Molybdenum, a silvery-white metal element, has held a significant position in the fields of science and industry since its discovery by the Swedish chemist Carl Wilhelm Scheele in 1778. Initially separated from a mineral mistaken for lead, molybdenum was later extracted as an element by Peter Jacob Hjelm in 1781. The discovery and naming of molybdenum not only marked a milestone in the history of chemical elements but also laid the foundation for subsequent scientific research and industrial applications.
In modern science and industry, molybdenum is extensively used in steel alloys, aerospace, electronic devices, and catalysts due to its high melting point, strength, and corrosion resistance. Its addition significantly enhances the high-temperature resistance and overall strength of materials, making it a key element in the manufacture of high-performance alloys and superalloys. The properties of molybdenum not only drive technological advancement but also have profound impacts on environmental protection and energy development.
What are the chemical properties of molybdenum?
Molybdenum, a Group 6 element in the fifth period of the periodic table, has an atomic number of 42 and exhibits multiple oxidation states, including +2, +3, +4, +5, and +6, with the +6 oxidation state being the most stable. Its lower oxidation state compounds display basic properties, while the higher oxidation state compounds are acidic.
- At room temperature, molybdenum is stable in air.
- At 400°C, it begins to oxidize, which is evident by a change in color.
- At 600°C, molybdenum rapidly oxidizes to form molybdenum trioxide (MoO₃).
- Above 700°C, steam strongly oxidizes molybdenum to molybdenum dioxide (MoO₂).
- Molybdenum does not react with hydrogen up to its melting point. However, when heated in hydrogen gas, it can absorb some hydrogen to form a solid solution.
- Below 1500°C, molybdenum does not react with nitrogen.
- Above 1500°C, molybdenum reacts with nitrogen to form nitrides; if the pressure is low, no reaction is observed even up to 2400°C.
- Carbon, hydrocarbons, and carbon monoxide start to react with molybdenum at 800°C, forming molybdenum carbide (Mo₂C).
- Carbon dioxide oxidizes molybdenum above 700°C.
- In the presence of moisture, all halogens react with molybdenum at room temperature.
- Molybdenum is stable in hydrochloric and sulfuric acids at room temperature but begins to dissolve slightly when heated to 80-100°C.
- Molybdenum slowly dissolves in nitric acid and aqua regia at room temperature, with the dissolution rate increasing upon heating.
- Molybdenum is stable in hydrofluoric acid but rapidly dissolves in a mixture of hydrofluoric and nitric acids. The effect of the high melting point of molybdenum
The effect of the high melting point of molybdenum
Molybdenum melting point vs other refractory metals
Material | Melting point (℃) | Thermal conductivity (W/m·K) | Density (g/cm3) |
Molybdenum (Mo) | 2623 | 138 | 10.2 |
3422 | 173 | 19.3 | |
3017 | 57 | 16.6 | |
2477 | 53 | 8.57 |
The effect of a high melting point
The high melting point allows molybdenum to maintain structural integrity in high-temperature environments, thereby enhancing the reliability and performance of the materials and having several implications for its industrial applications. It makes molybdenum an ideal material for creating high-temperature resistant materials, especially where extreme stability and strength are required.
What molybdenum is used for?
Steel Industry
Molybdenum, as a steel alloying element, boosts steel's high-temperature strength, toughness, corrosion resistance in various environments, and wear resistance, and improves hardenability, weldability, and heat resistance. It's an effective carbide former, used alone or with other alloys, and remains stable during steel production.
Agricultural Fertilizer
Using ammonium molybdate as a micronutrient fertilizer can significantly enhance the quality and yield of legumes, forage, and other crops.
Electrical and Electronics
Molybdenum is essential in electronics and lighting for its conductive and high-temperature properties, and its thermal expansion closely matches glass. It's used in lightbulb components and as electrode wire in EDM machining, improving precision in complex part production.
Automotive Spraying
Molybdenum's excellent high-temperature and corrosion resistance, along with its strong bond with steel, make it a primary thermal spray material in automotive part production. Sprayed molybdenum achieves a density of over 99% with a bond strength close to 10 kg/mm².
High-temperature Components
Molybdenum's high purity and resistance to heat and vaporization are ideal for components in high-temperature furnaces, often used in reduction and sintering processes under non-oxidizing conditions.
Molybdenum Alloys
The TZM alloy, enhanced with Ti, Zr, and C oxides or carbides, is used in aerospace, and nuclear industries, and for high-performance parts like X-ray anodes and molds. TEM alloy, with added rare earths, offers higher recrystallization temperatures and superior ductility.
Molybdenum's future is promising with its growing market and diverse applications. Continuous research and new technologies are key to its expanded use in various industries, promising innovative solutions and sustainable development.
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