Analysis Of The Microstructure And Viscosity Characteristics Of Red Mud-based Glass-ceramic

Red mud is a kind of harmful solid waste produced in the process of industrial production of alumina,its large-scale discharge and accumulation not only consumes a lot of land resources,but also seriously destroys the local ecological balance.Using red mud composite material to prepare glass-ceramics can not only solve the pollution problem caused by red mud,but also produce economic benefits and realize the transformation of waste into treasure.Because the preparation of glass-ceramics is usually carried out at high temperature,it is still insufficient to study the molten body and properties of glass with existing experimental instruments and methods,and molecular dynamics is a research method that is not limited by high temperature conditions,and can effectively analyze the microstructure and properties of glass at high temperature melting.In addition,the viscosity of glass-ceramics not only affects the melting,curing,heat treatment mechanism,post-processing and other processes of glass,but also affects the corrosion resistance,mechanical strength and other macro properties of glass-ceramics.For glass-ceramics,the viscosity of the system is related to the bonding energy between particles,tetrahedral types,content and coordination number in the network structure.In this thesis,molecular dynamics simulation was used to establish the microstructure and viscosity of red slime based glass-ceramics at 1800K,and the effects of different contents of steel slag,fly ash and gold tailings on the microstructure and system viscosity of red slime based glass-ceramics were analyzed.The microstructure of red mud-steel slag glass-ceramics was studied by molecular dynamics method.It was found that Si-O bond length and O-Si-O bond Angle had the smallest distribution,Al-O bond length and O-Al-O bond Angle had the second distribution,and Fe-O bond length and O-Fe-O bond Angle had the widest distribution in red mud-steel slag glass-ceramics.Si-O has a small number of five-coordination numbers.Fe-O and Al-O exist as four-coordination,five-coordination and six-coordination numbers.The mean azimuth shift of Na⁺is the largest,followed by Ca²⁺and O^2-,while the mean azimuth shift of Fe³⁺,Al³⁺and Si⁴⁺is small.The stability of the structures containing Si-O bonds in the microstructure is higher than that of the structures containing Fe-O and Al-O bonds.With the increase of steel slag content,the structure of[Si O₄]changes little,and the structure of[Al O₄]and[Fe O₄]changes greatly.The five and six coordination of Al-O,Si-O and Fe-O all decrease,the most stable four-coordination all increase,and the number of Si-O-Si bridged oxygen and[Si O₄]tetrahedrons keeps increasing.The number of Al-O-Al,Al-O-Fe,Fe-O-Fe,Al-O-Si and Si-O-Fe bridge oxygen decreased,the number of tetrahedrons[Fe O₄]and[Al O₄]decreased,and the total number of tetrahedrons in the system decreased,but the increase of the number of tetrahedrons[Si O₄]increased the binding force of the network structure and made the structure more stable.The superposition of these two factors leads to the viscosity of red mud-steel slag glass-ceramics decreasing first and then increasing.When the content of steel slag is 30%,the viscosity of the system is the smallest.The microstructure analysis of different components of red mud-fly ash glass-ceramics shows that the distribution range of Si-O bond length is small,mainly about 1.6（?）,the distribution range of Al-O bond length is large,and the distribution range of Fe-O bond length is widest,mainly between 1.7-2.3（?）.The O-Si-O bond Angle distribution is mainly near 108°,which belongs to the standard tetrahedral structure,and the O-Al-O bond Angle distribution range is large,mainly between 75 and 125°.Si-O exists in the form of four-coordination and five-coordination numbers.Al-O exists mainly in the form of four-coordination numbers,with a small number of five-coordination and six-coordination numbers.Fe-O has a large number of four,five and six-coordination numbers.The order of mean azimuth shift is K⁺>Na⁺>Ca²⁺>O^2->Al³⁺>Fe³⁺>Si⁴⁺.With the increase of fly ash,Si-O bond length has little change,while Al-O bond length and Fe-O bond length are more concentrated.The O-Si-O bond Angle hardly changed,the peak shape of O-Al-O bond Angle changed from sharp to gentle,and the O-Fe-O bond Angle changed from single peak to double peak.As the number of Al-O-Fe and Fe-O-Fe bridge oxygen decreases,the number of Al-O-Si and Si-O-Si increases,the number of tetrahedrons[Si O₄]and[Al O₄]increases,the number of tetrahedrons[Fe O₄]decreases,the mean azimuth shift of Si⁴⁺,O^2-and K⁺decreases,and the viscosity of the system increases.The analysis results show that adding fly ash to the system can make the network structure more stable and compact.In the microcrystalline glass-system of red mud and gold tailings,The number of five-coordination numbers of Si-O accounts for less than 2%of the total,and Al-O and Fe-O coexist in the form of four-coordination,five-coordination and six-coordination numbers.However,Al-O six-coordination numbers disappear when the content of gold tailings reaches40%.In the radial distribution function distribution diagram,the order of the first peak from small to large is Si-O,Al-O,Fe-O,Na-O,Ca-O and K-O,and the peak shape of the first peak is gradually gentle,so that the stability of Si-O structure is greater than that of Al-O structure and Fe-O structure.With the increase of gold tailings content,the number of Al-O-Si and Si-O-Si has been increasing,the number of Si-O-Fe has first increased and then decreased,and the number of Al-O-Fe,Fe-O-Fe and Al-O-Al bridge oxygen has been decreasing.The tetrahedrons of[Si O₄]and[Al O₄]and[Fe O₄]in the glass-ceramics of red mud and gold tailings have been increasing,and the tetrahedrons of[Al O₄]and[Fe O₄]have been decreasing.The mean azimuth shift of Si⁴⁺,O^2-and K⁺all decreased,and the viscosity increased,and the rate of increase gradually accelerated.After adding the same content of steel slag,fly ash and gold tailings,the four-coordination coordination percentage of Al³⁺,Si⁴⁺and Fe³⁺in the microcrystalline glass of red mud and gold tailings is the highest,and the tetrahedron and micronetwork structure of[Si O₄],[Al O₄]and[Fe O4]in the system are also the most stable.However,when the content of gold tailings is too high,due to its excessive viscosity,it will cause difficulties in the molding and crystallization of glass-ceramics.Therefore,in the preparation of red mud-gold tailings glass-ceramics,attention should be paid to the content of gold tailings is not too much to ensure that the preparation process is feasible.