Molecular Dynamics Simulation Of The Microstructure Of Red Mud Glass-ceramics

As a green building material,red mud glass ceramics have excellent physical and chemical properties,which are widely used in construction,electric power,chemical industry,machinery,transportation fields.The preparation temperature of the glass ceramics is over 1500℃.It is difficult to study the high temperature melting system with the existing analytical instruments.Molecular dynamics is an effective method to study high temperature glass ceramics,which can simulate the material system under limit conditions.In this thesis,molecular dynamics simulation method was used to establish the microscopic model of high temperature melt of red mud microcrystalline system.The influence of Fe₂O₃,SiO₂ and Al₂O₃ content on the microstructure of red mud microcrystalline system was calculated and analyzed.Effects of different Fe₂O₃ contents on microstructure of red mud glass-ceramics was calculated.It was found that the Fe₂O₃ content in the system had little effect on Si-O bond length.With the increasing of Fe₂O₃,Al-O bond lengths and peak width is more widely distributed,and there was a tendency to increase the distribution of bond angles between O-Si-O and O-Al-types.However,the three types of bridge oxygen including Al-O-Al,Al-O-Si and Si-O-Si decreased,another three types of bridge oxygen including Si-O-Fe,Fe-O-Fe and Al-O-Fe increased,which indicating that more Fe³⁺are involved in the construction of the network.When Fe₂O₃content is 30%,the amount of bridge oxygen in red mud glass-ceramics is the largest,the network structure is the densest,and the network is perfect.When the Fe³⁺content is more than30%,the[FeO₄]content of tetrahedron is not increasing,because the system had limited capacity for Fe³⁺.Therefore appropriate amount of Fe³⁺can promote crystallization of glass-ceramics.The influence of SiO₂ content on the microstructure of red mud microcrystal system was calculated.It was found that when the SiO₂ content is 50%,Al-O-Si and Fe-O-Si type bridging oxygen had the most amount,and the network had good integrity and compactness.The order of average azimuthal shift of each particle is Na⁺>Ca²⁺>Fe³⁺>Al³⁺>O^2->Si⁴⁺.With the increase of SiO₂ content,the mean square displacement of Si⁴⁺first decreases and then increases.When the SiO₂ content accounts for 50%,the mean square displacement is the smallest.which indicates that more Si⁴⁺participate in the network construction.However,when excessive Si⁴⁺was added,the system is full,and the excess Si⁴⁺was squeezed out of the network,which makes mean square displacement rise.The first peak value of the radial distribution function of Si-O is 1.59（?）,the first peak of Al-O is 1.73（?）.According to the first peak value of each particle,the order of force between particles is Si-O>Al-O>Fe-O>Ca-O>Na-O.Among them,the binding force between Si and O particles is the largest,which can form a stable structure and is not easy to be destroyed.The radial distribution function curves between Fe particles and other particles show that the radial distribution function curves of Al-Fe and Si-Fe is very similar,which indicated that the distribution of Fe atoms is better in the network structure[AlO₄]and[SiO₄].The influence of Al₂O₃ content on the microstructure of red mud microcrystal system was calculated.the O-Si-O bond angle is about 109°,the O-Al-O bond angle is about 103°.With the increase of alumina content,the distribution range of O-Si-O and O-Al-O type bond angle become larger,the change of O-Si-O peak shape is smaller,and the change range of O-Al-O peak shape is larger.Mean square displacement of Al particles first decreases and then increases,When the content of Al₂O₃ is 25%,the mean square displacement of Al particles is the smallest,and the network formed by the combination of Al and O particles is relatively stable.The content of Al₂O₃ is more than 25%,and the excess Al particles no longer participate in the network construction.The radial distribution function shows that the sharpness of the first peak between Si-O,Al-O,Fe-O,Ca-O and Na-O decreases gradually,and the position of the first peak appears later,which indicates that the stability of the network structure formed by the combination of particles decreases gradually.With the increase of Al₂O₃ content,the quantity of[FeO₄]and[SiO₄]was decreasing,and the quantity of[AlO₄]was increasing.the amount of Al-O-Al,Al-O-Si and Al-O-Fe bridging oxygen increased,The increase of the number of Al-O-Al,Al-O-Fe and Al-O-Si bridging oxygen in the red mud microcrystalline system also reflects that more and more Al particles participate in the network construction as network formers.