Preparation of Tungsten Coating Strengthened Molybdenum Crucible

In the industry, the melting of rare earth, vacuum evaporation and sapphire growth in the field of crucibles, mostly made of tungsten and molybdenum materials. This is due to the fact that tungsten has the characteristics of high melting point and high density. Currently, tungsten, molybdenum and molybdenum alloy crucibles are mostly obtained by powder metallurgy and press working.

In the industry, the melting of rare earth, vacuum evaporation and sapphire growth in the field of crucibles, mostly made of tungsten and molybdenum materials. This is due to the fact that tungsten has the characteristics of high melting point and high density. Currently, tungsten, molybdenum and molybdenum alloy crucibles are mostly obtained by powder metallurgy and press working.

Compared with pure tungsten materials, molybdenum has lower melting point and easier sintering and pressure processing. At room temperature, molybdenum is better in shape and easy to machine, so it is relatively easy and cheap to make molybdenum crucible. However, because the chemical properties of molybdenum material are more active than tungsten, especially in high temperature environment, it is easy to be attacked by metal solution and crack or hole, which leads to leakage of metal liquid, which makes the service life of crucible very short.

So, is there a way to integrate cost and performance? Yes, CVD is the use of chemical vapor deposition of molybdenum crucible plus tungsten coating, the process is as follows:

1.A crucible is processed into the required geometry and size according to the requirements of pure tungsten or pure molybdenum or molybdenum alloy.

2.Use the sandpaper to polish the inside and outside surfaces of the crucible, or use the sandblasting process to remove the surface oxide layer, then do ultrasonic caustic washing, ultrasonic acetone cleaning and oil removal, and then use ultrapure water to clean and blow dry the pure alcohol.

3.Using WF6 gas as raw material, reducing gas to H₂, in the substrate temperature condition of 350-600 DEG C, the crucible surface by chemical vapor deposition, the molar ratio of H₂ and WF₆ in 1:2-3.5, the deposition rate of chemical vapor deposition 0.2-0.6mm/h; tungsten coating thickness is 0.01-3mm, the crucible parts coated with CVD-W coating.

4.After the reaction is completed, close the WF6, stop heating, continue to pass the hydrogen to the furnace temperature below 100 degrees, then change the nitrogen to cool at room temperature, then remove the furnace and remove the sample, that is, the tungsten crucible parts which are coated with tungsten coating inside and outside the surface.

5.The crucible components coated with pure tungsten coating were put into a vacuum annealing furnace, evacuated to 1 × 10-3Pa below 50-500 ℃ / h slowly warmed to 600-1800 ℃, holding 0.5-5h, which means that tungsten crucible products coated with pure tungsten coating were obtained.

As a result, the pure tungsten coated molybdenum or molybdenum alloy material, can effectively solve the difficult process of pure tungsten crucible, defects of pure molybdenum crucible performance is not stable, effectively integrated cost and performance.

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