UMG-Si Production

About 10 kWhr/kg, and 10 kg/hr at 100kW process scale. [1]. Heated by induction, with graphite crucible as susceptor (starts the melt)

Melt

Process Step	Description	Typical Temp (°C)	Energy (kWh/kg Si)	Notes (100 kW scale effects)
Feedstock Selection & Blending	Crushing, sorting, magnetic separation, blending of MG-Si	Ambient	0.05–0.15	Mostly mechanical energy; minor relative contribution
Primary Melting & Slag Refining	Melt MG-Si (~1414°C), add CaO/SiO2 slag, impurity oxidation & partitioning	1450–1550	3.5–6.0	Dominant energy load; small furnaces have high radiant/convective losses
Gas Refining / Vacuum Refining	Removal of B, P via O2, H2O, H2, or vacuum evaporation	1500–1600	1.5–3.0	Inefficient gas utilization at small scale; vacuum pumps add parasitic load
Directional Solidification	Controlled solidification to segregate impurities (top cut removal)	1400 → 1200	2.0–4.0	Long cycle times → major heat loss; poor insulation penalizes small systems
Crushing, Classification, QC	Break ingot, remove impurity-rich zones, size grading, analysis	Ambient	0.2–0.5	Includes mechanical comminution and some analytical overhead
Optional Repeat Refining Passes	Re-melt and re-solidify for higher purity	1450–1550	2.0–5.0	Highly variable; depends on target purity (solar vs near-electronic grade)
Total (single pass, no repeats)	—	—	7.25–13.65	Typical practical range for small-scale UMG-Si
Total (with 1 repeat pass)	—	—	10–18+	Required for higher purity (approaching SoG-Si)

Melt + Vacuum

Subsystem	Description	Low-Cost Build ($)	Practical Build ($)	High-End Build ($)	Notes
Vacuum Chamber & Lid	Stainless steel chamber, flanges, seals (Viton/metal), viewport, structural frame	8,000–15,000	15,000–30,000	30,000–60,000	Must handle radiant heat from ~1500°C melt; water-cooled walls recommended
Feedthroughs & Ports	Electrical (coil), thermocouple, pressure gauge ports, gas inlet, vacuum port	1,500–3,000	3,000–8,000	8,000–15,000	Includes ceramic/metal vacuum feedthroughs and high-temp insulation interfaces
Roughing Pump	Rotary vane or dry scroll pump for initial pumpdown (atm → ~1e-2 bar)	2,000–4,000	4,000–8,000	8,000–15,000	Oil pumps cheaper but require filtration; dry pumps cleaner but more expensive
Roots Booster Pump	Increases pumping speed in mid-vacuum range	5,000–8,000	8,000–15,000	15,000–25,000	Critical for reducing cycle time at batch scale
High Vacuum Pump (Diffusion)	Achieves ~1e-3–1e-5 mbar for impurity evaporation	6,000–10,000	10,000–20,000	20,000–40,000	Lowest cost option; requires cooling and oil management
OR High Vacuum Pump (Turbo)	Cleaner alternative to diffusion pump	10,000–15,000	15,000–30,000	30,000–60,000	Preferred for contamination-sensitive silicon processing
Cold Trap / Baffles	Condenses SiO, P, and other vapors before pump	2,000–5,000	5,000–10,000	10,000–20,000	Prevents pump contamination; essential for longevity
Vacuum Gauges & Instrumentation	Pirani + Penning/cold cathode gauges, controllers	1,500–3,000	3,000–8,000	8,000–15,000	Dual-range measurement required for process control
Valves & Plumbing	Gate valves, foreline valves, bellows, piping	2,000–5,000	5,000–10,000	10,000–20,000	Must be vacuum-rated; include isolation and safety interlocks
Cooling System Upgrade	Water cooling for chamber, pumps, baffles	3,000–7,000	7,000–15,000	15,000–30,000	Often underestimated; diffusion pumps especially require stable cooling
Controls & Integration	PLC, interlocks, sequencing (pumpdown → heat → refine → vent)	2,000–5,000	5,000–15,000	15,000–40,000	Prevents operator error and protects pumps/furnace
Total (Diffusion Pump System)	—	25,000–45,000	45,000–90,000	80,000–150,000	Most cost-effective configuration
Total (Turbo Pump System)	—	30,000–55,000	60,000–120,000	100,000–200,000	Cleaner operation, higher capital cost