Molybdenum crucible needs to be selected according to the application scenario (such as high temperature, corrosive environment). The following are common methods and their characteristics:
- Chemical polishing
Principle: The acid/alkaline solution reacts with the molybdenum surface to remove the oxide layer and tiny defects.
Applicable scenarios: high-smooth surface required (such as optical crystal growth).
Advantages: The surface roughness can reach Ra0.02 μm, but trace impurities may be introduced.
- Electrochemical polishing
Principle: Apply current to the electrolyte to selectively dissolve the surface protrusions.
Advantages: No mechanical stress, suitable for thin-walled crucibles; can form a dense passivation layer.
Typical process:
Electrolyte: Phosphoric acid (85%) + sulfuric acid (15%)
Voltage: 10-20V
Time: 1-3 minutes
- Sand blasting
Principle: Abrasive (such as aluminum oxide) is ejected at high speed to impact the surface, creating roughness.
Applicable scenarios: occasions where coating adhesion needs to be enhanced.
Key parameters:
Abrasive particle size: 80-220 mesh
Injection pressure: 0.2- 0.5MPa
- Vacuum annealing
Principle: Eliminate processing stress at high temperature and form a dense oxide film at the same time.
Advantages:
Annealing temperature: 1200-1500℃
Protective atmosphere: Argon or vacuum
Improve high temperature oxidation resistance and reduce grain boundary defects.
- Plasma spraying
Principle: Spray ceramic coating (such as Al ₂ O ₃, ZrO ₂) on the surface of molybdenum substrate.
Advantages:
Coating thickness: 50-200μm
Improves corrosion and wear resistance, but thermal stress needs to be controlled.
- Physical Vapor Deposition (PVD)
Principle: Deposition of metal/ceramic films on the surface by evaporation or sputtering.
Advantages:
Coating uniformity: ±2%
Typical materials: TiN , CrN
Suitable for precision parts, but the cost is higher.
- Chemical Vapor Deposition (CVD)
Principle: Solid deposits are generated through chemical reactions at high temperatures.
Advantages:
Coating density: >99%
Typical applications: SiC coating to improve high temperature resistance and corrosion resistance.
- Laser surface treatment
Principle: The laser beam locally melts the surface, forming a remelted layer.
Advantages:
Hardened layer depth: 50-150μm
Improves wear resistance, but may introduce microcracks.
- Composite treatment process
Example:
Sandblasting + PVD: Sandblasting first increases the roughness, and then PVD coating improves adhesion.
Chemical polishing + CVD: Polish first to reduce the surface roughness, then CVD deposit SiC coating.
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