Effects of La2O3 on the Structure and Durability of Alkali Zirconium Silicate Glasses

Alkali zirconium silicate glasses containing 0–1.5 mol% La2O3 were synthesized using the conventional melt-quenching technique. The effects of La2O3 incorporation on the structure, chemical durability, and weathering resistance of the glass samples were investigated by X-ray diffraction (XRD), Raman spectroscopy, 29Si MAS NMR, X-ray absorption spectroscopy (XAS), and inductively coupled plasma optical emission spectrometry (ICP-OES). XRD confirmed the homogeneous incorporation of La2O3 into the glass matrix. XAS demonstrated that La3+ ions were present in the +3 oxidation state and were coordinated by six O2- ions. Raman spectroscopy revealed that increasing La2O3 concentration promoted the formation of Q2(La) and Q3(La) units, accompanied by a decrease in Q3 and Q4 units. These results suggest that La3+ ions are incorporated into the glass network through Si–O–La linkages, observed as Q2(La) and Q3(La) units in the Raman spectra. The 29Si MAS NMR analysis indicated a reduction in Q2 units and an increase in Q4 units. The reduction in Q2 of 29Si NMR compared to Raman may be attributed to several factors. Chemical durability tests indicated that Na+ leaching from samples immersed in solutions of varying pH decreased with increasing La2O3 content, while weathering tests demonstrated a reduction in Na+ accumulation on the glass surface, from 3.06 to 1.29 µg/cm2. These improvements in durability are attributed to La3+ ions, which enhance network rigidity and transform the role of Na+ ions from network modifiers to charge compensators, thereby reducing ion exchange with H+ ions.