Molecular Dynamics Simulation Of The Microstructure Of MgO-Al₂O₃-SiO₂-TiO₂ Glass-ceramics

The MgO-Al₂O₃-SiO₂-TiO₂（MAST）glass-ceramics is a new material with broad application prospects due to its excellent insulation,mechanical strength,thermal shock resistance,small dielectric constant and other properties.The preparation of glass-ceramics in this system is usually carried out at high temperature,but it is difficult to analyze the high-temperature melt with the existing experimental analysis means,so molecular dynamics simulation becomes an important research approach.In this paper,In this paper,molecular dynamics simulation software is used to establish the microstructure model of MgO-Al₂O₃-SiO₂-TiO₂ glass-ceramics,and appropriate relevant calculation parameters are determined,and the effect of TiO₂ and SiO₂ content on the high-temperature melt of MAST glass-ceramics is simulated and analyzed from various aspects.Based on the molecular dynamics calculation of MAST system glass-ceramics with different amounts of TiO₂,it is found that the addition of TiO₂ has little effect on the bonding between Si-O,including bond length and peak shape.The change of TiO₂content has a great impact on Al-O bond.With the increase of TiO₂ content,the length of Al-O bond is more widely distributed and the peak deformation becomes wider.The number of Si-O-Al is the largest among the MAST glass-ceramics high-temperature melts,accounting for almost half of the bridge oxygen number,followed by the number of Si-O-Si,then Al-O-Al.When the amount of TiO₂ added reached 5.2%,the number of Si-O-Al reached the maximum,accounting for 51%of the total bridge oxygen.The number of Si-O-Al began to decrease as the TiO₂ content continued to increase.With the increase of TiO₂ content,the total number of bridge oxygen firstly increases and then decreases.When the content of TiO₂ is 5.2%,the total number of bridge oxygen reaches the maximum,at which time the network structure of MAST system glass-ceramics is the most perfect.When the addition of TiO₂ increases,the number of Ti-O-Ti,Ti-O-Al and Ti-O-Si will increase accordingly,indicating that more Ti particles are involved in the construction of network structure.According to the radial distribution function,when the amount of TiO₂ added is 5.2%,the distribution among various particles is the most uniform,and the network structure is also the most uniform.Through comprehensive analysis,it is determined that when the addition amount of nucleating agent TiO₂ is about 5.2%,the system can obtain the most uniform network structure in the melting state.Moreover,when the amount of TiO₂ added reaches 5.2%,the amount of Si-O-Al accounting for the bridge oxygen reaches the maximum,51%.As the TiO₂ content continues to increase,the viscosity of the high-temperature melt increases,and the proportion of Si-O-Al in the bridge oxygen begins to decrease,then the MSD of Ti⁴⁺gradually decreases,and more Ti⁴⁺forms[TiO₄]are involved in the construction of the silicate network.It can be concluded from the radial distribution function that when the amount of TiO₂ added is 5.2%,the same particles have excellent dispersion and will not produce particle aggregation behavior.Through comprehensive analysis,it is determined that the densest network structure can be obtained in the melting state of the system when the addition amount of the nucleating agent TiO₂ is about 5.2%.Based on the molecular dynamics calculation of MAST system glass-ceramics by adding different amounts of SiO₂,it is found that the Si-O bond length is mainly distributed between 1.5-1.8?and the Al-O bond length is mainly distributed between1.6-2.0?in the high-temperature melt of this system.When the SiO₂ content changes of Si-O bond length,when the SiO₂ content increased,Al-O bond length distribution change is bigger,Al-O bond length distribution of peak shape becomes focus first and the distribution range is sharp decreases,and when the SiO₂ content reached 50%,Al-O bond length distribution in the sharpest and most on the left,then increases as the content of SiO₂ continued,Al-O bond length distribution of peak shape gradually begins to flatten out and the distribution range is big.Through radial distribution function analysis,it can be concluded that the binding ability between Si,Al,Ti,Mg particles and O particles in the system is getting lower and lower,and the stability of the cluster structure units formed between them gradually decreases.According to the distribution diagram of MSD of each particle,the order of MSD in the MAST system of microcrystalline glass high temperature system is Mg²⁺>Al³⁺>Ti⁴⁺>O^2->Si⁴⁺.When the addition of SiO₂ increased,the mean azimuth shift of Mg²⁺in the high-temperature melt gradually decreased,while the mean azimuth shift of Ti⁴⁺first increased and then decreased.The number of[SiO₄]increased with the increase of SiO₂addition,while the number of[AlO₄]and[TiO₄]both decreased.At the same time,the number of Si-O-Al began to gradually increase,when the content of SiO₂ was 57.1%,the number was the highest,and then the number began to decrease after increasing the content of SiO₂.With the increase of SiO₂,the number of Si-O-Si gradually increases,and the total amount of bridge oxygen gradually increases first and then gradually flattens out.When the content of SiO₂ is 57.1%,the total amount of bridge oxygen and the number of Si-O-Al are the most,and the structure of the silicate network obtained is the most perfect.