The 7N tellurium purification process combines zone refining and directional crystallization technologies. Key process details and parameters are outlined below:
1. Zone Refining Process
Equipment Design
Multi-layer annular zone melting boats: Diameter 300–500 mm, height 50–80 mm, made of high-purity quartz or graphite.
Heating system: Semi-circular resistive coils with temperature control accuracy of ±0.5°C and a maximum operating temperature of 850°C.
Key Parameters
Vacuum: ≤1×10⁻³ Pa throughout to prevent oxidation and contamination.
Zone travel speed: 2–5 mm/h (unidirectional rotation via drive shaft).
Temperature gradient: 725±5°C at the molten zone front, cooling to <500°C at the trailing edge.
Passes: 10–15 cycles; removal efficiency >99.9% for impurities with segregation coefficients <0.1 (e.g., Cu, Pb).
2. Directional Crystallization Process
Melt Preparation
Material: 5N tellurium purified via zone refining.
Melting conditions: Melted under inert Ar gas (≥99.999% purity) at 500–520°C using high-frequency induction heating.
Melt protection: High-purity graphite cover to suppress volatilization; molten pool depth maintained at 80–120 mm.
Crystallization Control
Growth rate: 1–3 mm/h with a vertical temperature gradient of 30–50°C/cm.
Cooling system: Water-cooled copper base for forced bottom cooling; radiative cooling at the top.
Impurity segregation: Fe, Ni, and other impurities are enriched at grain boundaries after 3–5 remelting cycles, reducing concentrations to ppb levels.
3. Quality Control Metrics
Parameter Standard Value Reference
Final purity ≥99.99999% (7N)
Total metallic impurities ≤0.1 ppm
Oxygen content ≤5 ppm
Crystal orientation deviation ≤2°
Resistivity (300 K) 0.1–0.3 Ω·cm
Process Advantages
Scalability: Multi-layer annular zone melting boats increase batch capacity by 3–5× compared to conventional designs.
Efficiency: Precise vacuum and thermal control enable high impurity removal rates.
Crystal quality: Ultra-slow growth rates (<3 mm/h) ensure low dislocation density and single-crystal integrity.
This refined 7N tellurium is critical for advanced applications, including infrared detectors, CdTe thin-film solar cells, and semiconductor substrates.
References:
denote experimental data from peer-reviewed studies on tellurium purification.
Post time: Mar-24-2025