Extending the service life of molybdenum crucibles lies in the correct operating environment, reasonable heating method, prevention of chemical corrosion and daily maintenance. Although molybdenum itself has a high melting point (2620°C), high strength and good thermal shock resistance, it is easy to oxidize, embrittle or react with certain substances at high temperatures, so special attention should be paid to the following points:
- Control the use environment
Avoid oxidation
Molybdenum begins to oxidize strongly above 600°C in air, forming volatile MoO₃. Therefore:
When used at high temperatures, it must be heated in a vacuum or inert atmosphere (such as argon or helium).
Never heat directly in air
Control water vapor and acid-base gases
Avoid contact with gases such as H₂O, HCl, H₂SO₄, NOₓ, etc., and be especially careful when heating aqueous samples.
- Optimize the heating and cooling procedures
Slowly warm up
Prevent internal stress cracking of materials caused by thermal shock;
It is recommended to use a step-by-step heating method (e.g., 5–10°C per minute) for initial use or after annealing.
Progressive Cooling
Do not move out of the high temperature area immediately after use, but cool slowly in the furnace to reduce the risk of thermal stress.
- Regular heat treatment and annealing
After repeated use, molybdenum may become brittle due to stress concentration. It is recommended that:
Periodically perform high temperature annealing (e.g. 1000–1200°C for 1 hour in vacuum or argon) to release internal stresses and restore ductility.
- Surface protection treatment
Coating protection (recommended)
To avoid reaction with the experimental material or to prevent corrosion, the inner or outer wall can be pre-coated with:
Boron nitride (BN) coating: anti-adhesion, anti-chemical reaction
Alumina (Al ₂ O ₃) spraying: Isolating molten salt and molten metal
Graphite film: suitable for vacuum and high temperature applications
- Correct loading and operation
Do not fill the container to the limit, leaving space for thermal expansion;
Avoid direct impact of heavy objects on the inner wall of the crucible;
Minimize the number of handling times to prevent cracks caused by mechanical impact;
Check for cracks, pores or delamination before use. If found, stop using.
- Clean up the experimental residue in time
If metal, oxide or molten salt remains in the molybdenum crucible for a long time after use, corrosion or stress concentration will occur;
It is recommended to use mechanical slag removal + organic solvent cleaning + vacuum drying after each experiment.
- Avoid contact with active or highly corrosive materials
Sulfur, phosphorus, halogen compounds, perchlorates, nitrates, etc. will corrode or embrittle molybdenum materials;
If it must be used, choose a corrosion-resistant composite crucible or use a protective coating.
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