Using molybdenum crucible on product purity mainly depends on its chemical stability, high temperature performance and processing technology. The following is a detailed analysis:
- The positive influence of molybdenum crucible on product purity
Chemical inertness
Does not react with most materials at high temperatures: Molybdenum does not react chemically with metals such as silicon, germanium, iron, nickel and their oxides below 1600°C, avoiding the introduction of impurities.
Low Solubility: The solubility of molybdenum in molten silicon is extremely low (<1 ppm), significantly reducing the risk of contamination.
Application scenarios:
Single crystal silicon growth: Molybdenum crucibles can maintain the purity of silicon and avoid impurity doping in the Czochralski method.
Rare earth metal smelting: In the preparation of rare earth permanent magnet materials such as NdFeB, molybdenum crucible can prevent the oxidation or volatilization of rare earth elements.
High temperature resistance
High melting point (2610℃): Molybdenum crucible can work stably above 2000℃, meeting the needs of smelting high-purity materials (such as the melting point of silicon is 1414℃).
Thermal shock resistance: Low thermal expansion coefficient (5.5×10 ⁻⁶ / ℃ ) reduces cracking caused by thermal stress and avoids the mixing of impurities.
High purity molybdenum material
Purity ≥99.95%: High-purity molybdenum crucibles have extremely low impurity content, further reducing the risk of contamination.
- Potential risks of molybdenum crucible to product purity
Oxidation Problem
High temperature oxidation: In air or oxygen environment, molybdenum is easily oxidized to form volatile MoO₃ (boiling point about 1155°C), resulting in material loss and introduction of impurities.
Solution:
Vacuum or inert gas protection: Use in vacuum or argon (Ar) atmosphere to avoid oxidation.
Surface coating: Use Mo₂C, ZrO₂ and other coatings to delay oxidation.
Processing pollution
Machining residue: Metal particles or lubricants may remain during the machining of the molybdenum crucible, which need to be removed by precision machining and cleaning.
Surface roughness: Surface defects may absorb impurities, so the surface finish must be ensured (Ra≤0.8 μm).
Impurity Diffusion
Molybdenum crucibles may slowly release trace impurities at high temperatures and need to be inspected and replaced regularly.
- Purity performance in different application scenarios
| Application Scenario | Purity Impact | Typical Cases |
| Single crystal silicon growth | Positive: Maintain high purity of silicon (> 9N) | Molybdenum crucible replaces quartz crucible in Czochralski single crystal silicon growth furnace |
| Rare earth metal smelting | Active: Prevent rare earth oxidation and volatilization | Preparation of NdFeB Permanent Magnet Materials |
| High temperature alloy melting | Neutral: need to pay attention to impurity diffusion | Nickel-based high-temperature alloy melting |
| Glass melting | Negative: Glass components may corrode molybdenum crucibles | Borosilicate glass melting (avoid using molybdenum crucibles) |
- Key measures to improve purity
Choose high-purity molybdenum material: ensure Mo ≥ 99.95% and reduce its own impurities.
Optimize processing technology: use precision processing technology (such as spinning and sintering) to control surface roughness.
Strict cleaning process: Use ultrasonic cleaning and high temperature degreasing to remove processing residues.
Environmental control: Use under vacuum or inert gas protection to avoid oxidation.
Regular inspection and replacement: Detect impurity content through ICP -MS and other means, and replace aging crucibles in time.
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