基于分子动力学的镁硅酸盐熔融特性机理研究

Melting Mechanism of Magnesium Silicate Based on Molecular Dynamics

在BMH势函数下采用分子动力学模拟计算研究了1600℃下MgO-SiO_(2)体系中Mg含量从34 mol%升高至62 mol%时体系微观结构的变化规律,得出了偏径向分布函数、平均键长、平均配位数、氧的分布及聚合度等结构特征,从微观结构的角度分析了宏观熔融特性变化的理论机理.研究结果表明:当Mg含量从34 mol%升高至62 mol%时,Mg-O的平均键长从1.97A增大至2.01A,平均配位数从4.19增至5.06,体系有序度降低.体系中桥氧键从68%左右降低至15%,非桥氧键从31%左右增加至64%,自由氧增加了约18%.Q^(4)从40%左右降低至2%,Q^(0)+Q^(1)从3%左右升高至57%,聚合度高的Q^(4)、Q^(3)分解为聚合度低的Q^(0)、Q^(1)、Q^(2),Si-O-Si存在比例降低、Mg-O-Mg升高,体系聚合度明显降低.与Mg含量在34-50 mol%范围相比,Mg含量在50-62 mol%范围内变化时配位数的变化更显著.

The molecular dynamics simulation method with BMH potential function was used to study the microstructure variation of MgO-SiO_(2) system with Mg content increasing from 34 mol%to 62 mol%at 1600℃.The structural characteristics,such as particle radical distribution function,average bond length,coordination number function,oxygen distribution and polymerization degree were obtained.And the theoretical mechanism of macroscopic melting characteristics variation was analyzed from the perspective of microstructure.The results showed that,as mole fraction of Mg increased from 34 mol%to 62 mol%,the mean bond length of Mg-O increased from 1.97A to 2.01A,the average coordination number raised from 4.19 to 5.06,the bridged oxygen bond decreased from about 68%to 15%,the non-bridged oxygen bond increased from about 31%to 64%,the free oxygen increased by 18%.Meanwhile,in the same range of Mg mole fraction,Q^(4) decreased from about 40%to 2%,Q^(0)+Q^(1) increased from about 3%to 57%.The reason of polymerization degree reducing can be summarized the Q^(4) and Q^(3) with high degree of polymerization decomposed to form Q^(0),Q^(1) and Q^(2) with low degree of polymerization,therefore,the results indicated that the ratio of Si-O-Si decreased while that of Mg-O-Mg increasing.Compared with the Mg mole fraction in range of 34-50 mol%,the effect of Mg mole fraction on average coordination number was more significant.