Study On The Influence Of La₂O₃ On The Structure Of High Temperature Melt Of SiO₂-CaO-Al₂O₃-MgO（-CaF₂）

Industrial wastes such as Bayan Obo tailings and fly ash can be used as raw materials to produce rare earth glass-ceramic products with excellent properties,which can not only alleviate the harm caused by tailings accumulation,but also realize the comprehensive utilization of tailings and create economic value.In the melt casting process of rare earth glass-ceramics,the physical properties of the melt can affect the melting and molding process of glass-ceramics and play a very important role in the performance regulation of products,while the physical properties of the melt are mainly affected by the structure.In this thesis,the chemical composition of Bayan Obo rare earth tailings glass-ceramics is taken as the basis,under the conditions of La₂O₃=0～3mol%,Ca O/Si O₂=0.25,0.4,0.55 or Al₂O₃=3,5,7mol%,Si O₂-Ca O-Al₂O₃-Mg O is selected as the base system to study the effect of La₂O₃on the high-temperature melt structure.On this basis,the effect of temperature on the melt structure is also investigated.Raman and X-ray photoelectron spectroscopy（XPS）methods were used to study the melt structure of quenched samples at 1550℃.The results showed that the variation of La₂O₃content has a greater influence on the T-O-T（T=Ca or Al）structure in the low frequency band than that in the high frequency band of Raman spectrum.An increase in La₂O₃content leads to t-o-t depolymerization,and the lower the Ca O/Si O₂ratio or the higher the Al₂O₃content of the system,the more obvious the depolymerization.An increase in La₂O₃content also leads to a decrease in the relative percentage of BO bonds and an increase in the relative percentage of NBO bonds in the system;a decrease in the relative percentage of Si-O₂bonds and an increase in the relative percentage of Si-O bonds;a decrease in the relative percentage content of[Al O₆]structural units and an increase in the relative percentage content of[Al O₄]structural units.The lower the Ca O/Si O₂ratio or the higher the Al₂O₃content of the system,the greater the variation.Further study of the change law of melt structure under the condition of adding Ca F₂was by Raman and XPS methods.It was found that f mainly existed in this system in the form of F^-and Ca-F bond,and trace amount of F existed in the form of Al-F bond.An increase in La₂O₃content can promote the fracture of Ca-F bond,so that Ca-F bond decreases and F^-and Al-F bond increase.When the network structure of La ion is depolymerized,the ion clusters are more dispersed and the connectivity of melt network structure is reduced under the dilution of F^-;and the formation of Al-F bond leads to the inability of aluminum oxyfluoride tetrahedron to enter the network structure,and the degree of polymerization of melt structure is further reduced.Since Ca F₂plays a certain dilution role in the melt,with the increase of Ca F₂content,Raman spectrum peak shape changes less,and there is a certain depolymerization effect on T-O-T and[Si O₄]structures,and there is a dual role of F in the melt to promote the depolymerization and dilution of network structure.