Removal behavior and mechanism of impurity Ti during secondary refining of industrial silicon using O2–H2O(g) mixed gas

The efficient removal of Ti from industrial silicon is a key challenge in producing high-purity silicon for photovoltaics and silicones. Conventional oxygen blowing refining is ineffective because Ti exhibits low activity and high stability in molten silicon. This work report that secondary refining using an O 2 –H 2 O(g) mixed gas achieves a Ti removal rate of 42.72% at 1550 °C, meeting the quality requirements for downstream applications. Electron probe microanalysis reveals that Ti, initially embedded in Al-Fe intermetallic phases, is transformed into a concentrated (Ti,Fe)Si 2 phase. Kinetic analysis shows that below 1500 °C the rate-controlling step is an interfacial chemical reaction (apparent activation energy ≈ 1220 kJ/mol), whereas above 1500 °C it shifts to liquid-phase mass transfer (activation energy ≈ 77.1 kJ/mol). Ab initio molecular dynamics (AIMD) simulations demonstrate that surface-active hydroxyl groups (OH) generated from O 2 –H 2 O(g) dissociation chemically adsorb onto Ti atoms, cleave Si–Ti bonds, and induce the formation of volatile Ti(OH) 4 clusters. The diffusion coefficient of active Ti is approximately six times that of bulk Ti, confirming a chemically enhanced migration pathway. This work overturns the conventional belief that Ti cannot be removed by gas blowing refining and provides a theoretical basis for developing an efficient, low-cost Ti removal process.