NaAlSi_3O_8熔体粒子扩散行为压力效应的分子动力学研究

Pressure dependence of self-diffusion in NaAlSi_3O_8 melt: A molecular dynamics study.

为了研究压力对钠长石成分熔体粒子微观扩散行为的影响,本文用分子动力学方法,探讨了2001.5K温度下,压力由50MPa上升到19862 MPa的过程中,熔体的微观结构、粒子自扩散系数随压力的变化规律。研究表明,在升压过程中,低次配位体^(|4|)Al和^(|4|)Si向5次和6次配位体转变,^(|5|)Al的含量在15 GPa达到极大值,而^(|5|)Si含量的极大值在20 GPa仍未出现。Na的自扩散系数随压力升高单调下降,Al、Si和O的自扩散系数随压力升高先增后减,在8～10GPa左右达到极大值,网架形成粒子自扩散系数的极大值与^(|4|)Al和^(|4|)Si含量的极大值对应的压力点不一致。所有粒子的自扩散系数与它们与0之间键的寿命呈线性负相关。

Molecular dvnamics simulations were used to study the pressure dependence of structure and self-diffusion in NaAlSi_3O_5 melt from 50 MPa to 19862 MPa at 2001.5 K. Four-coordinated Al and Si transform to five and six-coordinated complex with the increase of pressure. The content of Al reaches maximum at about 15 GPa whereas the maximum of Si doesn't appear up to 20 GPa. There is a remarkable difference between the self-diffusions coefficients of network-modifying and network-forming ions. In contrast to self-diffusion coefficient of Na, which decreases monotonously with the increment of pressure, the self-diffusion coefficients of Si, Al and O all initially increase, then decrease with the increase of pressure. In our simulation, peak in self-diffusions of network formers occurs around 8～10 GPa, which differs from the pressure at which Al and Si reach their maximum content. Furthermore, it's found that the self-diffusions of all ions are negatively and linearly correlated with the lifetimes of the bonds between ions and oxygen.