Ceramics-Silikáty 47, (2) 45 - 49 (2003) |
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Q-SPECIES IN ALKALI-DISILICATE GLASSES |
Macháček Jan, Gedeon Ondrej |
Department of Glass and Ceramics
Institute of Chemical Technology Prague
Technická 5, 166 28 Prague
Czech Republic
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Keywords: Alkali silicate glass, Molecular dynamics, Structure |
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 ↔ Qn-1 + Qn+1. Equilibrium constant of this equation is defined by
the relation kn = [Qn-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. |
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