Revisiting metastable immiscibility in SiO₂–Al₂O₃: Structure and phase separation of supercooled liquids and glasses

Abstract

Understanding and controlling liquid-liquid phase separation in aluminosilicates is crucial for optimizing glass properties. However, the metastable nature of aluminosilicates' phase separation has made it difficult to study experimentally, and uncertainty persists regarding the compositional and temperature extents of the miscibility gap. Here, we present new experimental evidence that suggests a consolute temperature between 1440 and 1590 • C and endmember compositions of 7 and 62 mol.% Al 2 O 3 for the phase-separated glasses. Using containerless melt processing, deeply supercooled liquids over the 0-60 mol.% Al 2 O 3 range are probed with in situ small-and wide-angle X-ray scattering, which simultaneously reveals changes in nanoscale density heterogeneity and atomic structure. Correlations between phase separation and atomic coordination environments are compared for liquids and glasses. Pair distribution function analysis shows mean O-(Si + Al) coordination increases with Al 2 O 3 content and decreases with temperature.

Molecular structure of ketoprofen-polyvinylpyrrolidone solid dispersions prepared by different amorphization methods

“…The red shading intensity represents relative magnitude Paper Pharmaceutics the four different compositions cross at common These isosbestic points 49,50 are indicative of a series of measurements with populations of two species or two contributions, and appearance of isosbestic points here is similar to other studies on structural changes across a binary compositional series. 51 In the PDFs, the trend in density is difficult to discern from the low-r region but can be inferred from the minimum in D(r) near r = 1.92 Å. The value of D(r) at this minimum increases with KTP content, suggesting a decrease in density consistent with the calculated densities for pure KTP and PVP.…”

“…For a physical mixture (PM), the X-ray scattering for a binary of KTP and PVP would be the same as a compositionally-weighted linear combination of the pure endmembers’ scattering, 51,57 approximately: S PM ( Q ) = w KTP S KTP ( Q ) + (1 − w KTP ) S PVP ( Q )where w KTP is the weight fraction of KTP. This relationship would result in S 1 and S 2 each exhibiting a linear trend vs. composition, which is shown in Fig.…”

“…RSC Pharmaceutics ally-weighted linear combination of the pure endmembers' scattering, 51,57 approximately:…”

The structure of CaO–MgO–Al2O3–SiO2 melts and glasses doped with FeOX–NiO

“…13 In wollastonite (CaSiO 3 ), the periodicity of the tetrahedral chain is modified to accommodate the larger CaO 6 polyhedra. The addition of alumina to silica can lead to phase separation in the liquid state, 14 but this liquid-liquid metastable immiscibility is greatly reduced upon the addition of additional cation. 15 Wilding et al 16,17 have performed x-ray diffraction measurements on liquid MgSiO 3 and sug-gested the structure comprises a sparse network of SiO 4 tetrahedra with highly mobile magnesium ions.…”

“…In wollastonite (CaSiO 3 ), the periodicity of the tetrahedral chain is modified to accommodate the larger CaO 6 polyhedra. The addition of alumina to silica can lead to phase separation in the liquid state, 14 but this liquid–liquid metastable immiscibility is greatly reduced upon the addition of additional cation 15 . Wilding et al 16,17 .…”