Study On Crystallization Behavior Of Iron Ore Phase In Steel Slag-based Silicate Glass

The rapid development of China's iron and steel industry has caused the emission of steel slag to remain high,and the comprehensive utilization rate of steel slag in my country is less than 30%.The conversion into glass-ceramics provides an important way for low-iron content steel slag and high value-added applications.However,the preparation of glass-ceramics from steel slag with high iron content and related research still need to be improved.The thesis focuses on the incomplete research on the crystallization behavior of two iron-bearing phases(diopside ferrian and magnetite)in steel slag-based glass-ceramics and their effects on the microstructure and properties of the materials.Firstly,two kinds of glass ceramics with diopside ferrian and magnetite as main crystalline phases were prepared by traditional melting process with converter slag from an iron and steel plant in Baotou.Then,the influence of Fe₂O₃content,Fe²⁺/Fe³⁺ratio and heat treatment system on the microstructure and performance of the prepared material was studied by Fourier transform infrared spectroscopy,X-ray diffraction spectroscopy,scanning electron microscopy,energy dispersive spectroscopy and Vickers hardness tester,and the best components and preparation process were optimized respectively.The results can be used for reference in the preparation of glass ceramics from silicate based solid waste with similar composition.The results show that:(1)In the diopside ferrian phase steel slag silicate glass,the increase of Fe₂O₃content makes the tendency of spontaneous crystallization of the glass melt enhanced and promotes the formation of magnetite nuclei,and the main crystalline phase of diopside ferrian grows on the surface of magnetite nuclei.at 25 wt%of Fe₂O₃content,the basic glass crystallizes during the formation process,and magnetite exists as a secondary crystalline phase,which hinders the precipitation of diopside.The increase of Fe²⁺/Fe³⁺does not change the main crystalline phase of the glass-ceramics,but is not conducive to the control of heat treatment temperature.The obtained diopside ferrian slag silicate glasses are soft magnetic materials,with Fe₂O₃content of 15 wt%and Fe²⁺/Fe³⁺of 0.5 for the best performance of glass-ceramics,hardness of 10.98 Gpa,density of 3.08 g/cm³,saturation magnetization strength of 2.48 emu/g and coercivity of499.09 Oe.The two-step heat treatment was superior to the one-step heat treatment,and the glass-ceramics samples treated with heat treatment regimes of 720?×120 min nucleation and 850?×120 min crystallization showed the best performance with a hardness of 10.54 Gpa and a density of 3.00 g/cm³.(2)In magnetite slag silicate glass,magnetite crystals are precipitated during the cooling of the melt,and both magnetite content and crystal size increase with increasing Fe₂O₃content,with the highest magnetite content at 44 wt%Fe₂O₃and high density and hardness values of 3.99 g/cm³and 10.73 Gpa,respectively.The magnetite content increases with the increase of Fe²⁺/Fe³⁺and then decreases with the increase of Fe²⁺/Fe³⁺,and the maximum magnetite content is at 0.5 Fe²⁺/Fe³⁺,with relatively high density and hardness values of 3.56 g/cm³and 9.64 Gpa,respectively.The magnetite crystals are distributed at the grain boundaries and in the iron-rich strips with a jagged stripe distribution.The magnetite content decreased after heat treatment,and the main crystalline phase changed to Fe Al₂O₄.The high temperature heat treatment promoted the transformation of magnetite crystals into Fe Al₂O₄,and the increase of Fe²⁺content also promoted the production of Fe Al₂O₄.The hardness values of the samples showed similar trends to those of the magnetite content,and the hardness value of M44 after850?×2 h heat treatment is the largest,which is 11.13 GPa.