Sintering molding is a common method for producing molybdenum crucibles, which is suitable for mass production and medium and low precision requirements.
step:
Raw material preparation
Choose high-purity molybdenum powder: Use molybdenum powder with a purity of ≥99.95%, the particle size is usually 1-10 microns, and ensure low impurities (carbon, oxygen, iron, etc.).
Powder processing: Screen the molybdenum powder to ensure uniform particle size, and add a small amount of binder (such as polyvinyl alcohol) if necessary to enhance the green strength.
Quality control: Testing of the chemical composition and physical properties of powders (e.g. flowability, apparent density).
Pressing
Mould design: Make graphite or metal mould according to the shape and size of the crucible.
Cold pressing: Molybdenum powder is loaded into the mold and pressed into a crucible green body under a hydraulic press at a pressure of 100-300 MPa.
Optional Isostatic Pressing: Cold Isostatic Pressing (CIP) equipment is used to apply uniform pressure to improve green body density and uniformity.
Pre-sintering
Sintering at 800-1200°C in a vacuum or hydrogen atmosphere furnace removes binders and moisture and enhances green body strength.
Control the heating rate (~5-10°C/min) to avoid cracking of the green body.
High temperature sintering
Sintering is carried out in a high temperature vacuum furnace or hydrogen atmosphere furnace at 1800-2200°C for 2-6 hours to combine the molybdenum powder particles and the crucible density reaches 90-95% of the theoretical density (~10.2 g/cm³).
Atmosphere control: Ensure there is no oxygen (vacuum degree <10 ⁻ ³ Pa or high-purity hydrogen) to prevent oxidation.
Cooling: Cool slowly (~5-10°C/min) to avoid thermal stress leading to cracking.
finishing
Machining: Remove surface defects and adjust crucible size and wall thickness by turning, milling or grinding.
Surface treatment: Polish the inner surface of the crucible to improve the finish and reduce material adhesion; or apply an anti-oxidation coating (such as alumina, silicide).
Cleaning: Use acid cleaning (dilute hydrochloric acid) or ultrasonic cleaning to remove surface impurities and ensure high purity.
Quality Inspection
Dimensional inspection: Measure the inner and outer diameters, wall thickness and height of the crucible to ensure it meets the design specifications.
Performance tests: density (>9.5 g/cm³), microstructure (grain size), chemical composition (impurity content).
Defect detection: Use ultrasound or X-rays to detect internal cracks, pores and other defects.
High temperature test (optional): simulates the use environment to test temperature resistance and chemical stability.
Packaging and storage
Protect the crucible from air and moisture by using anti-oxidation packaging (e.g. vacuum sealing or inert gas filling).
Store in a dry, non-corrosive gas environment.
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