Structure of liquid tricalcium aluminate
Structure of liquid tricalcium aluminate
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DOI：
10.1103/physrevb.95.064203
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发表时间：
2017-02-01
影响因子：
3.7
通讯作者：
Hennet, Louis
中科院分区：
文献类型：
--
作者：
Drewitt, James W. E.;Barnes, Adrian C.;Hennet, Louis
用Ca同位素替代中子衍射法（NDIS）测量了2073（30）K下空气动力悬浮和激光加热的液态铝酸三钙（Ca 3Al 2 O 6）的原子尺度结构。这些结果使得能够详细解析钙和铝原子周围的局部配位环境，包括直接确定液体部分结构因子S-CaCa（Q）和部分对分布函数（gCaCa）（r）。采用分子动力学（MD）模拟和反向蒙特卡罗（RMC）精细化方法，获得了详细的原子模型的液体结构。组成Ca 3Al 2 O 6位于CaO：Al 2 O3玻璃形成系统的富CaO极限。我们的研究结果表明，虽然显着解聚，液体Ca 3Al 2 O 6主要是由AlO 4四面体形成一个无限的网络，具有比预期的组合物的比例略高的桥接氧原子。钙为中心的多面体表现出广泛的分布的四到七倍的协调网站，与更高的协调钙优先键合桥氧。MD构型的分析揭示了液体中存在类似于10%未连接的AlO 4单体和Al 2 O 7二聚体。随着CaO浓度的增加，这些孤立的单元的数量增加，使得CaO：Al 2 O3液体的玻璃形成组合物的上限值可以用渗滤阈值来描述，在该渗滤阈值下，玻璃不再能够支持无限连接的AlO 4网络的形成。
The atomic-scale structure of aerodynamically levitated and laser-heated liquid tricalcium aluminate (Ca3Al2O6) was measured at 2073(30) K by using the method of neutron diffraction with Ca isotope substitution (NDIS). The results enable the detailed resolution of the local coordination environment around calcium and aluminum atoms, including the direct determination of the liquid partial structure factor, S-CaCa(Q), and partial pair distribution function, (gCaCa)(r). Molecular dynamics (MD) simulation and reverse Monte Carlo (RMC) refinement methods were employed to obtain a detailed atomistic model of the liquid structure. The composition Ca3Al2O6 lies at the CaO-rich limit of the CaO: Al2O3 glass-forming system. Our results show that, although significantly depolymerized, liquid Ca3Al2O6 is largely composed of AlO4 tetrahedra forming an infinite network with a slightly higher fraction of bridging oxygen atoms than expected for the composition. Calcium-centered polyhedra exhibit a wide distribution of four-to sevenfold coordinated sites, with higher coordinated calcium preferentially bonding to bridging oxygens. Analysis of the MD configuration reveals the presence of similar to 10% unconnected AlO4 monomers and Al2O7 dimers in the liquid. As the CaO concentration increases, the number of these isolated units increases, such that the upper value for the glass-forming composition of CaO: Al2O3 liquids could be described in terms of a percolation threshold at which the glass can no longer support the formation of an infinitely connected AlO4 network.