Sintering, hardness and cation inversion of nanocrystalline Beryllium – Magnesium aluminate ceramics

Beryllium-magnesium aluminate (Be0.1Mg0.9Al2O4 and Be0.2Mg0.8Al2O4) nanoparticles are synthesized by a coprecipitation method and sintered using Spark Plasma Sintering (SPS) to achieve near full density ceramics with grain sizes at the nanoscale. The sintered nanoceramics display grain sizes ranging from 14 to 33 nm, which are analyzed for optical transmission, Vickers hardness, and cation site inversion. When compared to Be-free MgAl2O4 nanoceramics, both Be0.1Mg0.9Al2O4 and Be0.2Mg0.8Al2O4 show transmissions ∼30% lower at wavelength in the infrared range. The samples show a Vickers hardness of ∼19.2 GPa with no apparent dependence on grain size. These values are consistently lower to those reported for beryllium-free MgAl2O4 spinel with similar grain size. 27Al and 9Be Nuclear Magnetic Resonance (NMR) spectroscopy reveals that beryllium does not have a significant effect on cationic site inversion in the spinel and, similar to beryllium-free MgAl2O4, inversion remains solely a function of grain size. The results indicate beryllium ions form solid-solutions with MgAl2O4 spinel structure and do not alter the grain boundaries significantly enough to influence the mechanical properties of nanocrystalline ceramics.