Coating technology can significantly improve the service life and performance of molybdenum crucibles in harsh environments such as high temperature, oxidation, and corrosion. Below we introduce in detail several common molybdenum crucible surface coating methods and the performance improvements they bring.
1. The main function of coating
Anti-oxidation protection: Molybdenum is easily oxidized above 800℃ in air, forming MoO₃ volatilization loss. The coating can isolate oxygen from contact.
Enhanced corrosion resistance: acts as a shield in molten salt, alkali metal or certain active metal environments.
Heat reflection/insulation: Reduces heat loss or thermal stress damage.
Improve surface finish: Improve material release, melting, cleaning and other performance.
Anti-adhesion performance: avoid raw materials from reacting or adhering to the molybdenum crucible.
Enhance mechanical stability and thermal fatigue life.
2. Common coating types and performance improvements
1. Alumina (Al₂O₃) coating
Function: Anti-oxidation and anti-corrosion;
Applicable to: heating in air atmosphere, molten salt experiment;
Preparation methods: thermal spraying, sol-gel, plasma spraying, etc.
2. Silicide coating (such as MoSi₂, WSi₂)
SiO₂) at high temperature;
Advantages: Suitable for long-term operation above 1500℃;
Applicable scenarios: single crystal furnace thermal field, sapphire crystal growth, etc.
3. Boron nitride (BN) coating
Function: Excellent anti-adhesion and lubricity;
Commonly used in: glass melting, ceramic preparation, metal powder sintering;
Advantages: Isolate material reactions and prevent sticking to the wall.
4. Silicon Carbide (SiC) or Carbon Coating
Function: Improve thermal shock stability and thermal conductivity;
Note: Use under reducing or inert atmosphere to avoid oxidation.
5. Zirconium-based ceramic coating (such as ZrO₂)
Function: high temperature stability, heat insulation, and prevention of thermal corrosion;
Applications: aerospace thermal barriers, alkali metal smelting, etc.
3. Coating method (process)
| Coating method | Features | Applications |
| Thermal Spraying | Fast film formation and adjustable thickness | Industrial mass application |
| Sol-Gel Method | Low cost, high density | Laboratory or precision equipment |
| Vacuum evaporation/magnetron sputtering | Uniform film and strong adhesion | Microelectronics, precision field |
| Chemical Vapor Deposition (CVD) | Dense film, high temperature resistance | High-end devices and special applications |
4. Selection Suggestions
High temperature oxidation resistance: MoSi ₂ and Al ₂ O ₃ are preferred;
Glass melt or alkaline material: BN or ZrO₂ is recommended;
Avoid material reactions or contamination: choose inert ceramic coatings;
Special electrical/optical scenarios: composite coatings or functional films can be used;
Ultra-high temperature or vacuum environment: CVD or EB-PVD deposition is recommended.
5. Notes
The coating must not significantly reduce the thermal conductivity or mechanical strength of the crucible;
The coating should match the thermal expansion coefficient of the molybdenum substrate to avoid thermal cracking;
The coating treatment should take into account the subsequent use atmosphere of the crucible (oxidizing vs reducing);
The coating should avoid falling off or peeling and require good adhesion.
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