Structural dependence of crystallization in glasses along the nepheline (NaAlSiO₄) ‐ eucryptite (LiAlSiO₄) join

Abstract

Lithium and sodium aluminosilicates are important glass‐forming systems for commercial glass‐ceramics, as well as being important model systems for ion transport in battery studies. In addition, uncontrolled crystallization of LiAlSiO4 (eucryptite) in high‐Li2O compositions, analogous to the more well‐known problem of NaAlSiO4 (nepheline) crystallization, can cause concerns for long‐term chemical durability in nuclear waste glasses. To study the relationships between glass structure and crystallization, nine glasses were synthesized in the LixNa1‐xAlSiO4 series, from x = 0 to x = 1. Raman spectra, nuclear magnetic resonance (NMR) spectroscopy (Li‐7, Na‐23, Al‐27, Si‐29), and X‐ray diffraction were used to study the quenched and heat‐treated glasses. It was found that different LiAlSiO4 and NaAlSiO4 crystal phases crystallize from the glass depending on the Li/Na ratio. Raman and NMR spectra of quenched glasses suggest similar structures regardless of alkali substitution. Li‐7 and Na‐23 NMR spectra of the glass‐ceramics near the endmember compositions show evidence of several differentiable sites distinct from known LixNa1‐xAlSiO4 crystalline phases, suggesting that these measurements can reveal subtle chemical environment differences in mixed‐alkali systems, similar to what has been observed for zeolites.

NaAlSiO4: Eu2+ Glass Ceramics: Self‐Reduced In Situ Growth and High‐Power LED/LD Lighting

“…[50,51] All the resonance bands are originated from [SiO 4 ] tetrahedra, however, the former is amorphous with broadened band and the latter is crystallized and ordered with sharp splitting peaks, being consistent with the results of XRD. Similarly, the resonance broadband at about 60 ppm assigned to the amorphous [AlO 4 ] tetrahedra also split into two narrowed bands at 59.3 and 65.2 ppm originated from the two distinct [AlO 4 ] tetrahedras in NASO crystal lattice, [50,51] in accordance with that of NASO phosphor (Figure 5e). Furthermore, as described in 23 Na MAS-NMR spectra in Figure 5f, a broad featureless peak in the range of −30-0 ppm belongs to sodium in aluminosilicate glasses.…”

Nepheline crystallization and the residual glass composition: Understanding waste glass durability

“…The nepheline phase appeared lighter in backscattered electron imaging than the residual glass in NP‐MC‐BNa‐1, but darker than the residual glass in both NP2‐23 and NP2‐23_High Al. Since the average atomic number for NaAlSiO 4 10 was higher than values calculated for all glasses, and therefore should have appeared brighter, this may indicate that Li is partially substituting for Na in the nepheline crystalline phase in these glasses, a phenomena observed elsewhere 24,25 …”

Crystallization study of rare earth and molybdenum containing nuclear waste glass ceramics

“…The simplified composition (SIMP), the RuO 2 ‐doped version (Ru‐SIMP), and the complex composition (CX) were all analyzed after 1 × SC and mixing with a known quantity of TiO 2 standard (SRM‐674b; National Institute of Standards and Technology), using Rietveld refinement and the Topas (Bruker) software, in order to obtain the amorphous fraction. Errors on the quantification of phases are estimated at a maximum of ~0.1 × mass% for major phases (oxyapatite), and 0.25 × mass% for minor phases (powellite), as assessed by similar detailed studies using the same quantitative XRD methods …”

“…Errors on the quantification of phases are estimated at a maximum of ~0.1 × mass% for major phases (oxyapatite), and 0.25 × mass% for minor phases (powellite), as assessed by similar detailed studies using the same quantitative XRD methods. 36,37 Additionally, hot-stage XRD was obtained on the same D8 Advance diffractometer. A powder of the SIMP glass was suspended in ethanol, placed onto a Pt heater strip, and allowed to dry.…”