Barium tungsten electrode (BaO-W electrode) is a key electrode material used in gas discharge lamps (such as high-pressure sodium lamps and metal halide lamps). Its production steps are as follows:
I. Raw Material Preparation
1. Tungsten Matrix:
Select high-purity (≥99.95%) tungsten rods or tungsten wires and process them into the required shape (such as tip, cylinder) through forging, drawing and other processes.
The surface needs to be polished or sandblasted to increase the specific surface area.
2. Barium Source:
Barium hydroxide (Ba(OH)?) or barium carbonate (BaCO?) is usually used as a precursor, which needs to be dried in advance (100-200℃) to remove crystal water.
II. Barium Introduction Process (Impregnation Method)
1. Solution Preparation:
Dissolve Ba(OH)? or BaCO? in deionized water to prepare a solution with a concentration of 5-15wt%.
A small amount of ammonia water can be added to adjust the pH value to 8-10 to promote the dissolution of Ba2?.
2. Immersion Treatment:
Immerse the pretreated tungsten substrate completely in the solution and keep it under vacuum or pressure for 1-6 hours to ensure that Ba2? fully penetrates into the pores of tungsten.
3. Drying and decomposition:
Dry after taking out (100-150℃), and then calcine at 400-600℃ to decompose Ba(OH)? into BaO.
III. Post-Treatment
1. Reduction Treatment:
Heat to 1200-1400℃ in a hydrogen atmosphere for 2-4 hours to remove the surface oxide layer and activate BaO.
2. Machining:
Finely process the electrode to ensure dimensional accuracy and surface roughness (Ra≤0.4μm).
3. Surface Modification:
Improve anti-welding performance through ion implantation or coating technology (such as TiN, ZrN).
IV. Quality Inspection
1. Composition Analysis:
Use XRF or EPMA (Electron Probe Microanalysis) to detect BaO content, requiring uniform distribution and total amount controlled at 5-15wt%.
2. Microstructure:
SEM observes the distribution of BaO in the tungsten matrix to avoid agglomeration or cracks.
3. Performance Test:
Thermionic Emission Current Density ≥ 5A/cm2 (1800K), anti-welding ability meets IEC standards.
