To verify the quality of molybdenum crucibles, a comprehensive evaluation is required from four dimensions: raw material purity, production process, performance testing, and appearance and size. The following are the specific methods:
- Raw material purity verification
Chemical composition analysis
Method: Molybdenum content is measured by spectroscopic analysis (such as ICP -OES) or X-ray fluorescence spectroscopy (XRF).
Standard: The molybdenum content of high-purity molybdenum crucible must be ≥99.95%, and the impurity content (such as iron, nickel, carbon, etc.) must be less than 0.05%.
Case: If the molybdenum content is lower than 99.9%, it may cause oxidation at high temperatures or a decrease in melting point, thus shortening the service life.
Metallographic structure inspection
Method: Observe the internal structure of the material through a metallographic microscope to confirm that there are no defects such as inclusions and holes.
Significance: Uniform and dense metallographic structure can improve high temperature resistance and thermal shock resistance.
- Production process verification
Density test
Method: Density is measured by Archimedes drainage method, or internal density is tested non-destructively by ultrasonic wave.
Standard: The density of sintered molybdenum crucible must be ≥9.8 g/cm³. Porosity may exist below this value, affecting thermal conductivity and mechanical strength.
Dimensional accuracy inspection
Method: Use a three-coordinate measuring machine or caliper to measure the inner diameter, outer diameter, height and wall thickness of the crucible. The tolerance must be controlled within ± 0.1mm.
Significance: Dimensional deviation may cause the crucible to not match the heating equipment, affecting thermal efficiency.
Surface treatment evaluation
Method: Visually check whether the surface is smooth, without cracks, scratches or oxide layer; check the corrosion resistance by salt spray test.
Standard: Surface roughness Ra≤1.6μm, no visible defects.
- Performance Test Verification
High temperature performance test
Method: Place the crucible in a high-temperature furnace, raise the temperature to above 2000℃, keep it warm for 2 hours, then cool it naturally and observe whether it is deformed or cracked.
Standard: No obvious deformation at high temperature and no cracks after cooling.
Antioxidant Test
Method: Heat in air at 1200℃ for 100 hours and weigh to detect oxidation weight gain.
Standard: Oxidation weight gain rate ≤ 0.5mg /cm²·h, high-quality molybdenum crucible can be as low as 0.1mg /cm²·h.
Thermal shock test
Method: Rapidly cool the crucible from 2000°C to room temperature (such as water quenching), repeat 10 times, and check whether it cracks.
Significance: To simulate the sudden temperature change in actual use and verify the thermal shock resistance.
- Appearance and size verification
Appearance inspection
Method: Check visually or with a magnifying glass whether the surface is smooth and free of pores, cracks, inclusions or oxidation spots.
Standard: Surface defect area ≤ 1% of the total area, no obvious scratches.
Dimensional tolerance
Method: Use a vernier caliper or a three-coordinate measuring machine to check the inner diameter, outer diameter, height and wall thickness.
Standard: The tolerance range depends on the application scenario. For example, precision casting needs to be controlled within ± 0.05mm.
- Other Verification Methods
Ultrasonic flaw detection
Method: Use ultrasonic detection to detect whether there are internal defects such as delamination and cracks.
Significance: Ensure the integrity of the internal structure of the crucible to avoid failure at high temperatures.
X-ray Inspection
Method: Use X-ray fluoroscopy to check internal defects such as pores, inclusions, etc.
Application: Suitable for scenarios with extremely high requirements on internal quality.
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