Molybdenum crucible usually needs to be preheated before use, which helps to avoid thermal stress cracking or cracks caused by sudden temperature rise. The preheating process can help the molybdenum crucible gradually adapt to the high temperature environment, thereby extending its service life and maintaining its structural integrity.
Necessity and steps of preheating:
Avoid thermal shock
Molybdenum crucible material has good thermal shock resistance at high temperatures, but if a cold crucible is placed directly in a high temperature environment, excessive thermal stress will be generated due to the rapid temperature change, causing the crucible to crack or break.
Preheating can gradually increase the crucible temperature and avoid damage caused by uneven thermal expansion.
Gradually heating up
It is recommended to adopt a gradual heating strategy, for example: 5–10°C per minute, especially for the first use or after annealing, to ensure that the temperature of the molybdenum crucible gradually approaches the working temperature.
The preheating temperature range is generally from room temperature to 500°C, gradually transitioning to the temperature required for the experiment.
Suitable for different experimental environments
If used in an inert atmosphere such as vacuum or argon, preheating can effectively reduce the moisture or oxidation effects of the gas and prevent the inner wall of the crucible from being corroded by oxides or water vapor.
If you are performing metal melting or crystal growth experiments, preheating allows the crucible to more evenly bear the heat load of the molten metal and avoid cracks caused by local overheating.
Avoid exposure to air
Avoid rapid heating in air, because molybdenum easily reacts with oxygen to form MoO ₃ at high temperatures, especially when it exceeds 600°C. Inert gas protection can be used during preheating to prevent oxidation of the crucible surface.
Preheating suggestions:
Preheating temperature: between room temperature and 500°C, adjusted according to the temperature requirements and atmosphere conditions of the experiment.
Heating rate: 5–10°C per minute is recommended, especially for first-time use of molybdenum crucibles.
Heating method: Use a furnace with high temperature control accuracy to avoid overheating. It is recommended to use inert gas (such as argon, helium) for protection to avoid oxidation.
Maintain uniform temperature: During the heating process, ensure that the crucible is heated evenly to avoid local overheating.
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