Structural role of chromium sulfate in modified borate glasses and glass ceramics

Abstract

Different glasses in the system xCr2(SO4)3-(60−x)B2O3–15CaO-15Na2O-10P2O5 where x ranging between 0 and 35 mol% has been prepared via ordinary melt quenching method. Fourier transform infrared (FTIR) spectroscopic measurements, X-ray diffraction (XRD) pattern, and scanning electron microscopy (SEM) are the main tools adopted for retrace structural changes correlated with increasing Cr2(SO4)3 content. XRD spectra of glasses of Cr2(SO4)3 ≤ 2 mol% have revealed that the amorphous structure is dominant within such region of composition. However, glasses containing higher Cr2(SO4)3 contents (x = 5–35 mol%) are characterized by the formation of specific polycrystalline phases within the glass network. Data based on FTIR absorption support the presence of BO3, BO4, SO4, and CrO4 functional groups which were randomly distributed within the main borate network. Besides, the density and molar volume of the studied samples were estimated and correlated with additional physical parameters. Based on the measured density, the concentration of Cr2(SO4)3, field strength (F), and inter-nuclear distance (ri) are calculated. It was concluded that the increase in Cr and S content leads to a decrease in inter-nuclear distance which agree with an increase in field strength and Vicker's micro-hardness number of the investigated glasses.