High‑Density MgAl2O4 Spinel Ceramics from Polymer‑Assisted Coprecipitated Nanopowder

Abstract

High-purity, sinter-active MgAl₂O₄ nanopowders were synthesized via a novel reverse chemical coprecipitation route using polyvinylpyrrolidone (PVP) as a polymeric surfactant. The method aims to eliminate sintering additives, reduce synthesis and sintering temperatures, and control the microstructure for advanced transparent ceramic applications. The precursor, comprising ammonium dawsonite and amorphous magnesium carbonate (AMC), was precipitated at pH 8–11, with optimal conditions at pH 11 for monophase formation, and calcined at 900–1200°C. The use of PVP stabilized the high-surface-area AMC phase (up to 600 m²/g) and enabled the formation of monophase spinel nanopowders at a reduced temperature of 900°C, with a specific surface area of 140 m²/g. The powders were densified by vacuum sintering at 1550°C without any additives. The resulting ceramics achieved a high relative density of >99% and a tailored microstructure with a mean grain size of 15–20 μm, depending on the precursor calcination temperature, which is critical for optical transparency. This polymer-assisted coprecipitation process presents a promising, additive-free route for fabricating high-density MgAl₂O₄ spinel ceramics suitable for optical and protective applications.