardness and reduced flexibility of the material.
These examples show how controlling the amount of oxygen in metal alloys affects their properties, allowing materials to be tailored to specific technical and environmental requirements.
The presence of oxygen in metal alloys is both an advantage and a challenge. Controlling oxygen concentration in production processes and designing materials that take advantage of its beneficial properties is crucial. Proper oxygen management allows the creation of alloys with high strength, corrosion resistance, and adaptability to specific operating conditions.
Iron Coal Chromium Nickel Vanadium Manganese Silicon Molybdenum tungsten Copper Tytan Aluminum Cobalt niobium Phosphorus Sulfur Oxygen Nitrogen