Structural evolution of high zirconia aluminosilicate glasses

Abstract

We report a detailed structural investigation of Ca-Na aluminosilicate glasses containing 0-20 wt% ZrO2 using X-ray absorption spectroscopy, Raman spectroscopy and 27 Al and 29 Si NMR. The X-ray absorption spectroscopy data reveal that Zr is predominantly present in ZrO6 octahedra but a significant Zr coordination change occurs with increasing ZrO2 content. Though Al and Zr are competing to be surrounded by charge balancing cations, 27 Al NMR data do not show the presence of high-coordinated Al species; thus charge-balancing cations are preferentially localized close to AlO4 tetrahedra rather than Zr polyhedra, explaining the increase in Zr coordination number that ultimately leads to limit Zr solubility in glasses. Raman and 29 Si NMR data indicates that Zr atoms are linked to the silicate network with a trend for higher degree of network connectivity at high zirconia content. Change in network connectivity and in Zr environment provide insights to understand chemical durability or crystallization in glasses.

Glass-forming ability and ZrO2 saturation limits in the magnesium aluminosilicate system

“…broad asymmetric bands at 450 and 800 cm -1 associated with the vibrations of Si-O-Si linkages, sharper "defect" lines at 490 and 600 cm -1 stemming from the breathing modes of four-and three-membered tetrahedral rings and, above 1000 cm -1 , the envelope for the stretching of bridging oxygens about SiO 4 tetrahedra [31][32][33][34][35]. In turn, an additional relatively broad band was observed in the spectra of ZrO 2 -doped S100 samples, centered at ~950 cm -1 and growing in intensity with increasing ZrO 2 content; a similar vibrational feature has been previously observed in SiO 2 -ZrO 2 gels [36], ZrO 2 -bearing borosilicate [37,38] and aluminosilicate glasses and assigned to the stretching of bridging oxygens about SiO 4 Q 3 units linked to a Zr polyhedron [39]. S100Zr2 and S100Zr4 could not be fully vitrified and accordingly display several supplementary sharp bands stemming from crystalline material (see treatment below).…”

“…In MAS glasses, however, 5-and 6fold-coordinated Al 3+ species have been shown to be predominant even in the absence of ZrO 2 , especially at peraluminous compositions [40]: the presence of these highly coordinated, modifier-like Al 3+ species (and the resulting lower network rigidity) may therefore represent a key factor for the solubility of ZrO 2 in the glasses studied within this work. In fact, Raman spectra of our Al 2 O 3 -rich samples highlighted more extensive structural responses to the addition of ZrO 2 (the noted broadening and shift of Raman features); on the contrary, the spectrum of SiO 2 appeared barely affected by the dopant if not through the appearance of the additional characteristic band at ~950 cm -1 , previously associated to occurrence of linkages between Q 3 units and Zr 4+ oxygen polyhedra [39].…”

“…However, our study confirms the key relevance of SiO 2 content and overall structural polymerization for the incorporation of Zr 4+ in silicate glasses: the saturation threshold of this oxide increased steadily along the silica-cordierite join and was shown to be even higher at peraluminous compositions. Clearly, this must be due to the difficulty of a fully polymerized [SiO 4 ] tetrahedral network to accommodate high amounts of Zr 4+ , which has been shown to assume preferentially a 6-or 7-fold oxygen coordination in SiO 2 -ZrO 2 xerogels and in aluminosilicate glasses, sharing edges with adjacent (Si,Al)-polyhedra [6,9,39,45].…”

“…In a subaluminous soda lime glass, ZrO 2 oversaturation was previously correlated to a gradual shift from 6-to 8-fold oxygen coordination around Zr 4+ ions, which would therefore prove less efficient than Al 3+ ions (invariably 4-coordinated even at high ZrO 2 content) in the competition for charge-balancing modifier cations [39]. In MAS glasses, however, 5-and 6fold-coordinated Al 3+ species have been shown to be predominant even in the absence of ZrO 2 , especially at peraluminous compositions [40]: the presence of these highly coordinated, modifier-like Al 3+ species (and the resulting lower network rigidity) may therefore represent a key factor for the solubility of ZrO 2 in the glasses studied within this work.…”

Dual effect of ZrO2 on phase separation and crystallization in Li2O–Al2O3–SiO2–P2O5 glasses

“…Figure 6 presents the Raman spectra of as‐quenched glasses. The region between 400 and 600 cm −1 corresponds to the bending vibrations of the bridging oxygen (BO) bonds of SiO 4 tetrahedra 35 . The band near 490 cm −1 indicated the presence of four‐membered rings, whereas the long tail at lower frequencies was attributed to the stretching vibration of oxygen bonds in high‐membered rings 36 .…”