Fundamental Research On The Structure And Viscosity Of Molten CaO-SiO₂-P₂O₅-FeO Slag

Viscosity is an important physical property of converter steel slag, which is of great significance to the oxidation metallurgical process in converter. In the present work, the microstructure and viscosity of quaternary molten Ca O-Si O2-P2O5-Fe O system which is an important component of the initial converter slag were calculated by means of molecular dynamics simulation(MD). The purpose of that is to explore the effect of basicity, Fe O and P2O5 on the microstructure and viscosity of the molten slag system. Additionally, Raman spectrometer and Infrared spectrometer were used to characterize the structure information of the molten slags. Besides, viscosities of different molten Ca O-Si O2-P2O5-Fe O slags were measured by a rotational viscometer at 1400℃. The effect of slag composition on viscosity were analyzed and the NPL model and Pal model was empirically modified based on the present experimental data. The relationship between microstructure structure and viscosity for molten Ca O-Si O2-P2O5-Fe O system was established by combining the calculated and experimental data.The bond lengths for atomic pair Ca-O, Si-O, P-O and Fe-O in molten Ca O-Si O2-P2O5-Fe O system are 2.30 ?, 1.61 ?, 1.53 ? and 2.05 ?, respectively. It was found that both Si and P are tetrahedral surrounded by four O atoms, however, both Ca and Fe are octahedral surrounded by six O atoms. The bond angle of O-Si-O in [Si O4] and O-P-O in [PO4] are 109.5° and 109°, respectively. With the increase of slag basicity and Fe O content, the proportion of Q0 in slag increased and proportion of Q2, Q3 and Q4 decreased gradually. This illustrates that the structure of molten slag becomes simpler. With the increase of P2O5 content, the proportion of Q0 and Q1 in slag decreased and proportion of Q2, Q3 and Q4 increased gradually. This reflects the structure of molten slag becomes more complicated. Correspondingly, the Raman spectrum and Infrared spectrum also show that the peaks center position of Qn shifted towards lower wavenumbers with the increasing of basicity and Fe O content, which means the structure of molten slag becomes simpler. Likewise, the peaks center position of Qn shifted towards higher wavenumbers with the increasing of P2O5 content, which means the structure of molten slag becomes more complicated.The sequence of the diffusion ability of different ions in molten Ca O-Si O2-P2O5-Fe O system is Ca>Fe>O>P>Si. The result of viscosity experiments showed that the viscosity of molten slag decreases with the increase of slag basicity and Fe O content. The viscosity of molten slag increases with the increase of P2O5 content. The viscosity values calculated by MD simulation are close to the experimental viscosity values. The NPL model and Pal model was empirically modified based on the experimental viscosity data, which can make viscosity prediction effectively for quaternary molten Ca O-Si O2-P2O5-Fe O system. There is an obvious linear function relationship between viscosity η calculated by modified NPL model and Pal model and the structure parameter Q(Si+P). The linear relationship can be expressed by η=0.09Q(Si+P)+0.13 and η=0.09Q(Si+P)+0.12, respectively. The slag viscosity decreases with the decreasing of polymerization degree of quaternary molten Ca O-Si O2-P2O5-Fe O slag system.