In the production of molybdenum crucible, oxygen content is a key factor affecting material properties (such as ductility and corrosion resistance). Controlling oxygen content requires starting from multiple links such as raw materials, processes, and equipment. The following are specific control methods:
- Raw material control
Select high purity molybdenum powder
Standard: Oxygen content ≤ 0.01wt % (such as Mo-1 grade molybdenum powder).
Measures: Prioritize the purchase of molybdenum powder produced by gas atomization or plasma rotating electrode method, which has lower oxygen content and uniform particle size.
Avoid raw material contamination
Storage: Molybdenum powder needs to be stored in a vacuum or inert gas (such as argon) environment.
Mixing: Use vacuum mixing equipment to prevent contact with air.
- Process Optimization
Sintering process
Vacuum sintering: Sintering at 1800-2200℃ and vacuum degree ≤1×10 ⁻³ Pa can effectively remove oxygen.
Hydrogen protection sintering: Sintering in a hydrogen atmosphere, hydrogen reacts with oxygen to generate water vapor and is discharged, and the oxygen content can be reduced to ≤ 0.005wt %.
Isostatic Pressing
Cold Isostatic Pressing (CIP): Pressurization in an inert gas environment to avoid oxidation.
Hot Isostatic Pressing (HIP): High temperature and high-pressure act simultaneously to further densify and reduce oxygen content.
Machining
Cutting fluid selection: Use cutting fluid containing extreme pressure additives to reduce oxidation caused by high temperature during processing.
Tool material: Use carbide or diamond tools to reduce friction heat.
- Equipment and Operation Control
Sintering equipment
Vacuum furnace: Check the sealing of the furnace body regularly to ensure that the vacuum degree meets the standard.
Hydrogen furnace: Control the hydrogen flow rate (e.g. 5-10 L/min) to ensure a reducing atmosphere.
Operation Specifications
Loading: Load and seal quickly to reduce contact time with air.
Heating rate: Control the heating rate (e.g. ≤5°C/min) to avoid local overheating and oxidation.
- Detection and Monitoring
Oxygen content detection
Method: The inert gas melting infrared absorption method is used, and the detection accuracy can reach 0.0001wt %.
Frequency: Each batch of raw materials and finished products needs to be tested.
Process Monitoring
Install oxygen sensors to monitor the oxygen content in the furnace in real time and adjust process parameters in time.
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