Effect Of La₂O₃ On Viscosity Of SiO₂-CaO-Al₂O₃-MgO Melt

During the utilization process of the Bayan Obo Mine,a large number of rare earth tailings are accumulated on the tailing dam.It caused not only waste of resources but also great environmental pollution.The rare-earth glass-ceramics with high added value is one of the ways to achieve comprehensive utilization of tailings.In particular,rare earths have played an important role in improving the structure and performance of glass-ceramics.In the production process of rare earth tailings glass-ceramics,viscosity is an important physical property which closely related to the processes of melting,clarification and forming of glass-ceramics.The effect of rare earth on the viscosity of high temperature melt has important significance and reference value for the production of glass-ceramics.This study is based on the basic chemical composition of rare-earth tailings glass-ceramics,with SiO₂-CaO-Al₂O₃-MgO-based melts as the research object.Focusing on the key issue of the influence of rare earths on the melt viscosity of glass-ceramics,the effects of La₂O₃ content,CaO/SiO₂ ratio,and Al₂O₃ content on the melt viscosity and structure of SiO₂-CaO-Al₂O₃-MgO were investigated.A model suitable for the research system is selected in the model,and the model is modified by the viscosity data to realize the prediction of the melt viscosity.Firstly,the melt viscosity of the pre-melted was measured by the cylinder rotation method.The results show that the melt viscosity decreases with increasing La₂O₃ content.Melt viscosity decreases with increasing CaO/SiO₂ ratio or decreasing Al₂O₃ content.The activation energy was calculated from the viscosity data.The activation energy decreased with the increase of the content of La₂O₃,it decreased with the increase of the CaO/SiO₂ratio,it increased with the increase of the content of Al₂O₃.The viscosity values of Riboud model,Urbain model and NPL model were calculated.The viscosity value calculated by Urbain model was the closest to the experimental value by those models.The experimental data was used to modify the parameters of the Urbain model.The average error of the modified Urbain model was 9.55%.The modified Urbain model can predict the melt viscosity well in this study.Finally,the melt structure of the quenched glass sample was analyzed by Raman spectroscopy.The relative percentage content of the Qⁿ?n=0,1,2,3?representing the silicon-oxygen tetrahedral structure was obtained by fitting the peaks of the Raman spectrum.The results showed that the relative percentage of Q⁰ was changed little and the relative percentage of Q¹ and Q² increased,meanwhile,the relative percentage of Q³ decreased with the increase of the content of La₂O₃.All the results showed the degree of melt polymerization gradually decreased.While the relative percentages of Q⁰,Q¹,and Q² increased,and the relative percentages of Q³ decreased with the CaO/SiO₂ ratio increased showing the degree of melt polymerization gradually decreased.,the relative percentage of Q⁰ decreases first and then increases,the relative percentage of Q¹ increases,the relative percentage of Q²decreases,the relative percentage of Q³ increases with the content of Al₂O₃ increased showing the degree of melt polymerization gradually increased.In summary,the addition of La₂O₃ can effectively reduce the degree of melt polymerization and play a role in destroying the silicon-oxygen tetrahedral network structure,thereby reducing the melt viscosity.