To determine whether the molybdenum crucible needs to be replaced, a comprehensive assessment is required from four dimensions: appearance inspection, size change, performance test and usage record. The following is a specific judgment method:
- Appearance inspection
| Inspection items | Judgment criteria | Suggestions |
| Cracks and deformation | The surface has cracks, perforations or obvious deformation (such as dents, bulges) | Replace immediately to avoid the risk of cracking at high temperatures |
| Oxidation degree | purple oxide layer (MoO₃) appears on the surface or the thickness exceeds 0.1mm | Replacement, the oxide layer may fall off and contaminate the product |
| Corrosion and contamination | There are metal spots on the surface, slag adheres to the surface, or chemical reactions occur with the crucible material (such as the formation of sulfides). | Replace, corrosion will reduce the service life |
| Coating peeling | Surface protective coatings (such as zirconium oxide coatings) peel off and blister | Replacement, coating failure accelerates crucible oxidation |
- Size Change
| Test items | Eligibility criteria | Abnormal manifestations | Suggestions |
| Inner diameter change | Tolerance range: ± 0.1mm (e.g. original inner diameter 100mm, 99.9-100.1mm is allowed) | The inner diameter is reduced by more than 0.2mm or deformed | Replacement affects evaporation uniformity |
| Height Change | Tolerance range ± 0.5mm | The height is shortened by more than 1mm or tilted | Replacement may cause material leakage |
| Wall thickness variation | The wall thickness reduction does not exceed 20% of the original thickness |
- Performance Test
| Test items | Test Method | Failure criteria | Suggestions |
| Temperature resistance test | Keep at 1800℃ for 2 hours and observe the deformation | Obvious deformation or cracks | Replacement, high temperature performance degradation |
| Thermal shock test | Rapid cooling from 1800℃ to room temperature, repeated 5 times | Cracks or breaks | Replacement, thermal shock resistance failure |
| Metal contamination test | After evaporating high-purity metals, detect the impurity content in the metal | Impurity content exceeds 0.1% | Replacement, crucible material contaminates metal |
- Usage Record Analysis
| Using Parameters | Warning criteria | Suggestions |
| Cumulative usage time | More than 1000 hours (the specific time varies according to the process) | Evaluation and replacement, material performance degradation at high temperature |
| Use times | Evaporation times exceed 50 times (metal evaporation process) or smelting times exceed 30 times (alloy smelting) | Evaluate replacement, repeated thermal cycling accelerates wear |
| Process parameters | use at high temperatures above 2000℃ or under frequent thermal shock conditions | Shorten the replacement cycle to 500 hours |
5.Comprehensive Judgment Process
Check the appearance first: cracks, deformation, and oxidation are the primary indicators of replacement.
Secondary inspection dimensions: inner diameter, height, and wall thickness that are out of tolerance need to be replaced.
Performance test verification: If the high temperature, thermal shock, and contamination tests fail, the unit must be replaced.
Combined with usage records: if the accumulated time, number of times or process parameters exceed the standard, evaluation and replacement are required.
- Replacement suggestions
Safety first: If cracks or deformations are found, stop using and replace immediately to avoid the risk of high-temperature cracking.
Cost optimization: If there is only oxidation or slight wear, surface repair (such as re-spraying the protective layer) can be attempted, but the performance needs to be verified.
Regular maintenance: It is recommended to conduct an appearance inspection every 3 months and a dimensional inspection every six months to extend the service life.
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