Effects Of High Magnetic Field On The Microstructures And Optical Properties Of Titania-Bearing Blast Furnace Slag And Its Constituents

The huge accumulation of Titania-Bearing Blast Furnace Slag（TBBFS）in Panzhihua has caused great waste of resources and environmental pollution.Although TBBFS has been studied for more than half a century,and some scientific achievements have been made,it is still difficult to achieve large-scale comprehensive utilization.According to the photocatalytic properties of TiO₂,it is found that the TBBFS has the photocatalytic effect of organic compounds decomposition and sterilization,which opens up a new path for comprehensive utilization.When a strong magnetic field is applied on the material directly,a great deal of new phenomena and new discoveries are produced,it is one of the hot spots in the fields of material research and preparation,but most of these researches are focused on metal materials.In this work,TBBFS and its main components,most of which are weak magnetic mineral,are treated by the magnetic field under high temperature,and the effects of strong magnetic field on the photocatalytic effect,microstructure,lattice constant,light absorption and energy absorption are discussed.It is a beneficial exploration for magnetic and comprehensive ultilization of TBBFS.The main research and conclusions of this paper can be divided into the following aspects:（1）The Ti element in TBBFS mainly exists in CaTiO₃.The treatment of magnetic field with different intensity at 800℃ has certain influence on the catalytic activity of TBBFS,in which the activity of TBBFS sample treated by 6T magnetic field is the best,and the higher magnetic field will decrease the photocatalytic activity of the TBBFS samples;Detection analysis on TBBFS treated by magnetic field shows that with the growth of magnetic field intensity,the peaks of XRD shift to the right,which means the corresponding interplanar spacing decreases,and the individual XRD peak height changes,indicating that the magnetic field has promoted some selective surface ordering;SEM shows that the magnetic field can aggravate the surface melting state of the TBBFS sample;UV-vis shows that the magnetic treatment reduces the light absorption in the short wave region and improves the absorption of light above 450nm;For the changes of Raman peak intensity,peak position of TBBFS after magnetic treatment,the main reason is the transformation of microstructure and chemical bond twist or tensile of perovskite CaTiO₃ and CaMg（SiO₃）₂;For the low precision,it is only found the 950cm-1 peak left shift with the magnetic field increasing in infrared spectroscopy.（2）Nano scale anatase TiO₂ and its doped samples are prepared by sol-gel method.The sample prepared by calcination at 400℃ has the best photocatalytic activity.When the concentration of Fe3+ ions is 10-4,the catalytic effect is the best.The magnetic field has a significant effect on the photocatalytic performance.At 400℃,after treatment under 3T for 0.5h,the catalytic performance of doped Fe3+ anatase samples can be improved significantly;At 1000℃,with the increasing of magnetic field strength,the lattice constant and interplanar spacing of rutile TiO₂ are smaller,and the changes of the magnetic field on the lattice constant is nonlinear,the significant changed occurred when the magnetic field strength is 6T,furthermore,only heat treatment again at 1000℃ without magnetic field can basically eliminate the strong magnetic field effect on lattice parameters;For all of Raman spectrum of the magnetic treatment rutile,there is little move in peak location but changes significantly in the peak intensity.The Raman peaks intensity of rutile treated with magnetic field of 6T are noticeably larger than that of 3T samples,but for the samples treated under more than 6T,there is no obvious change in Raman peaks;in addition,light absorption performance of rutile treated by 6T magnetic field is the worst.Photocatalysis performance of rutile is very poor,so catalytic experiments are not done.（3）Solid phase synthesis is employed to prepare CaTiO₃ through calcining the mixture of CaCO₃,TiO₂ powder at 1500℃ for 2h,and the doped cationic samples of CaTiO₃ are get by calcination of nitrate impregnated CaTiO₃ powders at 800℃.The light catalytic performance of CaTiO₃ doped with the same concentration of Fe3+,Mg2+,Mn2+（mol:mol=0.005）is reduced,Mn2+ samples are reduced especially seriously.The bandgap of CaTiO₃ is 3.50eV,after the introduction of doping impurity levels in the band,the light absorption performance is improved significantly.The larger the concentration is,the more obvious the red shift of absorption band edge is and the stronger the light absorption capacity is,the reason may be the doping cations contribute to photoinduced electron-hole pair on the composite,which lead to the reduction of the catalytic effect.Under the same doping concentration,the light absorbing properties of the treated samples are better than those of the non-magnetic ones.After the magnetic field treatment,XRD peaks of CaTiO₃ crystal powder left shift,the unit ell becomes large.UV-vis analysis shows that bandgap is narrowed through the magnetic treatment,the absorption band edge of all samples redshift,which improved the absorption of visible light.The band gap of all CaTiO₃ and related samples is wide,and the ability to degrade Methylene blue（MB）solution is very weak.（4）The preparation method of CaMg（SiO₃）₂ is similar to CaTiO₃.Castep simulation results show that the band gap of CaMg（SiO₃）₂ is about 5eV,and Mn2+,Fe3+ ions substitution of Mg2+ in doped samples,which means the impurity level is introduced and the absorption of light is promoted,simultaneously the experiments show that with the increase of doping concentration,light absorption performance is elevated.But under the condition of keeping the concentration unchanged,the light absorption performance does not increase with the increase of the magnetic field.The XRD peak of（311）crystal surface of CaMg（SiO₃）₂ is higher by the stronger of the magnetic field,which indicates that the magnetic treatment promotes the ordering of the crystalline surface.Raman spectra shows that the 671 cm-1 peaks of all samples are stronger than those of 1015cm-1 peaks before magnetic treatment,and the intensity of these two peaks is reversed in all samples after magnetic treatment;In addition,the magnetic treatment can also make the peaks of 330cm-1 and 395cm-1 more obvious,which indicates that the magnetic field can change the relative position of the ions and the distance between the planes,and increases the bonding polarizability of the corresponding chemical bonds.