Using molybdenum crucibles, preventing oxidation is key to ensuring their long-term stability and durability. Molybdenum easily reacts with oxygen in the air at high temperatures to form molybdenum trioxide (MoO₃), which can lead to surface damage, reduced strength, and even cracking of the crucible. The following are some effective measures to prevent oxidation of molybdenum crucibles:
- Use an inert atmosphere (argon, helium, etc.)
Argon protection: When using molybdenum crucibles at high temperatures, it is best to place them in an inert gas environment such as argon. Argon can prevent oxygen from reacting with molybdenum, thereby avoiding oxidation.
Helium can also be used as an inert atmosphere, with similar effects to argon, but at a higher cost.
In high temperature experiments such as crystal growth and metal smelting, the use of inert atmosphere protection can significantly extend the service life of the molybdenum crucible.
- Use a vacuum environment
A vacuum environment can effectively avoid the presence of oxygen, so when operating at high temperatures, using a vacuum furnace for experiments can effectively prevent oxidation.
In a vacuum, the molybdenum crucible will not be exposed to oxygen in the air, thus avoiding the formation of an oxide layer and maintaining its good high-temperature performance.
- Reduce heating temperature
When heating the molybdenum crucible, avoid heating it directly to very high temperatures, especially in the air. Excessive temperature will accelerate the rate of oxidation reaction.
If experimental conditions permit, the heating rate can be controlled and the temperature can be increased gradually to avoid the rapid formation of an oxide layer caused by sudden temperature changes.
- Molybdenum crucible surface coating
Coating protection: By coating the surface of the molybdenum crucible with a protective coating (such as boron nitride, graphite, alumina, etc.), the air can be effectively isolated to prevent oxidation.
Molybdenum nitride coating: In some high temperature operations, the molybdenum crucible may be coated with a layer of molybdenum nitride. This coating can protect the surface of the molybdenum crucible from oxidation.
- Avoid exposure to air
Prevent long-term exposure to air: Before using the molybdenum crucible, try to avoid exposing it to air for a long time. The longer the exposure time, the easier it is for oxidation to occur. Try to store and use it in a sealed environment.
- Reasonable control of cooling process
After the experiment, the cooling process of the molybdenum crucible should avoid rapid cooling. Rapid cooling may lead to surface stress accumulation and make the oxide layer more fragile.
The temperature should be slowly lowered to allow the molybdenum crucible to gradually return to room temperature.
- Special attention should be paid when using oxidizing atmosphere
If the experiment requires the use of an oxidizing atmosphere (such as oxygen, air, etc.), molybdenum alloys (such as molybdenum -tantalum alloys) can be selected. These alloys have stronger oxidation resistance than pure molybdenum.
In addition, the oxygen concentration and temperature should be properly controlled to reduce the rate of oxidation.
- Regular inspection and maintenance of molybdenum crucible
Regularly check whether there is an oxide layer on the surface of the molybdenum crucible to ensure that the surface is smooth and free of cracks. If there is an oxide layer accumulation or damage, it should be cleaned or replaced in time.
The surface oxides can be removed by hydrogen reduction.
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