The molybdenum crucible needs to be vacuum packaged and stored depends on the specific usage scenario and needs, but vacuum packaging is usually recommended under certain conditions to extend the service life and prevent oxidation. The following is a detailed analysis:
- Oxidation risk of molybdenum crucible
Oxidation Mechanism
Molybdenum begins to react with oxygen at temperatures above 400°C to form MoO₂ or MoO₃ oxide.
Temperature influence:
400-800℃: Slow oxidation to form a dense oxide film.
> 800℃: The oxidation rate increases sharply, the oxide film breaks, and the molybdenum matrix continues to be consumed.
Environmental impact:
Humidity: Water vapor accelerates oxidation, generating MoO₃ · nH₂O (molybdic acid).
Corrosive ions such as chloride ions (Cl⁻) accelerate the destruction of oxide films.
Oxidative effects
Structural damage: Oxidation causes the crucible wall thickness to decrease and the strength to drop.
Contamination risk: Oxidation products fall off and contaminate the sample.
Shortened service life: After the oxide film is destroyed, the molybdenum substrate is directly exposed and the oxidation rate increases exponentially.
- Necessity of vacuum packaging and preservation
Applicable scenarios
Recommended vacuum packaging:
Long-term storage (> 3 months).
High humidity environment (humidity > 60%).
Corrosive atmosphere (such as containing Cl₂, SO₂).
No vacuum packaging:
Short-term use (< 1 month).
Dry environment (humidity < 40%).
Inert gas protection (such as argon, nitrogen).
Advantages of vacuum packaging
Isolate from oxygen: Vacuum environment (< 1×10 ⁻ ³ Pa) effectively inhibits oxidation.
Prevent pollution: Avoid water vapor and corrosive gases from contacting the crucible.
Extended life: The oxidation rate is reduced by more than 90% (supported by experimental data).
- Vacuum Packaging Operation Suggestions
Packaging conditions
Vacuum degree: ≤ 1×10 ⁻ ³ Pa (avoid residual oxygen).
Packaging Materials:
First choice: aluminum foil composite film (moisture-proof and oxygen-blocking).
Alternative: Polytetrafluoroethylene (PTFE) bags (high temperature resistant).
Sealing method: heat sealing or vacuum packaging machine sealing.
Storage conditions
Temperature: Room temperature (20-25°C) or lower (such as refrigeration).
Humidity: ≤ 40% RH (can be used with desiccant).
Protect from light: Prevent ultraviolet rays from accelerating oxidation.
- Alternatives
Inert gas protection
Operation: Place the crucible in an argon or nitrogen atmosphere with an oxygen content < 10 ppm.
Applicability: Suitable for short-term storage or frequent use.
Surface coating
the crucible surface with aluminum oxide (Al₂O₃) or silicon nitride (Si₃N₄) coating.
Effect: Oxidation rate reduced by more than 50% (coating integrity needs to be checked regularly).
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