Ceramics-Silikáty 47 (2) 45-49 (2003)

Q-SPECIES IN ALKALI-DISILICATE GLASSES

J. MACHÁČEK, O. GEDEON

Glasses of composition M₂O.2SiO₂ (M = Li, Na, K, Rb and Cs) were obtained by means of molecular dynamics simulation. The structures of these glasses were analyzed with help of Q-species distribution. The influence of alkali oxide on a decay of Q-species is monitored according to the equation 2Qⁿ « Q^n-1 + Qⁿ⁺¹. Equilibrium constant of this equation is defined by the relation k_n = [Q^n-1][Qⁿ⁺¹]/[Qⁿ]². It was found that k₃ is decreasing in sequence Li > Na > K so that the decay of Q³ is preferred for smaller alkali ions. Systems with higher k₃ tend to create the silicate-rich regions (abundant in Q⁴) and alkali-rich regions where alkali ions are spread among chain-like structures formed by Q² units. For larger alkali size, k₃ increases as K < Rb < Cs. This phenomenon is probably caused by slower relaxation of simulated glasses with a large alkali ion.

Keywords: Alkali silicate glass, Molecular dynamics, Structure.