Molybdenum crucibles include high purity, high density, high melting point, excellent thermal conductivity, high strength and hardness, good thermal expansion coefficient control and corrosion resistance, as follows:
- Purity and density
Purity: ≥99.95%, some high-end products can reach above 99.97%. High purity ensures the chemical stability of the material at high temperatures and reduces oxidation or embrittlement caused by impurities.
Density: ≥ 9.8g /cm³, some sintered products can reach 10.2g /cm³. High density improves the material’s deformation resistance and thermal conductivity.
- Melting point and high temperature resistance
Melting point: 2610℃-2620℃, which is the key to keep the structure of molybdenum crucible stable in extremely high temperature environment (such as above 2000℃).
Operating temperature: conventional application range is 1100℃-1700℃, and can withstand high temperature of 2400℃ under special process.
- Thermal conductivity and thermal expansion
Thermal conductivity: Molybdenum has a high thermal conductivity, which ensures uniform temperature distribution and improves smelting efficiency.
Thermal expansion coefficient: Low thermal expansion coefficient (about 5.5×10 ⁻⁶ / ℃), reducing dimensional changes at high temperatures and avoiding thermal shock cracking.
- Strength and hardness
Tensile strength: ≥ 600MPa (annealed state), can be increased to over 800MPa through forging or rolling process
Hardness: Vickers hardness (HV) 200-300 (pure molybdenum), the hardness of molybdenum alloy can reach over HV1000.
300MPa at 1200℃, suitable for long-term high temperature environment.
- Corrosion resistance
Acid and alkali corrosion resistance: It has good resistance to most acids (such as hydrochloric acid, sulfuric acid) and alkalis, but strong oxidizing acids (such as nitric acid) should be avoided.
Resistance to molten metal corrosion: It can withstand the corrosion of molten aluminum, copper, nickel and other metals, and is suitable for metal smelting.
- Machinability
Machinability: Molybdenum has better ductility than tungsten and can be processed into complex shapes through turning, milling, drilling and other processes.
Surface quality: The surface roughness after processing is Ra≤0.4μm (standard for crucibles used in sapphire single crystal growth furnace), ensuring the quality of crystal growth.
- Fatigue and creep resistance
Fatigue resistance: It is not easy to crack under cyclic thermal stress and is suitable for high temperature oscillation environment.
Creep resistance: At high temperatures above 1000°C, the creep rate is less than 1×10 ⁻⁶ /h, ensuring long-term dimensional stability.
Detection Methods
Purity: Inductively coupled plasma mass spectrometry (ICP -MS).
Density: Archimedean drainage method.
Hardness: Vickers hardness tester.
Thermal expansion coefficient: laser dilatometer.
Corrosion resistance: Salt spray test or molten metal immersion test.
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