Simulation Of Melting Structure And Properties Of CaO-SiO₂-TiO₂ Slag

The appropriate fluoride?CaF₂?is usually added to the mold fluxes to adjust the macroscopic physical and chemical properties?such as viscosity,melting point and crystallization rate?and it is aimed to meet the requirements of continuous casting lubrication and heat transfer.In the process of continuous casting,fluoride can not only harm the environment and human health,but also pollute the cooling water and corrode the continuous casting equipment,and it can increase the cost of continuous casting process.Therefore,looking for the new materials to meet the demand for continuous casting has become the focus of continuous casting production.At present,CaO-SiO₂-Na2 O and CaO-SiO₂-TiO₂ fluorine-free flux slag has been researched and applied to continuous casting of some of steels.However,the application of CaO-SiO₂-TiO₂ fluorine-free flux slag caused a significant increase in the rate of sticky steel leakage after the continuous casting production.It is indicated that how to coordinate lubrication and heat transfer has become a problem on the CaO-SiO₂-TiO₂ fluorine-free flux slag.Because the macroscopic properties of matter are determined by their microstructure,Study on the effect of Ca F₂ and TiO₂ on the microstructure of the silicate system is very important for understanding and developing fluorine-free and low fluorine mold fluxes.In this paper,the effects of CaF₂ and basicity on the structure of CaO-SiO₂-Ca F₂ slag were studied by molecular dynamics simulation?MD?and spectroscopic experiments.Secondly,the effects of TiO₂ and basicity on the microstructure of silicate were studied.Finally,based on the simulation and experimental data,the relationship between component-structure-performance is established.The main contents of this paper are as follows:?1?The study of microstructure of CaO-SiO₂-Ca F₂ slag shows that the average bond lengths of Si-O,Ca-O,Si-F,Ca-F and O-O were 1.61,2.30-2.31,4.20-2.37,2.32-2.33 and 2.60-2.61? respectively.The average coordination numbers were 4.02-4.03,4.60-5.45,0.39-1.66,0.99-4.04 and 3.87-5.07,respectively.Both average bond lengths and average coordination numbers of different atom pairs are consisent with experimental results.It is found that CaF₂ is mainly used as a diluent in the microstructure of CaO-SiO₂-Ca F₂ slag,and a little part has the effect on reducing the slag polymerization degree.The results also show that CaF₂ is mainly presented in the form of diluent in the network structure by FT-IR and Raman spectra.While the increase of basicity decreases the degree of polymerization of microstructure.?2?The study of microstructure of CaO-SiO₂-TiO₂ slag shows that the average bond lengths of Si-O,Ca-O,Ti-O and O-O were 1.61,2.30-2.32,1.93-1.94 and 2.63-2.64?,respectively.The average coordination numbers were 4.02-4.06,5.93-6.33,5.61-5.78 and 7.68-8.03,respectively.Both average bond lengths and average coordination numbers of different atom pairs are consisent with experimental results.The results show that TiO₂ serves as a network former and enhances the connectivity of the network structure in the CaO-SiO₂-TiO₂ slag structure.The increase of basicity has the effect on simplifying the network structure.These results are consistent with the FT-IR and Raman spectroscopy.O-Si-O bond angle is distributed near 109 °,which is close to the standard tetrahedral network structure,the O-Ti-O bond angle is widely distributed,which is mainly related to the multi-coordination structure of Ti4+.?3?The viscosity of CaO-SiO₂-TiO₂ slag?1673K?was measured with the change of TiO₂ and basicity.Compared with the viscosity value obtained by MD simulation and Model calculation,with the increase of TiO₂ content,the viscosity of slag has a tendency of increasing,and with the increase of basicity,the viscosity of slag decreases continuously.The same trend also proves that the simulation can be used to predict the viscosity trend of melting slag.In addition,the relationship between microstructure and macroscopic properties of slag was established,and the linear relationship between the microstructure parameters and the viscosity was obtained.The viscosity value was increasing with the increase of the degree of polymerization.