Local Structural Changes in High-Alumina, Low-Lithium Glass-Ceramics During Crystallization

Area of Science:

• Materials Science
• Crystallization Science
• Nanomaterials

Background:

• High-alumina, low-lithium glass-ceramics are advanced materials with tunable properties.
• Understanding the phase transition and crystallization process is crucial for optimizing their performance.
• Controlling nucleation and crystal growth dictates the final microstructure and properties.

Purpose of the Study:

• To investigate the phase transition and crystallization mechanisms in ZnO-MgO-Li2O-SiO2-Al2O3 glass-ceramics.
• To elucidate the role of cation migration and structural units in forming specific crystalline phases.
• To correlate microstructure with mechanical and optical properties for potential applications.

Main Methods:

• Differential scanning calorimetry (DSC) and high-temperature X-ray diffraction (HT-XRD) for thermal analysis and phase identification.
• Field emission transmission electron microscopy (FE-TEM) for microstructure observation.
• Raman spectroscopy to analyze glass network structural changes during crystallization.

Main Results:

• Nucleation of (Zn, Mg)Al2O4 spinel crystals begins around 850 °C, driven by Zn and Mg aggregation around Al.
• Zr aggregation leads to the formation of ZrO2 nanocrystals.
• Raman spectroscopy indicates increased Q3 and Q4 units and bridging oxygens during spinel precipitation.
• Al participation in spinel nucleation suppresses undesirable Li-containing silicate phases.
• The resulting glass-ceramics feature nanocrystals of (Zn, Mg)Al2O4 and ZrO2.

Conclusions:

• The study successfully elucidates the nucleation and growth mechanisms in high-alumina, low-lithium glass-ceramics.
• Controlled cation migration and Al coordination are key to forming desired nanocrystalline phases.
• The resulting glass-ceramics exhibit high hardness (875 Hv), flexural strength (350 MPa), and transparency (81.5%).
• These properties make the material suitable for demanding applications like protective screens and transparent armor.