The surface oxidation and wettability of Mn and Si-alloyed steel after annealing at different conditions are studied with scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and a so-called de-wetting method. After exposure at 950 °C for 1 hour in an Ar + 5 vol pct H₂ gas atmosphere with dew points (DP) ranging from – 40 °C to 10 °C, oxides were observed along the grain boundaries or dispersed on the surface for the Fe–1.8 Mn steels while a continuous oxides layer was formed on Fe–1.9 Mn–0.94 Si steels (composition in weight fractions). The oxides formed at different DPs were predicted based on thermodynamic calculations. (Fe,Mn)O was formed on Fe–1.8 Mn steel at the whole range of DPs, while the oxide phase on Fe–1.9 Mn–0.94 Si steel depends on the DP. At low-DP SiO₂ were formed and with increasing the DP (Fe,Mn)SiO₃ or (Fe,Mn)SiO₃ + (Fe,Mn)₂SiO₄ were formed and finally (Fe,Mn)₂SiO₄ were formed. An increase of the fraction of Fe in the oxide with increasing DP for both steels was observed with XPS analysis. As a measure for the surface wettability, the contact angle of Pb droplets on the annealed steels surfaces was determined with SEM and image analysis software. Also, the contact angle of Pb on pure Fe and on the Mn and Si alloyed steels free of surface oxides was measured for comparison. The results show that the contact angle of Pb on the steel surfaces after annealing decreases with increasing DP. This improved wettability with increasing dew point is related to the Fe fraction of the oxides formed on the surface.

The increasing amount of silicon waste generated from the rapid developing photovoltaic industry calls for an economical silicon recycling process. The present work proposes a facile process with which silicon waste and ironmaking slag containing TiO₂ were used as raw materials to produce titanium silicides, a promising high added value material. The process was experimentally investigated in lab scale. The result shows that a high CaO/SiO₂ ratio in slag promotes the reaction. TiSi₂ and Ti₅Si₃ could be synthesized as principal products within 0.5 and 3 h with CaO/SiO₂ = 1.31 in mass, respectively. CaO-SiO₂ slag was produced as byproducts. Kinetic analysis indicates that silicon diffusion in slag is the rate-determining step of the reaction process. The reaction rate constant is around 1.0 × 10^-4 s, and the effective diffusion film thickness in slag side is around 10^-3 cm at the silicon-slag interface. Slag basicity is suggested to increase to 1.31 for a faster silicon diffusion and further promotion of the reaction rate.

A sustainable simultaneous synthesis method of TiB2-Ti5Si3 mixtures is developed as an alternative recovery route of silicon waste from the photovoltaics industry. TiO2-CaO-B2O3 ternary was reduced by molten silicon at 1500 °C, producing TiB2 within 3 h and Ti5Si3 within 10 h. The lab-scale experiments were designed to study the reaction kinetics of the reaction. SiO2 diffusion rate controlling kinetic model was derived to describe the reaction process. The reaction rate constant was recommended to be ∼5 × 10-4 s-1. B2O3 content in slag was suggested to have an insignificant effect on the reaction rate constant, whereas more titanium and boron could be reduced by silicon with higher B2O3 content in slag. Stability of the reaction interface was simulated using phase field model. A decreased interfacial tension in B2O3-containing system was indicated to be the reason for emulsification of phases.