Using a molybdenum crucible, the recommended heating rate should be determined based on the specific operating conditions and the crucible’s use environment. Usually, during the heating process of the molybdenum crucible, the heating rate should not be too fast to avoid thermal shock or cracks in the crucible due to excessive temperature changes. The following are some general heating rate recommendations:
Recommended heating rate:
Slow heating: Generally, the heating rate of the molybdenum crucible should be controlled between 1°C/min and 5°C/min. Such a heating rate can ensure a small temperature difference between the inside and outside of the crucible, reduce thermal stress, and thus reduce the risk of thermal shock and cracks.
Low temperature stage: During the initial heating stage, especially when starting from room temperature, it is recommended to choose a slower heating rate (1°C/min or 2°C/min) to avoid sudden temperature differences.
High temperature stage: When the temperature gradually approaches the target temperature, the heating rate can be increased appropriately, close to 5°C/min, but it is still necessary to avoid too fast heating, especially for very fragile molybdenum crucibles.
Adjust according to crucible thickness: For thicker molybdenum crucibles, a lower heating rate is recommended, because the internal temperature of thicker crucibles changes slowly when heated, and too fast heating may cause uneven surface and internal temperatures, thereby causing thermal stress. For thinner molybdenum crucibles, the heating rate can be slightly faster, but too fast heating should still be avoided.
Adjustment of heating curve: In some cases, the heating rate can be adjusted in stages. For example, the heating rate is slow in the initial stage, and then gradually accelerated after reaching a certain temperature to ensure uniform temperature inside the crucible and the furnace.
Key considerations:
Thermal shock risk: A heating rate that is too fast will cause a large temperature difference between the surface and the inside of the molybdenum crucible, which can easily cause cracks, especially when the crucible is still in a cooling state or has been damaged.
Oxidation Control: If the crucible is heated too quickly in air, the surface may oxidize quickly, affecting its performance. Therefore, it is recommended to use a slower heating rate in an oxidizing environment and consider using an inert gas (such as argon, nitrogen) to protect the crucible surface.
Furnace and atmosphere control: Pay attention to the atmosphere and temperature uniformity in the furnace during operation. If the atmosphere in the furnace is not uniform, the heating rate may need to be adjusted appropriately to avoid uneven heating.
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