Operation Manual

Bring the hot zone to 1600–1650 °C under a light argon blanket (50–150 mbar above ambient). Confirm thermal stability before feeding.

Enter the Fe stage with a low cathodic overpotential/current density. Monitor OES for iron emission lines as the metal accumulates in the sump. Tap or park iron once the sump reaches the planned mass.

Transition to the Si stage by stepping the potential upward 10–20 %. Watch silicon emission intensity and headspace oxygen signals. Keep the Fe sump slightly cooler to discourage alloying.

Manage bubble evolution and avoid vigorous stirring. If LIBS/OES indicates co-reduction or alloy formation, reduce potential, allow iron to settle, and resume once signals stabilize.

Ladle or tap molten silicon into a covered transfer crucible to minimize air exposure.

Move the crucible to the refining vessel, close the chamber, evacuate to ≤10 Pa, and ramp to 1600–1850 °C.

Hold for 30–90 min while monitoring the RGA. Falling phosphorous peaks indicate progress; a rise in SiO (m/z ~44) signals over-evaporation—tighten cold-trap cooling or adjust temperature accordingly.

Pour refined silicon into a Si₃N₄-coated quartz mold.

Directionally cool at 1–5 K min⁻¹ from bottom to top to segregate residual impurities toward the hot end.

Crop the tail section that concentrates impurities.

Optionally perform a mini float-zone pass on a small rod if semiconductor experiments are planned.