Molybdenum crucibles need to be inspected regularly, which is a key measure to ensure their safety and process stability. The following is a detailed analysis:
- Why is regular testing necessary?
High temperature oxidation and corrosion
Molybdenum begins to oxidize above 400°C to generate volatile MoO₃ , which leads to thinning of the crucible wall, reduced strength, and even perforation.
Example: If the crucible wall thickness is reduced from 5 mm to 3 mm , its load-bearing capacity will drop by 40%.
Heat stress damage
Frequent heating/cooling cycles can cause thermal cracks or deformation, affecting sealing and service life.
Data: After every 100 uses, the probability of fatigue damage to the crucible increases by 15%.
Metal contamination risk
Impurities in the melt (such as aluminum and titanium) may penetrate into the molybdenum matrix, resulting in the formation of intermetallic compounds and reducing purity.
Consequences: Melt purity decreases and product performance (such as conductivity and strength) does not meet standards.
- Testing Items and Standards
| Test items | Detection Methods | Eligibility criteria |
| Wall thickness measurement | Ultrasonic Thickness Gauge | ≥ 80% of original wall thickness |
| Oxide layer thickness | Metallographic microscope observation | ≤ 0.1mm |
| Crack detection | Penetrant Testing (PT) | No visible cracks |
| Metal contamination | Spectroscopic analysis ( ICP -OES) | Impurity content ≤ 0.01% |
| Dimensional deformation | Coordinate measuring machine | Deformation ≤ 0.1mm |
- Recommended testing frequency
Frequent use scenarios (such as daily use):
Inspect once every 50 uses, with a focus on wall thickness and oxide layer.
Medium frequency usage scenarios (such as weekly use):
Inspect once every 100 uses to add crack and size inspection.
Low-frequency usage scenarios (such as monthly use):
Test once every 200 uses and conduct a comprehensive inspection.
- Test results and countermeasures
| Test results | Countermeasures |
| Wall thickness < 80% | Stop using immediately and scrap it |
| Oxide layer> 0.1mm | Reapply an oxidation resistant coating (such as zirconium oxide) |
| Cracks exist | Assess the crack depth, if > 0.2mm, scrap |
| Metal contamination | Replace the crucible or use a higher purity melt material |
- Testing tools and costs
Basic testing:
Tools: Vernier caliper (wall thickness), magnifying glass (cracks), pH test paper (degree of oxidation).
Cost: Almost zero cost, suitable for daily self-inspection.
Professional testing:
Tools: Ultrasonic thickness gauge, metallographic microscope, spectrum analyzer.
Cost: A single test costs about 500-2000 yuan, depending on the test item.
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