Coordination properties and structural units distribution of Q_Tⁱ in calcium aluminosilicate melts from MD simulation

Abstract

The distribution of Al(j) and the structural units distribution of Q_Tⁱ in calcium aluminosilicate melts were studied by means of molecular dynamics simulation. The results show that provided there exists lower-field strength cation relative to Al³⁺, such as alkaline and alkaline earth metals, Al will be four-coordinated but not six-coordinated. Meanwhile, if there exist a large number of higher-field strength cations such as Si⁴⁺ and little lower-field strength cation, six-coordinated aluminum will be formed. The relation of structural units distribution of Q_Tⁱ with chemical composition shift was also extracted, showing that as Ca²⁺ exists, the distributions of Q_Siⁱ, Q_Alⁱ or Q_Tⁱ have the similar changing trend with the variation of component. Because of high-temperature effect, the Al-tetrahedral units in melts are greatly active and unstable and there exist dynamic transforming equilibria of Al(3) ⇋ Al(4) and Al(5) ⇋ Al(4). The three-coordinated oxygen and charge-compensated bridging oxygen are proposed to explain phenomena of the negative charge redundancy of AlO₄ and location of network modifier with charge-compensated function in aluminosilicate melts.

Keywords

Molecular dynamics simulation / calcium aluminosilicate melt / coordination number / structural unit of tetrahedra

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