Degree of Polymerization of the CaAl₂Si₂O₈
Aluminosilicate Glass

R. G. Kuryaeva

Institute of Mineralogy and Petrography, Siberian Division, Russian Academy of Sciences,
pr. Akademika Koptyuga 3, Novosibirsk, 630090 Russia

e-mail: rufina@uiggm.nsc.ru

Received April 1, 2006

Abstract—The pressure dependence of the refractive index for a glass of the composition 0.50SiO₂ · 0.25Al₂O₃ ·
0.25CaO at pressures up to 5.0 GPa is determined using a polarizing interference microscope and an apparatus
with diamond anvils. The densities and compressibilities of the glass are calculated from the measured refrac-
tive indices within the framework of the theory of photoelasticity. The results are compared with the data
obtained earlier for vitreous silica. The lower compressibility of the glass under investigation as compared to
the compressibility of fused silica is in agreement with the degree of polymerization that is calculated with due
regard for the formation of triclusters from the relationship NBO/T = (2O + 3O_t – 4T)/T, where NBO (nonbridg-
ing oxygen) is the number of nonbridging oxygen atoms; O is the number of gram-ions of oxygen, except for
of tricluster oxygen; O_t is the number of gram-ions of tricluster oxygen; and T is the total number of gram-ions
of network formers.

DOI: 10.1134/S1087659606050026

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