Solid-State Transformations of Mayenite and Core-Shell Structures of C12A7@C Type at High Pressure, High Temperature...

Area of Science:

• Materials Science
• Solid-State Chemistry
• High-Pressure Physics

Background:

• Mayenite (12CaO∙7Al2O3, C12A7) is a versatile ceramic with significant technological applications.
• Understanding its behavior under extreme conditions is crucial for developing advanced materials.
• Core-shell structures offer unique pathways for material synthesis and property modification.

Purpose of the Study:

• To investigate the impact of a carbon shell in C12A7@C core-shell structures on solid-state reactions.
• To analyze the phase evolution of C12A7 and C12A7@C when reacted with graphite and MgO under HPHT conditions.
• To compare the reaction products of pure C12A7 versus C12A7@C under identical HPHT treatments.

Main Methods:

• Synthesis of C12A7@C core-shell materials.
• High-Pressure, High-Temperature (HPHT) experiments at 4 GPa and 1450 °C.
• X-ray diffraction (XRD) and phase composition analysis of reaction products.

Main Results:

• Reaction of C12A7 with graphite yielded an aluminum-rich CaO∙6Al2O3 phase.
• C12A7@C reacted with graphite formed multiple unidentified calcium aluminate and carbide-like phases.
• Both C12A7 and C12A7@C reacted with MgO to form the spinel phase Al2MgO4, indicating the carbon shell did not impede MgO interaction.
• The accompanying solid-state products differed significantly between pure C12A7 and C12A7@C reactions with MgO.
• HPHT conditions completely destroyed the mayenite structure, forming new phases dependent on the precursor (C12A7 vs. C12A7@C).

Conclusions:

• The carbon shell in C12A7@C structures significantly influences the solid-state reaction pathways with graphite under HPHT.
• While the carbon shell does not prevent MgO interaction, it alters the secondary phase formation during spinel synthesis.
• HPHT processing fundamentally transforms mayenite, with the precursor structure (C12A7 or C12A7@C) dictating the final phase assemblage.