Molybdenum, this silvery-gray metal, isn't often seen in our daily lives, but it exists all around us in various forms. Whether in alloys, molybdenum wire for wire cutting, or molybdenum target testing, molybdenum quietly plays its role. The recent announcement by the Ministry of Commerce and the General Administration of Customs of export controls on certain molybdenum products underscores the importance of molybdenum.
In its pure form, molybdenum is a silvery-gray metal with a Mohs hardness of 5.5. Its melting point is a staggering 2623°C and boiling point is a staggering 4639°C, both of which are exceptionally high for naturally occurring elements. Only tantalum, osmium, rhenium, tungsten, and carbon have higher melting points. Molybdenum's oxidation begins at 300°C, which is exceptionally low for commercial metals. Furthermore, molybdenum has the lowest coefficient of thermal expansion, making it an excellent choice for many high-temperature applications.
Molybdenum does not exist in its pure metallic form on Earth, but rather occurs as various oxides in minerals. In its elemental form, molybdenum is a silvery-gray metal with the color of gray cast iron. It has the sixth-highest melting point of all elements. Molybdenum readily forms hard, stable carbides in alloys, resulting in approximately 80% of the world's molybdenum supply being used as an additive in steel, including high-strength and high-temperature alloys.
Most molybdenum compounds are slightly soluble in water, but molybdenum-containing minerals can form molybdenum ions (MoO2−4) when exposed to oxygen and water. Industrially, molybdenum compounds are used in high-pressure and high-temperature applications, such as pigments and catalysts, accounting for approximately 14% of global production.
Beyond its industrial applications, molybdenum is an essential trace mineral for all eukaryotic organisms, including humans. It is the metal with the highest atomic number among the essential elements for eukaryotic life. Various molybdenum-containing cofactor enzymes have diverse functions in organisms. Currently, some bacteria use molybdenum-containing enzymes as the most common catalysts for breaking the chemical bonds of atmospheric nitrogen molecules, enabling biological nitrogen fixation. At least 50 molybdenum-containing enzymes are known in bacteria and animals, although only bacterial and cyanobacterial enzymes are involved in nitrogen fixation. The molybdenum contained in these nitrogenases differs from that in other molybdenum-containing enzymes, but they all contain oxidized molybdenum as a cofactor. However, not all bacteria utilize molybdenum. In some bacteria and archaea, tungsten, a member of the same family as molybdenum, plays a physiological role similar to that of molybdenum in higher organisms.
In general, molybdenum is a very unique metallic element with a wide range of applications. It plays an indispensable role in both industrial production and in biology.
