当前位置: X-MOL 学术ACS Earth Space Chem. › 论文详情
Our official English website, www.x-mol.net, welcomes your feedback! (Note: you will need to create a separate account there.)
Structure and Properties of Albite Melt at High Pressures
ACS Earth and Space Chemistry ( IF 2.9 ) Pub Date : 2019-12-20 , DOI: 10.1021/acsearthspacechem.9b00187
Suraj K. Bajgain 1 , Mainak Mookherjee 1
Affiliation  

We have used first-principles molecular dynamics simulation to examine the high-pressure behavior of an aluminosilicate melt with albite stoichiometry (NaAlSi3O8). We have explored the equation of state and transport properties up to a pressure of 25 GPa and over a range of temperatures (2500–4000 K). Our results show that upon compression of up to 5 GPa, the initial densification in an albite melt occurs by the reduction of the T–O–T bond angle; however, the Si–O coordination remains virtually unchanged. Upon compression beyond 5 GPa, the densification occurs via changes in the T–O coordination. We also find that at lower isotherms, i.e., 2500–3000 K, the viscosity decreases upon compression and there is a concomitant enhancement of the diffusivity of the network-forming tetrahedral cations (silicon/aluminum) and oxygen anions. However, there is a reversal in the trend of viscosity and diffusivity upon further compression. For all of the temperatures explored in this study, at higher pressures, i.e., >10 GPa, the viscosity increases with increasing pressure, whereas the diffusivity decreases with increasing pressures. This behavior of the melt transport property at high pressures is expected, contrary to the observed behavior of melt transport at low pressures and low temperatures. The pressure-dependent anomalous transport properties are very likely related to the formation of the 5-fold coordinated aluminum ions that have a shorter lifetime compared to those of the more stable 4-fold and 6-fold coordinated units.

中文翻译:

高压下阿尔比特熔体的结构与性能

我们已经使用第一性原理分子动力学模拟来以钠长石化学计量法(NaAlSi 3 O 8)。我们已经研究了在25 GPa的压力下以及在一定温度范围(2500–4000 K)下的状态和传输特性方程。我们的结果表明,压缩至5 GPa时,钠长石熔体的初始致密化是通过降低T–O–T键角实现的。但是,Si-O协调几乎保持不变。压缩超过5 GPa时,通过T-O配位的变化发生致密化。我们还发现,在较低的等温线(即2500–3000 K)下,粘度在压缩时会降低,并且形成网络的四面体阳离子(硅/铝)和氧阴离子的扩散率也随之提高。然而,在进一步压缩时,粘度和扩散率的趋势发生了逆转。对于本研究中探索的所有温度,在较高压力下,即> 10 GPa时,粘度随压力增加而增加,而扩散率随压力增加而减小。与在低压和低温下观察到的熔体输送行为相反,在高压下这种熔体输送性能的行为是可预期的。与压力相关的异常传输特性很可能与5倍配位铝离子的形成有关,与更稳定的4倍和6倍配位单元相比,铝离子的寿命较短。
更新日期:2019-12-21
down
wechat
bug