Effect of the replacement of aluminum by magnesium on the compressibility and degree of polymerization of silicate glasses

摘要

The refractive index of Na_2MgSi_4O_(10) and Na2Al2Si4O12 glasses in the pressure range to 6.0 GPa was measured using a polarization-interference microscope and apparatus with diamond anvils. The changes in relative density, which characterize the compressibility of glasses, were calculated in the studied range of pressures from the measured refractive indices within the framework of the theory of photoelasticity. For the studied glasses, the degree of depolimerization was found to be NBO/T = 0.28 and 0.25 for Na _2MgSi_4O_(10) and Na_2Al _2Si_4O_(12) glasses, respectively. It is shown that the replacement of aluminum by magnesium in silicate glasses does not lead to a considerable decrease in compressibility, which suggests the predominant role of magnesium ions as network formers. A minor increase in compressibility when passing from Na2MgSi4O10 to Na _2Al_2Si_4O_(12) glass conforms with the corresponding decrease in the degree of depolymerization.