Chromium

Chromium is essential for the corrosion resistance of stainless steel because, when it comes into contact with oxygen, it contributes to forming a very thin and adherent surface layer rich in chromium. This layer makes it difficult for the metal to continue reacting with the environment and can regenerate if damaged, as long as conditions are appropriate. In general, stainless steels contain at least approximately 10.5% chromium by mass, although their specific resistance also depends on other elements and the media to which they are exposed.

Certain chromium compounds present intense and relatively stable colours, so they have been used as pigments in paints, ceramics and other materials. Among the historical examples are yellow chromium lead chromate pigments and green chromium oxides. However, some traditional pigments contain hazardous substances and their use is restricted in many contexts. Chromium(III) oxide, in particular, stands out for its green colour and stability, which favours certain industrial and artistic applications.

Chromium(III) oxide, formula Cr₂O₃, is a hard and chemically stable solid that can be used in certain polishing products. In the form of fine particles, it helps remove small surface imperfections and obtain smooth finishes on suitable materials, including certain metals. Its effectiveness depends on particle size, surface hardness and the procedure used. It is also used as a green pigment, so its presence in a product does not necessarily imply an abrasive function.

Chromium is incorporated into numerous steels for tools because it contributes to improving temperability, wear resistance and, in certain compositions, corrosion resistance. These properties help manufacture blades, drills, dies and tools capable of maintaining performance during prolonged use. The result depends on the amount of chromium and its combination with elements such as carbon, molybdenum or vanadium, as well as heat treatment. Not all chromium steels offer the same performance, as they are designed for different tasks.

Chroming consists of depositing a chromium layer on the surface of another material through a coating process, usually electrochemical. Depending on the type of treatment, it can provide a bright finish, improve wear resistance or reduce friction. Decorative chroming usually uses very thin layers, while hard chroming is used in industrial components subjected to friction. Surface preparation and process control are fundamental to obtaining a uniform layer with the desired properties.

Chromium is part of many alloys designed to work at high temperatures because it helps improve oxidation resistance and resistance to certain corrosive environments. In superalloys used in turbines and industrial equipment, it contributes to protecting the surface against the formation of harmful oxides. Its effect depends on the complete composition of the alloy, as other elements provide mechanical resistance, microstructural stability or additional protection. That is why chromium content is adjusted according to temperature and service conditions.

Some chromium(III) salts are used in industrial leather tanning because they can interact with chemical groups of collagen, the structural protein of skin. These interactions help stabilise the material's structure and improve properties such as heat resistance and durability. The process requires controlling chemical conditions to obtain leather with the desired characteristics. It is important to distinguish chromium(III), used in tanning, from chromium(VI), which presents different toxicological risks and requires specific controls.